贵州省两次超强凝冻过程的天气成因对比分析

利用贵州省84个台站常规观测资料、NCEP/NCAR逐日再分析资料以及NOAA逐月海表温度资料,对2008年和2011年贵州省出现的两次超强凝冻过程的降温幅度、影响站次、海温背景、环流场、温度场等进行了对比分析。结果表明:中等强度的东部型拉尼娜事件是两次过程的有利气候背景,东亚地区500 hPa西高东低的距平分布、850 hPa切变线的稳定维持、700 hPa西南急流、温度场上逆温区以及温度垂直剖面图的800~600 hPa之间的融化层均是两次过程的有利的形势条件。而2008年过程对应850 hPa切变线位置更为靠北,且其西南急流范围/强度、逆温区面积/强度、冷平流强度、融化层厚度/持续时间/中心温度均较2011年的明显偏强,这是导致2008年冬季凝冻过程影响更为明显的原因。

Comparative Analysis of Causes for Two Extreme Freezing Rains in Guizhou Province

Based on data from 84 observation stations in Guizhou Province and NCEP/NCAR reanalysis, a comprehensive comparative analysis of two extreme freezing rains that occurred in 2008 and 2011 are made through temperature declining amplitudes, affected stations, sea surface temperature patterns and circulation patterns. The results show that: the Eastern type of La Nina with medium intensity provided a favourable condition for the development of freezing rain in two cases. Besides, there were some similar circulation patterns in two cases, such as positive geopotential height anomalies over West Asia and negative geopotential height over East Asia at 500 hPa, stable maintenance of shear line at 850 hPa, southwest jet at 700 hPa, temperature inversion layer and melting layer between 800 to 600 hPa, which were conducive to the formation of freezing rain. However, compared to the case in 2011, it could be observed that the shear line located further north, southwest jet at 850 hPa and temperature inversion layer had stronger intensity and larger area, colder temperature advection and thicker melting layer with longer duration and higher centre temperature from the case in 2008, which could possibly result in more significant influence from freezing rains in 2008.