ALBERT

Description: Beyond multifractional Brownian motion: new stochastic models for geophysical modelling Nonlinear Processes in Geophysics, 20, 643-655, 2013 Author(s): J. Lévy Véhel Multifractional Brownian motion (mBm) has proved to be a useful tool in various areas of geophysical modelling. Although a versatile model, mBm is of course not always an adequate one. We present in this work several other stochastic processes which could potentially be useful in geophysics. The first alternative type is that of self-regulating processes : these are models where the local regularity is a function of the amplitude, in contrast to mBm where it is tuned exogenously. We demonstrate the relevance of such models for digital elevation maps and for temperature records. We also briefly describe two other types of alternative processes, which are the counterparts of mBm and of self-regulating processes when the intensity of local jumps is considered in lieu of local regularity: multistable processes allow one to prescribe the local intensity of jumps in space/time, while this intensity is governed by the amplitude for self-stabilizing processes .

Description: Quantification of model uncertainty in aerosol optical thickness retrieval from Ozone Monitoring Instrument (OMI) measurements Atmospheric Measurement Techniques Discussions, 6, 8509-8541, 2013 Author(s): A. Määttä, M. Laine, J. Tamminen, and J. P. Veefkind We study uncertainty quantification in remote sensing of aerosols in the atmosphere with top of the atmosphere reflectance measurements from the nadir-viewing Ozone Monitoring Instrument (OMI). Focus is on the uncertainty in aerosol model selection of pre-calculated aerosol models and on the statistical modelling of the model inadequacies. The aim is to apply statistical methodologies that improve the uncertainty estimates of the aerosol optical thickness (AOT) retrieval by propagating model selection and model error related uncertainties more realistically. We utilise Bayesian model selection and model averaging methods for the model selection problem and use Gaussian processes to model the smooth systematic discrepancies from the modelled to observed reflectance. The systematic model error is learned from an ensemble of operational retrievals. The operational OMI multi-wavelength aerosol retrieval algorithm OMAERO is used for cloud free, over land pixels of the OMI instrument with the additional Bayesian model selection and model discrepancy techniques. The method is demonstrated with four examples with different aerosol properties: weakly absorbing aerosols, forest fires over Greece and Russia, and Sahara dessert dust. The presented statistical methodology is general; it is not restricted to this particular satellite retrieval application.

Description: Non-extensivity and long-range correlations in the earthquake activity at the West Corinth rift (Greece) Nonlinear Processes in Geophysics, 20, 713-724, 2013 Author(s): G. Michas, F. Vallianatos, and P. Sammonds In the present work the statistical properties of the earthquake activity in a highly seismic region, the West Corinth rift (Central Greece), are being studied by means of generalized statistical physics. By using a dataset that covers the period 2001–2008, we investigate the earthquake energy distribution and the distribution of the time intervals (interevent times) between the successive events. As has been reported previously, these distributions exhibit complex statistical properties and fractality. By using detrended fluctuation analysis (DFA), a well-established method for detection of long-range correlations in non-stationary signals, it is shown that long-range correlations are also present in the earthquake activity. The existence of these properties motivates us to use non-extensive statistical physics (NESP) to investigate the statistical properties of the frequency-magnitude and the interevent time distributions, along with other well-known relations in seismology, such as the gamma distribution for interevent times. The results of the analysis indicate that the statistical properties of the earthquake activity can be successfully reproduced by means of NESP and that the earthquake activity at the West Corinth rift is correlated at all-time scales.

Description: The Greenhouse Gas Climate Change Initiative (GHG-CCI): comparative validation of GHG-CCI SCIAMACHY/ENVISAT and TANSO-FTS/GOSAT CO 2 and CH 4 retrieval algorithm products with measurements from the TCCON network Atmospheric Measurement Techniques Discussions, 6, 8679-8741, 2013 Author(s): B. Dils, M. Buchwitz, M. Reuter, O. Schneising, H. Boesch, R. Parker, S. Guerlet, I. Aben, T. Blumenstock, J. P. Burrows, A. Butz, N. M. Deutscher, C. Frankenberg, F. Hase, O. P. Hasekamp, J. Heymann, M. De Mazière, J. Notholt, R. Sussmann, T. Warneke, D. Griffith, V. Sherlock, and D. Wunch Column-averaged dry-air mole fractions of carbon dioxide and methane have been retrieved from spectra acquired by the TANSO-FTS and SCIAMACHY instruments on board GOSAT and ENVISAT using a range of European retrieval algorithms. These retrievals have been compared with data from ground-based high-resolution Fourier Transform Spectrometers (FTS) from the Total Carbon Column Observing Network (TCCON). The participating algorithms are the Weighting Function Modified Differential Optical Absorption Spectroscopy (DOAS) algorithm (WFMD, University of Bremen), the Bremen Optimal Estimation DOAS algorithm (BESD, University of Bremen), the Iterative Maximum A Posteriori DOAS (IMAP, Jet Propulsion Laboratory (JPL) and Netherlands Institute for Space Research algorithm (SRON)), the proxy and full-physics versions of SRON's RemoTeC algorithm (SRPR and SRFP respectively) and the proxy and full-physics versions of the University of Leicester's adaptation of the OCO (Orbiting Carbon Observatory) algorithm (OCPR and OCFP respectively). The goal of this algorithm inter-comparison was to identify strengths and weaknesses of the various so-called Round Robin data sets generated with the various algorithms so as to determine which of the competing algorithms would proceed to the next round of the European Space Agency's (ESA) Greenhouse Gas Climate Change Initiative (GHG-CCI) project, which is the generation of the so-called Climate Research Data Package (CRDP), which is the first version of the Essential Climate Variable (ECV) "Greenhouse Gases" (GHG). For CO 2 , all algorithms reach the precision requirements for inverse modelling ( 〈 8 ppb), with only WFMD having a lower precision (4.7 ppm) than the other algorithm products (2.4–2.5 ppm). When looking at the seasonal relative accuracy (SRA, variability of the bias in space and time), none of the algorithms have reached the demanding 〈 0.5 ppm threshold. For CH 4 , the precision for both SCIAMACHY products (50.2 ppb for IMAP and 76.4 ppb for WFMD) fail to meet the 〈 34 ppb threshold, but note that this work focusses on the period after the 2005 SCIAMACHY detector degradation. The GOSAT X CH 4 precision ranges between 18.1 and 14.0 ppb. Looking at the SRA, all GOSAT algorithm products reach the 〈 10 ppm threshold (values ranging between 5.4 and 6.2 ppb). For SCIAMACHY, IMAP and WFMD have a SRA of 17.2 ppb and 10.5 ppb respectively.

Description: The impact of initial spread calibration on the RELO ensemble and its application to Lagrangian dynamics Nonlinear Processes in Geophysics, 20, 621-641, 2013 Author(s): M. Wei, G. Jacobs, C. Rowley, C. N. Barron, P. Hogan, P. Spence, O. M. Smedstad, P. Martin, P. Muscarella, and E. Coelho A number of real-time ocean model forecasts were carried out successfully at Naval Research Laboratory (NRL) to provide modeling support and numerical guidance to the CARTHE GLAD at-sea experiment during summer 2012. Two RELO ensembles and three single models using NCOM and HYCOM with different resolutions were carried out. A calibrated ensemble system with enhanced spread and reliability was developed to better support this experiment. The calibrated ensemble is found to outperform the un-calibrated ensemble in forecasting accuracy, skill, and reliability for all the variables and observation spaces evaluated. The metrics used in this paper include RMS error, anomaly correlation, PECA, Brier score, spread reliability, and Talagrand rank histogram. It is also found that even the un-calibrated ensemble outperforms the single forecast from the model with the same resolution. The advantages of the ensembles are further extended to the Lagrangian framework. In contrast to a single model forecast, the RELO ensemble provides not only the most likely Lagrangian trajectory for a particle in the ocean, but also an uncertainty estimate that directly reflects the complicated ocean dynamics, which is valuable for decision makers. The examples show that the calibrated ensemble with more reliability can capture trajectories in different, even opposite, directions, which would be missed by the un-calibrated ensemble. The ensembles are applied to compute the repelling and attracting Lagrangian coherent structures (LCSs), and the uncertainties of the LCSs, which are hard to obtain from a single model forecast, are estimated. It is found that the spatial scales of the LCSs depend on the model resolution. The model with the highest resolution produces the finest, small-scale, LCS structures, while the model with lowest resolution generates only large-scale LCSs. The repelling and attracting LCSs are found to intersect at many locations and create complex mesoscale eddies. The fluid particles and drifters in the middle of these tangles are subject to attraction and repulsion simultaneously from these two kinds of LCSs. As a result, the movements of particles near the Deepwater Horizon (DWH) location are severely limited. This is also confirmed by the Lagrangian trajectories predicted by the ensembles.

Description: Multifractal properties of embedded convective structures in orographic precipitation: toward subgrid-scale predictability Nonlinear Processes in Geophysics, 20, 605-620, 2013 Author(s): M. Nogueira, A. P. Barros, and P. M. A. Miranda Rain and cloud fields produced by fully nonlinear idealized cloud resolving numerical simulations of orographic convective precipitation display statistical multiscaling behavior, implying that multifractal diagnostics should provide a physically robust basis for the downscaling and sub-grid scale parameterizations of moist processes. Our results show that the horizontal scaling exponent function (and respective multiscaling parameters) of the simulated rainfall and cloud fields varies with atmospheric and terrain properties, particularly small-scale terrain spectra, atmospheric stability, and advective timescale. This implies that multifractal diagnostics of moist processes for these simulations are fundamentally transient, exhibiting complex nonlinear behavior depending on atmospheric conditions and terrain forcing at each location. A particularly robust behavior found here is the transition of the multifractal parameters between stable and unstable cases, which has a clear physical correspondence to the transition from stratiform to organized (banded and cellular) convective regime. This result is reinforced by a similar behavior in the horizontal spectral exponent. Finally, our results indicate that although nonlinearly coupled fields (such as rain and clouds) have different scaling exponent functions, there are robust relationships with physical underpinnings between the scaling parameters that can be explored for hybrid dynamical-statistical downscaling.

Description: The effect of phase partitioning of semivolatile compounds on the measured CCN activity of aerosol particles Atmospheric Measurement Techniques Discussions, 6, 8413-8433, 2013 Author(s): S. Romakkaniemi, A. Jaatinen, A. Laaksonen, A. Nenes, and T. Raatikainen The effect of inorganic semivolatile aerosol compounds on the CCN activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase. Two different questions were studied: (1) how big fraction of semivolatiles is evaporated from particles before activation in the CCN counter? (2) How much the CCN activity can be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase? The results show that, to increase the CCN activity of aerosol particles, a very high gas phase concentration (as compared to typical ambient conditions) is needed. We used nitric acid as a test compound. A concentration of several ppb or higher is needed for measurable effect. In the case of particle evaporation, we used ammonium nitrate as a test compound and found that it partially evaporates before maximum supersaturation is reached in the CCN counter, thus causing an underestimation of CCN activity. The effect of evaporation is clearly visible in all supersaturations, leading to an underestimation of the critical dry diameter by 10 to 15 nanometres in the case of ammonium nitrate particles in different supersaturations. This result was also confirmed by measurements in supersaturations between 0.1 and 0.7%.

Description: A top-down model to generate ensembles of runoff from a large number of hillslopes Nonlinear Processes in Geophysics, 20, 683-704, 2013 Author(s): P. R. Furey, V. K. Gupta, and B. M. Troutman We hypothesize that total hillslope water loss for a rainfall–runoff event is inversely related to a function of a lognormal random variable, based on basin- and point-scale observations taken from the 21 km 2 Goodwin Creek Experimental Watershed (GCEW) in Mississippi, USA. A top-down approach is used to develop a new runoff generation model both to test our physical-statistical hypothesis and to provide a method of generating ensembles of runoff from a large number of hillslopes in a basin. The model is based on the assumption that the probability distributions of a runoff/loss ratio have a space–time rescaling property. We test this assumption using streamflow and rainfall data from GCEW. For over 100 rainfall–runoff events, we find that the spatial probability distributions of a runoff/loss ratio can be rescaled to a new distribution that is common to all events. We interpret random within-event differences in runoff/loss ratios in the model to arise from soil moisture spatial variability. Observations of water loss during events in GCEW support this interpretation. Our model preserves water balance in a mean statistical sense and supports our hypothesis. As an example, we use the model to generate ensembles of runoff at a large number of hillslopes for a rainfall–runoff event in GCEW.

Description: A mechanism for catastrophic filter divergence in data assimilation for sparse observation networks Nonlinear Processes in Geophysics, 20, 705-712, 2013 Author(s): G. A. Gottwald and A. J. Majda We study catastrophic filter divergence in data assimilation procedures whereby the forecast model develops severe numerical instabilities leading to a blow-up of the solution. Catastrophic filter divergence can occur in sparse observational grids with small observational noise for intermediate observation intervals and finite ensemble sizes. Using a minimal five-dimensional model, we establish that catastrophic filter divergence is a numerical instability of the underlying forecast model caused by the filtering procedure producing analyses which are not consistent with the true dynamics, and stiffness caused by the fast attraction of the inconsistent analyses towards the attractor during the forecast step.

Description: Spectral Aerosol Extinction Monitoring System (SÆMS): setup, observational products, and comparisons Atmospheric Measurement Techniques Discussions, 6, 8647-8677, 2013 Author(s): A. Skupin, A. Ansmann, R. Engelmann, and H. Baars A Spectral Aerosol Extinction Monitoring System (SÆMS) is presented that allows us to continuously measure the spectral extinction coefficient of atmospheric aerosol particles along an about 2.7 km long optical path at 30–50 m height above ground at Leipzig (51.3° N, 12.4° E), Germany. The fully automated instrument measures the ambient aerosol extinction coefficients from 300–1000 nm. The main goal of SÆMS observations are long-term studies of the relationship between particle extinction and relative humidity from below 40 % to almost 100 %. The setup is presented and observations (a case study and statistical results for 2009) are discussed in terms of time series of 550 nm particle optical depth, Ångström exponent, and particle size distribution retrieved from the spectrally resolved extinction. The SÆMS measurements are compared with simultaneously performed EARLINET lidar, AERONET photometer, and in situ aerosol observations of particle size distribution and related extinction coefficients at the roof of our institute. Consistency between the different measurements is found which corroborates the quality of the SÆMS observations.

Description: Validation of SCIAMACHY O 2 A band cloud heights using Cloudnet radar/lidar measurements Atmospheric Measurement Techniques Discussions, 6, 8603-8645, 2013 Author(s): P. Wang and P. Stammes For the first time two SCIAMACHY O 2 A band cloud height products are validated using ground-based radar/lidar measurements between January 2003 and December 2011. The products are the ESA Level 2 (L2) version 5.02 cloud top height and the FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A band) version 6 cloud height. The radar/lidar profiles are obtained at the Cloudnet sites of Cabauw and Lindenberg, and are averaged for one hour centered at the SCIAMACHY overpass time to achieve an optimal temporal and spatial match. In total we have about 220 cases of single layer clouds and 200 cases of multi-layer clouds. The FRESCO cloud height and ESA L2 cloud top height are compared with the Cloudnet cloud top height and Cloudnet cloud middle height. We find that the ESA L2 cloud top height has a better agreement with the Cloudnet cloud top height than the Cloudnet cloud middle height. The ESA L2 cloud top height is on average 0.44 km higher than the Cloudnet cloud top height, with a standard deviation of 3.07 km. The FRESCO cloud height is closer to the Cloudnet cloud middle height than the Cloudnet cloud top height. The mean difference between the FRESCO cloud height and the Cloudnet cloud middle height is −0.14 km with a standard deviation of 1.88 km. The SCIAMACHY cloud height products are further compared to the Cloudnet cloud top height and the Cloudnet cloud middle height in 1 km bins. For single layer clouds, the difference between the ESA L2 cloud top height and the Cloudnet cloud top height is less than 1 km for each cloud bin at 3–7 km, which is 24 % percent of the data. The difference between the FRESCO cloud height and the Cloudnet cloud middle height is less than 1 km for each cloud bin at 0–6 km, which is 85 % percent of the data. The results are similar for multi-layer clouds, but the percentage of cases having a bias within 1 km is smaller than for single layer clouds. Since globally about 60 % of all clouds are low clouds and 42 % are single-layer low clouds, we expect that globally for a large percentage of cases the FRESCO cloud height would be close to the cloud middle height.

Description: Characteristics of cloud liquid water path from SEVIRI on the Meteosat Second Generation 2 satellite for several cloud types Atmospheric Measurement Techniques Discussions, 6, 8743-8782, 2013 Author(s): A. Kniffka, M. Stengel, M. Lockhoff, R. Bennartz, and R. Hollmann In this study the temporal and spatial characteristics of liquid water path (LWP) of low, middle level and high clouds are analysed using space-based observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation 2 (MSG2) satellite. Both geophysical quantities are part of the dataset CLAAS (CLoud property dAtAset using SEVIRI) and are generated by EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF). In this article we focus on the statistical properties of LWP retrieved at daylight associated with the individual cloud type. Our results reveal that each cloud type possesses a characteristic LWP distribution. These frequency distributions are constant with time in the entire SEVIRI field of view, but vary for smaller regions like Central Europe. The average LWP is higher over land than over sea, in case of low clouds 15–27% for 2009 and the variance of the frequency distributions is enhanced. Also, the average diurnal cycle of LWP is related to cloud type where most pronounced diurnal variations were detected for middle level clouds. With SEVIRI it is possible to distinguish between intrinsic LWP variability and variations driven by cloud amount. The relative amplitude of the intrinsic diurnal cycle can exceed the cloud amount driven amplitude.

Description: Remote sensing of atmospheric trace gas columns: an efficient approach for regularization and calculation of total column averaging kernels Atmospheric Measurement Techniques Discussions, 6, 4999-5031, 2013 Author(s): T. Borsdorff, O. P. Hasekamp, A. Wassmann, and J. Landgraf A concept is proposed to retrieve the vertical column densities of atmospheric trace gases from remote sensing measurements. It combines the numerical simplicity of a least-squares profile scaling retrieval with the numerically robust calculation of the total column averaging kernel using an analytic expression. The approach enables calculation of the total column averaging kernel on arbitrary vertical grids. Formally, the proposed method is equivalent to Tikhonov regularization of the first kind with an infinite regularization strength. Due to its efficiency it is particularly suited for implementation in operational data processing with high demands on processing time. To demonstrate the method, we apply it to CO column retrieval from simulated measurements in the 2.3 μm spectral region and to O 3 column retrieval from the UV, which represents ideal measurements of a series of space-borne spectrometers like SCIAMACHY, TROPOMI, GOME, and GOME-2. For both spectral ranges, we consider clear-sky and cloudy scenes where clouds are modelled as an elevated Lambertian surface. Here, the smoothing error for the clear-sky and cloudy atmosphere is significant and reaches several percent, depending on the reference profile which is used for scaling. This underlines the importance of the column averaging kernel for a proper interpretation of retrieved column densities. Furthermore, we show that the total column smoothing error is affected by a discretization error when total column averaging kernels are not represented on a fine enough vertical grid. For both retrievals this effect becomes negligible by using a vertical grid with 20–40 equally thick layers between 0 and 50 km.

Description: Mixing layer height retrievals by multichannel microwave radiometer observations Atmospheric Measurement Techniques Discussions, 6, 4971-4998, 2013 Author(s): D. Cimini, F. De Angelis, J.-C. Dupont, S. Pal, and M. Haeffelin The mixing layer height (MLH) is a key parameter for boundary layer studies, including meteorology, air quality, and climate. MLH estimates are inferred from in situ radiosonde measurements or remote sensing observations from instruments like lidar, wind profiling radar, or sodar. Methods used to estimate MLH from radiosonde profiles are also used with atmospheric temperature and humidity profiles retrieved by microwave radiometers (MWR). This paper proposes an alternative approach to estimate MLH from MWR data, based on direct observations (brightness temperatures, Tb) instead of retrieved profiles. To our knowledge, MLH estimates directly from Tb observations has never been attempted before. The method consists of a multivariate linear regression trained with an a priori set of collocated MWR Tb observations (multi-frequency and multi-angle) and MLH estimates from a state-of-the-art lidar system. Results show that the method is able to follow both the diurnal cycle and the day-to-day variability as suggested by the lidar measurements, and also it can detect low MLH values that are below the full overlap limit (~ 200 m) of the lidar system used. Statistics of the comparison between MWR- and reference lidar-based MLH retrievals show mean difference within 10 m, RMS within 340 m, and correlation coefficient higher than 0.77. Monthly mean analysis for day-time MLH from MWR, lidar, and radiosonde shows consistent seasonal variability, peaking at ~ 1200–1400 m in June and decreasing down to ~ 600 m in October. Conversely, night-time monthly mean MLH from all methods are within 300–500 m without any significant seasonal variability. The proposed method provides results that are more consistent with radiosonde estimates than MLH estimates from MWR retrieved profiles. MLH monthly mean values agree well within 1 std with bulk Richardson number method applied at radiosonde profiles at 11:00 and 23:00 UTC. The method described herewith operates continuously and it is expected to work with analogous performances for the entire diurnal cycle, except during considerable precipitation, demonstrating new potential for atmospheric observation by ground-based microwave radiometry.

Description: Stratospheric aerosol particle size information in Odin-OSIRIS limb scatter spectra Atmospheric Measurement Techniques Discussions, 6, 5065-5099, 2013 Author(s): L. A. Rieger, A. E. Bourassa, and D. A. Degenstein The Optical Spectrograph and InfraRed Imaging System (OSIRIS) on-board the Odin satellite has now taken over a decade of limb scatter measurements that have been used to retrieve the Version 5 stratospheric aerosol extinction product. This product is retrieved using a representative particle size distribution to calculate scattering cross sections and scattering phase functions for the forward model calculations. In this work the information content of OSIRIS measurements with respect to stratospheric aerosol is systematically examined for the purpose of retrieving particle size information along with the extinction coefficient. The benefit of using measurements at different wavelengths and scattering angles in the retrieval is studied and it is found that incorporation of the 1530 nm radiance measurement is key for a robust retrieval of particle size information. It is also found that using OSIRIS measurements at different solar geometries simultaneously provides little additional benefit. Based on these results, an improved aerosol retrieval algorithm is developed that couples the retrieval of aerosol extinction and mode radius of a log-normal particle size distribution. Comparison of these results with coincident measurements from SAGE III show agreement in retrieved extinction to within approximately 10% over the bulk of the aerosol layer, which is comparable to Version 5. The retrieved particle size, when converted to Ångström coefficient, shows good qualitative agreement with SAGE II measurements made at somewhat shorter wavelengths.

Description: Sub-inertial modulation of nonlinear Kelvin waves in the coastal zone Nonlinear Processes in Geophysics, 20, 357-364, 2013 Author(s): D. V. Stepanov and V. V. Novotryasov Observational evidence is presented for interaction between nonlinear internal Kelvin waves at the ω t,i (where the ω t is the semidiurnal frequency and the ω i is the inertial frequency) and random oscillations of the background coastal current at the sub-inertial Ω frequency in the Japan/East Sea. Enhanced coastal currents at the sum ω + and difference ω-frequencies ω ± =ω t,i ± Ω have properties of propagating Kelvin waves, which suggests permanent energy exchange from the sub-inertial band to the mesoscale ω ± band. This interaction may be responsible for a greater-than-predicted intensification, steepening and breaking of boundary-trapped Kelvin waves. The problem of interaction between the nonlinear Kelvin wave at the frequency ω and the low-frequency narrowband noise with representative frequency Ω≪ω is investigated using the theory of nonlinear weak dispersion waves.

Description: SAGE version 7.0 algorithm: application to SAGE II Atmospheric Measurement Techniques Discussions, 6, 5101-5171, 2013 Author(s): R. P. Damadeo, J. M. Zawodny, L. W. Thomason, and N. Iyer This paper details the SAGE version 7.0 algorithm and how it is applied to SAGE II. Changes made between the previous (v6.2) and current (v7.0) versions are described and their impacts on the data products explained for both coincident event comparisons and time-series analysis. Users of the data will notice a general improvement in all of the SAGE II data products, which are now in better agreement with more modern data sets (e.g. SAGE III) and more robust for use with trend studies.

Description: Technical Note: Aeolian dust proxies produce visible luminescence upon intense laser-illumination that results from incandescence of internally mixed carbon Atmospheric Measurement Techniques Discussions, 6, 5173-5194, 2013 Author(s): L. Ma, T. Cao, and J. E. Thompson Mineral dust mimics dispersed in air produced visible luminescence between 550–800 nm when illuminated with a high peak power (MW range) Nd:YAG laser beam at 532 or 1064 nm. The luminescence persists for a few microseconds after the laser pulse and the measured emission spectrum is roughly consistent with a blackbody emitter at ≈4300 K. Both observations are consistent with assigning laser-induced incandescence (LII) as the source of the luminescence. However, light emission intensity from the mineral dust proxies is 240–4600 less intense than incandescence from fresh kerosene soot on a per-mass basis at laser pulse energies 90% on average. Heating to 350 °C reduced emission by 45–72%. Since black carbon soot and char (BC) oxidizes at elevated temperatures and BC is known to be present in soils, we conclude emission of light from the mineral dust aerosol proxies is likely a result of black carbon or char internally mixed within the soil dust sample. The reduction in LII response for samples heated to temperatures of 250–350 °C may result from partial oxidation of BC, but alternatively, could implicate a role for carbon present within organic molecules. The study suggests laser-induced incandescence measurements may allow quantitation of black carbon in soils and that soil dust is not truly an interferent in BC analysis by LII, but rather, a BC containing material.

Description: Application of wavelet transform for evaluation of hydrocarbon reservoirs: example from Iranian oil fields in the north of the Persian Gulf Nonlinear Processes in Geophysics, 20, 231-238, 2013 Author(s): M. R. Saadatinejad and H. Hassani The Persian Gulf and its surrounding area are some of the biggest basins and have a very important role in producing huge amounts of hydrocarbon, and this potential was evaluated in order to explore the target for geoscientists and petroleum engineers. Wavelet transform is a useful and applicable technique to reveal frequency contents of various signals in different branches of science and especially in petroleum studies. We applied two major capacities of continuous mode of wavelet transform in seismic investigations. These investigations were operated to detect reservoir geological structures and some anomalies related to hydrocarbon to develop and explore new petroleum reservoirs in at least 4 oilfields in the southwest of Iran. It had been observed that continuous wavelet transform results show some discontinuities in the location of faults and are able to display them more clearly than other seismic methods. Moreover, continuous wavelet transform, utilizing Morlet wavelet, displays low-frequency shadows on 4 different iso-frequency vertical sections to identify reservoirs containing gas. By comparing these different figures, the presence of low-frequency shadows under the reservoir could be seen and we can relate these variations from anomalies at different frequencies as an indicator of the presence of hydrocarbons in the target reservoir.

Description: Retrieval of aerosol parameters from the oxygen A band in the presence of chlorophyll fluorescence Atmospheric Measurement Techniques Discussions, 6, 3181-3213, 2013 Author(s): A. F. J. Sanders and J. F. de Haan We have investigated precision of retrieved parameters for a generic aerosol retrieval algorithm over vegetated land using the O 2 A band. Chlorophyll fluorescence is taken into account in the forward model. Fluorescence emissions are modeled as isotropic contributions to the upwelling radiance field at the surface and they are retrieved along with aerosol parameters. Precision is calculated by propagating measurement noise using the forward model's derivatives. We assume that measurement noise is dominated by shot noise; thus, results apply to grating spectrometers in particular. In a number of retrieval simulations, we describe precision for various atmospheric states, observation geometries and spectral resolutions of the instrument. Our results show that aerosol optical thickness, aerosol pressure, fluorescence emission and surface albedo can be simultaneously retrieved from the O 2 A band. We also show that most of the fluorescence signal is provided by filling-in of the O 2 A band and to a lesser extent by filling-in of Fraunhofer lines.

Description: McClear: a new model estimating downwelling solar radiation at ground level in clear-sky conditions Atmospheric Measurement Techniques Discussions, 6, 3367-3405, 2013 Author(s): M. Lefèvre, A. Oumbe, P. Blanc, B. Espinar, B. Gschwind, Z. Qu, L. Wald, M. Schroedter-Homscheidt, C. Hoyer-Klick, A. Arola, A. Benedetti, J. W. Kaiser, and J.-J. Morcrette A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave direct and global irradiances received at ground level under clear skies. McClear implements a fully physical modelling replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapor and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 10 5 times greater by adopting the abaci, or look-up tables, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear irradiances were compared to 1 min measurements made in clear-sky conditions in several stations within the Baseline Surface Radiation Network in various climates. For global, respectively direct, irradiance, the correlation coefficient ranges between 0.95 and 0.99, resp. 0.86 and 0.99. The bias is comprised between −14 and 25 W m −2 , resp. −49 and +33 W m −2 . The RMSE ranges between 20 W m −2 (3% of the mean observed irradiance) and 36 W m −2 (5%), resp. 33 W m −2 (5%) and 64 W m −2 (10%). These results are much better than those from state-of-the-art models. This work demonstrates the quality of the McClear model combined with MACC products, and indirectly the quality of the aerosol properties modeled by the MACC reanalysis.

Description: Experimental quantification of contact freezing in an electrodynamic balance Atmospheric Measurement Techniques Discussions, 6, 3407-3437, 2013 Author(s): N. Hoffmann, A. Kiselev, D. Rzesanke, D. Duft, and T. Leisner Heterogeneous nucleation of ice in a supercooled water droplet induced by an external contact with a dry aerosol particle has long been known to be more effective than freezing induced by the same nucleus immersed in the droplet. However, the experimental quantification of contact freezing is challenging. Here we report an experimental method allowing to determine the temperature dependent ice nucleation probability of size selected aerosol particles. The method uses supercooled charged water droplets suspended in a laminar flow of air containing aerosol particles as contact freezing nuclei. The rate of droplet–particle collisions is calculated numerically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. The calculation is verified by direct counting of aerosol particles collected by a levitated droplet. By repeating the experiment on individual droplets for a sufficient number of times, we are able to reproduce the statistical freezing behavior of a large ensemble of supercooled droplets and measure the average rate of freezing events. The freezing rate is equal to the product of the droplet–particle collision rate and the probability of freezing on a single contact, the latter being a function of temperature, size and composition of the contact ice nuclei. Based on these observations, we show that for the types of particles investigated so far, contact freezing is the dominating freezing mechanism on the time scale of our experiment.

Description: Separating mixtures of aerosol types in airborne High Spectral Resolution Lidar data Atmospheric Measurement Techniques Discussions, 6, 8269-8309, 2013 Author(s): S. P. Burton, M. A. Vaughan, R. A. Ferrare, and C. A. Hostetler Knowledge of aerosol type is important for source attribution and for determining the magnitude and assessing the consequences of aerosol radiative forcing. However, atmospheric aerosol is frequently not a single pure type, but instead occurs as a mixture of types, and this mixing affects the optical and radiative properties of the aerosol. This paper extends the work of earlier researchers by using the aerosol intensive parameters measured by the NASA Langley Research Center airborne High Spectral Resolution Lidar (HSRL-1) to develop a comprehensive and unified set of rules for characterizing the external mixing of several key aerosol intensive parameters: extinction-to-backscatter ratio (i.e. lidar ratio), backscatter color ratio, and depolarization ratio. We present the mixing rules in a particularly simple form that leads easily to mixing rules for the covariance matrices that describe aerosol distributions, rather than just scalar values of measured parameters. These rules can be applied to infer mixing ratios from the lidar-observed aerosol parameters, even for cases without significant depolarization. We demonstrate our technique with measurement curtains from three HSRL-1 flights which exhibit mixing between two aerosol types, urban pollution plus dust, marine plus dust, and smoke plus marine. For these cases, we infer a time-height cross-section of mixing ratio along the flight track, and partition aerosol extinction into portions attributed to the two pure types.

Description: Lidar-based remote sensing of atmospheric boundary layer height over land and ocean Atmospheric Measurement Techniques Discussions, 6, 8311-8338, 2013 Author(s): T. Luo, R. Yuan, and Z. Wang Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and ABL vertical structure over ocean (TWP_C2 cite) and land (SGP_C1) are analyzed. The new methods are also applied to satellite lidar measurements. The derived global marine boundary layer structure database shows good agreement with marine ABL stratiform cloud top height.

Description: Fast reconstruction of hyperspectral radiative transfer simulations by using small spectral subsets: application to the oxygen A band Atmospheric Measurement Techniques Discussions, 6, 8339-8370, 2013 Author(s): A. Hollstein and R. Lindstrot Hyperspectral radiative transfer simulations are a versatile tool in remote sensing but can pose a major computational burden. We describe a simple method to construct hyperspectral simulation results by using only a small spectral subsample of the simulated wavelength range, thus leading to major speedups in such simulations. This is achieved by computing principal components for a small number of representative hyperspectral spectra and then deriving a reconstruction matrix for a specific spectral subset of channels to compute the hyperspectral data. The method is applied and discussed in detail using the example of top of atmosphere radiances in the oxygen A band, leading to speedups in the range of one to two orders of magnitude when compared to radiative transfer simulations at full spectral resolution.

Description: An assessment of cloud top thermodynamic phase products obtained from A-Train passive and active sensors Atmospheric Measurement Techniques Discussions, 6, 8371-8411, 2013 Author(s): S. Zeng, J. Riedi, F. Parol, C. Cornet, and F. Thieuleux The A-Train observations provide an unprecedented opportunity for the production of high quality dataset describing cloud properties. We illustrate in this study the use of one year of coincident POLDER (Polarization and Directionality of the Earth Reflectance), MODIS (MODerate Resolution Imaging Spectroradiometer) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations to establish a reference dataset for the description of cloud top thermodynamic phase at global scale. We present the results of an extensive comparison between POLDER and MODIS cloud top phase products and discuss those in view of cloud vertical structure and optical properties derived simultaneously from collocated CALIOP active measurements. These results allow to identify and quantify potential biases present in the 3 considered dataset. Among those, we discuss the impacts of observation geometry, thin cirrus in multilayered and single layered cloud systems, supercooled liquid droplets, aerosols, fractional cloud cover and snow/ice or bright surfaces on global statistics of cloud phase derived from POLDER and MODIS passive measurements. Based on these analysis we define criteria for the selection of high confidence cloud phase retrievals which in turn can serve for the establishment of a reference cloud phase product. This high confidence joint product derived from POLDER/PARASOL and MODIS/Aqua can be used in the future as a benchmark for the evaluation of other cloud climatologies, for the assessment of cloud phase representation in models and the development of better cloud phase parametrization in the general circulation models (GCMs).

Description: Distributed allocation of mobile sensing swarms in gyre flows Nonlinear Processes in Geophysics, 20, 657-668, 2013 Author(s): K. Mallory, M. A. Hsieh, E. Forgoston, and I. B. Schwartz We address the synthesis of distributed control policies to enable a swarm of homogeneous mobile sensors to maintain a desired spatial distribution in a geophysical flow environment, or workspace. In this article, we assume the mobile sensors (or robots) have a "map" of the environment denoting the locations of the Lagrangian coherent structures or LCS boundaries. Using this information, we design agent-level hybrid control policies that leverage the surrounding fluid dynamics and inherent environmental noise to enable the team to maintain a desired distribution in the workspace. We discuss the stability properties of the ensemble dynamics of the distributed control policies. Since realistic quasi-geostrophic ocean models predict double-gyre flow solutions, we use a wind-driven multi-gyre flow model to verify the feasibility of the proposed distributed control strategy and compare the proposed control strategy with a baseline deterministic allocation strategy. Lastly, we validate the control strategy using actual flow data obtained by our coherent structure experimental testbed.

Description: Odin-OSIRIS detection of the Chelyabinsk meteor Atmospheric Measurement Techniques Discussions, 6, 8435-8443, 2013 Author(s): L. A. Rieger, A. E. Bourassa, and D. A. Degenstein On 15 February 2013 an 11 000 ton meteor entered Earth's atmosphere south east of Chelyabinsk creating a large fireball at 23 km altitude. The resulting stratospheric aerosol loading was detected by the Ozone Mapping and Profiler Suite (OMPS) in a high altitude polar belt. This work confirms the presence and lifetime of the stratospheric debris using the Optical Spectrograph and InfraRed Imaging System (OSIRIS) onboard the Odin satellite. Although OSIRIS coverage begins in mid-March, the measurements show a belt of enhanced scattering near 35 km altitude between 50° N and 70° N. Initially, enhancements show increased scattering of up to 15% over the background conditions, decaying in intensity and dropping in altitude until they are indistinguishable from background conditions by mid-May.

Description: Four-dimensional ensemble-variational data assimilation for global deterministic weather prediction Nonlinear Processes in Geophysics, 20, 669-682, 2013 Author(s): M. Buehner, J. Morneau, and C. Charette The goal of this study is to evaluate a version of the ensemble-variational data assimilation approach (EnVar) for possible replacement of 4D-Var at Environment Canada for global deterministic weather prediction. This implementation of EnVar relies on 4-D ensemble covariances, obtained from an ensemble Kalman filter, that are combined in a vertically dependent weighted average with simple static covariances. Verification results are presented from a set of data assimilation experiments over two separate 6-week periods that used assimilated observations and model configuration very similar to the currently operational system. To help interpret the comparison of EnVar versus 4D-Var, additional experiments using 3D-Var and a version of EnVar with only 3-D ensemble covariances are also evaluated. To improve the rate of convergence for all approaches evaluated (including EnVar), an estimate of the cost function Hessian generated by the quasi-Newton minimization algorithm is cycled from one analysis to the next. Analyses from EnVar (with 4-D ensemble covariances) nearly always produce improved, and never degraded, forecasts when compared with 3D-Var. Comparisons with 4D-Var show that forecasts from EnVar analyses have either similar or better scores in the troposphere of the tropics and the winter extra-tropical region. However, in the summer extra-tropical region the medium-range forecasts from EnVar have either similar or worse scores than 4D-Var in the troposphere. In contrast, the 6 h forecasts from EnVar are significantly better than 4D-Var relative to radiosonde observations for both periods and in all regions. The use of 4-D versus 3-D ensemble covariances only results in small improvements in forecast quality. By contrast, the improvements from using 4D-Var versus 3D-Var are much larger. Measurement of the fit of the background and analyzed states to the observations suggests that EnVar and 4D-Var can both make better use of observations distributed over time than 3D-Var. In summary, the results from this study suggest that the EnVar approach is a viable alternative to 4D-Var, especially when the simplicity and computational efficiency of EnVar are considered. Additional research is required to understand the seasonal dependence of the difference in forecast quality between EnVar and 4D-Var in the extra-tropics.

Description: Probabilistic approach to cloud and snow detection on AVHRR imagery Atmospheric Measurement Techniques Discussions, 6, 8445-8507, 2013 Author(s): J. P. Musial, F. Hüsler, M. Sütterlin, C. Neuhaus, and S. Wunderle The derivation of probability estimates complementary to geophysical data sets has gained special attention over the last years. The information about a confidence level of provided physical quantities is required to construct an error budget of higher level products and to correctly interpret final results of a particular analysis. Regarding the generation of products based on satellite data the common input consists of a cloud mask which allows discrimination between surface and cloud signals. Further the surface information is divided between snow and snow-free components. At any step of this discrimination process a misclassification in a cloud/snow mask propagates to higher level products and may alter their usability. Within this scope a novel Probabilistic Cloud Mask (PCM) algorithm suited for the 1×1 km Advanced Very High Resolution Radiometer (AVHRR) data is proposed which provides three types of probability estimates between: cloudy/clear-sky, cloudy/snow and clear-sky/snow conditions. As opposed to the majority of available techniques which are usually based on a decision-tree approach in the PCM algorithm all spectral, angular and ancillary information is used in a single step to retrieve the probability estimates from the pre-computed Look Up Tables (LUTs). Moreover, the issue of derivation of a single threshold value for a spectral test was overcome by the concept of multidimensional information space which is divided into small bins by an extensive set of thresholds. The discrimination between snow and ice clouds and detection of broken, thin clouds was enhanced by means of the Invariant Coordinate System (ICS) transformation. The study area covers a wide range of environmental conditions spanning from Iceland through central Europe to northern parts of Africa which exhibit diverse difficulties for cloud/snow masking algorithms. The retrieved PCM cloud classification was compared to the PPSv2012 and MOD35 collection 6 cloud masks, SYNOP weather reports, CALIPSO vertical feature mask version 3 and to MOD10A1 collection 5 snow mask. The outcomes of conducted analyses proved fine detection skills of the PCM method with comparable or better results than the reference PPS algorithm.

Description: Retrieval techniques for airborne imaging of methane concentrations using high spatial and moderate spectral resolution: application to AVIRIS Atmospheric Measurement Techniques Discussions, 6, 8543-8588, 2013 Author(s): A. K. Thorpe, C. Frankenberg, and D. A. Roberts Two quantitative retrieval techniques were evaluated to estimate methane (CH 4 ) enhancement in concentrated plumes using high spatial and moderate spectral resolution data from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). An Iterative Maximum a Posteriori Differential Optical Absorption Spectroscopy (IMAP-DOAS) algorithm performed well for an ocean scene containing natural CH 4 emissions from the Coal Oil Point (COP) seep field near Santa Barbara, California. IMAP-DOAS retrieval precision errors are expected to equal between 0.31 to 0.61 ppm CH 4 over the lowest atmospheric layer (height up to 1.04 km), corresponding to about a 30 to 60 ppm error for a 10 m thick plume. However, IMAP-DOAS results for a terrestrial scene were adveresly influenced by the underlying landcover. A hybrid approach using Singular Value Decomposition (SVD) was particularly effective for terrestrial surfaces because it could better account for spectral variability in surface reflectance. Using this approach, a CH 4 plume was observed immediately downwind of two hydrocarbon storage tanks at the Inglewood Oil Field in Los Angeles, California, with a maximum near surface enhancement of 8.45 ppm above background. At COP, the distinct plume had a maximum enhancement of 2.85 ppm CH 4 above background and was consistent with known seep locations and local wind direction. A sensitivity analysis also indicates CH 4 sensitivity should be more than doubled for the next generation AVIRIS sensor (AVIRISng) due to improved spectral resolution and sampling. AVIRIS-like sensors offer the potential to better constrain emissions on local and regional scales, including sources of increasing concern like industrial point source emissions and fugitive CH 4 from the oil and gas industry.

Description: Effects of solar activity and geomagnetic field on noise in CALIOP profiles above the South Atlantic Anomaly Atmospheric Measurement Techniques Discussions, 6, 8589-8602, 2013 Author(s): V. Noel, H. Chepfer, C. Hoareau, M. Reverdy, and G. Cesana By documenting noise levels in 6.5 yr of nighttime measurements by the spaceborne lidar CALIOP above the South Atlantic Anomaly (SAA), we show they contain information about the evolution of upwelling high-energy radiation levels in the area. We find the amount of noisy profiles is influenced by the 11 yr cycle of solar activity, fluctuates by ±5% between 2006 and 2013, and is anticorrelated with solar activity with a 1 yr lag. The size of the SAA grows as solar activity decreases, and an overall westward shift of the SAA region is detectable. We predict SAA noise levels will increase anew after 2014, and will affect future spaceborne lidar missions most near 2020. In other areas, supposedly unaffected by incoming sunlight, nighttime noise levels are much weaker but follow the same 11 yr cycle, superimposed with a one-year cycle that affects both hemispheres similarly and could be attributed to geomagnetic activity.

Description: Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence Atmospheric Measurement Techniques Discussions, 7, 12545-12588, 2014 Author(s): L. Guanter, I. Aben, P. Tol, J. M. Krijger, A. Hollstein, P. Köhler, A. Damm, J. Joiner, C. Frankenberg, and J. Landgraf Global monitoring of sun-induced chlorophyll fluorescence (SIF) can improve our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675–775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km × 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor 2 with respect to GOME-2, which comes together with an about 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to accurately map other important vegetation parameters, such as leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning.

Description: The Level 2 research product algorithms for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) Atmospheric Measurement Techniques Discussions, 4, 3593-3645, 2011 Author(s): P. Baron, J. Urban, H. Sagawa, J. Möller, D. P. Murtagh, J. Mendrok, E. Dupuy, T. O. Sato, S. Ochiai, K. Suzuki, T. Manabe, T. Nishibori, K. Kikuchi, R. Sato, M. Takayanagi, Y. Murayama, M. Shiotani, and Y. Kasai This paper describes the algorithms of the level-2 research (L2r) processing chain developed for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES). The chain has been developed in parallel to the operational chain for conducting researches on calibration and retrieval algorithms. L2r chain products are available to the scientific community. The objective of version 2 is the retrieval of the vertical distribution of trace gases in the altitude range of 18–90 km. An theoretical error analysis is conducted to estimate the retrieval feasibility of key parameters of the processing: line-of-sight elevation tangent altitudes (or angles), temperature and O 3 profiles. The line-of-sight tangent altitudes are retrieved between 20 and 50 km from the strong ozone (O 3 ) line at 625.371 GHz, with low correlation with the O 3 volume-mixing ratio and temperature retrieved profiles. Neglecting the non-linearity of the radiometric gain in the calibration procedure is the main systematic error. It is large for the retrieved temperature (between 5–10 K). Therefore, atmospheric pressure can not be derived from the retrieved temperature, and, then, in the altitude range where the line-of-sight tangent altitudes are retrieved, the retrieved trace gases profiles are found to be better represented on pressure levels than on altitude levels. The error analysis for the retrieved HOCl profile demonstrates that best results for inverting weak lines can be obtained by using narrow spectral windows. Future versions of the L2r algorithms will improve the temperature/pressure retrievals and also provide information in the upper tropospheric/lower stratospheric region (e.g., water vapor, ice content, O 3 ) and on stratospheric and mesospheric line-of-sight winds.

Description: Near infrared nadir sounding of vertical column densities: methodology and application to SCIAMACHY Atmospheric Measurement Techniques Discussions, 4, 3685-3737, 2011 Author(s): S. Gimeno García, F. Schreier, G. Lichtenberg, and S. Slijkhuis Nadir observations with the shortwave infrared channels of SCIAMACHY onboard the ENVISAT satellite can be used to derive information on atmospheric gases such as CO, CH 4 , N 2 O, CO 2 , and H 2 O. For the operational level 1b–2 processing of SCIAMACHY data a new retrieval code BIRRA (Beer InfraRed Retrieval Algorithm) has been developed: BIRRA performs a nonlinear least squares fit of the measured radiance, where molecular concentration vertical profiles are scaled to fit the observed data. Here we present the forward modeling (radiative transfer) and inversion (least squares optimization) fundamentals of the code along with the further processing steps required to generate higher level products such as global distributions and time series. Moreover, various aspects of level 1 (observed spectra) and auxiliary input data relevant for successful retrievals are discussed. BIRRA is currently used for operational analysis of carbon monoxide vertical column densities from SCIAMACHY channel 8 observations, and is being prepared for methane retrievals using channel 6 spectra. A set of representative CO retrievals and first CH 4 results are presented to demonstrate BIRRA's capabilities.

Description: Volatilizable biogenic organic compounds (VBOCs) with two dimensional gas chromatography-time of flight mass spectrometry (GC × GC-TOFMS): sampling methods, VBOC complexity, and chromatographic retention data Atmospheric Measurement Techniques Discussions, 4, 3647-3684, 2011 Author(s): J. F. Pankow, W. Luo, A. N. Melnychenko, K. C. Barsanti, L. M. Isabelle, C. Chen, A. B. Guenther, and T. N. Rosenstiel Two dimensional gas chromatography (GC × GC) with detection by time-of-flight mass spectrometry (TOFMS) was applied in the rapid analysis of air samples containing highly complex mixtures of volatilizable biogenic organic compounds (VBOCs). VBOC analytical methodologies are briefly reviewed, and optimal conditions are discussed for sampling with both adsorption/thermal desorption (ATD) cartridges and solid-phase microextraction (SPME) fibers. Air samples containing VBOC emissions from leaves of two tree species ( Cedrus atlantica and Calycolpus moritzianus ) were obtained by both ATD and SPME. The optimized gas chromatographic conditions utilized a 45 m, 0.25 mm I.D. low-polarity primary column (DB-VRX, 1.4 μm film) and a 1.5 m, 0.25 mm I.D. polar secondary column (Stabilwax® 0.25 μm film). Excellent separation was achieved in a 36 min temperature programmed GC × GC chromatogram. Thousands of VBOC peaks were present in the sample chromatograms; hundreds of tentative identifications by NIST mass spectral matching are provided. Very few of the tentatively identified compounds are currently available as authentic standards. Method detection limit values for a 5 l ATD sample were 3.5 pptv (10 ng m −3 ) for isoprene, methyl vinyl ketone, and methacrolein, and ~1.5 pptv (~10 ng m −3 ) for monoterpenes and sesquiterpenes. Kovats-type chromatographic retention index values on the primary column and relative retention time values on the secondary column are provided for 21 standard compounds and for 417 tentatively identified VBOCs. 19 of the 21 authentic standard compounds were found in one of the Cedrus atlantica SPME samples. In addition, easily quantifiable levels of at least 13 sesquiterpenes were found in an ATD sample obtained from a branch enclosure of Calycolpus moritzianus . Overall, the results obtained via GC × GC-TOFMS highlight an extreme, and largely uncharacterized diversity of VBOCs, consistent with the hypothesis that sesquiterpenes and other compounds beyond the current list of typically determined VBOC analytes may well be important contributors to global atmospheric levels of organic particulate matter.

Description: Corrigendum to "Breeding and predictability in the baroclinic rotating annulus using a perfect model" published in Nonlin. Processes Geophys., 15, 469–487, 2008 Nonlinear Processes in Geophysics, 18, 359-359, 2011 Author(s): R. M. B. Young and P. L. Read No abstract available.

Description: Correcting orbital drift signal in the time series of AVHRR derived convective cloud fraction using rotated empirical orthogonal function Atmospheric Measurement Techniques Discussions, 4, 3877-3890, 2011 Author(s): A. Devasthale, K. Karlsson, J. Quaas, and H. Grassl The AVHRRs instruments onboard the series of NOAA satellites offer the longest available meteorological data records from space. These satellites have drifted in orbit resulting in shifts in the local time sampling during the life span of sensors onboard. Depending on the amplitude of a diurnal cycle of the geophysical parameters derived, orbital drift may cause spurious trends in their time series. We investigate tropical deep convective clouds, which show pronounced diurnal cycle amplitude, to bracket an upper bound of the impact of orbital drift on their time series. We carry out a rotated empirical orthogonal function analysis and show that the REOFs are useful in delineating orbital drift signal and, more importantly, in correcting this signal in the time series of convective cloud amount. These results will help facilitate the derivation of homogenized data series of cloud amount from NOAA satellite sensors and ultimately analyzing trends from them. However, we suggest detailed comparison of various methods and their rigorous testing before applying final orbital drift corrections.

Description: Strategies for coupling global and limited-area ensemble Kalman filter assimilation Nonlinear Processes in Geophysics, 18, 415-430, 2011 Author(s): D. Merkova, I. Szunyogh, and E. Ott This paper compares the forecast performance of four strategies for coupling global and limited area data assimilation: three strategies propagate information from the global to the limited area process, while the fourth strategy feeds back information from the limited area to the global process. All four strategies are formulated in the Local Ensemble Transform Kalman Filter (LETKF) framework. Numerical experiments are carried out with the model component of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) and the NCEP Regional Spectral Model (RSM). The limited area domain is an extended North-America region that includes part of the north-east Pacific. The GFS is integrated at horizontal resolution T62 (about 150 km in the mid-latitudes), while the RSM is integrated at horizontal resolution 48 km. Experiments are carried out both under the perfect model hypothesis and in a realistic setting. The coupling strategies are evaluated by comparing their deterministic forecast performance at 12-h and 48-h lead times. The results suggest that the limited area data assimilation system has the potential to enhance the forecasts at 12-h lead time in the limited area domain at the synoptic and sub-synoptic scales (in the global wave number range of about 10 to 40). There is a clear indication that between the forecast performance of the different coupling strategies those that cycle the limited area assimilation process produce the most accurate forecasts. In the realistic setting, at 12-h forecast time the limited area systems produce more modest improvements compared to the global system than under the perfect model hypothesis, and at 48-h forecast time the global forecasts are more accurate than the limited area forecasts.

Description: Sensitivity studies for a space-based methane lidar mission Atmospheric Measurement Techniques Discussions, 4, 3545-3592, 2011 Author(s): C. Kiemle, M. Quatrevalet, G. Ehret, A. Amediek, A. Fix, and M. Wirth Methane is the third most important greenhouse gas in the atmosphere after water vapour and carbon dioxide. A major handicap to quantify the emissions at the Earth's surface in order to better understand biosphere-atmosphere exchange processes and potential climate feedbacks is the lack of accurate and global observations of methane. Space-based integrated path differential absorption (IPDA) lidar has potential to fill this gap, and a Methane Remote Lidar Mission (MERLIN) on a small satellite in Polar orbit was proposed by DLR and CNES in the frame of a German-French climate monitoring initiative. System simulations are used to identify key performance parameters and to find an advantageous instrument configuration, given the environmental, technological, and budget constraints. The sensitivity studies use representative averages of the atmospheric and surface state to estimate the measurement precision, i.e. the random uncertainty due to instrument noise. Key performance parameters for MERLIN are average laser power, telescope size, orbit height, surface reflectance, and detector noise. A modest-size lidar instrument with 0.45 W average laser power and 0.55 m telescope diameter on a 506 km orbit could provide 50-km averaged methane column measurement along the sub-satellite track with a precision of about 1 % over vegetation. The use of a methane absorption trough at 1.65 μm improves the near-surface measurement sensitivity and vastly relaxes the wavelength stability requirement that was identified as one of the major technological risks in the pre-phase A studies for A-SCOPE, a space-based IPDA lidar for carbon dioxide at the European Space Agency. Minimal humidity and temperature sensitivity at this wavelength position will enable accurate measurements in tropical wetlands, key regions with largely uncertain methane emissions. In contrast to actual passive remote sensors, measurements in Polar Regions will be possible and biases due to aerosol layers and thin ice clouds will be minimised.

Description: Information operator approach applied to the retrieval of the vertical distribution of atmospheric constituents from ground-based high-resolution FTIR measurements Atmospheric Measurement Techniques Discussions, 4, 3739-3785, 2011 Author(s): C. Senten, M. De Mazière, G. Vanhaelewyn, and C. Vigouroux The analysis of high spectral resolution Fourier Transform infrared (FTIR) solar absorption spectra is an important issue in remote sensing. If this is done carefully, one can obtain information, not only about the total column abundances, but also about the vertical distribution of various constituents in the atmosphere. This work introduces the application of the information operator approach for extracting vertical profile information from ground-based FTIR measurements. The algorithm is implemented and tested within the well-known retrieval code SFIT2, adapting the optimal estimation method such as to take into account only the significant contributions to the solution. In particular, we demonstrate the feasibility of the method in an application to ground-based FTIR spectra taken in the frame of the Network for the Detection of Atmospheric Composition Change (NDACC) at Ile de La Réunion (21° S, 55° E). A thorough comparison is made between the original optimal estimation method and this alternative retrieval algorithm, regarding information content, retrieval robustness and corresponding full error budget evaluation for the target species ozone (O 3 ), nitrous oxide (N 2 O), methane (CH 4 ), and carbon monoxide (CO). For O 3 and CH 4 , a comparison with the Tikhonov regularization method has also been made. It is shown that the information operator approach performs well and in most cases yields both a better accuracy and stability than the optimal estimation method. Additionally, the information operator approach has the advantage of being less sensitive to the choice of a priori information. The Tikhonov regularization results seem to be situated between both methods' results, as to profile retrievals, error budgets and column stability.

Description: Spectral methods for internal waves: indistinguishable density profiles and double-humped solitary waves Nonlinear Processes in Geophysics, 18, 351-358, 2011 Author(s): M. Dunphy, C. Subich, and M. Stastna Internal solitary waves are widely observed in both the oceans and large lakes. They can be described by a variety of mathematical theories, covering the full spectrum from first order asymptotic theory (i.e. Korteweg-de Vries, or KdV, theory), through higher order extensions of weakly nonlinear-weakly nonhydrostatic theory, to fully nonlinear-weakly nonhydrostatic theories and finally exact theory based on the Dubreil-Jacotin-Long (DJL) equation that is formally equivalent to the full set of Euler equations. We discuss how spectral and pseudospectral methods allow for the computation of novel phenomena in both approximate and exact theories. In particular we construct markedly different density profiles for which the coefficients in the KdV theory are very nearly identical. These two density profiles yield qualitatively different behaviour for both exact, or fully nonlinear, waves computed using the DJL equation and in dynamic simulations of the time dependent Euler equations. For exact, DJL, theory we compute exact solitary waves with two-scales, or so-called double-humped waves.

Description: Opportunistic validation of sulfur dioxide in the Sarychev Peak volcanic eruption cloud Atmospheric Measurement Techniques Discussions, 4, 3861-3875, 2011 Author(s): S. A. Carn and T. M. Lopez We report attempted validation of Ozone Monitoring Instrument (OMI) sulfur dioxide (SO 2 ) retrievals in the stratospheric volcanic cloud from Sarychev Peak (Kurile Islands) in June 2009, through opportunistic deployment of a ground-based ultraviolet (UV) spectrometer (FLYSPEC) as the volcanic cloud drifted over Central Alaska. The volcanic cloud altitude (~12–14 km) was constrained using coincident CALIPSO lidar observations. By invoking some assumptions about the spatial distribution of SO 2 , we derive averages of FLYSPEC vertical SO 2 columns for comparison with OMI SO 2 measurements. Despite limited data, we find minimum OMI-FLYSPEC differences of ~5–6 % which support the validity of the operational OMI SO 2 algorithm. These measurements represent the first attempt to validate SO 2 in a stratospheric volcanic cloud using a mobile ground-based instrument, and demonstrate the need for a network of rapidly deployable instruments for validation of space-based volcanic SO 2 measurements.

Description: A nonlinear method of removing harmonic noise in geophysical data Nonlinear Processes in Geophysics, 18, 367-379, 2011 Author(s): Y. Jeng and C.-S. Chen A nonlinear, adaptive method to remove the harmonic noise that commonly resides in geophysical data is proposed in this study. This filtering method is based on the ensemble empirical mode decomposition algorithm in conjunction with the logarithmic transform. We present a synthetic model study to investigate the capability of signal reconstruction from the decomposed data, and compare the results with those derived from other 2-D adaptive filters. Applications to the real seismic data acquired by using an ocean bottom seismograph and to a shot gather of the ground penetrating radar demonstrate the robustness of this method. Our work proposes a concept that instead of Fourier-based approaches, the harmonic noise removal in geophysical data can be achieved effectively by using an alternative nonlinear adaptive data analysis method, which has been applied extensively in other scientific studies.

Description: Inversion of tropospheric profiles of aerosol extinction and HCHO and NO 2 mixing ratios from MAX-DOAS observations in Milano during the summer of 2003 and comparison with independent data sets Atmospheric Measurement Techniques Discussions, 4, 3891-3964, 2011 Author(s): T. Wagner, S. Beirle, T. Brauers, T. Deutschmann, U. Frieß, C. Hak, J. D. Halla, K. P. Heue, W. Junkermann, X. Li, U. Platt, and I. Pundt-Gruber We present aerosol and trace gas profiles derived from MAX-DOAS observations. Our inversion scheme is based on simple profile parameterisations used as input for an atmospheric radiative transfer model (forward model). From a least squares fit of the forward model to the MAX-DOAS measurements, two profile parameters are retrieved including integrated quantities (aerosol optical depth or trace gas vertical column density), and parameters describing the height and shape of the respective profiles. From these results, the aerosol extinction and trace gas mixing ratios can also be calculated. We apply the profile inversion to MAX-DOAS observations during a measurement campaign in Milano, Italy, September 2003, which allowed simultaneous observations from three telescopes (directed to north, west, south). Profile inversions for aerosols and trace gases were possible on 23 days. Especially in the middle of the campaign (17–20 September 2003), enhanced values of aerosol optical depth and NO 2 and HCHO mixing ratios were found. The retrieved layer heights were typically similar for HCHO and aerosols. For NO 2 , lower layer heights were found, which increased during the day. The MAX-DOAS inversion results are compared to independent measurements: (1) aerosol optical depth measured at an AERONET station at Ispra; (2) near-surface NO 2 and HCHO (formaldehyde) mixing ratios measured by long path DOAS and Hantzsch instruments at Bresso; (3) vertical profiles of HCHO and aerosols measured by an ultra light aircraft. Depending on the viewing direction, the aerosol optical depths from MAX-DOAS are either smaller or larger than those from AERONET observations. Similar comparison results are found for the MAX-DOAS NO 2 mixing ratios versus long path DOAS measurements. In contrast, the MAX-DOAS HCHO mixing ratios are generally higher than those from long path DOAS or Hantzsch instruments. The comparison of the HCHO and aerosol profiles from the aircraft showed reasonable agreement with the respective MAX-DOAS layer heights. From the comparison of the results for the different telescopes, it was possible to investigate the internal consistency of the MAX-DOAS observations. As part of our study, a cloud classification algorithm was developed (based on the MAX-DOAS zenith viewing directions), and the effects of clouds on the profile inversion were investigated. Different effects of clouds on aerosols and trace gas retrievals were found: while the aerosol optical depth is systematically underestimated and the HCHO mixing ratio is systematically overestimated under cloudy conditions, the NO 2 mixing ratios are only slightly affected. These findings are in basic agreement with radiative transfer simulations.

Description: Modeling the ascent of sounding balloons: derivation of the vertical air motion Atmospheric Measurement Techniques Discussions, 4, 3965-4012, 2011 Author(s): A. Gallice, F. G. Wienhold, C. R. Hoyle, F. Immler, and T. Peter A new model to describe the ascent of sounding balloons in the troposphere and lower stratosphere (up to ~30–35 km altitude) is presented. Contrary to previous models, detailed account is taken of both the variation of the drag coefficient with altitude and the heat imbalance between the balloon and the atmosphere. To compensate for the lack of data on the drag coefficient of sounding balloons, a reference curve for the relationship between drag coefficient and Reynolds number is derived from a dataset of flights launched during the Lindenberg Upper Air Methods Intercomparisons (LUAMI) campaign. The transfer of heat from the surrounding air into the balloon is accounted for by solving the radial heat diffusion equation inside the balloon. The potential applications of the model include the forecast of the trajectory of sounding balloons, which can be used to increase the accuracy of the match technique, and the derivation of the air vertical velocity. The latter is obtained by subtracting the ascent rate of the balloon in still air calculated by the model from the actual ascent rate. This technique is shown to provide an approximation for the vertical air motion with an uncertainty error of 0.5 m s −1 in the troposphere and 0.2 m s −1 in the stratosphere. An example of extraction of the air vertical velocity is provided in this paper. We show that the air vertical velocities derived from the balloon soundings in this paper are in general agreement with small-scale atmospheric velocity fluctuations related to gravity waves, mechanical turbulence, or other small-scale air motions measured during the SUCCESS campaign (Subsonic Aircraft: Contrail and Cloud Effects Special Study) in the orographically unperturbed mid-latitude middle troposphere.

Description: Comparison of correlation analysis techniques for irregularly sampled time series Nonlinear Processes in Geophysics, 18, 389-404, 2011 Author(s): K. Rehfeld, N. Marwan, J. Heitzig, and J. Kurths Geoscientific measurements often provide time series with irregular time sampling, requiring either data reconstruction (interpolation) or sophisticated methods to handle irregular sampling. We compare the linear interpolation technique and different approaches for analyzing the correlation functions and persistence of irregularly sampled time series, as Lomb-Scargle Fourier transformation and kernel-based methods. In a thorough benchmark test we investigate the performance of these techniques. All methods have comparable root mean square errors (RMSEs) for low skewness of the inter-observation time distribution. For high skewness, very irregular data, interpolation bias and RMSE increase strongly. We find a 40 % lower RMSE for the lag-1 autocorrelation function (ACF) for the Gaussian kernel method vs. the linear interpolation scheme,in the analysis of highly irregular time series. For the cross correlation function (CCF) the RMSE is then lower by 60 %. The application of the Lomb-Scargle technique gave results comparable to the kernel methods for the univariate, but poorer results in the bivariate case. Especially the high-frequency components of the signal, where classical methods show a strong bias in ACF and CCF magnitude, are preserved when using the kernel methods. We illustrate the performances of interpolation vs. Gaussian kernel method by applying both to paleo-data from four locations, reflecting late Holocene Asian monsoon variability as derived from speleothem δ 18 O measurements. Cross correlation results are similar for both methods, which we attribute to the long time scales of the common variability. The persistence time (memory) is strongly overestimated when using the standard, interpolation-based, approach. Hence, the Gaussian kernel is a reliable and more robust estimator with significant advantages compared to other techniques and suitable for large scale application to paleo-data.

Description: Brief communication "On one mechanism of low frequency variability of the Antarctic Circumpolar Current" Nonlinear Processes in Geophysics, 18, 361-365, 2011 Author(s): O. G. Derzho and B. de Young In this paper we present a simple analytical model for low frequency and large scale variability of the Antarctic Circumpolar Current (ACC). The physical mechanism of the variability is related to temporal and spatial variations of the cyclonic mean flow (ACC) due to circularly propagating nonlinear barotropic Rossby wave trains. It is shown that the Rossby wave train is a fundamental mode, trapped between the major fronts in the ACC. The Rossby waves are predicted to rotate with a particular angular velocity that depends on the magnitude and width of the mean current. The spatial structure of the rotating pattern, including its zonal wave number, is defined by the specific form of the stream function-vorticity relation. The similarity between the simulated patterns and the Antarctic Circumpolar Wave (ACW) is highlighted. The model can predict the observed sequence of warm and cold patches in the ACW as well as its zonal number.

Description: A semi-phenomenological approach to explain the event-size distribution of the Drossel-Schwabl forest-fire model Nonlinear Processes in Geophysics, 18, 381-388, 2011 Author(s): S. Hergarten and R. Krenn We present a novel approach to explain the complex scaling behavior of the Drossel-Schwabl forest-fire model in two dimensions. Clusters of trees are characterized by their size and perimeter only, whereas spatial correlations are neglected. Coalescence of clusters is restricted to clusters of similar sizes. Our approach derives the value of the scaling exponent τ of the event size distribution directly from the scaling of the accessible perimeter of percolation clusters. We obtain τ = 1.19 in the limit of infinite growth rate, in perfect agreement with numerical results. Furthermore, our approach predicts the unusual transition from a power law to an exponential decay even quantitatively, while the exponential decay at large event sizes itself is reproduced only qualitatively.

Description: Potential and limitations of the MAX-DOAS method to retrieve the vertical distribution of tropospheric nitrogen dioxide Atmospheric Measurement Techniques Discussions, 4, 4013-4072, 2011 Author(s): T. Vlemmix, A. J. M. Piters, A. J. C. Berkhout, L. F. L. Gast, P. Wang, and P. F. Levelt Muliple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments can measure from the ground the absorption by nitrogen dioxide (NO 2 ) of scattered sunlight seen in multiple viewing directions. This paper studies the potential of this technique to derive the vertical distribution of NO 2 in the troposphere. Such profile information is essential in validation studies in which MAX-DOAS retrievals play a role. The retrieval algorithm used is based on a pre-calculated look-up table and assumes homogeneous mixing of aerosols and NO 2 in layers extending from the surface to a variable height. Two retrieval models are compared: one including and one excluding an elevated NO 2 layer at a fixed altitude in the free troposphere. An ensemble technique is applied to derive retrieved model uncertainties. Sensitivity studies demonstrate that MAX-DOAS based retrievals can make a distinction between an NO 2 layer that extends from the surface to a certain height (having a constant mixing ratio, or a mixing ratio that decreases with altitude) and an elevated NO 2 layer. The height of the elevated NO 2 layer can only be retrieved accurately when the aerosol extinction profile is known and the measurement noise is low. The uncertainty in this elevated NO 2 layer height provides the main source of uncertainty in the retrieval of the free tropospheric contribution to the tropospheric NO 2 column. A comparison was performed with independent data, based on observations done at the CINDI campaign, held in the Netherlands in 2009. Comparison with lidar partial tropospheric NO 2 columns showed a correlation of 0.78, and an average difference of 0.1× 10 15 molec cm −2 . The diurnal evolution of the NO 2 volume mixing ratio measured by in-situ monitors at the surface and averaged over five days with cloud-free mornings, compares quite well to the MAX-DOAS retrieval: a correlation was found of 0.8, and an average difference of 0.2 ppb.

Description: Double rank-ordering technique of ROMA (Rank-Ordered Multifractal Analysis) for multifractal fluctuations featuring multiple regimes of scales Nonlinear Processes in Geophysics, 18, 405-414, 2011 Author(s): S. W. Y. Tam and T. Chang Rank-Ordered Multifractal Analysis (ROMA), a technique capable of deciphering the multifractal characteristics of intermittent fluctuations, was originally applied to the results of a magnetohydrodynamic (MHD) simulation. Application of ROMA to measured fluctuations in the auroral zone, due to the dominant physical effects changing from kinetic to MHD as the scale increases, requires an additional level of rank-ordering in order to divide the domain of scales into regimes. An algorithm for the additional step in this double rank-ordering technique is discussed, and is demonstrated in the application to the electric field fluctuations in the auroral zone as an example. As a result of the double rank-ordering, ROMA is able to take into account the nonlinear crossover behavior characterized by the multiple regimes of time scales by providing a scaling variable and a scaling function that are global to all the time scales.

Description: Water isotopic ratios from a continuously melted ice core sample Atmospheric Measurement Techniques Discussions, 4, 4073-4104, 2011 Author(s): V. Gkinis, T. J. Popp, T. Blunier, M. Bigler, S. Schüpbach, and S. J. Johnsen A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We build an interface between an Infra Red Cavity Ring Down Spectrometer (IR-CRDS) and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of δ 18 O and δD on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub μl amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100 % efficiency in a home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on humidity levels. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 ‰ and 0.5 ‰ for δ 18 O and δD, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of δ 18 O and δD, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the framework of the NEEM deep ice core drilling project in Greenland, during the 2010 field season.

Description: A 3-D tomographic trajectory retrieval for the air-borne limb-imager GLORIA Atmospheric Measurement Techniques Discussions, 4, 3805-3859, 2011 Author(s): J. Ungermann, J. Blank, J. Lotz, K. Leppkes, T. Guggenmoser, M. Kaufmann, P. Preusse, U. Naumann, and M. Riese Infrared limb sounding from aircraft can provide 2-D curtains of multiple trace gas species. However, conventional limb sounders view perpendicular to the aircraft axis and are unable to resolve the observed airmass along their line-of-sight. GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) is a new remote sensing instrument able to adjust its horizontal view angle with respect to the aircraft flight direction from 45° to 135°. This will allow for tomographic measurements of mesoscale structures for a wide variety of atmospheric constituents. Many flights of the GLORIA instrument will not follow closed curves that allow measuring an airmass from all directions. Consequently, it is examined by means of simulations, what results can be expected from tomographic evaluation of measurements made during a straight flight. It is demonstrated that the achievable resolution and stability is enhanced compared to conventional retrievals. In a second step, it is shown that the incorporation of channels exhibiting different optical depth can greatly enhance the 3-D retrieval quality enabling the exploitation of previously unused spectral samples. A second problem for tomographic retrievals is that advection, which can be neglected for conventional retrievals, plays an important role for the time-scales involved in a tomographic measurement flight. This paper presents a method to diagnose the effect of a time-varying atmosphere on a 3-D retrieval and demonstrates an effective way to compensate for effects of advection by incorporating wind-fields from meteorological datasets as a priori information.

Description: High-resolution air quality monitoring from space: a fast retrieval scheme for CO from hyperspectral infrared measurements Atmospheric Measurement Techniques Discussions, 4, 3787-3803, 2011 Author(s): N. Smith, H.-L. Huang, E. Weisz, H. J. Annegarn, and R. B. Pierce The first results of the Fast Linear Inversion Trace gas System (FLITS) retrieval scheme are presented here for CO from IASI (Infrared Atmospheric Sounding Interferometer) measurements using RAQMS (Real time Air Quality Modelling System) as atmospheric background. FLITS is a simple linear inversion scheme with a stable performance that retrieves total column CO concentrations (molec cm −2 ) at single field-of-view (FOV) irrespective of cloud cover. A case study is presented here for a biomass burning plume over the Pacific on 29 March 2010. For each FOV a single tropospheric CO density, vertically integrated over 200–800 hPa, is retrieved with 12 channels in the spectral range 2050–2225 cm −1 . Despite variations in cloud cover and temperature, the degrees of freedom for signal (DFS) of the solution ranges between 0.8 and 0.95. In addition, the retrieval error is at least half the background error of 10 %, with dominant contribution from uncertainty in the measurement and temperature. With its stability and processing speed, FLITS meet two of the key requirements for operational processing. We conclude that the linear combination of space-borne measurements with a chemical transport model in the FLITS retrieval scheme holds potential for real-time air quality monitoring and evaluation of pollutant transport at high spatial resolution.

Description: Early in-flight detection of SO 2 via Differential Optical Absorption Spectroscopy: a feasible aviation safety measure to prevent potential encounters with volcanic plumes Atmospheric Measurement Techniques Discussions, 4, 2827-2881, 2011 Author(s): L. Vogel, B. Galle, C. Kern, H. Delgado Granados, V. Conde, P. Norman, S. Arellano, O. Landgren, P. Lübcke, J. M. Alvarez Nieves, L. Cárdenas Gonzáles, and U. Platt Volcanic ash constitutes a risk to aviation, mainly due to its ability to cause jet engines to fail. Other risks include the possibility of abrasion of windshields and potentially serious damage to avionic systems. These hazards have been widely recognized since the early 1980s, when volcanic ash provoked several incidents of engine failure in commercial aircraft. In addition to volcanic ash, volcanic gases also pose a threat. Prolonged and/or cumulative exposure to sulphur dioxide (SO 2 ) or sulphuric acid (H 2 SO 4 ) aerosols potentially affects e.g. windows, air frame and may cause permanent damage to engines. SO 2 receives most attention among the gas species commonly found in volcanic plumes because its presence above the lower troposphere is a clear proxy for a volcanic cloud and indicates that fine ash could also be present. Up to now, remote sensing of SO 2 via Differential Optical Absorption Spectroscopy (DOAS) in the ultraviolet spectral region has been used to measure volcanic clouds from ground based, airborne and satellite platforms. Attention has been given to volcanic emission strength, chemistry inside volcanic clouds and measurement procedures were adapted accordingly. Here we present a set of experimental and model results, highlighting the feasibility of DOAS to be used as an airborne early detection system of SO 2 in two spatial dimensions. In order to prove our new concept, simultaneous airborne and ground-based measurements of the plume of Popocatépetl volcano, Mexico, were conducted in April 2010. The plume extended at an altitude around 5250 m above sea level and was approached and traversed at the same altitude with several forward looking DOAS systems aboard an airplane. These DOAS systems measured SO 2 in the flight direction and at ± 40 mrad (2.3°) angles relative to it in both, horizontal and vertical directions. The approaches started at up to 25 km distance to the plume and SO 2 was measured at all times well above the detection limit. In combination with radiative transfer studies, this study indicates that an extended volcanic cloud with a concentration of 10 12 molecules cm −3 at typical flight levels of 10 km can be detected unambiguously at distances of up to 80 km away. This range provides enough time (approx. 5 min) for pilots to take action to avoid entering a volcanic cloud in the flight path, suggesting that this technique can be used as an effective aid to prevent dangerous aircraft encounters with potentially ash rich volcanic clouds.

Description: Catalytic oxidation of H 2 on platinum: a method for in situ calibration of hygrometers Atmospheric Measurement Techniques Discussions, 4, 3083-3095, 2011 Author(s): A. W. Rollins, T. D. Thornberry, R.-S. Gao, B. D. Hall, and D. W. Fahey Standard reference samples of water vapor suitable for in situ calibration of atmospheric hygrometers are not currently widespread, leading to difficulties in unifying the calibrations of these hygrometers and potentially contributing to measurement discrepancies. We describe and evaluate a system for reliably and quantitatively converting mixtures of H 2 in air to H 2 O on a heated platinum (Pt) surface, providing a compact, portable, adjustable source of water vapor. The technique is shown to be accurate and can be used to easily and predictably produce a wide range of water vapor concentrations (≈1 ppm−2 %) on demand. The result is a H 2 O standard that is suitable for in situ calibration of hygrometers, with an accuracy nearly that of the available H 2 standards (≈±2 %).

Description: A versatile and reproducible automatic injection system for liquid standard introduction: application to in-situ calibration Atmospheric Measurement Techniques Discussions, 4, 3233-3249, 2011 Author(s): G. Isaacman, N. M. Kreisberg, D. R. Worton, S. V. Hering, and A. H. Goldstein The quantitation of trace organic compounds in ambient organic aerosol is difficult due to the chemical complexity of these mixtures, but is needed to provide insight into their sources and formation processes. Compound-level characterization of organic aerosols is typically performed through sample collection followed by gas or liquid chromatography. With these methods, introduction of liquid standards has long been used as an effective means of quantifying trace compounds, but automating this technique for use with in-situ instrumentation has not previously been achieved. Here we develop an automatic injection system (AutoInject) for the introduction of liquids into a custom collection and analysis cell for improved quantitation in chromatographic measurements. The system consists of chilled reservoirs containing liquid standards from which a sample loop is loaded and then injected into the cell. The AutoInject is shown to have reproducibility over 106 injections with a relative standard deviation of 1.5 %, and have negligible injection-to-injection carryover. A 6-port selector allows injection of different liquid standards separately or simultaneously. Additionally, automatic injection of multiple sample loops is shown to generate a linear multi-point calibration curve. Tests conducted in this work focus on use with the T hermal desorption A erosol G as chromatograph (TAG), but the flexibility of the system allows it to be used for a variety of applications.

Description: Spatial resolution of tropical terrestrial CO 2 fluxes inferred using space-borne column CO 2 sampled in different earth orbits: the role of spatial error correlations Atmospheric Measurement Techniques Discussions, 4, 3251-3276, 2011 Author(s): P. I. Palmer, L. Feng, and H. Bösch We use realistic numerical experiments to assess the sensitivity of 8-day CO 2 flux estimates, inferred from space-borne short-wave infrared measurements of column-averaged CO 2 dry air mixing ratio X CO 2 , to the choice of Earth observing orbit. We focus on three orbits: (1) a low-inclination circular orbit used by the NASA Tropical Rainfall Measuring Mission (TRMM); (2) a sun-synchronous orbit used by the Japanese Greenhouse Gases Observing SATellite (GOSAT) and proposed for the NASA Orbiting Carbon Observatory (OCO-2) instrument; and (3) a precessing orbit used by the International Space Station (ISS). For each orbit, we assume an instrument based on the specification of the OCO-2; for GOSAT we use the relevant instrument specification. Sun-synchronous orbits offer near global coverage within a few days but have implications for the density of clear-sky measurements. The TRMM and ISS orbits intensively sample tropical latitudes, with sun-lit clear-sky measurements evenly distributed between a.m./p.m. For a specified spatial resolution for inferred fluxes, we find there is a critical number of measurements beyond which there is a disproportionately small decrease in flux uncertainty. We also find that including spatial correlations for measurements and model errors (of length 300 km) reduces the effectiveness of high measurement density for flux estimation and so should be considered when deciding sampling strategies. We show that cloud-free data from the TRMM orbit generally can improve the spatial resolution of CO 2 fluxes achieved by OCO-2 over tropical South America, for example, from 950 km to 630 km, and that combining data from these low-inclination and sun-synchronous orbits have the potential to reduce this spatial length further. Decreasing the length of the error correlations to 50 km, reflecting anticipated future improvements to transport models, results in CO 2 flux estimates on spatial scales that approach those observed by regional aircraft.

Description: Validation of first chemistry mode retrieval results from new limb- imaging FTS GLORIA with correlative MIPAS-STR observations Atmospheric Measurement Techniques Discussions, 7, 12691-12717, 2014 Author(s): W. Woiwode, O. Suminska-Ebersoldt, H. Oelhaf, M. Höpfner, G. V. Belyaev, A. Ebersoldt, F. Friedl-Vallon, J.-U. Grooß, T. Gulde, M. Kaufmann, A. Kleinert, M. Krämer, E. Kretschmer, T. Kulessa, G. Maucher, T. Neubert, C. Piesch, P. Preusse, M. Riese, H. Rongen, C. Sartorius, G. Schardt, A. Schönfeld, D. Schuettemeyer, M. K. Sha, F. Stroh, J. Ungermann, C. M. Volk, and J. Orphal We report first chemistry mode retrieval results from the new airborne limb- imaging infrared FTS (Fourier transform spectrometer) GLORIA and comparisons with observations by the conventional airborne limb- scanning infrared FTS MIPAS-STR. For GLORIA, the flights aboard the high-altitude research aircraft M55 Geophysica during the ESSenCe campaign (ESa Sounder Campaign 2011) were the very first in field deployment after several years of development. The simultaneous observations of GLORIA and MIPAS-STR during the flight on 16 December 2011 inside the polar vortex and under the conditions of optically partially transparent polar stratospheric clouds (PSCs) provided us the unique opportunity to compare the observations by two different infrared FTS generations directly. The retrieval results of temperature, HNO 3 , O 3 , H 2 O, CFC-11 and CFC-12 show reasonable agreement of GLORIA with MIPAS-STR and collocated in-situ observations. For the horizontally binned hyperspectral limb-images, the GLORIA sampling outnumbered the horizontal cross-track sampling of MIPAS-STR by up to one order of magnitude. Depending on the target parameter, typical vertical resolutions of 0.5 to 2.0 km were obtained for GLORIA and are typically by factors of 2 to 4 better compared to MIPAS-STR. While the improvement of the performance, characterisation and data processing of GLORIA are subject of ongoing work, the presented first results already demonstrate the considerable gain in sampling and vertical resolution achieved with GLORIA.

Description: Large eddy simulation of sediment transport over rippled beds Nonlinear Processes in Geophysics, 21, 1169-1184, 2014 Author(s): J. C. Harris and S. T. Grilli Wave-induced boundary layer (BL) flows over sandy rippled bottoms are studied using a numerical model that applies a one-way coupling of a "far-field" inviscid flow model to a "near-field" large eddy simulation (LES) Navier–Stokes (NS) model. The incident inviscid velocity and pressure fields force the LES, in which near-field, wave-induced, turbulent bottom BL flows are simulated. A sediment suspension and transport model is embedded within the coupled flow model. The numerical implementation of the various models has been reported elsewhere, where we showed that the LES was able to accurately simulate both mean flow and turbulent statistics for oscillatory BL flows over a flat, rough bed. Here we show that the model accurately predicts the mean velocity fields and suspended sediment concentration for oscillatory flows over full-scale vortex ripples. Tests show that surface roughness has a significant effect on the results. Beyond increasing our insight into wave-induced oscillatory bottom BL physics, sophisticated coupled models of sediment transport such as that presented have the potential to make quantitative predictions of sediment transport and erosion/accretion around partly buried objects in the bottom, which is important for a vast array of bottom deployed instrumentation and other practical ocean engineering problems.

Description: Dependence of sandpile avalanche frequency–size distribution on coverage extent and compactness of embedded toppling threshold heterogeneity: implications for the variation of Gutenberg–Richter b value Nonlinear Processes in Geophysics, 21, 1185-1193, 2014 Author(s): L.-Y. Chiao and Q. Liu The effects of the spatiotemporal evolution of failure threshold heterogeneity on the dynamics of fault criticality, and thus on regional seismogenesis, have attracted strong interest in the field of regional seismotectonics. The heterogeneity might be a manifestation of the macroscopic distribution and multiscale strength variation of asperities, the distinct regional stress level, and (microscopically) heterogeneous fault surface roughness or friction regimes. In this study, rather than attempting to mimic the complex microscale slipping physics on a fault surface, sandpile cellular automata were implemented with a straightforward toppling rule. The objective is to examine the influence of distinct configurations of the embedded heterogeneous toppling threshold field on the global system avalanche event statistics. The examination results revealed that increasing the coverage extent and decreasing the compactness of the heterogeneous failure threshold, rather than the magnitude, range of contrast, diversity, or the geometric configuration of the threshold heterogeneity, leads to a systematic increase in the scaling exponent of the avalanche event power law statistics, implying the importance of mutual interaction among toppling sites with distinct thresholds. For tectonic provinces with differing stress regimes evolving spatio temporally, it is postulated that the distinct extent and compactness of the heterogeneous failure threshold are critical factors that manifest in the reported dynamic variations of seismicity scaling.

Description: Comparison of nitric oxide measurements in the mesosphere and lower thermosphere from ACE-FTS, MIPAS, SCIAMACHY, and SMR Atmospheric Measurement Techniques Discussions, 7, 12735-12794, 2014 Author(s): S. Bender, M. Sinnhuber, T. von Clarmann, G. Stiller, B. Funke, M. López-Puertas, J. Urban, K. Pérot, K. A. Walker, and J. P. Burrows We compare the nitric oxide measurements in the mesosphere and lower thermosphere (60 to 150 km) from four instruments: ACE-FTS, MIPAS, SCIAMACHY, and SMR. We use the daily zonal mean data in that altitude range for the years 2004–2010 (ACE-FTS), 2005–2012 (MIPAS), 2008–2012 (SCIAMACHY), and 2003–2012 (SMR). We first compare the data qualitatively with respect to the morphology, focussing on the major features, and then compare the time series directly and quantitatively. In three geographical regions, we compare the vertical density profiles on coincident measurement days. Since none of the instruments delivers continuous daily measurements in this altitude region, we carried out a multi-linear regression analysis. This regression analysis considers annual and semi-annual variability in form of harmonic terms and inter-annual variability by responding linearly to the solar Lyman-α radiation index and the geomagnetic Kp index. This analysis helps to find similarities and differences in the individual data sets with respect to the inter-annual variations caused by geomagnetic and solar variability. We find that the data sets are consistent and that they only disagree on minor aspects. SMR and ACE-FTS deliver the longest time series in the mesosphere and they both agree remarkably well. The shorter time series from MIPAS and SCIAMACHY also agree with them where they overlap. The data agree within ten to twenty percent when the number densities are large, but they can differ by 50 to 100% in some cases.

Description: GPS radio occultation with TerraSAR-X and TanDEM-X: sensitivity of lower troposphere sounding to the Open-Loop Doppler model Atmospheric Measurement Techniques Discussions, 7, 12719-12733, 2014 Author(s): F. Zus, G. Beyerle, S. Heise, T. Schmidt, and J. Wickert The Global Positioning System (GPS) radio occultation (RO) technique provides valuable input for numerical weather prediction and is considered as a data source for climate related research. Numerous studies outline the high precision and accuracy of RO atmospheric soundings in the upper troposphere and lower stratosphere. In this altitude region (8–25 km) RO atmospheric soundings are considered to be free of any systematic error. In the tropical (30° S–30° N) Lower (

Description: Instability and change detection in exponential families and generalized linear models, with a study of Atlantic tropical storms Nonlinear Processes in Geophysics, 21, 1133-1143, 2014 Author(s): Y. Lu and S. Chatterjee Exponential family statistical distributions, including the well-known normal, binomial, Poisson, and exponential distributions, are overwhelmingly used in data analysis. In the presence of covariates, an exponential family distributional assumption for the response random variables results in a generalized linear model. However, it is rarely ensured that the parameters of the assumed distributions are stable through the entire duration of the data collection process. A failure of stability leads to nonsmoothness and nonlinearity in the physical processes that result in the data. In this paper, we propose testing for stability of parameters of exponential family distributions and generalized linear models. A rejection of the hypothesis of stable parameters leads to change detection. We derive the related likelihood ratio test statistic. We compare the performance of this test statistic to the popular normal distributional assumption dependent cumulative sum (Gaussian CUSUM) statistic in change detection problems. We study Atlantic tropical storms using the techniques developed here, so to understand whether the nature of these tropical storms has remained stable over the last few decades.

Description: A method to improve the determination of wave perturbations close to the tropopause by using a digital filter Atmospheric Measurement Techniques Discussions, 4, 1181-1197, 2011 Author(s): P. Alexander, A. de la Torre, P. Llamedo, R. Hierro, T. Schmidt, A. Haser, and J. Wickert Calculations of gravity wave activity all over the globe derived from GPS radio occultation temperature profiles led some years ago to the following question: are the wave amplitude enhancements systematically observed around tropopause levels due to physical processes or are they a simple artifact generated by any digital filter used to isolate the wave components? The latter alternative has been found to be the correct one. This has been concluded after almost a decade of work on global wave climatologies obtained from GPS radio occultation satellite data, which allowed to analyze, for the first time, a large amount of atmospheric profiles including both the troposphere and the stratosphere. We present a new filtering method which can be equally applied to temperature or refractivity profiles. The suggested technique significantly reduces artificial enhancements around the tropopause, which represents an improvement in comparison to previous applications of standard filters.

Description: An algorithm for retrieving black carbon optical parameters from thermal-optical (OC/EC) instruments Atmospheric Measurement Techniques Discussions, 4, 1233-1254, 2011 Author(s): A. Andersson, R. J. Sheesley, E. N. Kirillova, and Ö. Gustafsson Through absorption of sun light atmospheric black carbon (BC) is expected to influence regional/global climate by warming the atmosphere and dimming the surface. To evaluate the impact of these effects it is of interest to examine both the radiative properties of BC and the concentrations in air. Building on recent developments we present a novel application for combining these two aspects using the common thermal-optical (OC/EC) instrument. By correlating the OC/EC laser transmission with the FID-carbon detection non-carbon contributions to the light attenuation are detected. Such analysis allows the calculation of mass absorption cross-sections (MACs) for BC, corrected for certain in-organic components. This approach has been applied to data from two S S Asian and two SN S European sites, including a time series analysis for one of the SN S European sites. Taken together this study demonstrates broad applicability for this method while providing new insights into the optical properties of BC.

Description: Determination of field scale ammonia emissions for common slurry spreading practice with two independent methods Atmospheric Measurement Techniques Discussions, 4, 2635-2687, 2011 Author(s): J. Sintermann, C. Ammann, U. Kuhn, C. Spirig, R. Hirschberger, A. Gärtner, and A. Neftel At a cropland and a grassland site field scale ammonia (NH 3 ) emissions from slurry application were determined simultaneously by two approaches based on (i) eddy covariance (EC) flux measurements using high temperature Chemical Ionisation Mass Spectrometry (HT-CIMS) and on (ii) backward Lagrangian Stochastic (bLS) dispersion modelling using concentration measurements by three optical open path Fourier Transform Infrared (FTIR) systems. Slurry was spread on the fields in sequential tracks over a period of one to two hours. In order to calculate field emissions, measured EC/HT-CIMS fluxes were combined with flux footprint analysis of individual slurry spreading tracks to parameterise the NH 3 volatilisation with a bi-exponential time dependence. Accordingly, track-resolved concentration footprints for the FTIR measurements were calculated using bLS. Comparison of concentrations calculated from the parameterised fluxes with concentrations measured by impingers showed that the EC/HT-CIMS emissions on the two fertilisations corresponded to the impinger concentrations within 10 % while the bLS/FTIR results showed larger deviations. For both events, the period during fertilisation and the subsequent two hours contributed by more than 80 % to the total field emissions. Averaged over the two measurement methods, the cumulated emissions of the first day amounted to 17 ± 3 % loss of applied total ammoniacal nitrogen over the cropland and 16 ± 3 % over the grassland field.

Description: Empirical analysis and modeling of errors of atmospheric profiles from GPS radio occultation Atmospheric Measurement Techniques Discussions, 4, 2599-2633, 2011 Author(s): B. Scherllin-Pirscher, A. K. Steiner, G. Kirchengast, Y.-H. Kuo, and U. Foelsche The utilization of radio occultation (RO) data in atmospheric studies requires precise knowledge of error characteristics. We present results of an empirical error analysis of GPS radio occultation (RO) bending angle, refractivity, dry pressure, dry geopotential height, and dry temperature. We find very good agreement between data characteristics of different missions (CHAMP, GRACE-A, and Formosat-3/COSMIC (F3C)). In the global mean, observational errors (standard deviation from "true" profiles at mean tangent point location) agree within 0.3 % in bending angle, 0.1 % in refractivity, and 0.2 K in dry temperature at all altitude levels between 4 km and 35 km. Above ≈20 km, the observational errors show a strong seasonal dependence at high latitudes. Larger errors occur in hemispheric wintertime and are associated mainly with background data used in the retrieval process. The comparison between UCAR and WEGC results (both data centers have independent inversion processing chains) reveals different magnitudes of observational errors in atmospheric parameters, which are attributable to different background fields used. Based on the empirical error estimates, we provide a simple analytical error model for GPS RO atmospheric parameters and account for vertical, latitudinal, and seasonal variations. In the model, which spans the altitude range from 4 km to 35 km, a constant error is adopted around the tropopause region amounting to 0.8 % for bending angle, 0.35 % for refractivity, 0.15 % for dry pressure, 10 m for dry geopotential height, and 0.7 K for dry temperature. Below this region the observational error increases following an inverse height power-law and above it increases exponentially. The observational error model is the same for UCAR and WEGC data but due to somewhat different error characteristics below about 10 km and above about 20 km some parameters have to be adjusted. Overall, the observational error model is easily applicable and adjustable to individual error characteristics.

Description: Rank ordering multifractal analysis of the auroral electrojet index Nonlinear Processes in Geophysics, 18, 277-285, 2011 Author(s): G. Consolini and P. De Michelis In the second half of the 90s interest grew on the complex features of the magnetospheric dynamics in response to solar wind changes. An important series of papers were published on the occurrence of chaos, turbulence and complexity. Among them, particularly interesting was the study of the bursty and fractal/multifractal character of the high latitude energy release during geomagnetic storms, which was evidenced by analyzing the features of the Auroral Electrojet (AE) indices. Recently, the multifractal features of the small time-scale increments of AE-indices have been criticized in favor of a more simple fractal behavior. This is particularly true for the scaling features of the probability density functions (PDFs) of the AE index increments. Here, after a brief review of the nature of the fractal/multifractal features of the magnetospheric response to solar wind changes, we investigate the multifractal nature of the scaling features of the AE index increments PDFs using the Rank Ordering Multifractal Analysis (ROMA) technique. The ROMA results clearly demonstrate the existence of a hierarchy of scaling indices, depending on the increment amplitude, for the data collapsing of PDFs relative to increments at different time scales. Our results confirm the previous results by Consolini et al. (1996) and the more recent results by Rypdal and Rypdal (2010).

Description: Remote sensing of aerosols by using polarized, directional and spectral measurements within the A-Train: the PARASOL mission Atmospheric Measurement Techniques Discussions, 4, 2037-2069, 2011 Author(s): D. Tanré, F. M. Bréon, J. L. Deuzé, O. Dubovik, F. Ducos, P. François, P. Goloub, M. Herman, A. Lifermann, and F. Waquet The aerosol remote sensing from space has started in the 1980's using observations provided by geostationary satellites or by polar orbiting platforms not specifically designed for observing aerosols. As a result, the number of retrieved parameters was limited and retrievals in the visible restricted over ocean. Over land, because of the important surface contribution, the aerosol detection was performed in the UV (or in the dark blue) where most of the earth surfaces are dark enough but with overlap of multiple aerosols parameters, content, altitude and absorption. Instruments dedicated to aerosol monitoring are recently available and the POLDER instrument on board the PARASOL mission is one of them. By measuring the wavelength, angular and polarization properties of the radiance at the top of the atmosphere, in coordination with the other A-Train instruments, PARASOL can better quantify aerosol optical depths (AOD) and improve the derivation of the radiative and physical properties. The instrument, the inversion schemes and the list of aerosol parameters are described. Examples of retrieved aerosol parameters are provided as well as innovative approaches and further inversion techniques.

Description: Atmospheric influences on infrared-laser signals used for occultation measurements between Low Earth Orbit satellites Atmospheric Measurement Techniques Discussions, 4, 2689-2747, 2011 Author(s): S. Schweitzer, G. Kirchengast, and V. Proschek LEO-LEO infrared-laser occultation (LIO) is a new occultation technique between Low Earth Orbit (LEO) satellites, which applies signals in the short wave infrared spectral range (SWIR) within 2 μm to 2.5 μm. It is part of the LEO-LEO microwave and infrared-laser occultation (LMIO) method, recently introduced by Kirchengast and Schweitzer (2011), that enables to retrieve thermodynamic profiles (pressure, temperature, humidity) and accurate altitude levels from microwave signals and profiles of greenhouse gases and further variables such as line-of-sight wind speed from simultaneously measured LIO signals. For enabling trace species retrieval based on differential transmission, the LIO signals are spectrally located as pairs, one in the centre of a suitable absorption line of a target species (absorption signal) and one close by but outside of any absorption lines (reference signal). Due to the novelty of the LMIO method, detailed knowledge of atmospheric influences on LIO signals and of their suitability for accurate trace species retrieval did not yet exist. Here we discuss the atmospheric influences on the transmission and differential transmission of LIO signals. Refraction effects, trace species absorption (by target species, and cross-sensitivity to foreign species), aerosol extinction and Rayleigh scattering are studied in detail. The influences of clouds, turbulence, wind, scattered solar radiation and terrestrial thermal radiation are discussed as well. We show that the influence of defocusing, foreign species absorption, aerosols and turbulence is observable, but can be rendered small to negligible by use of the differential transmission principle and by a design with close frequency spacing of absorption and reference signals within 0.5 %. The influences of Rayleigh scattering and thermal radiation on the received signal intensities are found negligible. Cloud-scattered solar radiation can be observable under bright-day conditions but this influence can be as well made negligible by a design with a close time spacing (within 5 ms) of interleaved laser-pulse and background signals. Cloud extinction loss generally blocks SWIR signals, except very thin or sub-visible cirrus clouds, which can be addressed by a design allowing retrieval of a cloud layering profile from reference signals and its use in trace species retrieval when scanning through intermittent upper tropospheric cloudiness. Wind can have a small influence via Doppler shift resulting in a slightly modified trace species absorption in comparison to calm air, which can be made negligible by using a simultaneously retrieved wind speed profile or a moderately accurate (to about 10 m s −1 ) background wind profile. Considering all these influences, we conclude that the set of SWIR channels proposed for implementing the LMIO method (Kirchengast et al., 2010; Kirchengast and Schweitzer, 2011) provides adequate sensitivity to accurately retrieve eight greenhouse gas/isotope trace species of key importance to climate and atmospheric chemistry (H 2 O, 12 CO 2 , 13 CO 2 , C 18 OO, CH 4 , N 2 O, O 3 , CO) in the upper troposphere/lower stratosphere region outside clouds under all atmospheric conditions. Two further isotope species (HDO, H 2 18 O) can be retrieved in the upper troposphere.

Description: Effective density of Aquadag and fullerene soot black carbon reference materials used for SP2 calibration Atmospheric Measurement Techniques Discussions, 4, 4937-4955, 2011 Author(s): M. Gysel, M. Laborde, J. S. Olfert, R. Subramanian, and A. J. Gröhn The mass and effective density of black carbon (BC) particles generated from aqueous suspensions of Aquadag and fullerene soot was measured and parametrized as a function of their mobility diameter. The measurements were made by two independent research groups by operating a differential mobility analyser (DMA) in series with an aerosol particle mass analyser (APM) or a Couette centrifugal particle mass analyser (CPMA). Consistent and reproducible results were found in this study for different production lots of Aquadag, indicating that the effective density of these particles is a stable quantity and largely unaffected by differences in aerosol generation procedures and suspension treatments. The effective density of fullerene soot particles from one production lot was also found to be stable and independent of suspension treatments. Some difference to previous literature data was observed for both Aquadag and fullerene soot at larger particle diameters. Knowledge of the exact relationship between mobility diameter and particle mass is of great importance, as DMAs are commonly used to size-select particles from BC reference materials for calibration of single particle soot photometers (SP2), which quantitatively detect the BC mass in single particles.

Description: Two instruments based on differential optical absorption spectroscopy (DOAS) to measure accurate ammonia concentrations in the atmosphere Atmospheric Measurement Techniques Discussions, 4, 5037-5078, 2011 Author(s): H. Volten, J. B. Bergwerff, M. Haaima, D. E. Lolkema, A. J. C. Berkhout, G. R. van der Hoff, C. J. M. Potma, R. J. Wichink Kruit, W. A. J. van Pul, and D. P. J. Swart We present two Differential Optical Absorption Spectroscopy (DOAS) instruments built at RIVM, the RIVM DOAS and the miniDOAS. Both instruments provide virtually interference free measurements of NH 3 concentrations in the atmosphere, since they measure over an open path, without suffering from inlet problems or interference problems by ammonium aerosols dissociating on tubes or filters. They measure concentrations up to at least 200 μg m −3 , have a fast response, low maintenance demands, and a high up-time. The RIVM DOAS has a high accuracy of typically 0.15 μg m −3 for ammonia over 5-min averages and over a total light path of 100 m. The miniDOAS has been developed for application in measurement networks such as the Dutch National Air Quality Monitoring Network (LML). Compared to the RIVM DOAS it has a similar accuracy, but is significantly reduced in size, costs, and handling complexity. The RIVM DOAS and miniDOAS results showed excellent agreement ( R 2 = 0.996) during a field measurement campaign in Vredepeel, the Netherlands. This measurement site is located in an agricultural area and is characterized by highly variable, but on average high ammonia concentrations in the air. The RIVM-DOAS and miniDOAS results were compared to the results of the AMOR instrument, a continuous-flow wet denuder system, which is currently used in the LML. Averaged over longer time spans of typically a day the (mini)DOAS and AMOR results agree reasonably well, although an offset of the AMOR values compared to the (mini)DOAS results exists. On short time scales the (mini)DOAS shows a faster response and does not show the memory effects due to inlet tubing and transport of absorption fluids encountered by the AMOR. Due to its high accuracy, high uptime, low maintenance and its open path, the (mini)DOAS shows a good potential for flux measurements by using two (or more) systems in a gradient set-up and applying the aerodynamic gradient technique.

Description: Towards space based verification of CO 2 emissions from strong localized sources: fossil fuel power plant emissions as seen by a CarbonSat constellation Atmospheric Measurement Techniques Discussions, 4, 5147-5182, 2011 Author(s): V. A. Velazco, M. Buchwitz, H. Bovensmann, M. Reuter, O. Schneising, J. Heymann, T. Krings, K. Gerilowski, and J. P. Burrows Carbon dioxide (CO 2 ) is the most important man-made greenhouse gas (GHG) that cause global warming. With electricity generation through fossil-fuel power plants now as the economic sector with the largest source of CO 2 , power plant emissions monitoring has become more important than ever in the fight against global warming. In a previous study done by Bovensmann et al. (2010), random and systematic errors of power plant CO 2 emissions have been quantified using a single overpass from a proposed CarbonSat instrument. In this study, we quantify errors of power plant annual emission estimates from a hypothetical CarbonSat and constellations of several CarbonSats while taking into account that power plant CO 2 emissions are time-dependent. Our focus is on estimating systematic errors arising from the sparse temporal sampling as well as random errors that are primarily dependent on wind speeds. We used hourly emissions data from the US Environmental Protection Agency (EPA) combined with assimilated and re-analyzed meteorological fields from the National Centers of Environmental Prediction (NCEP). CarbonSat orbits were simulated as a sun-synchronous low-earth orbiting satellite (LEO) with an 828-km orbit height, local time ascending node (LTAN) of 13:30 (01:30 p.m.) and achieves global coverage after 5 days. We show, that despite the variability of the power plant emissions and the limited satellite overpasses, one CarbonSat can verify reported US annual CO 2 emissions from large power plants (≥5 Mt CO 2 yr −1 ) with a systematic error of less than ~4.9 % for 50 % of all the power plants. For 90 % of all the power plants, the systematic error was less than ~12.4 %. We additionally investigated two different satellite configurations using a combination of 5 CarbonSats. One achieves global coverage everyday but only samples the targets at fixed local times. The other configuration samples the targets five times at two-hour intervals approximately every 6th day but only achieves global coverage after 5 days. From the statistical analyses, we found, as expected, that the random errors improve by approximately a factor of two if 5 satellites are used. On the other hand, more satellites do not result in a large reduction of the systematic error. The systematic error is somewhat smaller for the CarbonSat constellation configuration achieving global coverage everyday. Finally, we recommend the CarbonSat constellation configuration that achieves daily global coverage.

Description: Tropospheric and total ozone columns over Paris (France) measured using medium-resolution ground-based solar-absorption Fourier-transform infrared spectroscopy Atmospheric Measurement Techniques Discussions, 4, 3337-3358, 2011 Author(s): C. Viatte, B. Gaubert, M. Eremenko, F. Hase, M. Schneider, T. Blumenstock, M. Ray, P. Chelin, J.-M. Flaud, and J. Orphal Ground-based Fourier-transform infrared (FTIR) solar absorption spectroscopy is a powerful remote sensing technique providing information on the vertical distribution of various atmospheric constituents. This work presents the first evaluation of a mid-resolution ground-based FTIR to measure tropospheric ozone, independently of stratospheric ozone. This is demonstrated using a new atmospheric observatory (named OASIS for "Observations of the Atmosphere by Solar absorption Infrared Spectroscopy"), installed in Créteil (France). Indeed, the information content of OASIS ozone retrievals is clearly sufficient to monitor separately tropospheric (from the surface up to 8 km) and stratospheric ozone. Daily mean tropospheric ozone columns derived from the Infrared Atmospheric Sounding Interferometer (IASI) and from OASIS measurements have been compared for summer 2009 and a good agreement of −5.6 (±16.1) % is observed. Also, a qualitative comparison between in-situ surface ozone measurements and OASIS data clearly shows OASIS's capacity to monitor seasonal tropospheric ozone variations, as well as ozone pollution episodes in summer 2009 around Paris. Two extreme pollution events were identified (on the 1 July and 6 August 2009) for which ozone partial columns from OASIS and predictions from a regional air-quality model (CHIMERE) were compared by respecting temporal and spatial coincidence criteria. Quantitatively, an average bias of 0.2 %, a mean square error deviation of 7.6 %, and a correlation coefficient of 0.91 was found between CHIMERE and OASIS. This demonstrates that a mid-resolution FTIR instrument in ground-based solar absorption geometry is a promising technique for monitoring tropospheric ozone.

Description: Measurements of Humidity in the Atmosphere and Validation Experiments (MOHAVE)-2009: overview of campaign operations and results Atmospheric Measurement Techniques Discussions, 4, 3277-3336, 2011 Author(s): T. Leblanc, T. D. Walsh, I. S. McDermid, G. C. Toon, J.-F. Blavier, B. Haines, W. G. Read, B. Herman, E. Fetzer, S. Sander, T. Pongetti, D. N. Whiteman, T. G. McGee, L. Twigg, G. Sumnicht, D. Venable, M. Calhoun, A. Dirisu, D. Hurst, A. Jordan, E. Hall, L. Miloshevich, H. Vömel, C. Straub, N. Kampfer, G. E. Nedoluha, R. M. Gomez, K. Holub, S. Gutman, J. Braun, T. Vanhove, G. Stiller, and A. Hauchecorne The Measurements of Humidity in the Atmosphere and Validation Experiment (MOHAVE) 2009 campaign took place on 11–27 October 2009 at the JPL Table Mountain Facility in California (TMF). The main objectives of the campaign were to (1) validate the water vapor measurements of several instruments, including, three Raman lidars, two microwave radiometers, two Fourier-Transform spectrometers, and two GPS receivers (column water), (2) cover water vapor measurements from the ground to the mesopause without gaps, and (3) study upper tropospheric humidity variability at timescales varying from a few minutes to several days. A total of 58 radiosondes and 20 Frost-Point hygrometer sondes were launched. Two types of radiosondes were used during the campaign. Non negligible differences in the readings between the two radiosonde types used (Vaisala RS92 and InterMet iMet-1) made a small, but measurable impact on the derivation of water vapor mixing ratio by the Frost-Point hygrometers. As observed in previous campaigns, the RS92 humidity measurements remained within 5 % of the Frost-point in the lower and mid-troposphere, but were too dry in the upper troposphere. Over 270 h of water vapor measurements from three Raman lidars (JPL and GSFC) were compared to RS92, CFH, and NOAA-FPH. The JPL lidar profiles reached 20 km when integrated all night, and 15 km when integrated for 1 h. Excellent agreement between this lidar and the frost-point hygrometers was found throughout the measurement range, with only a 3 % (0.3 ppmv) mean wet bias for the lidar in the upper troposphere and lower stratosphere (UTLS). The other two lidars provided satisfactory results in the lower and mid-troposphere (2–5 % wet bias over the range 3–10 km), but suffered from contamination by fluorescence (wet bias ranging from 5 to 50 % between 10 km and 15 km), preventing their use as an independent measurement in the UTLS. The comparison between all available stratospheric sounders allowed to identify only the largest biases, in particular a 10 % dry bias of the Water Vapor Millimeter-wave Spectrometer compared to the Aura-Microwave Limb Sounder. No other large, or at least statistically significant, biases could be observed. Total Precipitable Water (TPW) measurements from six different co-located instruments were available. Several retrieval groups provided their own TPW retrievals, resulting in the comparison of 10 different datasets. Agreement within 7 % (0.7 mm) was found between all datasets. Such good agreement illustrates the maturity of these measurements and raises confidence levels for their use as an alternate or complementary source of calibration for the Raman lidars. Tropospheric and stratospheric ozone and temperature measurements were also available during the campaign. The water vapor and ozone lidar measurements, together with the advected potential vorticity results from the high-resolution transport model MIMOSA, allowed the identification and study of a deep stratospheric intrusion over TMF. These observations demonstrated the lidar strong potential for future long-term monitoring of water vapor in the UTLS.

Description: A method to resolve the phase state of aerosol particles Atmospheric Measurement Techniques Discussions, 4, 6229-6248, 2011 Author(s): E. Saukko, H. Kuuluvainen, and A. Virtanen The phase state of atmospheric aerosols has impact on their chemical aging and their deliquescence and thus their ability to act as cloud condensation nuclei (CCN). The phase change of particles can be induced by the deliquescence or efflorescence of water or by chemical aging. Existing methods, such as tandem differential mobility analysis rely on the size change of particles related to the water uptake or release related to deliquescence and efflorescence. To address the need to study the phase change induced by mass-preserving and nearly mass-preserving processes a new method has been developed. The method relies on the physical impaction of particles on a smooth substrate and subsequent counting of bounced particles by condensation particle counter (CPC). The connection between the bounce probability and physical properties of particles is so far qualitative. To evaluate the performance of this method, the phase state of ammonium sulfate and levoglucosan, crystalline and amorphous solid, in the presence of water vapor was studied. The results show a marked difference in particle bouncing properties between substances – not only at the critical relative humidity level, but also on the slope of the bouncing probability with respect to humidity. This suggests that the method can be used to differentiate between amorphous and crystalline substances as well as to differentiate between liquid and solid phases.

Description: Fast simulators for satellite cloud optical centroid pressure retrievals, 1. evaluation of OMI cloud retrievals Atmospheric Measurement Techniques Discussions, 4, 6185-6228, 2011 Author(s): J. Joiner, A. P. Vasilkov, P. Gupta, P. K. Bhartia, P. Veefkind, M. Sneep, J. de Haan, I. Polonsky, and R. Spurr The cloud Optical Centroid Pressure (OCP) is a satellite-derived parameter that is commonly used in trace-gas retrievals to account for the effects of clouds on near-infrared through ultraviolet radiance measurements. A fast simulator is desirable in order to further expand the use of cloud OCP retrievals into the operational and climate communities for applications such as data assimilation and evaluation of cloud vertical structure in general circulation models. In this paper, we develop and validate a fast simulator that provides estimates of the cloud OCP given a vertical profile of optical extinction. We use a pressure-weighting scheme where the weights depend upon optical parameters of clouds and/or aerosol. A cloud weighting function is easily extracted using this formulation. We then use the fast simulator to compare two different satellite cloud OCP retrievals from the Ozone Monitoring Instrument (OMI) with estimates based on collocated cloud extinction profiles from a combination of CloudSat radar and MODIS visible radiance data. These comparisons are made over a wide range of conditions in order to provide a comprehensive validation of the OMI cloud OCP retrievals. We find generally good agreement between OMI cloud OCPs and those predicted by CloudSat. However, the OMI cloud OCPs from the two independent algorithms agree better with each other than either does with the estimates from CloudSat/MODIS. Differences between OMI cloud OCPs and those based on CloudSat/MODIS may result from undetected snow/ice at the surface, cloud 3-D effects, and the fact that CloudSat only observes a relatively small fraction of OMI pixel.

Description: Quantification of gas-phase glyoxal and methylglyoxal via the Laser-Induced Phosphorescence of (methyl)GLyOxal Spectrometry (LIPGLOS) method Atmospheric Measurement Techniques Discussions, 4, 6159-6183, 2011 Author(s): S. B. Henry, A. Kammrath, and F. N. Keutsch Glyoxal and methylglyoxal are key products of oxidative photochemistry in the lower troposphere. Reliable measurements of such compounds are critical for testing our understanding of volatile organic compound (VOC) processing in this region. We present a new method for obtaining sensitive, high time resolution, in situ measurements of these compounds via laser-induced phosphorescent decays. By exploiting the unique phosphorescent lifetimes for each molecule, this method achieves speciation and high-sensitivity quantification of both molecules (3σ limits of detection of 11 ppt v in 5 min for glyoxal and 243 ppt v in 5 min for methylglyoxal). Additionally, this method enables the simultaneous measurement of both glyoxal and methylglyoxal using a single, non-wavelength-tunable light source, which will allow for the development of inexpensive and turnkey instrumentation. The simplicity and affordability of this new instrumentation would enable the construction of a long-term, spatially distributed database of these two key species. This chemical map can be used to constrain or drive regional or global models as well as provide verification of satellite observations.

Description: Preface Large amplitude internal waves in the coastal ocean Nonlinear Processes in Geophysics, 18, 653-655, 2011 Author(s): R. Grimshaw, K. Helfrich, and A. Scotti No Abstract available.

Description: Temporal co-registration for TROPOMI cloud clearing Atmospheric Measurement Techniques Discussions, 4, 6249-6272, 2011 Author(s): I. Genkova, J. Robaidek, R. Roebeling, M. Sneep, and P. Veefkind The TROPOspheric Monitoring Instrument (TROPOMI) is planed for launch in 2014 on board of the Sentinel 5 Precursor (S5P) and is anticipated to provide high-quality and timely information on the global atmospheric composition for climate and air quality applications. TROPOMI will observe key atmospheric constituents such as ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, methane, formaldehyde and aerosol properties. The retrieval algorithms for the anticipated products require cloud information on a pixel basis. Most of them will use the cloud properties derived from TROPOMI's own measurements, such as the O 2 A-band measurements. However, the methane and the aerosol retrievals require very precise cloud clearing, which is difficult to achieve at the TROPOMI spatial resolution (7 × 7 km 2 ) and without thermal IR measurements. The current payload of the Sentinel 5 Precursor (S-5P) does not include a cloud imager, thus it is planned to fly the S5P mission in a constellation with another instrument yielding an accurate cloud mask. The cloud imagery data will be provided by the US NPOESS Preparatory Project (NPP) mission which will have the Visible Infrared Imager Radiometer Suite (VIIRS) on board (Scalione, 2004). VIIRS will have 22 bands in the VIS and IR spectral ranges, and will deliver data with two spatial resolutions: imagery resolution bands with a nominal pixel size of 370 m at nadir, and moderate resolution bands with nominal pixel size 740 m at nadir. The instrument is combining fine spatial resolution with high-accuracy calibration similar or superior to AVHRR. This paper presents results from investigating the temporal co-registration requirements for suitable time differences between the VIIRS measurements of clouds and the TROPOMI methane and aerosol measurements, so that the former could be used for cloud clearing. The temporal co-registration is studied using Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) data with 15 min temporal resolution (Veefkind, 2008a), and with data from the Geostationary Operational Environmental Satellite-10 (GOES-10) having 1 min temporal resolution. The aim is to understand and assess the relation between the amount of allowed cloud contamination and the required time difference between the two satellites' overflights. Quantitative analysis shows that a time difference of approximately 5 min is sufficient (in most conditions) to use the cloud information from the first instrument for cloud clearing in the retrievals using data from the second instrument. In recent years the A-train constellation demonstrated the benefit of flying satellites in formation. Therefore this study's findings will be useful and applicable for designing future Low Earth Orbit (LEO) satellite constellations.

Description: 1-D-Var retrieval of daytime total columnar water vapour from MERIS measurements Atmospheric Measurement Techniques Discussions, 4, 6811-6844, 2011 Author(s): R. Lindstrot, R. Preusker, H. Diedrich, L. Doppler, R. Bennartz, and J. Fischer A new scheme for the retrieval of total columnar water vapour from measurements of MERIS (Medium Resolution Imaging Spectrometer) on ENVISAT (ENVIronmental SATellite) is presented. The algorithm is based on a fast forward model of the water vapour transmittance around 900 nm, including a correction for atmospheric scattering. It provides the water vapour column amount for cloud-free scenes above land and ocean at a spatial resolution of 0.25 km × 0.3 km and 1 km × 1.2 km, depending on whether applied to the "full resolution" or the operational "reduced resolution" mode of MERIS. Uncertainties are provided on a pixel-by-pixel basis, taking into account all relevant sources of error. An extensive validation against various sources of ground-based reference data reveals a high accuracy of MERIS water vapour above land (root mean square deviations between 1 mm and 2.7 mm), apart from a wet bias of MERIS between 5 and 10% that is found in all comparison studies. This wet bias might be caused by spectroscopic uncertainties, such as the description of the water vapour continuum. Above ocean the accuracy is reduced, due to the uncertainty introduced by the unknown atmospheric scattering. Consequently, an increased root mean square deviation of ≥5 mm was found by comparing MERIS total columnar water vapour above ocean against SSM/I and ENVISAT MWR data. An increased wet bias of 2–3 mm is found over ocean, potentially du to a not properly working atmospheric correction scheme.

Description: Initial investigation of the wavelength dependence of optical properties measured with a new multi-pass aerosol extinction differential optical absorption spectrometer (AE-DOAS) Atmospheric Measurement Techniques Discussions, 4, 6315-6349, 2011 Author(s): R. T. Chartier and M. E. Greenslade Atmospheric aerosols directly affect climate by scattering and absorbing radiation. The magnitude of the impact is dependent upon the wavelength of light, but is often estimated near 550 nm. When light scattering and absorption by aerosols is approximated, the wavelength dependence of the refractive index for specific components is lost. As a result, climate models would have inherent uncertainties for aerosol contributions to radiative forcing when considering the entire solar spectrum. An aerosol extinction differential optical absorption spectrometer has been developed to directly measure aerosol extinction at mid-ultraviolet to near infrared wavelengths. The instrument consists of a spectrometer coupled to a closed White-type multi-pass gas cell with an adjustable path length of up to approximately 20 m. Laboratory measurements of various gases are compared with known absorption cross sections. Additionally, the extinction of monodisperse samples of polystyrene latex spheres are measured and compared to Mie theory generated with refractive index values from the literature to validate the new instrument. The polystyrene experiments also emphasize the ability of the new instrument to retrieve the wavelength dependent refractive index, especially in the ultraviolet wavelength regions where variability is expected. The spectrometer will be a significant advancement for determining wavelength dependent complex refractive indices in future laboratory studies as well as provide the ability to monitor ambient aerosol light extinction.

Description: Size distribution and structure of Barchan dune fields Nonlinear Processes in Geophysics, 18, 455-467, 2011 Author(s): O. Durán, V. Schwämmle, P. G. Lind, and H. J. Herrmann Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a cooperative behavior based on dune interaction. In Duran et al. (2009), we propose that the redistribution of sand by collisions between dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields but fail to reproduce their homogeneity along the wind direction.

Description: Combining 2-m temperature nowcasting and short range ensemble forecasting Nonlinear Processes in Geophysics, 18, 903-910, 2011 Author(s): A. Kann, T. Haiden, and C. Wittmann During recent years, numerical ensemble prediction systems have become an important tool for estimating the uncertainties of dynamical and physical processes as represented in numerical weather models. The latest generation of limited area ensemble prediction systems (LAM-EPSs) allows for probabilistic forecasts at high resolution in both space and time. However, these systems still suffer from systematic deficiencies. Especially for nowcasting (0–6 h) applications the ensemble spread is smaller than the actual forecast error. This paper tries to generate probabilistic short range 2-m temperature forecasts by combining a state-of-the-art nowcasting method and a limited area ensemble system, and compares the results with statistical methods. The Integrated Nowcasting Through Comprehensive Analysis (INCA) system, which has been in operation at the Central Institute for Meteorology and Geodynamics (ZAMG) since 2006 (Haiden et al., 2011), provides short range deterministic forecasts at high temporal (15 min–60 min) and spatial (1 km) resolution. An INCA Ensemble (INCA-EPS) of 2-m temperature forecasts is constructed by applying a dynamical approach, a statistical approach, and a combined dynamic-statistical method. The dynamical method takes uncertainty information (i.e. ensemble variance) from the operational limited area ensemble system ALADIN-LAEF (Aire Limitée Adaptation Dynamique Développement InterNational Limited Area Ensemble Forecasting) which is running operationally at ZAMG (Wang et al., 2011). The purely statistical method assumes a well-calibrated spread-skill relation and applies ensemble spread according to the skill of the INCA forecast of the most recent past. The combined dynamic-statistical approach adapts the ensemble variance gained from ALADIN-LAEF with non-homogeneous Gaussian regression (NGR) which yields a statistical \mbox{correction} of the first and second moment (mean bias and dispersion) for Gaussian distributed continuous variables. Validation results indicate that all three methods produce sharp and reliable probabilistic 2-m temperature forecasts. However, the statistical and combined dynamic-statistical methods slightly outperform the pure dynamical approach, mainly due to the under-dispersive behavior of ALADIN-LAEF outside the nowcasting range. The training length does not have a pronounced impact on forecast skill, but a spread re-scaling improves the forecast skill substantially. Refinements of the statistical methods yield a slight further improvement.

Description: Retrieval of sulphur dioxide from the infrared atmospheric sounding interferometer (IASI) Atmospheric Measurement Techniques Discussions, 4, 7241-7275, 2011 Author(s): L. Clarisse, D. Hurtmans, C. Clerbaux, J. Hadji-Lazaro, Y. Ngadi, and P.-F. Coheur Thermal infrared sounding of sulphur dioxide (SO 2 ) from space has gained appreciation and popularity as a valuable complement to ultraviolet sounding. There are several strong absorption bands of SO 2 in the infrared, and atmospheric sounders, primarily designed for weather forecasting, have therefore often the ability to globally monitor SO 2 abundances. Most of the observed SO 2 is found in volcanic plumes. In this paper we outline a novel algorithm for the sounding of SO 2 above ~500 hPa altitude using high resolution infrared sounders and apply it to measurements of the infrared atmospheric sounding interferometer (IASI). The main features of the algorithm are a wide applicable total column range (over 4 orders of magnitude, from 0.5 to 5000 dobson units), a low theoretical uncertainty (3–5%) and near real time applicability. We make an error analysis and demonstrate the algorithm on the recent eruptions of Sarychev, Kasatochi, Grimsvötn, Puyehue-Cordón Caulle and Nabro.

Description: Effect of wind speed on aerosol optical depth over remote oceans, based on data from the Maritime Aerosol Network Atmospheric Measurement Techniques Discussions, 4, 7185-7209, 2011 Author(s): A. Smirnov, A. M. Sayer, B. N. Holben, N. C. Hsu, S. M. Sakerin, A. Macke, N. B. Nelson, Y. Courcoux, T. J. Smyth, P. Croot, P. K. Quinn, J. Sciare, S. K. Gulev, S. Piketh, R. Losno, S. Kinne, and V. F. Radionov The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (onboard or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (∼0.004–0.005), even for strong winds over 10 m s −1 . The relationships show significant scatter (correlation coefficients typically in the range 0.3–0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used.

Description: Influence of aerosol and surface reflectance variability on hyperspectral observed radiance Atmospheric Measurement Techniques Discussions, 4, 7211-7240, 2011 Author(s): C. Bassani, R. M. Cavalli, and P. Antonelli Physically based retrievals of aerosol properties from remotely sensed data usually requires extensive assumptions on particulate type and vertical distribution, and ground surface reflectivity. New satellite missions, based on high spectral resolution instruments, such as PRISMA (Hyperspectral Precursor and Application Mission), represent a valuable opportunity to mitigate the dependency of the retrieval accuracy from the such (a-priori) information. This paper aims to address the potential of these new observing systems in retrieving aerosol properties specifically over coastal areas. Goal has been achieved by using simulated radiances obtained combining two aerosol models (urban and continental), and two reflecting surfaces, dark (water) and bright (sand) for the PRISMA instrument. Results showed that, in the continental regime, the expected instrument sensitivity would allow for retrieval accuracy of the optical thickness at 550 nm of 0.02 or better, with a dark surface surrounded by dark areas. Study also showed that for the urban regime, the surface plays a more significant role, with a bright surface surrounded by dark areas providing the best conditions for the aerosol load retrievals, and dark surfaces representing less suitable situations for accurate retrievals independently of the surroundings. Moreover the results obtained, led the authors to the conclusions that high resolution observations of Earth spectrum between 400 and 1000 nm, through the use of a physically based inversion system, would allow for a significant improvement of the retrieval accuracy for anthropogenic/natural aerosol, over coastal regions.

Description: How to average logarithmic retrievals Atmospheric Measurement Techniques Discussions, 4, 7159-7183, 2011 Author(s): B. Funke and T. von Clarmann Calculation of mean trace gas contributions from profiles obtained by retrievals of the logarithm of the abundance rather than retrievals of the abundance itself are prone to biases. By means of a system simulator, biases of linear versus logarithmic averaging were evaluated for both maximum likelihood and maximum a priori retrievals, for various signal to noise ratios and atmospheric variabilities. These biases can easily reach several ten percent. As a rule of thumb we found for maximum likelihood retrievals that linear averaging better represents the true mean value in cases of large local natural variability and high signal to noise ratios, while for small local natural variability logarithmic averaging often is superior. In the case of maximum a posteriori retrievals, the mean is dominated by the a priori information used in the retrievals and the method of averaging is of minor concern. For larger natural variabilities, the appropriateness of the one or the other method of averaging depends on the particular case because the various biasing mechanisms partly compensate in a hardly predictable manner. This complication arises mainly because of the fact that in logarithmic retrievals the weight of the prior information depends on abundance of the gas itself. No simple rule was found on which kind of averaging is superior, and instead of suggesting simple recipes we cannot do much more than to create awareness of the traps related with averaging of mixing ratios obtained from logarithmic retrievals.

Description: An intercomparison of radar-based liquid cloud microphysics retrievals and implication for model evaluation studies Atmospheric Measurement Techniques Discussions, 4, 7109-7158, 2011 Author(s): D. Huang, C. Zhao, M. Dunn, X. Dong, G. G. Mace, M. P. Jensen, S. Xie, and Y. Liu To assess if current radar-based liquid cloud microphysical retrievals of the Atmospheric Radiation Measurement (ARM) program can provide useful constraints for modeling studies, this paper presents intercomparison results of three cloud products at the Southern Great Plains (SGP) site: the ARM MICROBASE, University of Utah (UU), and University of North Dakota (UND) products over the nine-year period from 1998 to 2006. The probability density and spatial autocorrelation functions of the three cloud Liquid Water Content (LWC) retrievals appear to be consistent with each other, while large differences are found in the droplet effective radius retrievals. The differences in the vertical distribution of both cloud LWC and droplet effective radius retrievals are found to be alarmingly large, with the relative difference between nine-year mean cloud LWC retrievals ranging from 20% at low altitudes to 100% at high altitudes. Nevertheless, the spread in LWC retrievals is much smaller than that in cloud simulations by climate and cloud resolving models. The MICROBASE effective radius ranges from 2.0 at high altitudes to 6.0 μm at low altitudes and the UU and UND droplet effective radius is 6 μm larger. Further analysis through a suite of retrieval experiments shows that the difference between MICROBASE and UU LWC retrievals stems primarily from the partition total Liquid Water path (LWP) into supercooled and warm liquid, and from the input cloud boundaries and LWP. The large differences between MICROBASE and UU droplet effective radius retrievals are mainly due to rain/drizzle contamination and the assumptions of cloud droplet concentration used in the retrieval algorithms. The large discrepancy between different products suggests caution in model evaluation with these observational products, and calls for improved retrievals in general.

Description: Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations Atmospheric Measurement Techniques Discussions, 5, 2221-2271, 2012 Author(s): P. Liebing, K. Bramstedt, S. Noël, V. Rozanov, H. Bovensmann, and J. P. Burrows SCIAMACHY is a passive imaging spectrometer onboard ENVISAT, designed to obtain trace gas abundances from measured radiances and irradiances in the UV to SWIR range in nadir, limb and occultation viewing modes. Its grating spectrometer introduces a substantial sensitivity to the polarization of the incoming light with nonnegligible effects on the radiometric calibration. To be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization Measurement Devices (PMDs). While for the nadir viewing mode the measured atmospheric polarization has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study regarding the limb viewing mode has not yet been performed. This paper aims at an assessment of the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other air- or spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison with radiative transfer simulations by SCIATRAN V3.1(Rozanov et al., 2012) using a wide range of atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable of performing calculations of the multiply scattered radiance in a~spherically symmetric atmosphere. The study shows that the limb polarization data exhibit a large systematic bias which is decreasing with wavelength. The most likely reason for this bias is an instrumental phase shift which changes the relative contributions of different Stokes vector components to the PMD signal as compared to on-ground calibration measurements. It is also shown that it is in principle feasible to recalibrate the polarization sensitivity using the in-flight data and the VRTM simulations, enabling also the monitoring of its degradation. Together with an optimization of the algorithm used to calculate the in-flight polarization data an improved polarization correction can increase the radiometric accuracy of SCIAMACHY limb radiance spectra substantially.

Description: First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change Atmospheric Measurement Techniques Discussions, 5, 1355-1379, 2012 Author(s): F. Forster, R. Sussmann, M. Rettinger, N. M. Deutscher, D. W. T. Griffith, N. Jones, and P. K. Patra We present the intercalibration of dry-air column-averaged mole fractions of methane (XCH 4 ) retrieved from solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC) in the mid-infrared (MIR) versus near-infrared (NIR) soundings from the Total Carbon Column Observing Network (TCCON). The study uses multi-annual quasi-coincident MIR and NIR measurements from the stations Garmisch, Germany (47.48° N, 11.06° E, 743 m a.s.l.) and Wollongong, Australia (34.41° S, 150.88° E, 30 m a.s.l.). Direct comparison of the retrieved MIR and NIR time series shows a phase shift in XCH 4 seasonality, i.e. a significant time-dependent bias leading to a standard deviation (stdv) of the difference time series (NIR-MIR) of 8.4 ppb. After eliminating differences in a prioris by using ACTM-simulated profiles as a common prior, the seasonalities of the (corrected) MIR and NIR time series agree within the noise (stdv = 5.2 ppb for the difference time series). The difference time series (NIR-MIR) do not show a significant trend. Therefore it is possible to use a simple scaling factor for the intercalibration without a time-dependent linear or seasonal component. Using the Garmisch and Wollongong data together, we obtain an overall calibration factor MIR/NIR = 0.9926(18). The individual calibration factors per station are 0.9940(14) for Garmisch and 0.9893(40) for Wollongong. They agree within their error bars with the overall calibration factor which can therefore be used for both stations. Our results suggest that after applying the proposed intercalibration concept to all stations performing both NIR and MIR measurements, it should be possible to obtain one refined overall intercalibration factor for the two networks. This would allow to set up a harmonized NDACC and TCCON XCH 4 data set which can be exploited for joint trend studies, satellite validation, or the inverse modeling of sources and sinks.

Description: Spatial patterns of linear and nonparametric long-term trends in Baltic sea-level variability Nonlinear Processes in Geophysics, 19, 95-111, 2012 Author(s): R. V. Donner, R. Ehrcke, S. M. Barbosa, J. Wagner, J. F. Donges, and J. Kurths The study of long-term trends in tide gauge data is important for understanding the present and future risk of changes in sea-level variability for coastal zones, particularly with respect to the ongoing debate on climate change impacts. Traditionally, most corresponding analyses have exclusively focused on trends in mean sea-level. However, such studies are not able to provide sufficient information about changes in the full probability distribution (especially in the more extreme quantiles). As an alternative, in this paper we apply quantile regression (QR) for studying changes in arbitrary quantiles of sea-level variability. For this purpose, we chose two different QR approaches and discuss the advantages and disadvantages of different settings. In particular, traditional linear QR poses very restrictive assumptions that are often not met in reality. For monthly data from 47 tide gauges from along the Baltic Sea coast, the spatial patterns of quantile trends obtained in linear and nonparametric (spline-based) frameworks display marked differences, which need to be understood in order to fully assess the impact of future changes in sea-level variability on coastal areas. In general, QR demonstrates that the general variability of Baltic sea-level has increased over the last decades. Linear quantile trends estimated for sliding windows in time reveal a wide-spread acceleration of trends in the median, but only localised changes in the rates of changes in the lower and upper quantiles.

Description: Characterization and airborne deployment of a new counterflow virtual impactor inlet Atmospheric Measurement Techniques Discussions, 5, 1515-1541, 2012 Author(s): T. Shingler, S. Dey, A. Sorooshian, F. J. Brechtel, Z. Wang, A. Metcalf, M. Coggon, J. Mülmenstädt, L. M. Russell, H. H. Jonsson, and J. H. Seinfeld A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterization tests, and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (~15 l min −1 ) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterized the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7–13.1 μm. The percentage error between cut size measurements and predictions from aerodynamic drag theory are less than 13%. The CVI was deployed on the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California between July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter.

Description: Improved cloud screening in MAIAC aerosol retrievals using spectral and spatial analysis Atmospheric Measurement Techniques Discussions, 5, 1575-1595, 2012 Author(s): A. Lyapustin, Y. Wang, I. Laszlo, and S. Korkin An improved cloud/snow screening technique in the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is described. It is implemented as part of MAIAC aerosol retrievals based on analysis of spectral residuals and spatial variability. Comparisons with AERONET aerosol measurements and a large-scale MODIS data analysis show strong suppression of aerosol optical depth outliers due to unresolved clouds and snow. At the same time, the developed filter does not reduce the aerosol retrieval capability at high 1 km resolution in strongly inhomogeneous environments, such as near centers of the active fires. Despite significant improvement, the optical depth outliers in high spatial resolution data are and will remain the problem to be addressed by the application-dependent specialized filtering techniques.

Description: Measuring variations of δ 18 O and δ 2 H in atmospheric water vapour using laser spectroscopy: an instrument characterisation study Atmospheric Measurement Techniques Discussions, 5, 1597-1655, 2012 Author(s): F. Aemisegger, P. Sturm, P. Graf, H. Sodemann, S. Pfahl, A. Knohl, and H. Wernli Variations of stable water isotopes in water vapour have become measurable at a measurement frequency of about 1 Hz in recent years using novel laser spectroscopic techniques. This enables us to perform continuous measurements for process-based investigations of the atmospheric water cycle at the time scales relevant for synoptic meteorology. An important prerequisite for the interpretation of data from automated field measurements lasting for several weeks or months is a detailed knowledge about instrument properties and the sources of measurement uncertainty. We present here a comprehensive characterisation and comparison study of two commercial laser spectroscopic systems based on cavity ring-down spectroscopy (Picarro) and off-axis integrated cavity output spectroscopy (Los Gatos Research). The uncertainty components of the measurements were first assessed in laboratory experiments, focussing on the effects of (i) water vapour mixing ratio, (ii) measurement stability, (iii) uncertainties due to calibration and (iv) response times of the isotope measurements due to adsorption-desorption processes on the tubing and measurement cavity walls. Based on the experience from our laboratory experiments we set up a one-week field campaign for comparing measurements of the ambient isotope signals of the two laser spectroscopic systems. The optimal calibration strategy determined for both instruments was applied as well as the correction functions for water vapour mixing ratio effects. The root mean square difference between the isotope signals from the two instruments during the field deployment was 2.3‰ for δ 2 H, 0.5‰ for δ 18 O and 3.1‰ for deuterium excess. These uncertainty estimates from field measurements compare well to those found in the laboratory experiments. The present quality of measurements from laser spectroscopic instruments combined with a calibration system opens new possibilities for investigating the atmospheric water cycle and the land-atmosphere moisture fluxes.

Description: On closure parameter estimation in chaotic systems Nonlinear Processes in Geophysics, 19, 127-143, 2012 Author(s): J. Hakkarainen, A. Ilin, A. Solonen, M. Laine, H. Haario, J. Tamminen, E. Oja, and H. Järvinen Many dynamical models, such as numerical weather prediction and climate models, contain so called closure parameters. These parameters usually appear in physical parameterizations of sub-grid scale processes, and they act as "tuning handles" of the models. Currently, the values of these parameters are specified mostly manually, but the increasing complexity of the models calls for more algorithmic ways to perform the tuning. Traditionally, parameters of dynamical systems are estimated by directly comparing the model simulations to observed data using, for instance, a least squares approach. However, if the models are chaotic, the classical approach can be ineffective, since small errors in the initial conditions can lead to large, unpredictable deviations from the observations. In this paper, we study numerical methods available for estimating closure parameters in chaotic models. We discuss three techniques: off-line likelihood calculations using filtering methods, the state augmentation method, and the approach that utilizes summary statistics from long model simulations. The properties of the methods are studied using a modified version of the Lorenz 95 system, where the effect of fast variables are described using a simple parameterization.

Description: Consistency between Fourier transform and small-volume few-wave decomposition for spectral and spatial variability of gravity waves above a typhoon Atmospheric Measurement Techniques Discussions, 5, 1763-1793, 2012 Author(s): C. I. Lehmann, Y.-H. Kim, P. Preusse, H.-Y. Chun, M. Ern, and S.-Y. Kim Convective gravity wave (GW) sources are spatially localized and emit at the same time waves with a wide spectrum of phase speeds. Any wave analysis therefore compromises between spectral and spatial resolution. Future satellite borne limb imagers will for a first time provide real 3d volumes of observations. These volumes will be however limited which will impose further constraints on the analysis technique. In this study a three dimensional few-wave appoach fitting sinusoidal waves to limited 3-D volumes is introduced. The method is applied to simulated GWs above typhoon Ewiniar and GW momentum flux is estimated from temperature fluctuations. Phase speed spectra as well as average profiles of positive, negative and net momentum fluxes are compared to momentum flux estimated by Fourier transform as well as spatial averaging of wind fluctuations. The results agree within 10–20%. The few-wave method can also reveal the spatial orientation of the GWs with respect to the source. The relevance of the results for different types of measurements as well as its applicability to model data is discussed.

Description: MODIS 3 km aerosol product: algorithm and global perspective Atmospheric Measurement Techniques Discussions, 6, 69-112, 2013 Author(s): L. A. Remer, S. Mattoo, R. C. Levy, and L. Munchak After more than a decade of producing a nominal 10 km aerosol product based on the dark target method, the MODIS aerosol team will be releasing a nominal 3 km product as part of their Collection 6 release. The new product differs from the original 10 km product only in the manner in which reflectance pixels are ingested, organized and selected by the aerosol algorithm. Overall, the 3 km product closely mirrors the 10 km product. However, the finer resolution product is able to retrieve over ocean closer to islands and coastlines, and is better able to resolve fine aerosol features such as smoke plumes over both ocean and land. In some situations, it provides retrievals over entire regions that the 10 km product barely samples. In situations traditionally difficult for the dark target algorithm, such as over bright or urban surfaces the 3 km product introduces isolated spikes of artificially high aerosol optical depth (AOD) that the 10 km algorithm avoids. Over land, globally, the 3 km product appears to be 0.01 to 0.02 higher than the 10 km product, while over ocean, the 3 km algorithm is retrieving a proportionally greater number of very low aerosol loading situations. Based on collocations with ground-based observations for only six months, expected errors associated with the 3 km land product are determined to be greater than for the 10 km product: ± 0.05 ± 0.25 AOD. Over ocean, the suggestion is for expected errors to be the same as the 10 km product: ± 0.03 ± 0.05 AOD. The advantage of the product is on the local scale, which will require continued evaluation not addressed here. Nevertheless, the new 3 km product is expected to provide important information complementary to existing satellite-derived products and become an important tool for the aerosol community.

Description: Effect of sampling variation on error of rainfall variables measured by optical disdrometer Atmospheric Measurement Techniques Discussions, 5, 8895-8924, 2012 Author(s): X. C. Liu, T. C. Gao, and L. Liu During the sampling process of precipitation particles by optical disdrometers, the randomness of particles and sampling variability has great impact on the accuracy of precipitation variables. Based on a marked point model of raindrop size distribution, the effect of sampling variation on drop size distribution and velocity distribution measurement using optical disdrometers are analyzed by Monte Carlo simulation. The results show that the samples number, rain rate, drop size distribution, and sampling size have different influences on the accuracy of rainfall variables. The relative errors of rainfall variables caused by sampling variation in a descending order as: water concentration, mean diameter, mass weighed mean diameter, mean volume diameter, radar reflectivity factor, and number density, which are independent with samples number basically; the relative error of rain variables are positively correlated with the margin probability, which is also positively correlated with the rain rate and the mean diameter of raindrops; the sampling size is one of the main factors that influence the margin probability, with the decreasing of sampling area, especially the decreasing of short side of sample size, the probability of margin raindrops is getting greater, hence the error of rain variables are getting greater, and the variables of median size raindrops have the maximum error. To ensure the relative error of rainfall variables measured by optical disdrometer less than 1%, the width of light beam should be at least 40 mm.