1998年长江流域夏季降水异常的一个物理机制

A POSSIBLE MECHANISM FOR THE ABNORMAL SUMMER RAINFALL OVER YANGTZE RIVER VALLEY IN 1998

关键词:  长江流域夏季降水  空间谱分析  Galerkin方法  热力强迫  副热带高压

Key words:  summer rainfall over Yangtze valley  spatial spectrum analysis  Galerkin method  thermal forcing  subtropical high

摘要:

根据1998年北半球夏季6、7、8月逐月500hPa高度场实测资料,利用具有双重筛选功能的二维空间谱分析方法,分别获得了能大致反映1998年北半球6、7、8月500hPa高度场分布特征的3组空间波集,每组包含15个空间波。分别利用这3组空间谱函数,从Galerkin途径出发,获得了1998年长江流域夏季降水异常的一个物理机制:在前期典型ElNiño型海温异常,以及5月后ElNiño型海温异常减弱,Laniña型海温异常分布建立的这些外部异常热力强迫作用下,导致大气环流出现不同的非线性内部动力过程,6月大气环流演变中波波相互作用和波流相互作用较弱,7、8月的大气环流演变中尽管波波相互作用明显,但波流相互作用仍然很弱。波流相互作用的持续偏弱,导致了1998年夏季西太平洋副热带高压位置持续偏南,夏季强降雨带持续稳定于长江流域。

Abstract:

Based on observed height data,three-set spatial waves mainly describing the characteristics on the North Hemispheric 500 hPa height field of June,July and August in 1998 were obtained with 2-dimension spatial spectrum analysis method.There were 15 waves in each set.Based on the three-set spatial spectrum functions,a possible mechanism for the abnormal summer rainfall over Yangtze River valley in 1998 was obtained with the Galerkin method.The mechanism indicated that forced by a special sea surface temperature anomaly distribution which belonged to the El Niño pattern before May,then to the decreasing El Niño pattern,and finally to the La Niña pattern,there were different inner nonlinear dynamic processes in the atmospheric circulation.In June,there were weaker wave-wave and wave-mean flow interactions.Although there was stronger wave-wave interaction,there was weaker wave-mean flow interaction.The persistently weaker wave-mean flow interaction made the western Pacific subtropical to be positioned more southward than normal during the summer of 1998,and then cause the heavy rainfall belt to maintain over the Yangtze River valley.