從風雨狀態下的降雨量觀測談2009年莫拉克颱風之降雨量

From the Viewpoint of Rainfall Measurement under Windiness Condition to Talk Rainfall of Typhoon MORAK in 2009

郭玉麟(Yuh-Lin Kuo) ； 徐森雄(Sen-Hsiung Hsu)

《水保技術》 5卷3期 (2010/07) Pp. 178-183

https://doi.org/10.30040/JSWCT.201007.0006

摘要

本研究之目的在求瞭解降雨受風速影響後所造成之降雨傾斜角及其雨量短少率，觀測地點位於屏東科技大學氣象站，除原有之雨量自記計、風速自記計外，並增設五口式雨量自記計。觀測期間自2000年8月至2004年8月，共收集近500筆有效資料進行分析。得悉降雨傾斜角隨風速之變大而變大，其線性關係甚高。在10分鐘降雨強度小於2mm條件下時，降雨傾斜角隨風速變化之斜率最大，但在不分降雨強度狀態下，10 分鐘平均風速爲5 ms^(-1) 時，降雨角度爲23°；10分鐘平均風速爲10ms^(-1)時，降雨角度爲32°；10分鐘平均風速爲15ms^(-1)時，降雨角度爲41°。雨量短少率在一小時降雨強度大於10mm條件下，平均風速爲10ms^(-1)時，雨量短少率爲17%，平均風速爲18ms^(-1)時，雨量短少率爲29%，但在10分鐘降雨強度大於10mm條件下，平均風速爲5ms^(-1)時，雨量短少率爲35%，平均風速爲10ms^(-1)時，雨量短少率爲58%，可知當降雨強度一定時，風速愈大，雨量之短少率愈大。2009年8月7日，中度颱風莫拉克侵襲台灣，自8月7日至8月10日之降雨量，在阿里山達2,965mm、高雄達835.5mm，但若依本研究所提出之雨量觀測值訂正係數來校正，則阿里山之降雨量將上修爲3,409.8mm、高雄之降雨量將上修爲1,211.5mm，如此之豪大雨，更突顯了造成台灣南部與東部縣市嚴重水患之緣由。

關鍵字

雨量觀測 ； 風速 ； 降雨角度 ； 雨量短少率 ； 莫拉克颱風

並列摘要

The purpose of this study was to investigate the effects of wind speed upon the measurement of rainfall. The study site was established at the meteorological station of the National Pingtung University of Science and Technology. A five-opening directional rain gauge, standard rain gauge and aero vane type self-recorded device were installed. From August 2000 to August 2004, about 500 events of effective data were obtained, and the results were summarized as follows: When the rainfall intensity was constant, the rainfall angle increased when the wind speed increased. And under overall stage of rainfall intensity, the 10 minutes average wind speed reached 5 ms-1, with the rainfall angle at about 23°. The rainfall angle was about 32°, when the 10 minutes average wind speed reached 10 ms-1. The rainfall angle was about 41°, when the 10 minutes average wind speed reached 15 ms-1. Under the condition of hourly rainfall intensity more than 10 mm, the rate of rainfall loss was about 17% when the average wind speed reached 10 ms-1. When the average wind speed reached 18 ms-1 the rate of rainfall loss was about 29%. Under the condition of the rainfall intensity more than 10 mm10min-1, the rate of rainfall loss was about 35% when the average wind speed reached 5 ms-1, When the average wind speed reached 10 ms-1 the rate of rainfall loss was about 58%. So when the rainfall intensity was constant, the rate of rainfall loss increased when the wind speed increased. The function of standard rain gauge is influenced by wind speed and rainfall intensity. These two factors cause rainfall losses in rainfall measurement. The rainfall loss can be modified by the given adjusting factors. No.18 typhoon MORAK invaded Taiwan on 7 Aug, 2009. The accumulated rainfall at Alishan was 2,965 mm and Kaohsiung was 835.5 mm from 7 Aug to 10 Aug. If corrected by the revised coefficient of this study, the accumulated rainfall will be revised upward to 3,409.8 mm at Alishan and 1,211.5 mm at Kaohsiung.

並列關鍵字

Rainfall Observation ； Wind Speed ； Rainfall Angle ； Rainfall Loss Rate ； Typhoon