Influence Factors Of Winter Temperature Variability And Its Anomaly In Northeast China

Using a dataset of daily maximum and minimum temperature of1957-2010from90stations in Northeast China,74circulation indices provided by the National Climate Center of China, NCAR/NCEP reanalysis data, I analyze the variation of the Northeast China winter mean temperature and extreme temperature events and the effects of urbanization on the long-term trends of the extreme temperature indices, with an objective to reveal the temporal and spatial variation of winter temperatures in the region, and the in-phase and out-of-phase relationships between the temperature series and the circulation indices. I also develop a statistical prediction model for winter temperature anomalies by applying a few of key factors. The main conclusions of the paper are as follows:(1) Northeast China winter undergoes a significant warming, with an average rate of0.45℃/10a, and a more rapid rate since the mid-1980s. Winter mean temperature fluctuated without obvious linear trend before1980s, but it showed a significant rising trend since the mid-early1980s. Cold winters concentrated in the1960s and1970s, and the warm winters occurred more frequently in the1990s, with the intensity of warm winters significantly increased and the intensity of cold winters significantly reduced.(2) Using the method of REOF decomposition, The Northeast China region is divided into two sub-regions, with the centers located in southwestern Liaoning and northern Heilongjiang respectively. In the two sub-regions, cold and warm winters see a quite different occurrence. There were only3common cold winters and7common warm winters between the two sub-regions during the period1957-2010,(3) I analyze the characteristics of change of the6extreme temperature indices, and I find that warm nights and warm days all significantly increase, cold nights, cold days and continuous cold days all significantly decrease, and diurnal temperature range (DTR) gradually decrease in Northeast China. The decrease of cold nights is the largest, with the rates of-3.335days/10a in the North, and-1.85days/10a in the South, and the regional average rate of-2.431days/10a for the whole region. The decreasing trend of the regional average cold nights is significant at the0.001confidence level.Urbanization effects on the extreme temperatures indices series are investigated by comparing the regional average trends and the rural stations, and it is found that the effects are mostly significant, especially for the cold indices. (4) Northeast China winter temperature is significantly related to a few of circulation factors over the same period. The correlations with the Eurasian zonal circulation index are relatively good in the south. The winter mean temperature is also related to the previous abnormal circulation factors, including the previous January to November subtropical high and polar vortex area index. It is found that significant correlations exist for5Subtropical High Area indices and2Polar Vortex Area indices, with their relationship with winter temperature being better in the north of the region.(5) Cconsidering the confidence levels of the single-factor correlations and partial correlations and using the method of the backward selection, the3best predictors are obtained. They are the August eastern Pacific Subtropical High index (175W-115W) in August, the Asian Polar Vortex Area index (Area One,60E-150E) in October, and the Northern Hemisphere Polar Vortex Area index (Area Five,0-360) in August. A "best" regression equation is established, and it is verified, showing a good predicting skill for Northeast China winter temperature anomalies. It is also shown that the key predictors, the eastern Pacific Subtropical High and the Polar Vortex, are not independently affect the Northeast China temperature. Rather, they are interrelated and synergistically affect the variability of winter temperature of the study region. The underlying mechanism needs to be further investigated.