Saharan Air Layer and Its Aerosol-cloud-radiation Interactions – a NU-WRF Simulation of an HS3 Event

There was a dust outbreak on August 24-25, 2013 over the Saharan region and a heavy dust plume, measured by high aerosol optical depth observed by MODIS, extended deep into the Atlantic Ocean. This dust-laden air features the Saharan Air Layer (SAL) that is also extremely hot and dry. The role of the SAL in tropical storm formation and intensification remains an open scientific question. The Hurricane and Severe Storm Sentinel (HS3) mission was designed to address the question through the substantial measurements over three hurricane seasons using two Global Hawks unmanned aircrafts that were equipped with a set of instruments geared toward environmental measurements and understandings of storm inner-core structure and processes. A Global Hawks flight spanning over 6 hours in the SAL on August 24-25, 2013 provided an excellent opportunity for investigation of SAL structures and aerosol-cloud-radiation interactions. The NASA's Unified WRF (NU-WRF) is an observational driven regional modeling system that represents chemistry, aerosol, cloud, precipitation and land processes at satellite-resolved spatial scales. The Goddard Chemistry Aerosol Radiation and Transport module has fully been 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 the measurements by the cloud physics lidar, dropsonde, and AERONET. A series of sensitivity experiments have also been carried out to probe the role of aerosol-cloud-radiation interactions on dust transport, atmospheric energy balance, and precipitation.