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- ItemVariability of Cosmogenic 35S in Rain—Resulting Implications for the Use of Radiosulfur as Natural Groundwater Residence Time Tracer(Basel : MDPI, 2020) Schubert, Michael; Knöller, Kay; Tegen, Ina; Terzi, LucreziaInformation about groundwater residence times is essential for sustainable groundwater management. Naturally occurring radionuclides are suitable tools for related investigations. While the applicability of several long-lived radionuclides has been demonstrated for the investigation of long residence times (i.e., years, decades, centuries and more), studies that focus on sub-yearly residence times are only scarcely discussed in the literature. This shortage is mainly due to the rather small number of radionuclides that are generally suitable for the purpose and show at the same time adequately short half-lives. A promising innovative approach in this regard applies cosmogenic radiosulfur (35S). 35S is continuously produced in the stratosphere from where it is conveyed to the troposphere or lower atmosphere and finally transferred with the rain to the groundwater. As soon as the meteoric water enters the subsurface, its 35S activity decreases with an 87.4 day half-life, making 35S a suitable time tracer for investigating sub-yearly groundwater ages. However, since precipitation shows a varying 35S activity during the year, setting up a reliable 35S input function is required for sound data evaluation. That calls for (i) an investigation of the long-term variation of the 35S activity in the rain, (ii) the identification of the associated drivers and (iii) an approach for setting up a 35S input function based on easily attainable proxies. The paper discusses 35S activities in the rain recorded over a 12-month period, identifies natural and anthropogenic influences, and suggests an approach for setting up a 35S input function applying 7Be as a pro
- ItemAtmospheric Dynamics and Numerical Simulations of Six Frontal Dust Storms in the Middle East Region(Basel : MDPI, 2021) Hamzeh, Nasim Hossein; Karami, Sara; Kaskaoutis, Dimitris G.; Tegen, Ina; Moradi, Mohamad; Opp, ChristianThis study analyzes six frontal dust storms in the Middle East during the cold period (October–March), aiming to examine the atmospheric circulation patterns and force dynamics that triggered the fronts and the associated (pre-or post-frontal) dust storms. Cold troughs mostly located over Turkey, Syria and north Iraq played a major role in the front propagation at the surface, while cyclonic conditions and strong winds facilitated the dust storms. The presence of an upper-atmosphere (300 hPa) sub-tropical jet stream traversing from Egypt to Iran constitutes also a dynamic force accompanying the frontal dust storms. Moderate-Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations are used to monitor the spatial and vertical extent of the dust storms, while model (Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), Copernicus Atmospheric Monitoring Service (CAMS), Regional Climate Model-4 (RegCM4)) simulations are also analyzed. The WRF-Chem outputs were in better agreement with the MODIS observations compared to those of CAMS and RegCM4. The fronts were identified by WRF-Chem simulations via gradients in the potential temperature and sudden changes of wind direction in vertical cross-sections. Overall, the uncertainties in the simulations and the remarkable differences between the model outputs indicate that modelling of dust storms in the Middle East is really challenging due to the complex terrain, incorrect representation of the dust sources and soil/surface characteristics, and uncertainties in simulating the wind speed/direction and meteorological dynamics. Given the potential threat by dust storms, more attention should be directed to the dust model development in this region. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.