Analysis Of The Characteristics And Causes Of Variation Of Winter Temperature In Northeast China

Winter temperature in the northeast China has an upward trend from 1951 to 2010 in genernal, the linear trend is 0.38℃/10a, and it has apparently interdecadal periodic variation. The result of MK testing shows that a temperature mutation was occurred between 1986 and 1987. The results of trend-EOF show that a consistent trend appeared presents the whole northeast China. The trend-PC1 demonstrated that a distinctly interdecadal periodic variation and a long-term uptrend emerged. It has significantly related to sea surface temperature (SST) in the Indian Ocean, because the global warming signal exists in both of them. When the Indian Ocean SST is positive anomaly, the distribution of every circulation field are conducive to the rise of temperature in northeast region. The upward trend of winter air temperature in northeast China is essentially the local response to global warming.After the removal of global warming Signal, two modals exist in the EOF results, the first EOF mode depicts a consistently region-wide spatial distribution, the second EOF mode describes a temperature inverted distribution between northern and southern parts of the region. These two modes can explain the variance over 80%.The features of winter air temperature in northeast China is mainly the superposition of the two patterns, and the second mode is extremely important. The PC1 has significantly related to arctic oscillation (AO) index, when AO index at high phase, the distribution of every circulation field are conducive to the rise of temperature in northeast region. White, the PC2 has a close connection with SST over the eastern equatorial Pacific, when El Nino happens, the distribution of every circulation field are conducive to the rise of temperature in south part of northeast region, and the decline of temperature in north part of northeast region.Through the contrast testing between before (from 1951 to 1984) and after (from 1987 to 2009), the major patterns of divided periods EOF analyses are consistent with the pattern of the full time EOF analysis, the leading modes are consistently region-wide spatial distribution, the second modes are inverted distribution between northern and southern parts of the region. Before the mutation, the PC1 significantly relates to the Indian Ocean SST in autumn and winter, and the PC2 mainly significantly relates to the Kuroshio SST in winter. After the mutation, the PC1 has no significantly relationship with the Indian Ocean SST, while the PC2 primarily significantly relates to the eastern equatorial Pacific and the western north Pacific SST. In addition to the effect of the ocean, the AO also has important effect on the mutation. The AO index mutated in the mid-1980s, it may cause the temperature mutation in the northeast winter.The difference between summer and winter temperature of northeast China between 1951 and 2009 is on the decline as a whole, and it has a mutation between 1986 and 1987. By using EOF analysis on the difference of between summer and winter temperature, it’s found that the first pattern is the leading pattern, depicts a consistently region-wide spatial distribution, and the PCI presents a obvious downward trend and decadal variation characteristic, indicating that the difference over northeast China has a decline trend with different degree only, which means that the monsoon intensity difference between summer and winter is decline. Meanwhile, the monsoon intensity difference between summer and winter index presents a downward trend, which proofs the intensity between the summer and winter monsoon has downward trend indeed. It also displays the potential for using the difference between summer and winter temperature in northeast China to measure the relative strength of summer and winter monsoon severity changes.