Study On The Mechanism Of A Typhoon Rainstorm Process

This paper conducts a basic synoptic analysis of a typhoon storm that occurred in Shanghai from August 23 to August 24,2015,and uses the potential vorticity inversion method and numerical simulation method to analyse the water vapor conditions,vapor transport,thermal conditions,and power of the heavy rain process.A comprehensive understanding of the mechanism of the typhoon rainstorm was obtained.Mainly conclusions are drawn as follows:(1)The torrential rain process was triggered mainly by the convergence of cold air from the south and typhoon from the warm,moist air from the ocean surface.The upper-air situation is reflected by the cold trough at the south and the inverted trough extending from the north of the typhoon at the lower reaches of the Yangtze River,Exchange.The intensity of the typhoon "swans" can also correspond to periods of heavy precipitation.(2)Typhoon "Swan" is the main source of water vapor contribution for the heavy rain,and the easterly airstream circulating around the typhoon continues to send water vapor to the rainstorm area.Excluding the "swan" associated disturbance field,the total amount of water vapor in the precipitation area was greatly reduced,and the corresponding water vapor flux of the typhoon itself was larger,accounting for 53.3%of the total input water vapor flux,further illustrating the typhoon periphery.The circulation contributes a lot of water vapor input to the precipitation process.At the same time,after removing the typhoon-like pseudo-temperature,the large-value zone and the warm-wet tongue in the original analysis field disappeared.The entire southeast coast was controlled by the continental dry-cold air mass,and the large temperature-saturation gradient zone(front zone)disappeared.The "swan" also provided the key thermal conditions for the occurrence of heavy rain.(3)Combined with the results of model simulation and actual conditions,there is a convergence of water vapor in the rainstorm area and the water vapor transport path of the typhoon's outer easterly air flow.The precipitation area has sufficient water vapor conditions.There are wet and dry stratifications on the upper and lower layers,weak cold advection at the upper levels,weak warm advection at the lower levels,which allows unstable energy to accumulate,and vertical wind shear at the lower levels promotes the release of deep unstable energy.(4)Before the torrential rain occurred,there was a cold air in North China.When the heavy rain occurred,the cold air mass moved to the Yangtze River basin near 30°N.The Shanghai area is in the northwestern airstream in front of a high altitude trough and has been controlled by dry cold air.At the lower levels,typhoon-induced warm and humid air currents and unstable energy are continuously generated.When high-level cold air intrudes,the atmosphere's stratification changes and unstable energy is released.Adequate water vapor conditions combined with dynamic lift conditions and thermal processes together triggered the typhoon rainstorm process and allowed it to sustain development.