Spatial And Temporal Variation Of Precipitation And Analysis On The Factors Affecting Snowfall In Northeast China In Recent50Years

As the most important food producing area and a major industrial center,Northeast China palys an important part in the development of the national economy,so the analysis on the characteristics of precipitation events in this area is very necessary.Based on the daily precipitation and temperature data collected from90surface weather stations in Northeast China,the NCEP/NCAR re-analysis data and the NOAA SST data,the spatial and temporal variability of precipitation and the factors affecting snowfall in Northeast China in recent50years have been studied through correlation and composite analysis.The main results are as follows:(1)The annual precipitation,seasonal precipitation and different grades precipitation all decrease from southeast to northeast.The annual precipitation data from1961-2010has a slightly negative trend with the same trend during summer and autumn seasons.However,precipitation during spring and winter seasons has a significant positive trend.Different grades rainfalls show a decreasing trend,with different grads snowfalls showing an increasing trend.The increase of precipitation during spring and winter are mainly associated with the increase of precipitation intensity,and decrease of precipitation during summer and autumn are mainly associated with the decrease of precipitation frequency.The proportion of extreme heavy rainfall and snowfall increase after1987. The different grades precipitation days show the similar characteristic with precipitation,but a significant reduction in the50years of the region’s average annual precipitation days.(2)Four seasonal precipitations are quit different in Northeast China,which is located in the high latitudes. The difference between four seasons is gradually decreasing in recent50years. However, the uniformity of interannual precipitation in recent20years has a significant positive trend,likely to cause more droughts and floods. Precipitation days show similar characteristics, but the degree of uneven distribution of precipitation days is less than that of precipitation.The temporal variability of precipitation extreme climate index indicates that the droughts and floods in summer and autumn occur more frequently and severely, the degree to strengthen the trend of an increasing trend,and spring and winter moisture levels show an increasing trend.The spatial uniformity of annual precipitation is observed the shift mutation in the early1990s,which will raise the likelihood of drought and flood events occurring simultaneously in different regions,especially in summer and autumn.The spatial uniformity of precipitation days is observed in1990,the spatial difference of precipitation days after the mutation has been intensified.(3)The circulation characteristics of heavy snowfall events in winter when they appears in Northeast China can be divided into three styles:the low trough of Mongolia,Lake Baikal vortex and converge air style.West and south wind prevails over the bay of Bengal,which is formed by combining the southeast air current from north part of West Pacific subtropical high,and northward move. Sometimes,the warm and moist air from the Sea of Japan can transport to the Northeast China through the southeast flow of Lake Baikal vortex, converging the cold southward air and then respectively cause heavy snowfall events in the northern or eastern part of the Northeast China.In typical more snow years, the occurrences of low trough on500hPa height field over Northeast China are frequent.Large-scale upward motions combine with local-scale updrafts develop into strong slanted climbing airflows and the warm-moist air through the south flow is more intense. The circulation is beneficial for the generation of heavy snows in Northeast China.(4) The SST in Kuroshio Current region has an obvious positive relation with the snowfall in winter by air-sea interaction.When the SST in Kuroshio Current region is higher than the same period of normal years,the air temperature and geopotential height over Kuroshio Current region are also higher,while the East Asia trough and cold air are weaker, and the stronger SST in Kuroshio Current region can bring more water vapor to Northeast China,snowfall in winter is heavier than normal years.There is a significant negative correlation between Pacific SSTA(ENSO) and winter snowfall in Northeast China.However,it shows a certain lag.The ENSO signal affects the snowfall of Northeast China in winter of following year. When the SST in Nino3.4area of autumn and winter is lower than the same period of normal years, the circulation patterns in the following winter are conducive to snowfall of Northeast China.These circulation patterns may teleconnection achieve trough some sea air processes.