ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 43 Issue 6 > 2017,43(6):665-674. DOI:10.7519/j.issn.1000-0526.2017.06.003 Prev Next
Impacts of LowLevel Temperature Advection on the Precipitation Type of Heavy RainSnow Process in North China
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Abstract:
By using the data of conventional surface and sounding observations as well as the associated NCEP FNL and GFS reanalysis data, the features of precipitation type of heavy rainsnow process in North China during 3-4 November 2012 are studied in this paper. It is found that in the periphery of lowlevel vortex, the rain and snow separatrix is identical with the 0℃ isotherm and streamline convergence zone between northerly and southerly wind at 925 hPa. However, near the center of lowlevel vortex, the rain and snow separatrix takes on a feature of anticlockwise revolving from the northwest quadrant to the center of the vortex. In the early stage of cyclone developing, snow is located at the northnortheast quadarant to northwest quadrant of the 850 hPa vortex while the precipitation type at southeast quadrant is rain. As the extratropical cyclone intensifies, temperature at the southwest quadrant of lowlevel vortex drops quickly due to the lowlevel cold advection. Therefore, the snow area gradually expands southward along the wind flow of the west side of lowlevel vortex and takes on a cyclonicshaped distribution ultimately. The temporal evolution of precipitation type depends on the temperature advection of the whole lowlevel troposphere (850-950 hPa). When there is warm temperature advection in either 900-850 hPa or 950-900 hPa level, the precipitation type may still be rain even if cold advection exists in other levels. The cold temperature advection of northwest wind at the west side of lowlevel vortex is very important to snow. When the lowlevel wind transforms to eastly wind, the lowlevel cold advection disappears, and finally, the precipitation type involves to rain.
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P458
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