The Influence of Dust Radiative Effects on the Energetics of Tropical Easterly Waves

The Sahara Desert in North Africa is the largest source of dust in the world, where over sixty million tons of dust particles are lifted annually and transported within the Saharan Air Layer (SAL) across the Atlantic Ocean and reaches the Caribbean Sea, the Gulf of Mexico, Amazon Basin and the United States. Dust particles in the SAL have a robust influence on regional and global climate through their impacts on radiation, clouds, hydrological cycle, and atmospheric circulation.

We used 22 years of daily satellite observations and reanalysis data to explore the relationships between dust in the SAL and the development of the tropical easterly waves, also known as African Easterly Waves (AEWs).

Our findings indicate that the diabatic heating, induced by dust aerosols within SAL, acts as an additional energy source to enhance the growth of AEWs, which leads to an increase in the meridional temperature gradients within the baroclinic zone, where transient eddies extract available potential energy from the mean-flow and convert it to Eddy Kinetic Energy (EKE), This suggests that dust-induced diabatic heating can fuel the EKE of the AEWs and enhance the baroclinicity of the region. This study also showed that dust outbreaks over the tropical Atlantic Ocean precede the development of baroclinic waves downstream of the African easterly jet (AEJ), which implies that the radiative effect of dust has the capability to trigger the generation of the transient eddies within the AEJ-AEWs system.

These empirical relationships are further examined in our atmospheric general circulation model simulations using the Community Earth System Model (CESM) with and without the dust radiative effect. This supports the hypothesis linking dust radiative effects to the energetics of the AEWs.