A Severe Convection Weather of Jiangxi in April 2003

Convection weather is one of the most severely disastrous weather phenomena in China, with features of small spacial scale, short life span, sudden emergence and great damaging force.It is always very difficult to make an accurate analysis and forecast for severe convection weather in the daily operational work.With the application of Doppler radar and the development of numerical weather prediction technology, the know ledge about the severe convection weather and the related mechanisms is also improved in recent years.Effective ways have been developed in some countries to be applied in the analysis and forecast for severe weather.Examples can be found in U S A, where parameter estimation, graphics identification and statistical characteristics based on climate have been put into operational use for forecast of hailstones and tornadoes, and proved to be useful in improving the accuracy.Much improvement is also made in China Meteorological Administration in recent years in severe weather observation, many new instruments, such as radars, automatic weather stations, lightening detection and GPS/MET vapor detection instruments etc have been gradually put into operational use.These new data definitely provide forecasters and researchers good opportunities to study the severe convection weather and improve the forecast accuracy.Using NCEP/NCAR daily meteorological reanalysis data, sounding data, TBB and Doppler radar images, a typical convection induced severe weather process occurred on April 12—13, 2003 in Jiangxi and northern Fujian is diagnosed and analyzed, the result shows that this severe convection weather takes place under favorable conditions of upper trough coupling with a low-level vortex and shear environments. Lower level southwesterly jet contributes as a vapor transportation passage.Dry and cold airs of upper level overlapping upon wet and warm airs in low er level create a convectively unstable layer.Under this condition, convective weather could be easily initiated and high instability energy releases with suitable triggering mechanism. Several mesoscale convective clouds involve in the development of the severe weather, and deep convection mostly concentrates on the frontal parts of the clouds where TBB isolines converging with high gradient.Also the Doppler radar images show that the maximum reflection up to 79 dBz is reported during hail-fall, and bow echo could be observed.Convective available potential energy (CAPE) is a meaningful sign in the process of convection event.Before the severe weather, CAPE grow s gradually and accumulates.The severe weather initiates soon after the CAPE reaches its peak values, then with CAPE's releasing and becoming weak rapidly, severe weather downgrades.Dry air intrusion to mid-level from upper level plays an important role in the development of convection.Energy-front zone and strong vertical vorticity-pole provides thermodynamic and dynamic conditions for this severe convection weather.