Abstract:

 Based on diurnal minimum temperature data at 58 meteorological stations in Liaoning province from 1971 to 2011, the spatial and temporal characteristics of cold wave were analyzed. The results indicate that there are two centers of large values for annual mean frequency of cold wave. One center is located in the northeast Liaoning province, and another is in Jianping of western Liaoning province. The most widespread strong cold wave events occur in November. Regional cold wave mainly occurs in 1970s, which is in an insignificantly decreasing trend in recent 41 years. Cold wave often appears from middle ten days of October and early  ten days of May of next year, and it concentrates between early ten days of December and last ten days of February of next year, especially in January. There are a 20-year, 13-year, 8-year and 4-year cycles for regional cold wave. Weather patterns affecting regional cold wave include a small trough type, a horizontal trough type and an east moving type of low trough. The indexes forecasting regional cold wave are as follows: there is an increasing temperature process at least one day before regional cold wave happens; temperature of 500hPa cold centre is less than or equal to -40℃; the central value of high pressure system is above 1050 hPa, and pressure is more than 1030 hPa in the center of splitting smaller high pressure; jet stream is greater than or equal to 24 m.s-1 at 500 hPa and 12 m.s-1 at 850 hPa; isotherm density at 850 hPa around Liaoning province is above 5 strips /10 latitude, and angle between wind direction and isotherms is greater than 60°.

Key words: Cold wave, Morlet wavelet analysis, EOF decomposition, Physical forecast index