Characteristic Analysis of Abnormal-Weakening Summer Precipitation in Tianjin under the Influence of Bohai Sea High

¹ Binhai New Area Meteorological Office of Tianjin, Tianjin 300457, China
² Tianjin Weather Modification Office, Tianjin 300074, China

^* Corresponding author: swallownx@163.com

Abstract

To investigate the characteristics of Bohai High, the daily precipitation data of Beijng-Tianjin region during June to September from 2006 to 2015, national basic automatic weather stations data of 5 minute, NCEP/NCAR 1°×1° reanalysis data as well as CINRAD/SA data of Tianjin, from the definition of and the distribution characteristics of precipitation in Beijng-Tianjin region, the concept of regional precipitation reduction in summer in the context of Bohai High was given. This was done by classifying large-scale synoptic circulation and synthetic diagnosis method. The results show that: (1) Bohai High has the most significant effect of abnormal weaken precipitation in the eastern of Tianjin, while has a relatively mild effect in the northern of Tianjin. (2) According to the characteristics of large-scale circulation situation, the synoptic processes over heavy rain are classified into three patterns: upper-level trough pattern (I), cold vortex pattern (II) and the interaction between subtropical high and western trough (III). Except that water vapor come from the Bohai Sea and the Yellow Sea for Type II, for the other two patterns the water vapor were related to remote supplies from the South China Sea and the East China Sea. The Bohai High of Type Iand III were thick warm negative vorticity system whereas the Type II was a shallow negative vorticity system. (3) The abnormally weakened of Bohai High were related to their depths and duration, the deeper and the longer duration of Bohai High, the stronger weakening effect on the precipitation in Tianjin.