青藏高原东北部春季冷空气次数变化及其诊断分析

Variation of Cold Air Frequency in Spring and Its Diagnostic Analysis in the Northeast of Tibet Plateau

利用青藏高原东北部68个台站1961—2015年春季(3—5月)地面气温观测资料,统计整理了春季各月冷空气过程的强度指数I(含次数)序列,应用气候诊断方法分析了区域冷气次数的变化特征及其成因。结果表明:在变化的趋势上,1961—2015年青藏高原东北部春季冷空气过程次数的气候变化倾向率为-0.290次/10 a,减少的趋势不显著;柴达木盆地区、南部区的减少趋势与青藏高原东北部一致,东部区的增多趋势与青藏高原东北部相反。在周期变化上,青藏高原东北部和3个分区,3、5、7、8年准周期出现的频次相对较高,25年等其他准周期出现的频次相对较低。1991—2015年(1961—1980年),500 hPa层贝加尔湖地区春季高度值持续偏高(偏低)是导致青藏高原东北部春季冷空气过程次数持续偏少(偏多)的主要成因之一。春季乌拉尔山高压脊、巴尔喀什湖至贝加尔湖低压槽、里海至咸海高压脊持续偏强,容易引导北方南下的冷空气从偏西北路径和偏北路径影响中国,青藏高原东北部位于冷空气南下的通道上,冷空气过程次数容易偏多;相反,冷空气过程容易次数偏少。

Using 68 stations’ground temperature observation data in the northeast of Tibet Plateau from 1961 to 2015,we studied the strength index I(including frequency)sequence of cold air process in spring months,analyzed the characteristics of regional cooling air frequency and its origins by using climate diagnostic method.The results showed that:the tendency rate of climate change of cold air process frequency in spring from 1961 to 2015 was decreasing and the decrease rate was-0.290 per 10 years,this process was not significant.The decreasing trend in Qaidam and the southern part was in accordance with that in the northeast of Tibet Plateau,but the increasing trend in the eastern part was opposite to it.In terms of periodic variation,the quasi-periodic around 3,5,7,8 years’frequency was relatively high but the 25 years and other quasiperiodic frequency were relatively low.The continuing spring height value on the high(low)side at 500 hPa in Baikal Lake region was one of the main factors causing less(more)cold air process in the northeast of Tibet Plateau from 1991 to 2015(from 1961 to 1980).In spring,the continuing strong high-pressure ridge of Uralf Mountain,low-pressure trough from Balkhash Lake to Baikal Lake and high-pressure ridge from Caspian Lake to Aral Sea could easily lead the northern cold air to influence China by northwestern and northern paths.The northeast of Tibet Plateau was on the passage of cold air southward,so the cold air process tended to be more frequent;on the contrary,the cold air process frequency tended to be less.