全球变暖背景下青藏高原夏季气温在对流层上下反相变化及其与降水和环流的关系

本文利用NCEP/NCAR月平均再分析资料及中国596个测站月降水资料,采用线性倾向估计、经验正交函数分解(EOF)、相关分析、合成分析等方法,对青藏高原夏季对流层气温垂直变化及其与降水和环流的关系进行了分析。气温垂直变化特征分析表明:自1971年以来,青藏高原夏季对流层低层至对流层中上部气温呈现显著增暖趋势,对流层上部气温呈现显著变冷趋势,高原对流层低层至中上部气温及对流层上部气温在年际、年代际尺度上均呈较显著负相关,且均存在2~4 a及8~13 a的周期;夏季青藏高原地区沿27.5°N~40°N平均的气温距平垂直分布的EOF分解第一模态特征向量在对流层表现为"下降温上增温"的反相变化,其时间系数呈显著负趋势,且存在1978年及1994年的突变点。高原夏季气温在对流层的上下反相变化与我国夏季降水的关系在年际、年代际尺度上均显示:当高原对流层低层至对流层中上部升温而对流层上部降温时,我国夏季降水表现为南方型,其中以江南至华南地区降水显著偏多而我国东北地区降水显著偏少为主要分布特征;另外,长江流域的局部地区及我国西北的部分地区降水也明显偏少,而华北东部的局部地区、青藏高原中部及东部地区以及新疆西北部地区降水明显偏多;降水异常分布在年代际尺度上比年际尺度更显著。环流分析显示:当高原对流层低层至对流层中上部升温而对流层上部降温时东亚中高纬度地区为异常高压控制,中低纬度地区受异常低压影响。环流场与降水分布有较好的配置关系。

Reversed Phase Change of the Temperature in the Upper and Lower Troposphere over the Tibetan Plateau in Summer and Its Relationships to Precipitation and Atmospheric Circulation under the Background of Global Warming

Using linear-trend estimates, empirical orthogonal function(EOF) analysis, correlation and composite analysis, the vertical variation of temperature in the troposphere over the Tibetan Plateau in summer and its relationships to precipitation and atmospheric circulation are examined, based on monthly NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data and precipitation data from 596 stations in China. The characteristics of the vertical variation of temperature reveal that the temperature in the lower to middle-upper troposphere over the Tibetan Plateau in summer shows a significant warming trend since 1971, while the temperature in the high troposphere shows a significant cooling trend. In terms of interannual and interdecadal the temperature in the lower to middle-upper troposphere and the high troposphere are negatively correlated, and all have the cycles of 2-4 and 8-13 years. The first EOF mode of the vertical temperature anomaly averaged along 27.5°N-40°N over the Tibetan Plateau in summer shows a reversed phase change of an increase in the lower to middle-upper troposphere and a decrease in the high troposphere. Its time coefficient shows a long-term positive trend, and there is abrupt change in 1978 and 1994. The relationships between the interannual and interdecadal reversed phase change of temperature, i.e., an increase in the lower to middle-upper troposphere and a decrease in the high troposphere over the Tibetan Plateau in summer, and precipitation in China in summer, are explored. When the temperature over the Tibetan Plateau increases in the lower to middle-upper troposphere and decreases in the high troposphere, summer rainfall in China shows a southern type pattern, in which more precipitation in the regions south of the Yangtze River and southern China and less precipitation in the northeast of China are the main distributional characteristics. In addition, less precipitation occurs in the local areas of the Yangtze River Basin and some areas of northwestern China, while more precipitation occurs in the local areas of the eastern part of North China, the central and eastern regions of the Tibetan Plateau, and northwest Xinjiang. The abnormal interdecadal distribution of precipitation is more significant than the interannual distribution. Analysis of the circulation reveals that when the temperature over the Tibetan Plateau increases in the lower to middle-upper troposphere and decreases in the high troposphere, there is abnormally high pressure in middle and high latitude regions of East Asia, while in middle and low latitude areas there is abnormally low pressure. Meanwhile, a relatively significant relationship is found between circulation and precipitation.