| Over the eastern tropical Atlantic Ocean, episodic outbreaks of mineral dust off the African continent are observed to move westward in association with the propagation of African easterly waves (AEW), which are often the precursor of the tropical cyclones (TC). However, the effect of the dust outbreaks on the AEW/TC development is uncertain and has been the subject of considerable debate, of which some studies show the dust layer has a negative impact on TC development, some show its role is positive, and some argue there is rather little evidence to substantiate a significant interaction.;In this study, we established the dust-AEW relationship through analyzing Aerosol Optical Thickness (AOT) data from MODIS in the period June 1-October 31, 2003-2007, and confirmed its negative correlation with relative vorticity extracted from ECMWF operational analysis. However, if considering the fact that the mineral dust usually spreads out around the northern periphery of the vortex, the correlation between the vortex and the AOT at the north of the vortex is found positive, indicating that the disturbances and Saharan dust outbreaks usually take place at the same time.;Since the statistical relationship does not necessarily mean causality, we implemented the NASA/GSFC radiative transfer model, both shortwave and longwave, with the Weather Research and Forecasting (WRF) model for numerical experiments to investigate if dust radiative effect plays a role on the development of AEW. In the sensitivity test of 36 different aerosol conditions, 31 show significant intensifying effect and 5 show no significant effect. When aerosols act to stabilize the unstable southern region or destabilize the stable northern region, the intensifying effect is the strongest. Furthermore, we conducted a pair of simulations for 60 AEW disturbances in the period August 1-September 30, 2003-2007, and found that the aerosol-induced intensifying effect was present in 58 cases. An analysis of the Lorenz energy cycle and the potential vorticity budget shows that the effect of the aerosols on the diabatic heating of the vortex column, albeit relatively small, enhances deep convection and promotes a large, additional release of latent heat which intensifies the AEW disturbance. |
