臺灣地形對雨量之增減作用：濁水溪至高屏溪流域的降水分布－（中）合成分析及模擬

On the Topographic Effects of Precititation and Its Distribution over Southwest Taiwan-Part 2: Composite and Numerical Study

劉廣英(Koung-Ying Liu) ； 張忍成(Jin-Chen Chang)

《大氣科學》 16卷2期 (1988/06) Pp. 141-150

摘要

經由個案分析（本文上篇）可知，研究區內的降水分布與地形及低層風場有密切的關係。平均而言，平地測站之雨量僅及山區最大雨量測站的15%左右的雨量遞增（減）率大致與山坡的爬升（下降）率相同。本文為上述個案分析之續，文中除將研究區歷次大雨個案作合成分析（包括原個案分析之甲乙二線及新加之丙丁兩線共四條），以進一步了解降水量與地形之關係，及降水量分布的地形特徵，另外並透過一簡單的模式作數值模擬。就合成分析而言，在甲乙兩線上仍可見到（一）沿海平地的大雨副中心；（二）雨量增（減）率與山坡升（降）率大致相符；（三）背風面在近山頂處降水量仍大但迅即驟減；（四）平地測站的平均降水量約為山區最大平均值的20%；及（五）西南－東北走向山谷（即袋形山谷）的「底」部有較大的雨量等現象，與個案分析結果相符，顯示以上五者為研究區內降水隨地形改變的主要特徵丙丁二線除第（一）項不明顯外其餘特徵亦同。至於數值模擬的結果，當乘以調節係數0.35時與實測值頗為近似，同時，經由模式檢定可知，（1）影響山區降水量最大的因子是風場；（2）最大降水率發生於地形最陡處；（3）當整層空氣的平均RH≥85%後，RH增加雨量反減；（4）低層風速愈小，垂直速度愈大時，平均雨量與山區雨量愈接近；（5）加入平流作用後有較佳的模擬效果。

關鍵字

地形降水 ； 降雨分布（分析及模擬）

並列摘要

As in the first part eight heavy rain events in the southwest part of Taiwan are analyzed along two different lines with different directions and slopes. The results gave a very diversed outlook of tropographic effects on rainfall amont and rainfall distribution. In order to make the problem more clearly a composite study and numerical simulation are carried out in this part. In summary our results can be listed as follows:1. The composite study shows that: (1) there are two peaks of rainfall along each line, one is on the coast region, another one is, except line C, on the top area of the topography; (2) precipitation increased in amount rapidly from 1/3 to 1/2 (from surface) of the slope to the mountain top; (3) a very prounced rainfall peak, as shown in line C, occured on the northeast top of the SW to NE valley; (4) the rainfall amont of the mountaineous area, in the mean, is about 5 times as greater than that of its related plane area.2. From the numerical sudy we know that: (1) our model can, more or less, simulate the observed condition; (2) horizontal wind field, surface temperature, relative humidity of the air colume and the synoptic scale vertical motion are the factors which influence the precipitations, among them the horizontal wind and tile surface temperature are more important ones; (3) for the relative humidity when it increased from, say, 85% to 100% the rainfall amont, on the contrary, will be decreasing due to the reduction of the conditional instability; (4) in the mountain area the precipition is mostly influenced by the gradient of the slope, therefore most heavy rain occured in the tippest area; (5) when the surface temperature is high, horizontal wind is weak, synoptic scale vertical motion is strong the rainfall amont of the plane area will increase and much more than that of its related mountain area, therefore the difference between the two is reduced.The adjustment of the model and other related work will be carried out in the third part.

並列關鍵字

orographic precipitation ； rainfall distribution (analysis & modeling)