Climatology of warm season cold vortices in East Asia: 1979–2005

Abstract

The cold vortex is a major high impact weather system in the northeast China in warm season (May–September). An analysis was made in this study to document the distribution, size, origin, temporal variations of cold vortices, and their influence on warm season rainfall and severe weather during 1979–2005 in East Asia using the 500-hPa geopotential height of NCEP/DOE reanalysis data and a station precipitation dataset of China. All statistics except for precipitation and severe weather are made for two regions. Region I (20–70° N, 70–160° E) covers a broad area comprising the northern China-Siberian region to the northwestern Pacific coast and region II (35–60° N, 115–145° E), which is within region I, covers the northeast China and its surrounding areas only. Region II is a cold vortex rich region with an annual frequency of occurrence of 4 to 7. Cold vortex events occurred in May and June have higher frequency, longer duration, and larger size than those in other months in warm season in both regions I and II. Cold vortex events in region II have longer average duration and larger size than those in region I. The annual frequency of cold vortex events displays an interannual variability. In general, it is lower in both El Nino and La Nina years than in neutral years. Cold vortices contribute significantly to the annual warm season rainfall in northeastern China. The precipitation caused by cold vortices in northeastern China in warm season can be over 100 mm per year, accounting for 20–60% of the total warm season precipitation. Moreover, about 53% (22.4%) of hailstorm (rainstorm) days were caused by cold vortices in warm season in northeastern China during 1979 to 2005.