| 摘要: | 2019年TASSE於6、7月展開，其中2019年7月22日午後雷暴事件，造成台北都會區淹水，降雨中心在大安森林公園測站，最大降水時雨量接近200 mmhr^(-1)，本研究利用IBM_VDRAS(Variational Doppler Radar Analysis System based on immersed boundary method)系統、中央氣象局測站以及台灣大學storm tracker觀測資料對此個案進行分析。
分析結果顯示，初始階段海風將暖濕空氣帶入內陸，在桃園、新竹以及雙北山區形成零星對流胞，發展階段各對流胞包圍台北盆地，冷池外流加上地形效應使得台北盆地中心輻合狀況良好，加上中層水氣充足以及條件不穩定，此時台北盆地環境十分有利對流生成，至成熟階段時，主要對流於台北盆地中心（大安森林公園）上空長起，在後續的一個小時下了超過100毫米的累積降水，期間經歷了胞合併，使得上升運動增強，並延長強降水時間，造成大安森林公園周邊地區淹水，到了消散階段，台北盆地改吹陸風，盆地中心由輻合場轉為輻散，且中心地表為下沉運動，新的對流經台北盆地西南方往桃園、新竹傳遞。
本研究亦利用IBM_VDRAS分析場計算發展、成熟、消散階段時，此午後雷暴個案在視熱源(Q1)以及視水氣匯(Q2)的垂直分佈，結果顯示Q1呈單峰結構，在成熟期最大加熱高度約在5km(575mb) 左右，大小約在3~4(_^o)C/hr，Q2在成熟期呈現雙峰結構，底層最大乾化高度約在1.75km(824mb)，大小約在4(_^o)C/hr，上層最大乾化高度約在5.25km(540mb)左右，大小在3~4(_^o)C/hr。
從結果來看，IBM_VDRAS藉由同化雷達資料，得到完整的的三維氣象場，可以清楚分析對流胞傳遞、合併時，垂直剖面的變化，以及水氣、雨水混合比等參數的定量變化，也可以得到午後雷暴發展、成熟、消散期Q1、Q2的垂直分佈，是非常好的分析工具。
;During the TASSE(Taipei Summer Storm Experiment), a severe afternoon thunderstorm developed within Taipei basin on 22 July 2019, which produced intense rainfall in Daan Forest Park(max rainfall rate ~ 200mm hr-1) and caused urban-scale flooding. This study utilized IBM_VDRAS (Variational Doppler Radar Analysis System based on immersed boundary method), radar data, CWB weather station data and stormtracker data to analysis this case
At initial stage, sea breeze brought moist air into inland, and caused convection initiation at mountain region of Taipei, Taoyuan, Hsinchu. At developing stage, The environment was suitable for main convection developing because 1).Taipei basin was surrounded by scattered convection, the outflow of these convection converged with sea breeze and terrain, 2).sufficient mid-level water vapor and conditional unstable environment. At mature stage, the main convection initiated at center of Taipei basin and produced over 100mm accumulated precipitation within one hour, cell merge happened at this stage and increased the vertical velocity, extended the lifetime of this main convection, also caused a severe flooding in Daan Forest Park and its adjacent areas. At dissipation stage, land breeze happened, the divergence filed of Taipei basin center transformed from convergence to divergence, and new initiated convection propagated from Taipei basin to Taoyuan and Hsinchu.
This study also took advantage of IBM_VDRAS three-dimensional analysis to calculate the developing, mature and dissipation stage Q1, Q2 vertical profile, which could analyze the relationship between this afternoon thunderstorm case and environment. The result showed that Q1 had one peak pattern with max heating layer about 5km(575mb) on mature stage, Q2 had double peak pattern with low level max drying layer about 1.75km(824mb) and high level max drying layer about 5.25km(540mb) .
From the result we mentioned, by assimilating radar data, IBM_VDRAS is a very powerful ,useful system which can retrieve analysis well, and can help us to analyze the process of cell propagation , cell merge and other parameter quantitatively . |
