The influence of desertic aerosols on tropical cyclones

The role of dust on cyclogenesis has been recently investigated (Dunion and Velden, 2004 ; Evans et al., 2006). The above authors claim that dust could inhibit in many different ways deep convection and corresponding cyclogenesis and further cyclone evolution for two main reasons :

- Dust may contribute to decreasing SSTs as a result of additional reflexion of solar radiation

- For radiative reasons (absorption), dust may create a temperature inversion layer

Further, dust is transported in dry fast moving (jet) Saharan air masses crossing the Atlantic ocean and its presence over the Atlantic attests for additional evaporative cooling of convective clouds and for the presence of an important wind shear.

In order to verify the role of African dust on cyclogenesis and tropical cyclone evolution, TOMS/EP/OMI aerosol index data corresponding to a tropical North Atlantic window (0-30N, 20-80W) have been used in this study in relation to cyclonic trajectories for the periods 1981-1992 and 1997-2006. The mapping of the successive positions of tropical cyclones on an aerosol index map in the given window leads to two main observations.

For only 7% of the cyclonic days, the tropical storm or hurricane is located on, or in the vicinity of a dust region, thus suggesting that cyclones develop and evolve preferably in dust free regions. Further, in this case, dust contributes in the same proportion to an increase and a decrease in intensity of the considered tropical storm or hurricane. In order to clarify the role of dust on cyclonic evolution, i.e. the dust plays no role or plays different roles (inhibition or strengthening) according to other air mass characteristics, further investigations are necessary.