【摘要】 本文根据季节转换前后副高脊面附近经向温度梯度变号的本质,利用相关分析和合成分析等方法研究了季节转换年际变化与外部影响因子的联系.结果表明,冬春季青藏高原热状况和ENSO(El Ni o/Southern Oscillation,厄尔尼诺/南方涛动)是决定亚洲季风区季节转换年际变化的主要因素.当冬、春季海温呈现El Ni o异常时,Walker环流减弱,于是西太平洋暖池区对流活动受到抑制,而赤道东太平洋对流活动加强则强迫赤道印度洋地区产生绝热下沉运动,使得印度洋地区大气偏暖,结果增大了南北向温度梯度,季节转换往往偏晚.反之,季节转换偏早.初春高原上空对流层中高层的气温异常对于判断季节转换迟早有很好的指示意义.更多还原

【Abstract】 Based on the reversal of the middle and upper tropospheric meridional temperature gradient near the ridge surface of the Asian subtropical anticyclone during seasonal transition,correlation and composite analyses are employed to study the interannual variability of the Asian monsoon seasonal transition and its relation to external forcing.Results show that ENSO and thermal state over the Qinghai-Xizang Plateau in the preceding winter and spring are two dominant factors responsible for the interannual variability of the Asian monsoon seasonal transition.When the El Nio event occurs during winter and spring,Walker circulation is weakened so that deep convection is suppressed over the western Pacific warm pool,while enhanced convection over the eastern equatorial Pacific induces adiabatic descending motion over the equatorial Indian Ocean.Consequently,air temperature over the equatorial Indian Ocean gets warmer,meridional temperature gradient over Asian sector becomes larger,and the seasonal transition is later than normal.The middle and upper tropospheric temperature anomalies over the Qinghai-Xizang Plateau in early spring are good indicative of predicting abnormal seasonal transition.更多还原