伴隨米雷颱風(2011)之大屯山地形降水機制分析

Mechanisms of Orographic Precipitation over Mt. Da-Tun Associated with Typhoon Meari (2011)

陳渲屏(Syuan-Ping Chen)

指導教授 ： 游政谷

國立臺灣大學/理學院/大氣科學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902688

摘要

本研究使用高時空解析度之地面雨量資料及都卜勒雷達觀測，探討伴隨米雷颱風(2011)的地形降水加強之可能物理機制。當米雷颱風經過距台灣約300公里之東北方海面上時，颱風環流為北台灣地區帶來強勁北/西北風(約20~25公尺/秒)，同時於北台灣大屯山區造成強降水。本個案研究區域—大屯山，為一鄰近北台灣海岸之三維獨立山脈，山脈高度約海拔一公里。於10小時之主要研究期間內，觀測顯示強烈降雨(超過250毫米)大致落在大屯山之山脊區域。透過雷達資料分析，顯著地形降水加強大致發生在低層2公里以下之大氣，且受地形加強之降雨量約是颱風背景降水的兩到三倍。
透過雙都卜勒雷達風場反演做降水粒子的軌跡回追以及定量之理論估計，結果顯示當高層降水粒子落下至低層時，過程中增加之降水量與種饋機制(seeder-feeder processes)有高度相關。比起單純氣塊舉升凝結機制，理論之雨滴收集率方程能較佳量化本個案大屯山區觀測到之降水加強量。然而，當颱風背景降水伴隨著強對流胞移入大屯山時，種饋機制的估計會顯著低估降水加強量且有較大之誤差。因此，除了種饋機制之外，對流胞受地形影響所產生之快速氣流及降水結構改變，也是影響本個案降水加強之重要過程。

關鍵字

颱風降水 ； 地形降水加強 ； 舉升凝結機制 ； 種饋機制 ； 對流胞降水加強

並列摘要

With temporally and spatial high-resolution rain gauge data and Doppler radar observations, this study is aimed to explore the physical mechanisms responsible for the orographic precipitation associated with Typhoon Meari (2011). The occurrence of heavy precipitation for this typhoon event was concentrated over Mt. Da-Tun as Meari passed over regions ~300 km northeast of Taiwan and brought strong northerly/northwesterly flow (20-25 m s-1) impinging on northern Taiwan. Mt. Da-Tun, the study area, is a three-dimensional, isolated mountain barrier located adjacent to the northern coast of Taiwan and has terrain peaks at approximately 1 km (MSL, Mean Sea Level).Intense rainfall (>250 mm) was observed nearby the mountain crest of Mt. Da-Tun within 10 h during the period of primary interest. Analyses indicate that the layer of orographic enhancement of precipitation was primarily confined to the lowest 2 km (MSL). The enhanced rainfall was observed to be 2-3 times greater than the typhoon background precipitation.
By tracking hydrometeor trajectory and performing theoretically quantitative calculations, it is found that the increased amount of precipitation water as elevated hydrometeors fell into the low levels was closely related to the precipitation enhancement due to seeder-feeder processes. The enhanced precipitation over mountains is much better quantified by theoretical accretion rate than upslope-lifting-induced precipitation. Moreover, the seeder-feeder calculation tended to be underestimated and have larger errors, when convective elements of intense reflectivity embedded within typhoon background precipitation moved into Mt. Da-Tun. In addition to the seeder-feeder effect that is more suitable for stratiform background precipitation scenario, the rapid modification of airflow and precipitation associated with landfalling convective elements by topography is also an important process contributing to the orographic enhancement of precipitation for the present case.

並列關鍵字

Typhoon precipitation ； Orographically enhanced precipitation ； Upslope lifting ； Seeder-feeder mechanisms ； Rainfall enhancement of convective cells

參考文獻

王寶貫，1997: 雲物理學。國立編譯館主編，渤海堂文化公司印行，台北，382頁。

鄭凌文，2015: 莫拉克颱風之地形降水機制研究-雷達觀測及地形降水診斷模式發展。中國文化大學地學研究所博士論文，26-33頁。

Bader, M. J., and W. T. Roach, 1977: Orographic rainfall in warm sectors of depressions. Quart. J. Roy. Meteor. Soc., 103, 269-280.

Beard, K. V., 1976: Terminal velocity and shape of cloud and precipitation drops aloft. J. Atmos. Sci, 33, 851-864.

Bergeron, T., 1968: Studies of the orogenic effect on the areal fine structure of rainfall distribution, Rep. 6, Meteorological Institute, Uppsala University, Uppsala, Sweden, 42 pp.