副熱帶東亞梅雨槽縱向一波長之合成結構分析

Structure over One Longitudinal Wavelength of a Composite Mei-Yu Trough in Subtropical East Asia

陳泰然(George Tai-Jen Chen)

《大氣科學》 11卷1期 (1984/03) Pp. 121-139

摘要

本文選取1975年與1977年的八個梅雨個案，分析在100˚～140˚E間由850mb梅雨槽與每2.5˚經度之子午線相交點，垂直向兩旁延伸至高度脊間一個縱向波長內，在生命初期、中期與末期之合成綜觀結構與渦度收支。結果顯示，低對流層梅雨槽上波動之緯向波長約與理論值相近～2000km。850mb高度場與渦度場在經向之相位一致，顯示其地轉近似性。500mb及以下各層濕軸初期在850mb槽南，中期北移至槽上或槽北，末期移回槽南。850mb與700mb最大上升運動區主軸約與該層最大相對濕度區主軸一致，在槽南或槽上。500mb與300mb最大上升運動主軸亦均在槽鄰近。槽北脊區主要為下降運動，槽南脊區在850mb雖為下降，但在700mb以上則大都具微弱上升。渦度收支分析顯示，渦度平流項不利槽之南移，輻合生成項在生命各階段對梅雨槽強度之維持皆為正貢獻，剩餘項（積雲對流、山脈地形摩擦）則在減弱槽的強度。

並列摘要

Eight cases of Mei-Yu systems in 1975 and 1977 are selected to study the synoptic structure and vorticity budget over one longitudinal wavelength between 100˚E and 140˚E for the initial-, middle- and ending stage of the 850mb Mei-Yu trough. Results show that the latitudinal wavelength on the lower tropospheric Mei-Yu trough is about 2000 km in good agreement with the theoretical value. Longitudinal distributions of geopotential height and vorticity at 850 mb are in phase indicating a quasi-geostrophic structure. It is also observed that wet axis at all levels analyzed is located to the south of 850 mb trough at initial stage, moves northward over and to the north of the trough at middle stage, then moves back to the south of the trough at ending stage. The maximum upward motion and the maximum relative humidity are in phase at 850 and 700 mb and are located over and to the south of the trough. The maximum upward motion axis at 500 and 300 mb is also located in the vicinity of the trough. Ridge area to the north of the trough is mainly dominated by downward motion. Although this is also true to the south of the trough at 850 mb, weak upward motions are found at 700 mb. Vorticity budgets indicate that the vorticity advection process is a negative contributor to the southward movement of the trough. Generation term due to the horizontal convergence plays a major role in maintaining the intensity of the Mei-Yu trough at all three stages of life cycle. Finally residual term (cumulus convection and orographic/terrain frictional effects) is found to be detrimental to the Mei-Yu trough.