ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Comparison of Environmental Conditions and Causes of Two Types of Severe Precipitation Affected by Low Vortex Shear in Hehuang Valley
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Abstract:
Based on the ground observation， NCEP 1°×1° reanalysis， FY-2G TBB， model data and radar mosic data of two type severe precipitations under the influence of low vortex shear in the Qinghai Hehuang Valley in the past three years， the comparative analysis is conducted about the environmental conditions and causes of different types of severe precipitation under the influence of the same circulation background， and also about the preliminary assessment of the model’s forecasting capabilities. The results show that the mixed severe precipitation weather with thunderstorm， hail， thunderstorm and gale is called severe precipitation type Ⅰ， and the severe precipitation weather dominated by pure short-term severe precipitation is called severe precipitation type Ⅱ. The low vortex shear was the impact system of the two types of severe precipitation. The severe precipitation type Ⅰ 400-300 hPa high-altitude cold advection intrusion promoted the eastward movement of the low vortex shear system， and the development of the ground cold front formed an occluded front in the Hehuang Valley. The severe precipitation type Ⅱ was blocked by the westward advance of the subtropical high, and the low vortex shear system and the ground cold front weakened and disappeared. Severe precipitation type I mainly had strong high-altitude dry-cold jets， high sinking convective effective potential energy， high temperature difference between 700 hPa and 400 hPa， and strong vertical wind shear all provided power conditions for the occurrence of severe convection， and the severe weather produced was mainly gale and hail. The severe precipitation type Ⅱ had a higher height of 0℃ layer and -20℃ layer， a higher uplift and condensation height， and the severe weather produced was dominated by short-term severe precipitation. The characteristics of the severe precipitation type Ⅰ cloud map were mainly manifested in the cold vortex cloud system with a high degree of organization developed in the afternoon.The initial center value of TBB was between -45℃ and -35℃， and the TBB dropped to -75℃ to -40℃ in the developing stage. In the meantime， the type Ⅱ cloud image of severe precipitation was mainly characterized by scattered massive convective cloud system. The initial center value of TBB was around -35℃， and TBB dropped to -70℃ to -50℃ in the developing stage. Ground convergence lines were two types of severe precipitation trigger systems.The pseudo-equivalent potential temperature value of the severe precipitation type Ⅱ was greater than that of the severe precipitation type Ⅰ， and was dominated by thermal forcing.The vertical velocity of the severe precipitation type Ⅰ was greater than that of the severe precipitation type Ⅱ， which was dominated by dynamic forcing. The global model assimilation forecasst system had more advantages than the mesoscale weather numerical forecast system. The two models of ECMWF and CMA-MESO could better characterize the 500 hPa low vortex shear. The ECMWF model could better simulate the effective convective potential energy， and the three models could predict precipitation magnitude obviously larger and the center of precipitation was more northward and westward， and the mesoscale weather numerical forecast system of China Meteorological Administration CMA-MESO had a slight advantage in precipitation forecasting.
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