Abstract
Abstract. Modification of the intensity of a low level jet (LLJ) and near-surface wind speed by mineral dust is important as it has implications for dust emission and its long-range transport. Using the Weather Research and Forecasting with Chemistry (WRF/Chem) regional model, it is shown that direct radiative forcing by mineral dust reduces temperature in the lower atmosphere, but increases it in the layers aloft. The surface cooling is shown to be associated with a reduction of turbulent kinetic energy (TKE) and hence vertical mixing of horizontal momentum. Changes in the vertical profile of temperature over the regions that are under the influence of a LLJ are shown to result in an intensification of the LLJ and near-surface wind speed, but a decrease of winds aloft. These changes in the wind speed profile differ from results of previous research which suggested a decrease of wind speed in the lower atmosphere and its increase in the upper boundary layer.
Highlights
The Sistan Basin in eastern Iran and western Afghanistan has long been found to be an important source of mineral dust (McMahon, 1906; Middelton, 1986), because erodible sediment is continuously supplied from Hamoun Lake and the region is under the influence of the strong northerly “wind of 120 days” (ACJGR)
Model results indicate that the peak near-surface wind speed in mid-morning is in response to the existence of a northerly LLJ and associated transfer of momentum from the jet level down to the surface as the daytime mixed layer evolves (ACJGR)
The strong northerly “wind of 120 days” and the LLJ play a key role in dust emission and its subsequent long-range meridional transport, but direct radiative forcing by mineral dust influences the strength of the “wind of 120 days”
Summary
Basin is considered to be the moDst aactativeSsyosurtceems of long-range transport of wind-blDowantaduSsty(sTtoedmd set. Influence the stability of the atmosphere (MillDeirsceut sasli.o, n2s004), basin may occur at any time throughout the year, but they which can change the intensity of the LLJ and near-surface are more frequent from mid-May to mid-September when wind speed (Jacobson and Kaufman, 2006; Alizadeh Choothe strong northerly “wind of 120 days” H(loycdallryoklonogwyn aasnd bari et al, 2012). The impact of mineral dust on vertical profiles of wind speed over the regions that are under the influence of a LLJ is currently unexplored.
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