Long-Term Variations of Tropospheric Circulations in the Western Pacific Region as Derived from GMS Cloud Winds

Abstract

Long-term variations of large-scale circulations in the western Pacific regions are investigated by using cloud wind data derived from GMS during 6 years from 1978 to 1984. Comparison between monthly mean winds obtained by the satellite and those by the upper-air sonde observations indicates that upper cloud winds generally correspond to 200-mb winds and lower cloud winds correspond to about 850-mb winds.
6-year averaged monthly mean winds reveal that upper and lower winds in the western Pacific are largely affected by monsoon circulation systems. In the upper troposphere northeasterlies dominate in the equatorial western Pacific to the southeast of the Tibetan High during northern summer, while southeasterlies prevail during winter affected by an anticyclonic circulation generated over the Australian monsoon region.
The first mode of winds obtained by an Empirical Orthogonal Function (EOF) analysis corresponds to wind anomalies associated with the 1982-83 El Nino event. Upper winds and lower winds of this eigenvector suggest that there exists a large-scale east-west circulation with rising motion in the eastern Pacific and sinking motion in the western Pacific. The first eigenvector also possesses an upper cyclonic anomaly circulation in the western Pacific subtropics.
Wind anomalies corresponding to the western Pacific-Japan oscillation of the heat source found by Nitta (1986) are obtained by both EOF and composite analyses. When convective activities are intense in the western Pacific subtropics near 20°N, an upper cyclonic cell is found to the northwest of the heat source center and an anticyclonic cell appears north of the cyclonic cell. It is suggested that these anomaly circulations might have strong influence on large-scale summer-time circulations in the East Asia.