ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Analysis on Weather Causes of an Elevated Thunderstorm in Henan in Early Spring 2012
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Abstract:
The conventional observation, new generation weather radar, lightning locating monitoring and NCEP 1°×1° analysis data are used to analyze the synoptic causes of the elevated thunderstorm in early spring of 2012 that was accompanied by a variety of weather phenomena and a flow configuration model of the elevated thunderstorm is established. The results showed that: (1) the elevated thunderstorm occurs in the circulation situation of warm trough moving eastward and developing in middle latitudes. The near neutral conditions instability stratification above the top of the boundary layer (biased in favor of weak conditional instability), which is in the forcing effect of positive vorticity advection in front of trough and warm and wet advection at low levels, makes a larger range of strong upward motion above 700 hPa so that easterly winds in the rear of surface cold high has a role of cooling cushion on the production of the elevated convection. (2) There is a strong inverse temperature layer in the lower atmosphere where elevated thunderstorm exists. The warm and wet southwest low level jet in front of temperature ridge at 700 hPa provides ample moisture and energy for production of an elevated thunderstorm, causing weak conditions with unstable stratification and higher dew point above the top of low level temperature inversion. The combination of the two leads to the weak and most unstable convective available potential energy MUCAPE, whose value is between 10 and 50 J·kg-1. The elevated convection is caused by uplift of warm and wet block near and above the top of the inversion layer, corresponding to 1.0-3.0 m·s-1 maximum updrafts within thunderstorms. (3) The elevated thunderstorm occurs in strong baroclinic environment, where there is a strong dynamic instability, in the lower level 0-6 km and 0-3 km vertical wind shear values are (3.0-3.7)×10-3 s-1 and (5.0-5.3)×10-3 s-1 respectiveny. (4) The -10℃ and -20℃ layers in this process are respectively in the height of 5 km and 6.5 km, and the height of weak convective cloud top is more in the 6-8 km or above, exceeding the height of the freezing level and easily leading to the occurence of lightning. (5) From the flow configuration model, warm trough at high altitude, the strongly developed temperature ridge at middle and high layer, the warm and wet southwest low level jet at 700 hPa and cold boundary center, cold temperature trough, surface cold high pressure etc., make up a noteworthy affecting system. When these weather systems are favorable for configuration, the low level temperature inversion, the establishment of weak condition unstable stratification at middle layer and the likelihood of elevated thunderstorms should be concerned.
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