青藏高原地区地表热力异常与夏季东亚环流和江淮降水的关系

Relationship between the Tibetan Plateau surface thermal anomalies and the summer circulation over East Asia and rainfall in the Yangtze and Huaihe River areas.

  • 摘要: 利用NCEP/NCAR再分析月平均资料和中国160个站降水资料,以及由国家气候中心提供的西太平洋副高脊线指数资料,分析了青藏高原地区多年平均地表温度季节转换(3—6月)的空间特征,结合均方差分析,确定高原主体(28°—38°N,75°—100°E)、高原东部以北区域(38°—48°N,90°—105°E)和高原西部以北区域(38°—45°N,75°—90°E)为关键区,分析了1951—2002年5月不同关键区地表温度的空间变化与夏季东亚季风环流和江淮降水的关系。结果发现,这3个区域地表温度异常均对夏季东亚850 hPa环流有显著的影响。5月高原和其以北区域地表温度异常存在较大尺度的热力对比,由此,将高原主体和其以北区域的温度异常之差定义为一个指数,反映这种热力差异。相关分析发现:当5月这一热力差异增大(减小)时,夏季东亚中高纬的中高层(500—200 hPa平均)西风加强(减弱),且西风中心轴线位置南移(北抬);造成西太平洋副热带高压脊线位置偏南(偏北),致使夏季东亚季风环流偏弱(偏强),江淮流域降水增多(减少)。

     

    Abstract: The relationship between the surface thermal anomalies (STA) over the Tibetan Plateau (TP) and the summer rainfall over the Yangtze and Huaihe River (Jianghuai) areas, has been studied by many researchers. However, most previous studies focused on the temporal variation of STA,and less attention was paid to the correlation between the spatial variation of STA over TP and the Jianghuai summer rainfall.The present paper aims to explore this correlation.By use of the NCEP/NCAR Reanalysis monthly mean data, the precipitation data at 160 stations in China, and the index data of the Western Pacific subtropical high ridgeline (WPSHR) provided by the National Climate Center of China, the spatial features of the mean surface temperature over the TP and its circumjacent areas during the seasonal transition (March to June) are analyzed.By mean square deviation analyses,three areas are selected:1) the TP main area(28°-38°N,75°-100°E), 2) the area to the northeast of the TP(38°-48°N,90°-105°E), and 3) the area to the northwest of the TP(38°-45°N,75°-90°E). The relationship between the spatial variation of STA over the three areas in May and the summer circulation over East Asia and rainfall over the Jianghuai areas from 1951—2002 is further investigated. The results show that the STA over the three areas are evidently related to the 850 hPa summer circulation.A large-scale thermal contrast exists between the TP and the area to its north in May, and an index is defined to reflect the intensity of the large-scale thermal contrast.When the thermal contrast enhances (weakens), the south-north gradient of the mean air temperature in the mid-upper troposphere (500—200 hPa) enhances (weakens), too.This results in the speeding up (slowing down) of the westerly winds in the mid-upper troposphere and their shifting to further south (north).The WPSHR also shifts to further south (north) than normal. So the East Asian summer monsoon weakens (strengthens), and the rainfall increases (decreases) over Jianghuai areas.

     

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