Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area
Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area
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DOI：
10.1029/2005jd006666
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发表时间：
2006-06
影响因子：
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通讯作者：
T. Takemi;M. Yasui;Jixia Zhou;Li-chao Liu
中科院分区：
文献类型：
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作者：
T. Takemi;M. Yasui;Jixia Zhou;Li-chao Liu
[1]本文利用一系列高分辨率的数值模拟方法，对中纬度沙漠地区晴天条件下由边界层和积云对流引起的沙尘排放和输送的动力学过程进行了研究。模拟集检查的灰尘动力学垂直风切变，上层风速和潮湿的对流的敏感性。模拟结果定性地捕捉到了北方沙漠地区激光雷达观测到的沙尘层的日变化。干对流在边界层内垂直混合粉尘中起主要作用。如果积云对流也起作用，则不仅在边界层内而且在自由对流层内的尘埃质量浓度都增加。干对流和湿对流的耦合效应是很重要的，因为对流是更增强的耦合效应比没有潮湿的过程，此外运输上层更高的动量到表面，加强地面风，因此粉尘排放。白天边界层上层风速超过地面沙尘排放阈值是地面增风的必要条件。虽然在晴天的一个日周期中，沙尘的上升量要比与一个天气扰动有关的小得多，但在较长的时间尺度上，由于晴天过程而产生的沙尘排放总量可能不能忽略。这表明，一个合适的参数化的干，湿对流在晴朗的天气需要在大尺度模拟。
[1] A series of high-resolution simulations explicitly resolving diurnally varying convective motion is performed for investigating the dynamical processes of dust emission and transport induced by boundary layer and cumulus convection under fair-weather conditions in a midlatitude desert area. The simulation set examines the sensitivity of the dust dynamics to vertical wind shear, upper level wind speed, and moist convection. The simulated results qualitatively capture the diurnal variation of the dust layer observed by lidar in a desert area in northern China. Dry convection plays a primary role in vertically mixing dust within the boundary layer. If cumulus convection also comes into play, mass concentration of dust increases not only within the boundary layer but also in the free troposphere. A coupled effect of dry and moist convection is important because convection is more enhanced with the coupled effect than without moist processes and in addition transports upper level higher momentum down to the surface, intensifying surface winds and hence dust emission. A wind speed exceeding the threshold for surface dust emission is necessary at the upper levels of the daytime boundary layer for the surface wind enhancement. Although the amount of dust lifted is much smaller during a single diurnal cycle of fair weather than is associated with a single case of synoptic disturbances, the total amount of dust emission due to fair-weather processes may not be neglected in a longer timescale. This suggests that a proper parameterization for dry and moist convection in fair weather needs to be employed in large-scale simulations.