Spatiotemporal distribution characteristics and attribution of extreme regional low temperature event

Based on an objective identification technique for regional low temperature event（OITRLTE）, the daily minimum temperature in China has been detected from 1960 to 2013. During this period, there were 60 regional extreme low temperature events（ERLTEs）, which are included in the 690 regional low temperature events（RLTEs）. The 60 ERLTEs are analyzed in this paper. The results show that in the last 50 years, the intensity of the ERLTEs has become weak; the number of lasted days has decreased; and, the affected area has become small. However, that situation has changed in this century.In terms of spatial distribution, the high intensity regions are mainly in Northern China while the high frequency regions concentrate in Central and Eastern China. According to the affected area of each event, the 60 ERLTEs are classified into six types. The atmospheric circulation background fields which correspond to these types are also analyzed. The results show that, influenced by stronger blocking highs of Ural and Lake Baikal, as well as stronger southward polar vortex and East Asia major trough at 500-h Pa geopotential height, cold air from high latitudes is guided to move southward and abnormal northerly winds at 850 h Pa makes the cold air blow into China along diverse paths, thereby forming different types of regional extreme low temperatures in winter.

MULTIMODEL CONSENSUS FORECASTING OF LOW TEMPERATURE AND ICY WEATHER OVER CENTRAL AND SOUTHERN CHINA IN EARLY 2008

Based on the daily mean temperature and 24-h accumulated total precipitation over central and southern China, the features and the possible causes of the extreme weather events with low temperature and icing conditions,which occurred in the southern part of China during early 2008, are investigated in this study. In addition, multimodel consensus forecasting experiments are conducted by using the ensemble forecasts of ECMWF, JMA, NCEP and CMA taken from the TIGGE archives. Results show that more than a third of the stations in the southern part of China were covered by the extremely abundant precipitation with a 50-a return period, and extremely low temperature with a 50-a return period occurred in the Guizhou and western Hunan province as well. For the 24- to 216-h surface temperature forecasts, the bias-removed multimodel ensemble mean with running training period(R-BREM) has the highest forecast skill of all individual models and multimodel consensus techniques. Taking the RMSEs of the ECMWF 96-h forecasts as the criterion, the forecast time of the surface temperature may be prolonged to 192 h over the southeastern coast of China by using the R-BREM technique. For the sprinkle forecasts over central and southern China, the R-BREM technique has the best performance in terms of threat scores(TS) for the 24- to 192-h forecasts except for the 72-h forecasts among all individual models and multimodel consensus techniques. For the moderate rain, the forecast skill of the R-BREM technique is superior to those of individual models and multimodel ensemble mean.

Distribution Characteristics of Winter Continuous Extreme Low Temperature in China

[Objective] The research aimed to study the distribution characteristics of winter continuous extreme low temperature in China. [Method] Based on the daily minimum temperature data in winter during 1961-2008 in 195 observatories, the continuous extreme low temperature event (cold night) which happened in winter in China and the distribution characteristics of accumulated temperature anomaly in 48 years were analyzed by using the actual probability distribution threshold method. [Result] Besides in Northeast China, Northwest China and Qinghai-Tibet Plateau where the geographical position was northerly, and the altitude was high, the long-time (above 5 d) extreme low temperature event was also easy to happen in the south of Yangtze River, especially in Guizhou, Guangxi, Hunan and so on. The continuous extreme low temperature event in the middle and lower reaches of Yellow River was the least. Started from the metaphase of the 1980s, the frequency trend of continuous extreme low temperature event decreased. But in 1992, 2000 and 2007, the low temperature event which continued above 7 d was more than the average. The accumulated cold in January in 48 years was the strongest. The second one was in February, and the smallest was in December. The accumulated cold in Northeast China and the north of Inner Mongolia was the biggest in December and January. The accumulated cold in the north of Xinjiang was the biggest in February. In the whole winter, the accumulated cold in Qinghai-Tibet Plateau was the smallest. The chilling injury was easier to happen in Guizhou, Guangxi and Hunan than other south areas in December and February. The occurrence probability of chilling injury in most areas of Szechwan Basin, Yunnan and Qinling Mountains in central China was smaller than that in other areas. [Conclusion] The research provided the reference basis for analyzing the influence of chilling injury on the agriculture in China.

Study on Temporal-spatial Change Characteristics of the Extremely Low Temperature Climate Event in Winter of China

[ Objective] The research aimed to study temporal-spatial change characteristics of the extremely low temperature climate event in winter of China. [MethodI By using actual probability distribution threshold value method, EOF analysis method and the daily minimum temperature data in winter of 1961 -2008 at 195 observatories of China, temporal-spatial change characteristics of the extremely low temperature climate event in win- ter of China in 48 years were analyzed. [ Result] Threshold value calculated by actual probability distribution was higher than that by traditional method, and increase magnitude in east was bigger than that in west, which could describe climatic change situation in China in 48 years better than traditional method. Cold night number in winter of China did not decrease as latitude declined, and it was more in south and north and was less in Yellow River basin and northwest China. Cold night number was the most in northeast Inner Mongolia. Interannual change of the cold night number presented decline tendency. From the 1960s to the eady 1970s, cold night number consistently increased, and change in middle and late periods of the 1960s was severe. From the early 1970s to the middle 1980s, fluctuation of the cold night number was bigger, and increase of the cold night number was the most in 1976. Cold night number from 1986 to the 21= century continuously declined. Change of the cold night number was the most obvious in east region, Guizhou and north Guangxi. Cold night number in northeast China and north Inner Mongolia presented inverting change relationship with that in Yunnan - Kweichow Plateau and Hexi Corridor. [ Conclusion] The research provided reference for eady warning of the extremely low temoerature event in China.