Climatic characteristics and main weather conceptual model of spring rainstorm in Jining during the past 45 years

According to the daily precipitation data of 11 national observatory stations in Jining area during the period of 45 years from 1970 to 2014, the temporal and spatial distribution characteristics, rain intensity characteristics, weather circulation situation and main influencing systems of spring rainstorms in Jining area were analyzed. The results show that the spatial distribution of spring rainstorms in Jining area is quite different from each other, and the rainstorm area is located in the midwestern and the southeast part of Jining. The number of spring rainstorm days in the Weishan area is the most in Jining. The annual spring rainstorms in Jining show a slow increasing trend, especially since the year 2003, the occurrence frequency of rainstorms has increased significantly, and the strongest rainstorm occurred on May 26, 2013. Based on the weather situation and the main influencing system of massive spring rainstorms, a concept model of rainstorm weather in Jining was developed. The model shows that when massive rainstorm occurs, mid and high latitude region at 500 hPa mostly has a weather situation of high in east and low in west; the 850 hPa low vortex or low-level wet warm shear line is the main system of wide range spring rainstorms. The model also shows that low level jet with southwest or southeast wind transports water vapor to the rainstorm area and the subtropical high pressure zone dominates eastern region of the South China Sea, which blocks the webtisr' s moving eastward, and makes the southwest airflow transport vapor to the Shandong for a prolonged time. The block of high pressure in mid-high latitude in the Sea of Japan makes low vortex or shear line move eastward slow, which helps maintain strong precipitation for a long time. Moreover, There are often high level jets in north and south sides of Shangdong when rainstorms occur, and the atomosphere above Jining shows the situation of high level divergence, and there is no obvious northwest-toward cold air acitivity on the ground.