The Climatological Effect of Saharan Dust on Global Tropical Cyclones in a Fully Coupled GCM

Climate of the tropical North Atlantic and West Africa is known to be sensitive to both the atmospheric burden and optical properties of aerosolized mineral dust. We investigate the global climatic response to an idealized aerosol radiative forcing from Saharan-born mineral dust, comparable to the observed changes between the 1960s and 1990s, using simulations with the high resolution, fully coupled GFDL Climate Model 2.5 Forecast-oriented Low Ocean Resolution version (CM2.5-FLOR) and a range of realistic optical properties, with a specific focus on tropical cyclones.

The radiative response at the top of the atmosphere and at the surface is in agreement with previous studies displaying a strong local response dependent on the amount of aerosol absorption versus scattering. These differences result in opposing regional hydrologic and thermodynamic effects of dust both in the atmosphere and in the upper ocean.

In all simulations, dust causes a decrease in tropical cyclone activity across the North Atlantic Ocean, as determined by a tropical cyclone tracking scheme, with the largest response occurring in the most absorbing and scattering optical regimes. These changes are partially corroborated by common local genesis potential indexes. The tropical cyclone track density anomalies have the strongest correlations with changes in local thermodynamic properties in the most absorbing cases. Conversely, anomalies in the most scattering cases have the strongest correlations with changes in local dynamical properties. There are also large changes in the Western North Pacific and South Indian Oceans in these simulations which remain largely unexplained. Several climate indicies are explored to explain the non-local response to the dust forcing and a relationship between accumulated cyclone energy and ToA radiative flux anomalies is described.