A NU-WRF Simulation of Saharan Air Layer Structure and Its Impact on Radiation

Although a key scientific goal of the NASA Hurricane and Severe Storm Sentinel (HS3) investigation was to examine the impact of the Saharan Air Layer (SAL) on tropical cyclone intensity, a secondary objective was to provide detailed measurements of the SAL even in the absence of significant tropical disturbances. To achieve both goals, a NASA Global Hawk unmanned aircraft was equipped with the NCAR/NOAA dropsonde system, the University of Wisconsin S-HIS interferometer sounder, and the Goddard Cloud Physics Lidar to measure vertical profiles of temperature, humidity, winds, and dust. The Global Hawk was deployed over three Atlantic hurricane seasons (2012-2014). On August 24-25, 2013, the Global Hawk sampled a large dust outbreak associated with a non-developing African Easterly Wave over the eastern Atlantic Main Development Region. This case provided an excellent opportunity for investigation of the SAL structure and aerosol-cloud-radiation interactions. The NASA's Unified WRF (NU-WRF) is an regional modeling system that represents chemistry, aerosol, cloud, precipitation and land processes at down to near cloud-resolving spatial scales. The Goddard Chemistry Aerosol Radiation and Transport module has been fully coupled with the Goddard microphysics and radiation schemes in NU-WRF that allows investigations of direct and indirect aerosol effects in the climate/weather system. The NU-WRF has been employed to simulate this SAL event and the results have been compared to measurements by the Global Hawk and AERONET. A series of sensitivity experiments have also been carried out to probe the role of aerosol-cloud-radiation interactions on dust transport and atmospheric energy balance. The results show that NU-WRF captured this SAL location and 3D structure reasonably. Its impact on radiation will be described.