Dust-Induced Changes on Energy and Activity of Atmospheric Waves Using a Global Climate Model

Because of the importance of dust particles in Earth’s climate system, considerable efforts have been made to model dust distributions and properties in global climate models. Using NCAR global climate model as well as NASA’s observations and reanalysis data-sets, we provided evidence that explains the role of dust-induced changes on kinetic energy of the tropical easterly waves. The climate of the Western African continent and the Eastern Atlantic Ocean is highly variable and strongly influenced by the complex dynamics of the tropical waves also known as African Easterly Waves (AEWs). The main goal of this study is to investigate the causality underlying the mechanistic impacts of Saharan dust on development of the waves. We implemented advanced diagnostic methods to explore the energetic roles of dust particles embedded within the wave systems.

This study explains the influences of dust radiative forcing on amplification of the waves in tropical storm tracks. We showed that dust radiative forcing has the capability to act as an additional energetic source to fuel the developments of the AEWS. We gained further insights into the mechanisms that explain coupling of wave activity with dust radiative forcing that motivate variations in instability and development of tropical waves in a region of the world that is vulnerable to impacts from such variability. Because the tropical easterly waves contribute to cyclogenesis and formation of hurricanes, the results of this study are linked to quantify the roles of dust in Atlantic cyclogenesis.

The Community Earth System Model version 1.2.2.1 (CESM; Shields et al., 2012) is utilized to accomplish the simulations. Three different resolutions are used to present changes in wave characteristics induced by dust. Our simulations are conducted for 100 years with preindustrial CO₂ and slab-ocean model (SOM) that calculates the SST from the surface heat fluxes. In particular, the model uses a prescribed climatological Q-flux (i.e. the ocean energy flux divergence that accounts for the effect of the ocean circulation on SST and is associated with net heat flux) from a fully-coupled control run. Our numerical experiments include (1) control run, (2) dust-off and (3) doubled dust in the selected dust domain (N.H. Africa and the Middle-East) over the entire vertical levels of model.

The second Modern-Era Retrospective Analysis for Research and Applications (MERRA2; Randle et al., 2016) datasets were also used in this study to identify the thermal and dynamical characteristics of the tropical waves and to quantify the radiative forcing of the atmosphere by Saharan dust plumes. Dust is simulated in the MERRA2 with radiatively coupled version of the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART; Colarco et al., 2010) aerosol model, which has been strongly constrained by the assimilation of numerous satellite observations. In this manner, the MERRA2 data provides the best estimate of the state of the atmosphere from the present day back to the year 1979.