ALBERT

Description: [1]  Detailed tracing of an exhaust plume from a rocket's initial trajectory is a scientifically and diagnostically useful technique. It can provide detailed information on the atmosphere's mean winds, wind shears, turbulent regime and physical state over a wide altitude range from 50 to 200 km. We analyze Soyuz rocket exhaust plumes from Plesetsk on 21 May 2009 and 27 June 2011, which uncovered significantly different atmospheric states and underlying dynamics. The first case showed highly dynamical conditions in the mesosphere, characterized by vortex structures, wind shears and small-scale turbulent eddies. The estimated turbulent energy dissipation rates ranged 330-460 mW kg −1 . A characteristic balloon-shaped trail was observed at altitudes between 105 and 160 km, having rapid expansion rates of 500-800 m s −1 over the time period of 2 min which can be explained by complex gas dynamic processes in the rocket wake involving the collision of shock waves. In the second case, we show evidence that the rocket exhaust trail persisted without any changes during its motion from Plesetsk via Denmark to the UK for 9 hours, indicating extremely stable atmospheric conditions. This case introduces a new state of the summer mesosphere – remarkably quiet conditions, probably never observed before. The rocket plumes studied, related to the initial rocket trajectory, are essentially twilight phenomena as seen from the ground using wideband spectrum cameras, that is the Sun should be below the horizon by 6°. For the first time, we analyze the dynamics of rocket exhaust products at the initial trajectory in the mesosphere and lower thermosphere using detailed photographic imaging taken from the ground.

Description: Retrievals of aerosol optical depth (AOD) and related parameters from satellite measurements typically involve prescribed models of aerosol size and composition, and are therefore dependent on how well these models are able to represent the radiative behavior of real aerosols. This study uses aerosol volume size distributions retrieved from Sun-photometer measurements at 11 Aerosol Robotic Network (AERONET) island sites, spread throughout the world's oceans, as a basis to define such a model for pure (unpolluted) maritime aerosol. Volume size distributions are observed to be bimodal and approximately lognormal, although the coarse mode is skewed with a long tail on the low-radius end. The relationship of AOD and size distribution parameters to meteorological conditions is also examined. As wind speed increases, so do coarse-mode volume and radius. The AOD and Ångström exponent show linear relationships with wind speed, although with considerable scatter. Links between aerosol properties and near-surface relative humidity, columnar water vapor, and sea surface temperature are also explored. A recommended bimodal maritime model, which is able to reconstruct the AERONET AOD with accuracy of order 0.01–0.02, is presented for use in aerosol remote sensing applications. This accuracy holds at most sites and for wavelengths between 340 nm and 1020 nm. Calculated lidar ratios are also provided, and are in the range of other studies, although differ more strongly from those currently used in Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) processing.

Description: Large fine mode–dominated aerosols (submicron radius) in size distributions retrieved from the Aerosol Robotic Network (AERONET) have been observed after fog or low-altitude cloud dissipation events. These column-integrated size distributions have been obtained at several sites in many regions of the world, typically after evaporation of low-altitude cloud such as stratocumulus or fog. Retrievals with cloud-processed aerosol are sometimes bimodal in the accumulation mode with the larger-size mode often ∼0.4–0.5 μm radius (volume distribution); the smaller mode, typically ∼0.12 to ∼0.20 μm, may be interstitial aerosol that were not modified by incorporation in droplets and/or aerosol that are less hygroscopic in nature. Bimodal accumulation mode size distributions have often been observed from in situ measurements of aerosols that have interacted with clouds, and AERONET size distribution retrievals made after dissipation of cloud or fog are in good agreement with particle sizes measured by in situ techniques for cloud-processed aerosols. Aerosols of this type and large size range (in lower concentrations) may also be formed by cloud processing in partly cloudy conditions and may contribute to the “shoulder” of larger-size particles in the accumulation mode retrievals, especially in regions where sulfate and other soluble aerosol are a significant component of the total aerosol composition. Observed trends of increasing aerosol optical depth (AOD) as fine mode radius increased suggests higher AOD in the near-cloud environment and higher overall AOD than typically obtained from remote sensing owing to bias toward sampling at low cloud fraction.

Description: Partitioning of mineral dust, pollution, smoke, and mixtures using remote sensing techniques can help improve accuracy of satellite retrievals and assessments of the aerosol radiative impact on climate. Spectral aerosol optical depth (τ) and single scattering albedo (ωo) from Aerosol Robotic Network (AERONET) measurements are used to form absorption (i.e., ωo and absorption Ångström exponent (αabs)) and size (i.e., extinction Ångström exponent (αext) and fine mode fraction of τ) relationships to infer dominant aerosol types. Using the long-term AERONET data set (1999–2010), 19 sites are grouped by aerosol type based on known source regions to (1) determine the average ωo and αabs at each site (expanding upon previous work), (2) perform a sensitivity study on αabs by varying the spectral ωo, and (3) test the ability of each absorption and size relationship to distinguish aerosol types. The spectral ωo averages indicate slightly more aerosol absorption (i.e., a 0.0 〈 δωo ≤ 0.02 decrease) than in previous work, and optical mixtures of pollution and smoke with dust show stronger absorption than dust alone. Frequency distributions of αabs show significant overlap among aerosol type categories, and at least 10% of the αabs retrievals in each category are below 1.0. Perturbing the spectral ωo by ±0.03 induces significant αabs changes from the unperturbed value by at least ∼±0.6 for Dust, ∼±0.2 for Mixed, and ∼±0.1 for Urban/Industrial and Biomass Burning. The ωo440nm and αext440–870nm relationship shows the best separation among aerosol type clusters, providing a simple technique for determining aerosol type from surface- and future space-based instrumentation.

Description: Although the substorm current wedge (SCW) is recognized as a basic 3-D current system of the substorm expansion phase, its existing models still do not extend beyond a cartoon-like sketch, and very little is known of how well they reproduce magnetic variations observed in the magnetosphere during substorms. A lack of a realistic quantitative SCW model hampers testing model predictions against large sets of spacecraft data. This paper (1) presents a computationally efficient and flexible model with a realistic geometry of field-aligned currents, conveniently parameterized by the SCW strength, longitudinal width, and position, all derived from ground-based midlatitude magnetic variations; and (2) tests the model against INTERMAGNET network observations during substorms and compares its predictions with space magnetometer data. The testing demonstrated significant and systematic discrepancies between the observed and predicted magnetic variations, depending on spacecraft location, concurrent magnetotail configuration, and substorm phase. In particular, we found that the net SCW current derived from the midlatitude field variations corresponds to only a relatively small and variable fraction of the distant 3-D substorm current, inferred from spacecraft data in the lobe and at geosynchronous distance. The discrepancy can be partly attributed to additional region 2 polarity field-aligned currents in the same longitudinal sector, associated with azimuthal diversion of the earthward plasma flow when it encounters the region of strong quasi-dipolar field in the inner magnetosphere.

Description: An analysis of the time series of MODIS-based and AERONET aerosol records over Beijing reveals two distinct periods, before and after 2007. The MODIS data from both the Terra and Aqua satellites were processed with the new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. A comparison of MAIAC and AERONET AOT shows that whereas MAIAC consistently underestimated peak AOT values by 10–20% in the prior period, the bias mostly disappears after mid-2007. Independent analysis of the AERONET dataset reveals little or no change in the effective radii of the fine and coarse fractions and of the Ångström exponent. At the same time, it shows an increasing trend in the single scattering albedo, by ∼0.02 in 9 years. As MAIAC was using the same aerosol model for the entire 2000–2010 period, the decrease in AOT bias after 2007 can be explained only by a corresponding decrease of aerosol absorption caused by a reduction in local black carbon emissions. The observed changes correlate in time with the Chinese government's broad measures to improve air quality in Beijing during preparations for the Summer Olympics of 2008.

Description: Interdependence between El-Niño/Southern Oscillation and Indian monsoon is analyzed with the use of Granger causality estimation from data for the period 1871–2006. Four different versions of the Niño-3 and Niño-3.4 index are used to check robustness of the results. We reveal a non-symmetric bidirectional and even alternating character of coupling that extends previous knowledge about the presence of negative correlation and intervals of phase synchrony between the processes.

Description: Data on the directional changes of a full magnetization vector during cycling to cryogenic temperatures can provide important insights into the low-temperature magnetic properties of natural and synthetic materials. These data also provide an empirical basis for the application of low-temperature treatments in paleomagnetism, for example, the removal of viscous magnetization in magnetite-bearing rocks. However, existing instruments only allow continuous measurement of magnetization along a single axis, hampering experimental and theoretical advances in rock magnetism and the implementation of low-temperature techniques into regular paleomagnetic practices. Here we describe development of a novel low-temperature insert designed in collaboration with William S. Goree Inc., which allows measurement of directional behavior of a full magnetization vector during zero-field low-temperature cycling. Pilot experiments on well-controlled polycrystalline samples of pseudo-single-domain (PSD) and multidomain magnetite as well as on a natural sample containing PSD magnetite indicate that the orientation of a saturation isothermal remanent magnetization (SIRM) imparted at room temperature remains constant during low-temperature cycling to 20 K. This observation lends additional support to low-temperature cycling as a cleaning technique in paleomagnetism. The SIRM imparted in an individual crystal of magnetite showed systematic, albeit small changes upon both cooling and warming through the Verwey temperature, which may reflect switching between the easy magnetization directions. However, the switching effect may be significantly attenuated by crystallographic twinning in magnetite below the transition. Overall, our results demonstrate the potential of the directional low-temperature magnetometry for the advancement of our understanding of the properties of natural and synthetic materials.

Description: [1]  In this study aerosol optical depths over oceans are analyzed from satellite and surface perspectives. Multi-angle Imaging SpectroRadiometer (MISR) aerosol retrievals are investigated and validated primarily against Maritime Aerosol Network (MAN) observations. Furthermore, AErosol RObotic NETwork (AERONET) data from 19 island and coastal sites is incorporated in this study. 270 MISR/MAN comparison points scattered across all oceans were identified. MISR on average overestimates aerosol optical depths (AODs) by 0.04 as compared to MAN; the correlation coefficient and RMSE are 0.95 and 0.06, respectively. A new screening procedure based on retrieval region characterization is proposed, which is capable of substantially reducing MISR retrieval biases. Over 1000 additional MISR/AERONET comparison points are added to the analysis to confirm the validity of the method. The bias reduction is effective within all AOD ranges. Setting a clear-flag fraction (CFF) threshold to 0.6 reduces the bias to below 0.02, which is close to a typical ground-based measurement uncertainty. Twelve years of MISR data are analyzed with the new screening procedure. The average over ocean AOD is reduced by 0.03, from 0.15 to 0.12. The largest AOD decrease is observed in high latitudes of both hemispheres, regions with climatologically high cloud cover. It is postulated that the screening procedure eliminates spurious retrieval errors associated with cloud contamination and cloud adjacency effects. The proposed filtering method can be used for validating aerosol and chemical transport models.

Description: Single scattering albedo (SSA) retrievals obtained with CIMEL sun-sky radiometers from the AERONET aerosol monitoring network were used to make comparisons with simultaneous in-situ sampling from aircraft profiles carried out by the NASA Langley Aerosol Group Experiment (LARGE) team in the summer of 2011 during the coincident DRAGON-MD (Distributed Regional Aerosol Gridded Observational Network-Maryland) and DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) experiments. The single scattering albedos (interpolated to 550 nm) derived from AERONET measurements for aerosol optical depth (AOD) at 440 nm ≥ 0.4 (mean SSA: 0.979) were on average 0.011 lower than the values derived from the LARGE profile measurements (mean SSA: 0.99). The maximum difference observed was 0.023 with all the observed differences within the combined uncertainty for the stated SSA accuracy (0.03 for AERONET; 0.02 for LARGE). Single scattering albedo averages were also analyzed for lower aerosol loading conditions (AOD ≥ 0.2) and a dependence on aerosol optical depth was noted with significantly lower single scattering albedos observed for lower AOD in both AERONET and LARGE datasets. Various explanations for the SSA trend were explored based on other retrieval products including volume median radius and imaginary refractive index as well as column water vapor measurements. Additionally, these SSA trends with AOD were evaluated for one of the DRAGON-MD study sites, Goddard Space Flight Center, and two other Mid-Atlantic AERONET sites over the long-term record dating to 1999.