Abstract
Based on the conventional meteorological data and the NCEP/NCAR 1° × 1° reanalysis data and those related to mid-scale automatic station, satellite cloud picture and radar return, with the dynamic diagnosis analysis method, an analysis is made on the process of the convective rainstorm of quasi-stationary front triggered by the weak cold air on June 4-7, 2014, showing: 1) the process occurred in the event of convection of a stationary front triggered by the eastward moving south trough and the southward moving weak cold air from west under the background of circulation of two ridges and one trough at the Asian-European mid-high latitude and weakening and southeastward moving subtropical high; 2) a system configuration that contributes to convective rainstorms formed in the event of the convergence of low-level moisture, upper-level divergence and the continuous vertical ascending motion after the 200 hPa upper-level jet stream moved westwards from east and the 850 hPa southwest jet stream intensified; 3) after the intrusion by weak cold air of the meso-scale katallobaric area formed by the accumulated warm moist air of Guangxi before the intrusion, the warm moist air rose to trigger convection; convection cells developed and spread nearby the boundary between anallobaric area and katallobaric area, during which total 5 MCSs developed and each formed a rainstorm center at the part where the MCSs coincide; a meso-scale katallobaric area forms and develops 2 - 5 hours earlier than convection, so that it is also a warning of heavy rains.
Highlights
As a main disastrous weather during the pre-rainy season in Guangxi, a rainstorm is closely associated with the south trough, shear line, southwest jet stream and front activities
On June 4-7, 2014, under the common impact of the eastward moving 500 hPa south trough, stationary front and south-west warm-wet airflow, Guangxi was hit by a continuous large-scale rainstorm from north to south, with most areas hit by rainstorm and downpour, individual towns hit by extraordinary rainstorm and part towns hit by 8 - 9-level gale together with thunder and lightning
From 0:00 a.m. to 8:00 a.m. of June 4, meso-scale allobaric field was distributed from east to west on a high-to-low basis (Figure 8(b)), northerly wind prevailed in the anallobaric area of northeast Guangxi, while southeaster prevailed in the katallobaric area of northwest Guangxi; there was shear of wind direction and wind speed in the anallobaric area and the katallobaric area, providing a mesoscale condition for the occurrence and development of the convective rainstorm
Summary
As a main disastrous weather during the pre-rainy season (from April to June) in Guangxi, a rainstorm is closely associated with the south trough, shear line, southwest jet stream and front activities. On June 4-7, 2014, a large-scale rainstorm hit Guangxi together with severe convection weather like thunder, lightning and gale, leading to heavy casualties and property loss Through analyses, this occurred for the reason that weak cold air diffused southwards from the highland. In combination with the conventional meteorological data and the NCEP/ NCAR 1 ̊ × 1 ̊ reanalysis data, midscale automatic station, satellite cloud picture and radar return, the paper makes a meteorological diagnosis and meso-scale analysis of the rainstorm and discusses the cause and the characteristics of the meso-scale convective system leading to the continuous short-term heavy rainfall, providing a basis for further understanding the triggering of convective storms by weak cold air from highlands and forming forecast experience for application and reference. This is of great significance for the prevention of a series of natural disasters caused by heavy rains, the protection of the people’s personal safety and the reduction of the people’s property
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