In this study, we address the variations of bare soil surface microwave brightness temperatures and evaluate the performance of a dielectric mixing model over the desert of Kuwait. We use data collected in a field survey and data obtained from NASA Soil Moisture Active Passive (SMAP), European Space Agency Soil Moisture and Ocean Salinity (SMOS), Advanced Microwave Scanning Radiometer 2 (AMSR2), and Special Sensor Microwave/Imager (SSM/I). In situ measurements are collected during two intensive field campaigns over bare, flat, and homogeneous soil terrains in the desert of Kuwait. Despite the prevailing dry desert environment, a large range of soil moisture values was monitored, due to precedent rain events and subsequent dry down. The mean relative difference (MRD) is within the range of ±0.005 m3·m−3 during the two sampling days. This reflects consistency of soil moisture in space and time. As predicted by the model, the higher frequency channels (18 to 19 GHz) demonstrate reduced sensitivity to surface soil moisture even in the absence of vegetation, topography and heterogeneity. In the 6.9 to 10.7 GHz range, only the horizontal polarization is sensitive to surface soil moisture. Instead, at the frequency of 1.4 GHz, both polarizations are sensitive to soil moisture and span a large dynamic range as predicted by the model. The error statistics of the difference between observed satellite brightness temperature (Tb) (excluding SMOS data due to radio frequency interference, RFI) and simulated brightness temperatures (Tbs) show values of Root Mean Square Deviation (RMSD) of 5.05 K at vertical polarization and 4.88 K at horizontal polarization. Such error could be due to the performance of the dielectric mixing model, soil moisture sampling depth and the impact of parametrization of effective temperature and roughness.
Van Den Broeke, M. S., and H. Alsarraf, 2016: Polarimetric radar observations of dust storms at 4 (9)
The normal surface pressure distribution in the Middle East includes high pressure over the eastern Mediterranean Sea and low pressure over the southeastern Arabian Peninsula. The resulting west-east pressure gradient leads to summertime northerly or northwesterly shamal winds across the Arabian Peninsula, which typically result in many days per month with substantial lofted dust, leading to considerable human health and transportation impacts. It would be helpful to understand how the regional pressure gradient may change in the future, as the strength of this gradient exerts predominant control over the strength of the shamal wind. One factor possibly leading to changes in the strength of the pressure gradient is climate variability. We have simulated the regional climate under a presentday scenario (2006-2010) and a mid-century scenario (2056-2060) using the Weather Research and Forecasting (WRF) model. Our results indicate a weakening of the regional pressure gradient by mid-century, resulting in lower average wind speeds and fewer days conducive to dust storms across the Arabian Peninsula.
The goal of this study is to validate and analyze NASA’s Soil Moisture Active Passive (SMAP) products over the desert of Kuwait. The study period was between April 2015 and April 2020. The study domain includes a mission candidate calibration/validation (Cal/Val) site that comprises six permanent soil moisture stations used to verify SMAP estimates. In addition, intensive field campaigns were conducted within and around the candidate Cal/Val site during the study period to collect additional thermogravimetric samples. The mean difference (MD), root mean squared difference (RMSD), unbiased root mean square difference (ubRMSD), and correlation coefficient (R) were computed to assess the agreement between SMAP SM products and in situ observations. The comparison of the six ground station sensors’ observations with the thermogravimetric samples led to an absolute mean bias (AMB) of 0.034 m3 m−3, which was then used to calibrate the sensors and bias-correct their measurements. The temporal consistency of the readings from the test site and calibrated sensors was assessed using the mean relative difference (MRD) and its standard deviation of relative difference (SDRD). Using a sampling density analysis, it was determined that a minimum of four ground stations would be required to validate the test site. Furthermore, the consistency between SMAP satellite soil moisture data and those derived from the Soil Moisture and Ocean Salinity (SMOS) satellite operated by the European Space Agency, and their agreement with in situ samples, was analyzed. The comparison of SMAP and SMOS soil moisture data with in situ observations showed that both satellites successfully captured the spatial and temporal distribution of soil moisture. For SMAP and SMOS, the lowest ubRMSE statistics were 0.043 m3 m−3 and 0.045 m3 m−3, respectively, which are slightly higher than the mission target of 0.04 m3 m−3.
CapsuleThe purpose of this study is to present two case studies, one dominated by synoptic-scale forcing and the other by mesoscale forcing, to determine the effects of wind patterns on visibility and aerosol transport in the Arabian Peninsula. Citation: Alsarraf H, Van Den Broeke MS (2015) Using High-Resolution WRF Model Simulations to Investigate the Relationship between Mesoscale Circulations and Aerosol Transport over Kuwait. AbstractTwo case studies have been investigated using high-resolution WRF model simulations. The purpose of these case studies is to determine the effects of wind patterns on visibility and aerosol transport in the region. In the first case study, strong synoptic-scale forcing led to a large-scale pressure gradient resulting in strong wind and longrange aerosol transport. In the second case study, the mesoscale land/sea breeze offset weak synoptic-scale forcing near the coast. The daytime sea breeze and nighttime land breeze limited the ventilation of air masses and allowed recirculation of contaminants and aerosols near the shoreline, which may strongly influence visibility and air quality locally.
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