The Effect of Saharan Dust on North Atlantic Hydroclimate and Tropical Cyclones in a High-Resolution GCM

Abstract:

Climate of the tropical North Atlantic and West Africa is sensitive to dust optical properties as shown by our previous work (Strong et al., 2015) using a fully coupled global climate model (GCM). However, that study was limited by the relatively coarse resolution of the GCM which could not resolve explicitly sub-scale processes important to the simulation of tropical cyclones (TCs).

Using simulations with the higher resolution, fully coupled GFDL Climate Model 2.5, Forecast-oriented Low Ocean Resolution version (CM2.5-FLOR), for several realistic sets of optical properties, we investigate the climatic response across the tropical Atlantic basin to an idealized aerosol radiative forcing from Saharan-born mineral dust, comparable to the observed changes between the 1960s and 1990s, with a focus on the hydrological cycle and TCs. CM2.5-FLOR has a higher resolution atmosphere which is able to resolve TCs and has been shown to accurately reproduce the observed tropical cyclone climatology.

In the first part, we will show that the sign of the radiative response at the top of the atmosphere (ToA) changes between the more absorbing dust and more scattering dust simulations, in agreement with previous studies. Conversely, the radiative response at the surface is generally comparable between sets of optical properties. These differences result in opposing regional hydrologic and thermodynamic effects of dust both in the atmosphere and in the upper ocean.

In the second part, the effect of Saharan-born mineral dust on TCs will be analyzed. In all simulations, dust causes a decrease in tropical cyclone activity in the North Atlantic with the largest response occurring in the most absorbing and scattering optical regimes. We also note significant changes in the West Pacific in these simulations. The changes in tropical cyclone activity are found to not be explained by common genesis potential indexes, but a relationship between accumulated cyclone energy and ToA radiative flux anomalies proves promising.

Strong, J., G. Vecchi, and P. Ginoux, 2015: The Response of the Tropical Atlantic and West African Climate to Saharan Dust in a Fully Coupled GCM. J. Climate. doi:10.1175/JCLI-D-14-00797.1, in press.