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Investigating the dust effects on the modulation of large-scale circulations and cloud activities over North Africa and the Eastern Atlantic Ocean using a fully coupled regional atmosphere-dust-ocean model


This study examines how dust-cloud-radiation interactions modulate large-scale circulations and reduce meteorological variable errors over North Africa and the Atlantic Ocean using a fully coupled atmosphere-dust-ocean model. Two one-month numerical experiments in June 2020 are conducted: activation (DON) and deactivation (DOFF) of dust-radiation-cloud interactions. Model results show that the dust effects correct large-scale circulations that greatly reduce the biases and root mean square errors (RMSEs) of meteorological variables in the atmosphere. The improvement on these errors is mainly attributed to the improvement of the temperature and energy fields, which modify the vertical instability and the wind field through the thermal wind relation. The intensity and the northward shift of the African easterly jet (AEJ) are corrected by the gradient of the dust heating. As a result, the maximum RMSE of 650-hPa wind speed is reduced by 90% over the major error region. In addition, the 750-hPa temperature RMSE is improved by as much as 91%. Near the surface, the maximum RMSEs of 10-m wind, 2-m temperature, and 2-m moisture are reduced by 83%, 91%, and 72%, respectively. The Intertropical Discontinuity (ITD) zone and the Intertropical Convergence Zone (ITCZ) are shifted to the north due to the intensified southwesterly monsoonal flow over this region. These near-surface wind changes are mainly caused by the dust radiative heating, which creates a low-pressure anomaly and a convergent cyclonic circulation anomaly underneath the dust plume. The influence of dust on cloud activities, in particular those initiated to the south of the ITD, and cloud-relevant variables (e.g., wind) are also examined. Because of the dust-induced low-level circulation, when a dust plume propagates along the ITD region, the area-mean south-northerly wind (12ºN to 24ºN and 5ºW to 15ºE) becomes weaker (i.e., northerly flow) as the dust plume enters the region, and becomes stronger (i.e., southerly) as the dust plume exits the region. Compared to DOFF, dust enhances the northward moisture transport at this ITD region when stronger southerly winds occur, and as a result, storms have a higher likelihood to develop stronger and farther into the north.

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