摘要
利用NCEP/NCAR再分析资料和观测的台站降水资料研究了1991年梅雨期间江淮洪涝区降水的季节内振荡及其环流特征,着重考察了不同层次副热带高压的低频变化与降水的关系.小波分析表明1991年江淮梅雨期间降水低频振荡的主周期是15～35 d.在低空,15～35 d振荡以异常反气旋(气旋)的形式在中国东南沿海地区交替出现,调控着西太平洋副热带高压进入(退出)南海.低空的这种低频环流型与高空的偶极型涡旋对相耦合,偶极型涡旋对使得南亚高压东伸(西退),形成有利(不利)江淮流域降水的环流形势.江淮流域降水的低频振荡与500hPa北太平洋副热带高压的低频变化及其传播密切相关.当北太平洋西部的位势高度偏高、中部位势高度偏低时,江淮流域降水偏多;反之偏少.这种低频振荡可能起源于北太平洋中部夏威夷群岛附近,然后沿着副热带高压脊线附近向西传播到中国东南沿海.
The NCEP/NCAR reanalysis data and observed daily rainfall from gauge stations were used to investigate the intraseasonal variability on heavy rainfall and its related atmospheric circulation anomalies during the 1991 meiyu period. It is emphasized that the intraseasonal variartions of the subtropical high at different levels have close relationships with the 1991 extreme flood over the Yangtze-Huaihe river basin. Wavelet analyses show that the intraseasonal variation in the 1991 meiyu rainfall over the Yangtze-Huaihe river basin was mainly controlled by the 15 - 35 days （25-day mode） oscillation. An examination of circulation features suggests that the 15 - 35day oscillation exhibited as an anomalous anticyclone （cyclone） in lower troposphere existing alternatively over the coast of southeastern China, which modulates the western North Pacific subtropical anticyclone shifting southwestward into （northeastward out of） South China Sea. Such a lower tropospheric flow pattern was coupled with a dipole anomaly in the upper troposphere, and the latter regulated the South Asian anticyclone extending northward and eastward （contracting southward and westward）, forming a favorable （an unfavorable） circulation environment for heavy rainfall over the Yangtze-Huaihe river basin. The intraseasonal oscillation in the Meiyu rainfall was also closely related with the 15 - 35-day mode of the 500 hPa North Pacific subtropical high and its westward propagation. During the active phase with excessive rainfall over the Yangtze-Huaihe river basin, the 500 hPa geopotential height exhibited positive anomaly over the western North Pacific and negative anomaly over the central North Pacific. Opposite circulation anomaly was for break period. The 15 - 35-day oscillation of the 500 hPa North Pacific subtropical high might originate from around Hawaiian Islands, and then propagated westward along the vicinity of subtropical high ridgeline into the coast of southeastern China.
出处
《气象学报》
CAS
CSCD
北大核心
2005年第5期762-770,共9页
Acta Meteorologica Sinica
基金
国家自然科学基金项目(40135020
40221503
40375022
40325015和40475027)
