Dust Radiative Effects on Atmospheric Thermodynamics and Tropical Cyclogenesis over the Atlantic Ocean Using WRF/Chem Coupled with an AOD Data Assimilation System

摘要

Abstract. This study investigated the dust radiative effects on atmospheric thermodynamics and tropical cyclogenesis over the Atlantic Ocean using WRF-Chem coupled with an aerosol data assimilation (DA) system. MODIS AOD data were assimilated with the Gridpoint Statistical Interpolation three-dimensional variational DA scheme to depict the Saharan dust outbreak events in 2006 summer. Comparisons with Ozone Monitoring Instrument (OMI), AErosol RObotic NETwork (AERONET) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations showed that the system was capable of reproducing the dust distribution. Two sets of 180-hr forecasts were conducted with the dust radiative effects activated (RE_ON) and inactivated (RE_OFF), respectively. Differences between the RE_ON and RE_OFF forecasts showed that low-altitude (high-altitude) dust inhibits (favors) convection owing to changes in convective inhibition. Heating in dust layers immediately above the boundary layer increases inhibition whereas sufficiently elevated heating allows cooling above the boundary layer that reduces convective inhibition. Semi-direct effects are also noted in which clouds are altered by thermodynamic changes, which then alter cloud-radiative temperature changes. The analysis of a tropical cyclone (TC) suppression case on Sep. 5 shows evidence of enhanced convective inhibition by direct heating in dust, but also suggests that the low-predictability dynamics of moist convection reduces the determinism of the effects of dust on time scales of TC development (days).