Thursday, 8 August 2013
Holladay-Halsey (DoubleTree by Hilton Portland)
The first mixed rainfall-snowfall event occurred in the late autumn, from 3 to 5 November 2012, due to the impact of the strong cold air burst and the development of an extratropical cyclone was undergone over North China. This event was characterized by strong precipitation intensity, broad range, early first snowfall occurrence, multiple precipitating hydrometeors coexistence with dramatic temperature drop and gale. The structure and evolution characteristics of the extratropical cyclone was analyzed using general observation and NCEP reanalysis dataset. The results show that: The cyclone was generated from surface warm trough in the north of Yellow River Area and intensified when upper cold vortex developed and moved over the surface front. The baroclinicity forcing was the trigger mechanism in the lower troposphere. The upper vorticity advection promoted the rapid development of the cyclone. The cyclonic vorticity occurred at the middle troposphere, and extended to upper and lower troposphere. At the weakening stage, the cyclonic vorticity diminished first at the middle-upper troposphere and then diminished slowly at the lower level. The analysis of diabatic heating shows that: the horizontal and vertical advection of vapor affected the development the cyclone. At the lower level, the advection of warm and wet air caused the vapor and temperature increasing, and intensified the instability that was in favor of rain and snow occurred. As warm and wet air was cutoff in the matured stage, the cyclone decayed gradually. Cold-air advection at the lower level was the dominant term at weakening stage of cyclone.
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