熱帯対流圏上部の擾乱の性質

Abstract

The characteristics of the disturbances near the equatorial tropopause were examined. Particularly, the amplification mechanism of the Kelvin wave and its relation with the basic state were carefully investigated. Most of the disturbances with period larger than several days have maximum amplitude near the tropopause. The amplitude near the tropopause is at most two times larger than 200 hPa. It can be explained by 1) density decrease with heoght 2) weak dissipation in the upper troposphere 3) wind shear near the tropopause and 4) N increase with height. However, remarkable amplification of Kelvin wave with period larger than 20 days in specific year

season (sometimes its amplitude is larger than 20 ms-1) cannot be fully explained in that way.In about ten years (1983-1993), such remarkable amplifications were observed several times, mainly in the northern winter and spring. It is suggested that the longitudinal change of the basic zonal wind can make effect in such amplification; amplification appears in the region where the basic easterly becomes stronger as we go to the east.