ALBERT

Beschreibung: The loss of protons in the outer part of the inner radiation belt (L = 2 to 3) during the 6 April 2000 SEP event has been investigated using test particle simulations that follow full Lorentz trajectories with both magnetic and electric fields calculated from an empirical model. The electric fields are calculated as inductive fields generated by the time changing magnetic field, which is achieved by time stepping TS05. The simulation results are compared with proton measurements from the HEO satellite for three different energy ranges (8.5 - 35 MeV, 16 - 40 MeV, and 27 - 45 MeV) as well as previous modeling work done. In previous work, inner zone radiation belt loss during geomagnetic storms has been modeled by simulating field line curvature scattering in static magnetic field snapshots with no electric field. The inclusion of the inductive electric field causes an increase in loss to lower L shells, improving the agreement with the satellite data.

Beschreibung: Abstract Simulating times of high geomagnetic activity are an important part of the continuing efforts to understand space weather and its impacts on humanity. Recent improvements to the Ring‐current Atmosphere interactions Model with Self‐Consistent magnetic field (RAM‐SCB) have been undertaken, with the purpose of expanding the accuracy and robustness of the model during these highly active times. The improvements include a number of changes to the functionality of both the RAM model and the self‐consistent magnetic field calculation. In addition, the models have been modernized and rewritten in an effort to make them more user friendly and understandable. The effect of these changes is shown by simulating the day of 17 March 2013, which saw Sym‐H drop below −100 nT and included a magnetosphere push‐in within geosynchronous orbit. The comparison between the previous model configuration and this new configuration is investigated by calculating a series of metrics for the relation between the observed and modeled Sym‐H, as well as the 〉10‐keV electron flux measured by the HOPE and MAGEIS instruments aboard RBSP‐B and the simulated electron flux. These metrics show that the improvements to the model have increased the accuracy of the model for the given simulation.

Beschreibung: The effects of chemical two-way mixing on the Extratropical Transition Layer (ExTL) near the subtropical jet (STJ) is investigated by stratospheric tracer-tracer correlations. To this end, in-situ measurements were performed west of Africa (25- 32°N) during the TACTS/ESMVal mission in August/September 2012. The Atmospheric chemical Ionization Mass Spectrometer AIMS sampling HCl and HNO 3 was for the first time deployed on the new German High Altitude and LOng range research aircraft HALO. Measurements of O 3 , CO, ECMWF analysis and the tight correlation of the unambiguous tracer HCl to O 3 and HNO 3 in the lower stratosphere were used to quantify the stratospheric content of these species in the ExTL. With increasing distance from the tropopause the stratospheric content increased from 10% to 100% with differing profiles for HNO 3 and O 3 . Tropospheric fractions of 20% HNO 3 and 40% O 3 were detected up to a distance of 30 K above the tropopause.

Beschreibung: Abstract This paper presents the first analysis of Van Allen Probes measurements of the cold plasma density and electric field in the inner magnetosphere to show that intervals of strong modulation at the solar rotation period occur in the locations of the outer plasmasphere and plasmapause (~0.7 RE peak‐to‐peak), in the large‐scale electric field (~0.24 mV/m peak‐to‐peak), and in the cold plasma density (~250 cm‐3 – ~70 cm‐3 peak‐to‐peak). Solar rotation modulation of the inner magnetosphere is more apparent in the declining phase of the solar cycle than near solar maximum. The periodicities in these parameters are compared to solar EUV irradiance, solar wind dawn‐dusk electric field, and Kp. The variations in the plasmapause location at the solar rotation period anti‐correlate with solar wind electric field, magnetospheric electric field, and Kp, but not with EUV irradiance, indicating that convective erosion is the dominant physical process controlling the plasmapause at these timescales.

Beschreibung: Novel airborne in-situ measurements of inorganic chlorine, nitrogen oxide species and ozone were performed inside the lower Antarctic polar vortex and at its edge in September 2012. We focus on one flight during the TACTS/ESMVal campaign with the German research aircraft HALO, reaching latitudes of 65° S and potential temperatures up to 405 K. Using the early-winter correlations of reactive trace gases with N 2 O from ACE-FTS, we find high depletion of chlorine reservoir gases up to ∼ 40 % (0.8 ppbv) at 12 km to 14 km altitude in the vortex and 0.4 ppbv at the edge in subsided stratospheric air with mean ages up to 4.5 years. We observe denitrification of up to 4 ppbv, while ozone was depleted by 1.2 ppmv at potential temperatures as low as 380 K. The advanced instrumentation aboard HALO enables high resolution measurements with implications for the oxidation capacity of the lowermost stratosphere.

Beschreibung: As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a key role in microbial respiration and carbon cycling, but little is known on DOM distribution and cycling in the ETSP. DOM optical properties give important insights on DOM sources, structure and biogeochemical reactivity. Here, we present data and a conceptual view on distribution and cycling of chromophoric (CDOM) and fluorescent (FDOM) DOM in and above the oxygen minimum zone (OMZ) off Peru. Five fluorescent components were identified during PARAFAC analysis. Highest intensities of CDOM and of the amino acid-like fluorescent component (C3) occurred above the OMZ and coincided with maximum chl a concentrations, suggesting phytoplankton productivity as major source. High intensities of a marine humic-like fluorescent component (C1), observed in subsurface waters, indicated in situ microbial reworking of DOM. FDOM release from inner shelf sediment was determined by seawater analysis and continuous glider sensor measurement and included a humic-like component (C2) with a signature typical for terrestrially derived humic acids. Upwelling supplied humic-like substances to the euphotic zone. Photo-reactions were likely involved in the production of a humic-like fluorescent component (C5). Our data show that variable biological and physical processes need to be considered for understanding DOM cycling in a highly dynamic coastal upwelling system like the ETSP off Peru. This article is protected by copyright. All rights reserved.

Beschreibung: [1]  This work reassesses the global atmospheric budget of H 2 with the TM5 model. The recent adjustment of the calibration scale for H 2 translates into a change in the tropospheric burden. Furthermore, the ERA Interim data from ECMWF used in this study shows slower vertical transport than the operational data used before. Consequently, more H 2 is removed by deposition. The deposition parametrisation is updated because significant deposition fluxes for snow, water and vegetation surfaces were calculated in our previous study. Timescales of 1–2 hours are asserted for the transport of H 2 through the canopies of densely vegetated regions. The global scale variability of H 2 and δD [H 2 ] is well represented by the updated model. H 2 is slightly overestimated in the SH because too little H 2 is removed by dry deposition to rainforests and savannahs. The variability in H 2 over Europe is further investigated using a high resolution model sub-domain. It is shown that discrepancies between the model and the observations are mainly caused by the finite model resolution. The tropospheric burden is estimated at 165±8 TgH 2 . The removal rates of H 2 by deposition and photochemical oxidation are estimated at 53±4 and 23±2 TgH 2 /yr, resulting in a tropospheric lifetime of 2.2±0.2 yr.

Beschreibung: Implementation of nonpoint source (NPS) pollution control strategies at the watershed scale hinges on abating pollutant movement from the landscape to water bodies at minimum cost. This paper presents an integrated simulation-optimization approach for targeted implementation of agricultural conservation practices at the watershed scale. A multiobjective genetic algorithm (NSGA-II) with mixed discrete-continuous decision variables was coupled with a distributed watershed model, Soil and Water Assessment Tool (SWAT), to identify optimal types and locations of conservation practices for nutrient and pesticide control at the watershed scale. Previous optimization studies have used binary representation of nonpoint source pollution controls, even though many could be better characterized as continuous variables. In this study, a novel discrete-continuous decision variable, also known as mixed-variable, representation was used to enhance the versatility of the approach by evaluating more options during the search process. Application of the proposed framework in the Eagle Creek Watershed, Indiana, indicated that the optimal suite of conservation practices from the mixed-variable NSGA-II was more effective in meeting water quality targets at lower costs than the solution from binary-variable optimization. However, the mixed-variable approach was considerably more computationally demanding for assessing tradeoffs between environmental and economic factors. A method for hybridization of binary- and mixed-variable NSGA-II methods in the context of nonpoint source pollution control practices was developed to enhance the computational efficiency of the optimization procedure. As a result, the number of model simulations required for convergence to the Pareto-optimal solutions was reduced by 96 percent. The conceptual complexity and computational requirements of optimization-based approaches are impediments to their wider application for targeted implementation of NPS pollution control strategies. The methods and finding of this study address these issues and could result in a more effective implementation of management strategies at the watershed scale.

Beschreibung: A continuous SCS CN method that considers time-varied SCS CN values was developed based on the original SCS CN method with a revised soil moisture accounting approach to estimate runoff depth for long-term discontinuous storm events. The method was applied to spatially distributed long-term hydrologic simulation of rainfall-runoff flow with an underlying assumption for its spatial variability using a GIS-based spatially distributed Clark's unit hydrograph method (Distributed-Clark; hybrid hydrologic model), which is a simple few parameter runoff routing method for input of spatiotemporally varied runoff depth, incorporating conditional unit hydrograph adoption for different runoff precipitation depth-based direct runoff flow convolution. Case studies of spatially distributed long-term (total of 6 years) hydrologic simulation for four river basins using daily NEXRAD quantitative precipitation estimates (QPEs) demonstrate overall performances of Nash-Sutcliffe efficiency ( E NS ) 0.62, coefficient of determination ( R 2 ) 0.64, and percent bias ( PBIAS ) 0.33% in direct runoff and E NS 0.71, R 2 0.72, and PBIAS 0.15% in total streamflow for model result comparison against observed streamflow. These results show better fit (improvement in E NS of 42.0% and R 2 of 33.3% for total streamflow) than the same model using spatially averaged gauged rainfall. Incorporation of logic for conditional initial abstraction in a continuous SCS CN method, which can accommodate initial runoff loss amounts based on previous rainfall, slightly enhances model simulation performance; both E NS and R 2 increased by 1.4% for total streamflow in a 4-year calibration period. A continuous SCS CN method-based hybrid hydrologic model presented in this study is, therefore, potentially significant to improved implementation of long-term hydrologic applications for spatially distributed rainfall-russnoff generation and routing, as a relatively simple hydrologic modeling approach for the use of more reliable gridded types of QPEs.

Beschreibung: The loss of protons in the outer part of the inner radiation belt (L = 2 to 3) during the 17 March 2015 geomagnetic storm was investigated using test particle simulations that follow full Lorentz trajectories with both magnetic and electric fields calculated from an empirical model. The simulation results presented here are compared with proton pitch angle measurements from the Van Allen Probe satellites Relativistic Electron Proton Telescope (REPT) instrument before and after the CME-shock driven storm of 17-18 March 2015, with minimum Dst = -223 nT, the strongest storm of Solar Cycle 24, for four different energy ranges with 30, 38, 50, and 66 MeV mean energies. Two simulations have been run, one with an inductive electric field and one without. All four energy channels show good agreement with the Van Allen Probes REPT measurements for low L (L 〈 2.4) in both simulations but diverge for higher L values. The inclusion of the inductive electric field, calculated from the time changing magnetic field, significantly improves the agreement between simulation and REPT measurements at L 〉 2.4. A previous study using the Highly Elliptical Orbiter 3 (HEO-3) spacecraft also showed improved agreement when including the inductive electric field but was unable to compare effects on the pitch angle distributions.