東亞夏季季風肇始期之分析：高階量變數變化特徵及中緯度與熱帶系統之作用

The Onset Characteristics in the East Asian Summer Monsoon: Higher Order Moment Analysis and the Influence of the Mid-latitude and Tropical Systems

王作台(Jough-Tai Wang) ； 鄧靜君(Annie C. Dang) ； 陳鏡良(Chin-Liang Chen) ； 胡志文(J.-W. Hwu)

《大氣科學》 29卷4期 (2001/12) Pp. 315-341

摘要

This paper examines the onset characteristics of the East Asian summer monsoon.The dramaticchange of the large-scale variables and the higher order moments(fundamental variables,moisture sink,heatsource,wind shear,height gradient etc.)was identified.The impact of the mid-latitude and tropical system tothe onset of the East Asian summer monsoon is also studied.It was found that after the onset of the summer monsoon in the South China Sea(SCS)region,theSCS became a heat source and moisture sing region.It is related to the intensification of the convectivesystem.The latent heat release is critical component for the heat source in that region.However,in theIndochina(land)region,its role as heat source and moisture sink reduced distinctively after the monsoononset.The results also identified the kinetic energy minimum at 500 hPa during the period of monsoon onset.While the area mean of vertical wind shear,Q1 and Q2 possess a dramatic change about one pentad beforethe onset.And all those dramatic change are all associated with the retreat of the subtropical high to the East.Regarding the impact of the tropical system and the mid-latitude influence to the SCS monsoon onset,it was found that both systems do play some role for the monsoon onset.Some case study revealed that forthe year that mid-latitude influence dominates,the mid-latitude system can advance southward to the 20°N.However,for the year dominated by the tropical system in affecting the onset,then southward advancementof the mid-latitude is limited to the 30°N.

關鍵字

東亞季風 ； 季風肇始 ； 高階量變數

並列摘要

This paper examines the onset characteristics of the East Asian summer monsoon.The dramaticchange of the large-scale variables and the higher order moments(fundamental variables,moisture sink,heatsource,wind shear,height gradient etc.)was identified.The impact of the mid-latitude and tropical system tothe onset of the East Asian summer monsoon is also studied.It was found that after the onset of the summer monsoon in the South China Sea(SCS)region,theSCS became a heat source and moisture sing region.It is related to the intensification of the convectivesystem.The latent heat release is critical component for the heat source in that region.However,in theIndochina(land)region,its role as heat source and moisture sink reduced distinctively after the monsoononset.The results also identified the kinetic energy minimum at 500 hPa during the period of monsoon onset.While the area mean of vertical wind shear,Q1 and Q2 possess a dramatic change about one pentad beforethe onset.And all those dramatic change are all associated with the retreat of the subtropical high to the East.Regarding the impact of the tropical system and the mid-latitude influence to the SCS monsoon onset,it was found that both systems do play some role for the monsoon onset.Some case study revealed that forthe year that mid-latitude influence dominates,the mid-latitude system can advance southward to the 20°N.However,for the year dominated by the tropical system in affecting the onset,then southward advancementof the mid-latitude is limited to the 30°N.

並列關鍵字

East Asian Monsoon ； Onset ； Higher order moments