2012蘇拉颱風期間大屯山地形降水特徵及其過程

Abstract

本研究使用高時空解析度之都卜勒雷達、地面雨量筒觀測和地形降水診斷模式來瞭解蘇拉颱風(2012)影響台灣時，在大屯山的地形降水特徵及其可能的過程。當蘇拉颱風自台灣東岸往北移動時，北台灣受到颱風影響觀測到強烈的東北/東風(約18~36公尺/秒)，並於大屯山區發生強降水。大屯山位在北台灣海岸，為約海拔一公里的三維獨立山脈。在主要的研究期間(約13小時)，在大屯山山頂的附近區域累積超過450毫米的雨量。在較早的降雨時段，颱風背景降水呈現較為層狀的特徵，同時環境風較強(約30~36公尺/秒)。到了較晚的降水時段，颱風背景降水呈現較為對流的型態，並伴隨較弱的環境風(約18~30公尺/秒)。透過觀測分析與地形降水模式的模擬，我們發現種雲播雲機制較能掌握颱風背景降水為層狀時的地形降水加強。另外在背景降水為對流特徵時，地形舉升造成的低層上升運動影響了對流胞內的環流結構，其降水加強的雲微物理過程似乎變得較為複雜。

Based on the analyses of high-resolution Doppler radar, rain gauge data, and the orographic precipitation diagnostic model, this study tries to identify the detailed characteristics and intensity of orographic enhancement precipitation over Da-Tun Mountain (hereafter DT) during Typhoon Saola (2012). In this typhoon event, the occurrence of heavy precipitation was concentrated over DT as Saola moved northwestward, approached Taiwan, and brought strong northeasterly/eastly flow (18-36 m s-1) impinging over the northern coast of Taiwan. DT, is a three-dimensional, isolated mountain barrier located on the northern coast of Taiwan with peaks of approximately 1 km MSL. Over 450 mm of rainfall during the 13-h study period was observed over the mountain crest, and two rainfall stages were identified. For the first stage at the earlier time, the typhoon background precipitation was mostly characterized by stratiform precipitation with relatively stronger upstream winds (30-36 m s-1), whereas the second stage was characterized by more convective background precipitation and relatively weaker upstream winds (18-30 m s-1). The simulations of the diagnostic model revealed that the seeder-feeder mechanisms could better quantify the rainfall enhancement during the first stage with stratiform background rainfall. Under convective background rainfall during the second stage, orographic lifting of low-level oncoming winds might modulate the convective cells’ circulation and precipitation, further complicating the microphysical processes of orographically enhanced precipitation.