Momentum Budgets of a Subtropical Squall Line Determined from Dual-Doppler Data

副熱帶颮缐之動量收支：雙都普勒雷達資料分析

林永哲(Yeong-Jer Lin) ； 沈畦(Hsi Shen) ； 鄭方政(Fang-Chen Cheng) ； Robert W. Pasken

《Terrestrial, Atmospheric and Oceanic Sciences》 1卷4期 (1990/12) Pp. 321-336

摘要

本文採用熱力反求法來了解IOP#2中一個副熱帶颮線之結構。1987年5月17日本地標準時間凌晨0040，0043，0046，0049及0052之雙都普勒雷達資料經過客觀分析後內挿至45×25的水平網格上，網格問距爲1km.垂直方面自0.3至8.8公里共分不等間隔十層。垂直風速場用非彈性連續方程向下積分及變分調整的方式計算。擾動壓力場及擾動溫度場則由都普勒風場透過動量方程反求得出。這些動力場及熱力場必須經過內部檢驗後方能做進一步的詮譯。
結果顯示颮線内向西傾斜之對流上升氣流區中水平動量在垂直颮線方向之分量是向下傳送，而和颮線平行方向之分量則向上傳送。動量收支的結果可看出平均水平動量及擾動水平動量的幅合可以增强平均水平動量，而輻散則使期減弱。這些結果和copt所分析熱帶颮線很類似。本文使用都普勒風場計算之動量收支及水平動量之垂直傳輸情形有助於MCS與平均流間交互作用之了解。

並列摘要

A thermodynamic retrieval method was employed to investigate some structural features of a subtropical squall line during IOP-2.Dual-Doppler data,　centered at 0040,0043,0046,0049,and 0052 LST 17 May 1987,were objectively analyzed in the horizontal domain of 45km by 25 km using 1km grid spacing. There were 10 analysis levels in the vertical ranging from 0.3 to 8.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Fields of deviation perturbation pressure and temperature were retrieved from the Doppler derived winds using the three momentum equations. These fields were subjected to internal consistency checks to determine the level of confidence before interpretation.
Results show that the vertical transport of horizontal momentum normal to the line is downward corresponding to the west-tilted convective updrafts, while the line-parallel component results in an upward momentum transport. Momentum budget calculations show that the horizontal and vertical flux convergences/divergences of horizontal momentum by the mean and eddy motions contribute largely to the growth/decay of mean horizontal momentum. These findings are in qualitative agreement with those of tropical squall lines during COPT81.The dynamic interaction between the mesoscale convective system and its environment can be studied using the momentum budget equations and vertical fluxes of horizontal momentum estimated from the Doppler derived winds.