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

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 at higher (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 the highand 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 ietstream over eastern Asia.