Using the conventional meteorological observation data, the sounding data, NCEP 1°×1° reanalysis data and the satellite data, The large-scale circulation background, vertical structural features and triggering mechanism of the first rainstorm rainstorm in Shandong rainy season from 6-7 July 2017 were analyzed. The results showed that:This warm-season rainstorm process is that the westerly belt system on the northwestern side of the subtropical high interacts with the warm-humid southwest flow from low latitudes, and is accompanied by the advantageous background of low-altitude and ultra-low-altitude south-west winds, shear lines and thermal low ground pressure. During the heavy rains, the atmosphere was in a truly unstable state, with deep wet and warm clouds, low cloud heights, and high precipitation efficiency. The torrential rain also experienced a process of vertical wind shear changed from weak to strong. The rapid strengthening and downward propagation of the southwest wind stream in the lower troposphere triggers the release of unstable energy, which provides trigger conditions for the occurrence of heavy rainfall. High-level westerly jet stream provides a strong "suction" effect, forming a strong upward movement. The top of the cloud-blackbody bright temperature (TBB) zone corresponds to heavy precipitation. Water vapor and infrared cloud images can effectively reveal the occurrence, development and demise of the weather system as well as the dynamic and vapor characteristics of the upper troposphere. The effect of warm advection on vertical movement is even more pronounced. The prediction of low-altitude and ultra-low-level jet streams can be used as a forecast point for daily warm-storm events.
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