Abstract
Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively coupled to the circulation; passive transport, in which the dust is radiatively decoupled from the circulation. The theory is built around a dust conservation equation for dust-coupled AEWs in zonal-mean African easterly jets. The theory predicts that, for both the passive and active cases, the dust transports will be largest where the zonal-mean dust gradients are maximized on an AEW critical surface. Whether the dust transports are largest for the radiatively passive or radiatively active case depends on the growth rate of the AEWs, which is modulated by the dust heating. The theoretical predictions are confirmed via experiments carried out with the Weather Research and Forecasting model, which is coupled to a dust conservation equation. The experiments show that the meridional dust transports dominate in the passive case, while the vertical dust transports dominate in the active case.
Highlights
The importance of Saharan dust transport to the Earth system has propelled research that spans nearly a half century [1]
This study is framed around two questions that were not addressed in previous studies: first, to what extent do the passive and active dust transports by African easterly waves (AEWs) differ in amount and location and, second, what are the physical and dynamical interactions that control the differences
The Weather Research and Forecasting (WRF)-dust model consists of the Advanced Research WRF (ARW) dynamical core (v3.7) and a 12 bin dust model developed by Chen et al [12,32]
Summary
The importance of Saharan dust transport to the Earth system has propelled research that spans nearly a half century [1]. They showed that the dust caused the fastest growing AEW to increase its linear growth rate from 13% to 90% for aerosol optical depths (AODs) ranging from 1.0 to 2.5 They showed that the energy generation was largest where the meridional dust gradient was maximized near a critical surface. This study is framed around two questions that were not addressed in previous studies: first, to what extent do the passive and active dust transports by AEWs differ in amount and location and, second, what are the physical and dynamical interactions that control the differences To answer these questions, we combine theory and modeling, as described
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