欧亚地形对不同季节大气环流影响的数值模拟研究

NUMERICAL MODELING OF THE INFLUENCE OF EURASIAN OROGRAPHY ON THE ATMOSPHERIC CIRCULATION IN DIFFERENT SEASONS

  • 摘要: 利用气候模式F-GOALS的大气谱分量SAMIL,设计了有、无欧亚地形的对比试验。通过分析其高度差异、流场差异、降水差异和温度差异得到欧亚地形对不同季节大气环流影响的特征。结果表明,欧亚地形对大气环流和气候的影响随季节变化而变化,基本可分为冬季型(11月~次年4月),夏季型(6~9月)及转化型(5月,10月),在中高纬高低层呈相当正压结构。冬季型高度差异以35°N和100°E为界,在北面呈西高东低,南面呈西低东高。夏季型在西太平洋地区为北高南低,在大陆上空为上正下负。850 hPa流场差异场的冬季型在西太平洋北/南部为气旋式/反气旋式环流,在大陆上以“青藏高原(TP)偶极流型”为主要特征;夏季的副热带以环绕青藏高原的气旋性环流和西太平洋的反气旋环流为主要特征。地形强迫的冬半年“TP偶极型”加强了冬季西伯利亚冷空气活动,形成了江南的春雨和华南的早汛期降水。地形强迫的夏季流型形成了孟加拉湾-青藏高原中东部的强降水差异,使东亚降水向北伸展,并引起亚洲降水分布的调整。

     

    Abstract: Two experiments based on the spectral atmospheric component “SAMIL” of the Climate Model “F-GOALS” are presented: one is with full orography and the other is without Eurasian orography. The influences of Eurasian orography on the atmospheric circulation in difference seasons are obtained by analyzing the differences between the two experiments of geopotential height, streamline function, precipitation and temperature. Results show that such influences are seasonal dependant. The features can be classified into winter pattern (November-next year April), summer pattern (June-September) and transition pattern (May and October), with an equivalent barotropic vertical structure appearing over the high and middle latitudes. For the height difference, the winter pattern is characterized by the north-south and west-east seesaws along 35°N and 100°E, with high to the west and low to the east in north, and low to the west and high to the east in south. The summer pattern is featured as high in the north and low in the south over Western Pacific, and upper layer positive and lower layer negative over the continent. As to the streamline difference at 850 hPa, the winter type is characterized as cyclonic/anticyclonic circulations over the northern/southern Western Pacific, and a “TP dipole pattern” over the continent. Whereas the summer patter in the subtropics is featured by a cyclonic circulation surrounding the TP and an anticyclonic circulation over west Pacific. The orography forced “TP dipole pattern” enhances the winter cold break from Siberia and forms the spring persistant precipitation over the south of Yangtze River and the premonsoon precipitation over South China. The orography forced summer pattern forms the strong difference of precipitation from the Bay of Bengal to the central and eastern TP, enables the rain band to extend northward, and redistributes the precipitation over Asia.

     

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