南アジアにおける突発的メソ気象擾乱発生に関わる環境場の特徴について

Abstract

南アジアにおいて発生する竜巻等の突発的メソ気象擾乱発生に関わる環境場の特徴について調べた。これら突発的なメソ気象擾乱の多くをもたらすとされる組織化した積乱雲（マルチセルやスーパーセル）の発生と発達に重要な大気の熱的安定度と風の鉛直シアーに注目し，これらをパラメーター化して定量的に評価し，その時間的・空間的分布を調べた。その結果，プレモンスーン期バングラデシュ付近で熱的不安定度と風の鉛直シアーが共に顕著に増大することが示され，積乱雲が組織化してより発達したものになりやすい環境場であることが示された。

The environmental characteristics related to the outbreak of meso-scale meteorological disturbances such as tornado are investigated. The thermodynamic instability and vertical shear which are important for the occurrence of an organized cumulonimbus cloud (multicell and supercell) that often causes sever meso-scale disturbances are noticed and the spatial and temporal distribution of them in the South Asia is quantitatively investigated. It is shown that the thermodynamic instability and vertical shear are considerably increasing in and around Bangladesh during the pre-monsoon season. This indicates that the organized cumulonimbus cloud tends to occur in and around Bangladesh during pre-monsoon season. This result is consistent with the climatological fact that severe meso-scale disturbances (tornado, hail, gust and so on) concentrate in Bangladesh and adjoining north east India.