A Case Study on Dynamic and Thermal Structures and Mechanism of β-Mesoscale Snowstorm
The composite Doppler radar data, automatic meteorological observing station data and conventional observation data were used to analyze the dynamic and thermal structures and evolution of the β-mesoscale weather system in west of Bohai Bay, which caused snowstorm on 20～21 December 2008. In addition, the methods of 4DVAR single Doppler radar retrieval and results of mesoscal numerical simulation were used. The results are as followings: Firstly, the occluded cold frontal system under background of cold air returning from east-north area was the weather system caused this snowstorm, which was different from extratropical cyclone occluded frontal in its area, live circle, structure. There are three snowstorm 3 phases including eastern weaker cold front, occluded front and western stronger cold front. Echo top in whole snowfall was under 3～4 km and reflectivity was below 35 dBz. Snowfall pooled in eddy phase. Secondly, the cyclonic circulation existed on the ground and low level of troposphere, which was help for maintaining of snowing echoes and upward flow. Thirdly, by section-cross of potential pseudo-equivalent temperature and U vector, warm and wet air mass exited and was lifted between east and west cold front. The west cold front was more precipitous than east and two cold fronts formed cold-style occluded frontal system. The transfer of water-vapour from Bohai bay had been existing under 900 hPa levels in live-circle of snowstorm. In return-flow snow phase and eddy phase, another water-vapour belt over 750 hPa levels played important pole on snowstorm. Lastly, with occluded cold frontal system disappearing, strong wind turned up nearby 900 hPa levels and descended at first.
β-mesoscale snowstormOccluded cold frontal systemDynamic and thermal structures
NETL
NSTL
万方数据
维普
