Abstract:

Based on the data from the conventional meteorological and automated stations, NCEP (National Centers for Environmental Prediction) 1°×1° reanalysis and satellite black body temperature, formation reasons for a continuous heavy rainfall that occurred in Jilin province on August 13-15, 2018 were analyzed.The results show that "three zones" (westerly zone, subtropical zone and tropical zone circulation) are the large scale circulation backgrounds for the formation of this heavy rainfall.From the water vapor flux throughout the atmosphere, it reveals that an abundant water vapor delivering by the southwest airstream at the periphery of subtropical high and the southeast airstream at the periphery of a typhoon coming from a long distance away is supplied to the heavy rainfall zone.This heavy rainfall process can be divided into two phases.First, a positive moist potential vorticity disturbance existing at the high levels slides along the pseudo-equivalent potential temperature front zone and forms an unstable atmospheric stratification that has adequate water vapor and high unstable energy.Compared with the first phase, the water vapor and thermal conditions are weak, and unstable energy is small in the second phase.From the satellite images, it shows an MCC (Mesoscale Convective Complexes) and meso-scale α convective cloud.When the MCC cloud is in a thriving stage, cyclonic vorticity and meso-scale convergence exist at the low level and anticyclone vorticity and meso-scale divergence exists at the high level.The shear line at 925 hPa and convergence line at the surface are the meso-scale initiation condition for this heavy rainfall.

Key words: Water vapor flux throughout the atmosphere, Pseudo-equivalent potential temperature, Potential vorticity, MCC (Mesoscale Convective Complexes)