关键词: 异常降水, 环流形势, 物理量诊断

Abstract: Based on the conventional observations and the NCEP (National Centers for Environmental Prediction) reanalysis data,physical mechanism of precipitation anomaly in Liaoning province in July of 2013 was analyzed.The results show that the anomalous high precipitation in Liaoning province in July of 2013 occurs under the background of anomalous atmospheric circulation.The intensities of Ural Mountain ridge and Baikal Lake trough are stronger.The activity of cold air enhances,and it moves along a southward path.There is a longitudinal strong front along the zone of 40°-50°N in the East Asia regions,which favors the formation and development of a cyclone system.The location of the subtropical high ridge line shifts about 2° further north compared with its normal location.There are warm moist air flows at the northwest side of the subtropical high.In July,when the cold air over the middle and high latitudes travels southward and invades to the 40°N region,it meets with the warm and moist air coming from the low and middle latitudes there,leading warm moist air ascending and resulting in rainstorms.There are mainly three influencing systems,i.e.,the North China cyclone,the Mongolia cyclone cold front and the shear line in the west side of the subtropical high.The physical mechanism of rainstorm is different among these systems.The water vapor sources of the North China cyclone are the most abundant among the three rainstorm events.They are generally from the western Pacific Ocean,the South China Sea,the East China Sea,the Yellow Sea,as well as the Bay of Bengal.The water vapor in the rainstorm region is mainly transported northward by the southwesterly and southerly winds along outside of the subtropical high.The strongest regions for water vapor convergence and transport are located in the northern part of the East China Sea and the Yellow Sea.The high-level air jet is influenced by intensity of Baikal Lake trough.Under different influence systems,the evolution and intensity of high-level jet,the distribution and intensity of low-level jet,as well as the locations of the high-level divergence and low-level convergence zones to the axis of high- and low-level jets are different.The strong water vapor convergence resulting from the coupling development of high- and low-level jets and the intense vertical upward movements bringing by the overlapping effect between high-level divergence and low-level convergence,make the top of the water vapor convergence of the North China cyclone rainstorm reaching 850 hPa,and those of the Mongolia cyclone cold front and the shear line in the west side of subtropical high pressure rainstorms reaching near 900 hPa or lower.The thermal analysis indicates that dry and cold air invades into the middle layer of the environmental atmosphere during the three rainstorm events,which increases the convective instability in precipitation.

Key words: Anomalous precipitation, Circulation situation, Physical quantity diagnosis