The Relationship Between Winter Persistent Abnormal Low Temperature In North China And Atmosphere Low-frequency Oscillation

Based on1959~2010NCEP/NCAR2.5°×2.5°daily reanalysis data and daily observed temperature data in China, persistent abnormal low temperature is defined in this paper. On the basis of the definition, characteristics of winter persistent abnormal low temperature in North China are studied. Then the main relationship between winter persistent abnormal low temperature in North China and atmosphere low-frequency oscillation activities are found. Lastly, a statistical forecasting mode for the winter low temperature in the North China has established, and then tested. More details are as follows.(1) The definition of persistent abnormal low temperature in winter of the North China: asked for the daily regional average temperature is less than or equal to-10.0°C, and for7days in5days or more for cold days (during this the only allow continuously happen one day piece). If two consecutive days the temperature is higher than-10.0℃is considered the end of the event.(2) During1959-2008, persistent abnormal low temperature happened26times in North China,and average every time duration of7.8days. Persistent abnormal low temperature has the obvious inter-decadal change characteristics. There is a trend that persistent low temperature in winter abnormal events happened less during60s to90s and happened more after21st century.(3) Study found that:the persistent abnormal low temperature process corresponding to the establishment of a ridge of high pressure in the Ural Mountains development and demise and the East Asia trough to maintain, deepen and weaken.(4) Meanwhile, analysis found that:winter temperature and wind field have10-20d and30-60d time scale periodic variation in North China, and30-60d time scale change cycle to give priority to. Both10--20d and30-60d time scale low frequency activities influence to persistent abnormal low temperature events greatly.(5) The relationship between winter persistent abnormal low temperature in North China and atmosphere low-frequency atmospheric circulation is closely related.10-20d low-frequency cyclones in the Northeast and North China, anticyclone in Central Siberian Plateau, and30-60days of time scales of the low-frequency anticyclone near the Western Siberian Plateau, cyclone near the sea of Japan are the important low-frequency system caused by persistent abnormal low temperature events.(6) Further study found that, low-frequency fluctuate usually transmission from the west to the east and spread from high latitudes to low latitudes to influence in north China. Factors of those areas have good correlations with the persistent abnormal low temperature15-20d later, and they can be used as the key signals in the extended-range forecast.(7) The low frequency in North China winter temperature forecast analysis results show that, whether it is in the10-20d or30-60d of low-frequency temperature forecast temperature to the wind filed in North China, low frequency by the Mongolian Plateau region the most closely related to the relationship between the real low-frequency temperature. The effect can be accurately reported several low frequency in the low-frequency cooling process. It can help to improve extended rage forecast skill of low temperature in winter temperatures in North China forecast.