东亚地区低频振荡的经向传播及中纬度的低频波动

MERIDIONAL PROPAGATION OF EAST ASIAN LOW-FREQUENCY MODE AND MIDLATITUDE LOW-FREQUENCY WAVES

本文利用1981年6—9月欧洲中期天气预报中心(ECMWF)网格点资料分析了东亚地区低频(准40天)振荡的传播特性与结构特征,发现在120°E经度上的高空(低空)副热带地区有一个低频纬向风(经向风)经向传播的分离带(汇合带),指出中纬度低频纬向风振荡是准地转的,且高低空振荡同位相。同时揭示出:亚洲地区中纬度(35°N)高空低频纬向风的向东传播是波长为60—90个经度、移速为1.5—2.0个经度/d的中纬度低频波动东移的结果。这种低频涡旋移至东亚沿海地区常会发展,这种发展可能与急流中心附近正压不稳定能量的供给有关。

Based on June to September 1981 ECMWF grid datasets, analysis is done of the characteristics of the propagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia. Results show a separating (confluence) belt for the meridional propagation of low-frequency zonal (meridional) winds athigher (lower) levels over subtropical latitudes at 120°E, revealing that the oscillation of the zonal winds is quasi-geostrophic in nature and in phase in thehigh- and low-level. It is also found that the eastward propagation of the high-level zonal winds around 35°N in East Asia is the result of eastward march of midlatitude low-frequency waves with 60°-90° longitude wavelength and speed of 1.5°-2.0° longitudes per day. In addition, such low-frequency vortices, when moving over the coastwise region, tend to develop, accompanied by sharp oscillation in the westerly Jetstream over eastern Asia.