季节转换期间副热带高压带形态变异及其机制的研究 Ⅲ:热力学诊断

STUDY ON MODEL VARIATION OF SUBTROPICAL HIGH AND ITS MECHANISM DURING SEASONAL TRANSITION PART Ⅲ: THERMODYNAMIC DIAGNOSES

利用NCEP/NCAR再分析资料从能量收支的角度探讨了气候平均状态下副热带高压形态变异和季节转换的物理机制。在考察温度场和加热场季节变化的基础上 ,发现中国江南地区春季降水所形成的非绝热加热源非常显著 ,该热源对后期亚洲季节转换有影响。副热带高压脊面附近经向温度梯度反转取决于温度脊所在纬度位置的变化。温度脊北移是由脊轴北侧的增温率大于脊轴附近的增温率而造成的。热力学方程诊断结果表明 ,亚洲各季风区 (孟加拉湾、南海和南亚 )季节转换的热力机制不同。导致孟加拉湾温度脊显著北跳的主要因素在季风爆发初期是经向暖平流 ,爆发以后是下沉运动 ;引起南海地区经向温度梯度反转的因素有经向暖平流、纬向暖平流和江南地区的非绝热加热 ,特别是经向暖平流的贡献更大 ;造成南亚季风区经向温度梯度逆转的原因是下沉增温。

The mechanisms for the variation in the configuration of subtropical anticyclone during seasonal transition are explored from energy budget using the NCEP/NCAR reanalysis data. Based on the seasonal variations of temperature and heating fields, it is found that the significant diabatic heating associated with spring precipitation over southern China has impacts on subsequent Asian seasonal transition. The reversal of meridional temperature gradient in the vicinity of the WEB (boundary surface between westerly to north and easterly to south)in the middle and upper troposphere also depends on the latitude where temperature ridge locates. The northward shift of the temperature ridge results from the fact that the local temperature increase to the north of the WEB is more than that in its vicinity. The diagnostic results through thermodynamic equation show that thermal mechanism in seasonal transition is different from area to area over the Asian monsoon region. The abrupt northward shift of temperature ridge over eastern Bay of Bengal is mainly due to meridional warm advection at its initial transition, but due to descent after the transition. The abrupt northward jump of temperature ridge over South China Sea is caused by warm meridional advection, warm zonal advection and diabatic heating associated with precipitation over southern China, among them the warm meridional advection is more significant. The reversal of meridional temperature gradient over South Asia is mainly a result of subsidence.