Identifying Regional Prolonged Low Temperature Events in China

This study examined regional prolonged low temperature (PLT) events in China from the observational station data for the period 1960--2008 using the new criteria. The new definition of a site PLT event is that the daily minimum temperature does not exceed the 10th percentile threshold of the local daily minimum temperature climatology for at least 5 days at a station. The regional PLT event is defined as at least five adjacent stations exhibiting site PLT simultaneously for >5 d. Under the new definition, 552 regional PLT events were identified, and three indices: duration, extent, and intensity, as well as a comprehensive index (CI) were used to quantify the event severity. In addition, geographical patterns and temporal variations of regional PLT events were investigated using three event categories: strong, moderate, and weak. Spatially, strong events were mainly located in the north of Xinjiang and along the Yangtze River to the south of the Yangtze River; moderate events occurred in Xinjiang and south of the Yangtze River; and weak events occurred south of the Yellow River. The variation for the annual frequency of regional PLT events in China in the last 49 years showed a significant decreasing trend with a rate of -1.99 times per decade, and the significant transition decade was the 1980s.