THE CHARACTERISTICS AND NUMERICAL SIMULATION OF DIURNAL VARIATIONS OF LOW-LEVEL JET AND MEIYU FRONT HEAVY RAINFALL
ZHOU Jing
ZHENG Yong-jun
MIAO Chun-sheng
LUO Ya-li
Abstract：This study investigates the characteristics of diurnal variations of southwesterly low-level jet (LLJ) and five heavy rainfall events over Yangtze-Huaihe River basin during June 2011 by analyzing the ERA-interim reanalysis data and surface automatic weather stations data.It is found that the southwesterly LLJ and the precipitation have the same evident diurnal variations in the five processes,which is strong in nocturnal-to-early morning hours (0200-0800 BST) and weak in the afternoon (1400 BST) hours.It is mainly attributed to inertial oscillation at nighttime and vertical mixing in the boundary layer during daytime.The enhancement of the southwesterly LLJ leads to the enhancement of the Meiyu front water vapor convergence,which contributes to the enhancement of rainfall at nighttime.Then with the reduction or disappearance of the southwesterly LLJ,the rainfall also weakens.The WRF numerical simulation successfully reproduces the observed evolution of precipitation and the southwesterly LLJ,and it is proved that the diumal variations of the LLJ and rainfall are mainly attributed to the diurnal variations of ageostrophic winds.With the enhancement of the vertical mixing in the boundary layer during daytime,the winds become subgeostrophic.With the disappearance of the vertical mixing at nighttime,inertial oscillation under the balance of the pressure gradient force and Carioles force tum the winds into supergeotrophic winds.
Keywords：Meiyu front heavy rainfallsouthwesterly LLJcharacteristics of diurnal Variationsageostrophic windssolar heating
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：12( 750-761 )