一次冷锋型沙尘暴过程对流层—平流层交换的数值模拟

Primary Numerical Simulation Analysis on Tropo-stratosphere Exchange of Cold Front Duststorm Process

利用观测资料、ERA-Interim再分析资料，结合MM5数值模拟结果，对一次强沙尘暴过程的沙尘对流层-平流层输送问题进行初步分析。结果表明：高空强冷空气下传、地面冷锋强烈发展和对流层中低层斜压强迫是本次沙尘暴过程的主要影响因素。在系统发展和减弱的整个过程中，西南急流和高空冷空气下传是斜压不稳定形成的主导因素。与冷锋锋面匹配的对流层顶折叠沿纬向呈“V”形分布，其底部到达550hPa左右，同时伴随高空急流接近垂直下落，急流核位于高空槽的南侧和东侧，且南侧最强。高空位涡下传与西南急流共同作用，促使冷锋前气旋强烈发展，气流上升运动中心位于500hPa和600hPa，但其外围气流未直接穿过对流层顶。对流层顶折叠区上升气流在300-500hPa与高空槽底部偏西、偏南气流叠加，以斜升或准垂直的形态穿过对流层顶折叠底部进人平流层。气旋发展过程中，冷空气下沉并向东南扩展，暖空气则向西北方向爬升。平流层一对流层的净输送主要发生在高空位涡下传过程，高空位涡停止下传后，出现对流层-平流层净输送，且强度随时间呈增长趋势。

Using observational and ERA-Interim reanalysis result, the Tropo-Stratosphere Exchange （TSE） of cold front data, combined with the MM5 numerical simulation duststorm Process was conducted. The result showed, the strong cold air download, the ground cold front strongly developing and the lower troposphere baroclinic forcing are the main factors affecting the super dust storm process. The southwest jet stream and the strong cold air down- load play significant roles in forming the baroclinic forcing. The folded tropopause was showing V-shaped with its bottom approaching near 550 hPa; at the same time jet stream is vertical dropping accompanyingly with its center located in the south and east of upper trough, and that on the south side is the strongest. The fierce development of cold front cyclones benefited from combined action of the high altitude vorticity download and southwest jet stream. The air currents rising activity centre lay in the 500 hPa and 600 hPa, and the periphery current did not pass through the tropopause fold into the stratosphere directly. Between 300 hPa and 500 hPa around the tropopause fold region, the resultant wind between the ascending air currents and the western and southern wind, passed through the folded tropopause into stratosphere para-vertically or aslant upwards. The cold air dropped down and extended to the southeast while the warm air rised to the northwest in the development of cyclone. The net stratosphere-tropo- sphere transportation occurred accompanying with the progress of high altitude vorticity downward transportation. After that, the net troposphere-stratosphere transportation took place and its strength exhibited a growing trend over time.