本研究於 2009 年開始建立大屯山區密集降雨觀測系統(Da-Tun Rain Gauge Network, DTRGN)，並於2010 年底完成初步的雛形。該觀測系統之設置理念乃基於山區的雨量觀測站稀疏，時常無法解析地形降水強度與分佈情形，加上大屯山區緊臨北海岸，在颱風與東北季風環境下，常具有雨量極大值。因此，我們選取北台灣大屯山區來建置密集的自動雨量觀測站，設站地點大多為山頂及斜坡等降雨潛在集中區域，以提供高時間與空間解析度之地面雨量觀測資料。
本研究初步選取 2011 年 1 月至 2013 年 2 月冬季期間 18 個東北季風降水個案，利用大屯山地面雨量資料檢視山區的降水分佈及強度特徵，並以 NCEP-FNL 資料描述地形上游環境條件，來嘗試了解兩者之間的可能關聯。對於這些個案而言，地形上游環境大略為中性穩定之大氣，其低層環境相當潮溼，且具有較大的 Froude number。雨量分析顯示山區降水在數公里內就有相當大的變化，加入 DTRGN 觀測資料能顯著提升對於地形降水分佈及強度的掌握程度。另外，研究也發現強降雨區域不只出現在迎風面斜坡及山頂附近，也有可能會發生在山谷區域，分析顯示山谷加強降水效應與地形上游風向密切相關。進一步探討地形上游環境氣象因子（風速[ws]、混合比[γ]及靜力穩定度[N]）與個案降水強度最大值(RMAX )的相關性，統計分析顯示風速與靜力穩定度的倒數皆與降水強度有正相關。而透過交錯統計相關分析，我們發現 ws γN –1的物理量與 RMAX 的相關性最佳。這些研究結果對於未來了解或預報台灣冬季地形降水強度有很好的參考價值。

Mt. Da-Tun Rain gauge network (DTRGN) had been initially constructed in 2010. Given very few rainfall stations over mountains, they usually cannot capture the detailed distributions of orographic precipitation. Mt. Da-Tun (DT) is located nearby the northern coast of Taiwan and frequently produces the rainfall maximum in the typhoon environments and during the northeasterly monsoon season. Therefore, this study had deployed automatic rain-gauge stations over DT, which can provide high temporal and spatial resolution of surface rainfall measurements over this barrier. The rain-gauge stations of DTRGN are mostly located over the potentially concentrated rainfall area such as those near the mountain crest and windward slopes.
In this study, eighteen winter rainfall events associated with northeasterly monsoon flow during the period from January 2011 to February 2013 were chosen for detailed analysis. The primary focus of this study is on investigating the detailed aspects of the intense orographic precipitation over DT. NCEP-FNL data was also used in this study to describe the upstream conditions. This study also attempts to explore the relationship between upstream conditions and precipitation distributions. Upstream conditions associated with the studied evennts were characterized by nearly neutral convective instability, large Froude number, and moist northeasterly oncoming flow, implying the importance of orographically forced lifting on the development of precipitation. The analysis results show that the precipitation over mountains has considerable variations within a few kilometers. Local maxima of orographic precipitation were observed to occur over the windward slopes, near the mountain crest, and even the valley region. Our analyses indicate that the degree of the precipitation enhancement over valley depends strongly on the wind direction of upstream oncoming flow. Examination of the correlation between upstream meteorological factors (wind speed [ws], mixing ratio [γ], and static stability [N]) and the maximum of rainfall intensity (RMAX) over mountains indicates that RMAX exhibits a general trend to increase with ws and N –1. Further statistical analysis indicates that ws γN –1 and RMAX have best correlation. The results from the study represent good references to the future forecast or research of winter orographic rainfall in Taiwan.