水分子在大氣中產生三相變化時，會吸收或釋放極大的能量，進而改變大氣的能量分佈以及垂直穩定度。因此可知水氣對於天氣變化來說，是佔有很大影響因素的地位。所以若能有效分析可降量與降水間相互關係，是有助於了解與評估天氣系統之形成與演變。而在降水發生時，最直接影響的就是大氣或地面上水氣含量的改變，因此本文利用1991至2005年台北及花蓮氣象站探空氣球觀測資料，並配合地面氣象資料，分析各季可降水量比值(RHs)與相對濕度RH對於不同降雨事件類別所發生之趨勢變化，以驗證RHs與降雨發生的相關性。接著利用台北及花蓮地面氣象站之地面溫度(Ts)資料，對兩時段飽和可降水量(PWs)建立關係式，以獲得可連續時間估算PWs之模式。然後採用2003年花蓮探空站最近距離之新城GPS測站所估算的PW(探空站與GPS站相距約4.6公里)，並將該測站逐時 資料，加入花蓮探空站所建立各月PWs估算模式，進而求得連續時間的RHs。另外配合對應之逐時自動雨量站資料(GPS站與雨量站相距約1.3公里)，探討以模式間接求得的RHs於新城測站，在各月份及颱風個案降雨發生前後連續時間序列之變化情形。進而確立RHs相較於RH而言，對於降水發生是具有較高準確性與靈敏性的。

There are some relationship between the amount of water vapor in the atmosphere and rainfall. The goal of this investigation is to study the relationship between precipitable water (PW) and rainfall. Two data sets are used, namely radiosonde data acquired at the Taipei and Hualien weather station of Central Weather Bureau (CWB) from year 1991 to year 2005, and data of ground based GPS station operated by PEPU 2003.Then put the surface temperature (Ts) data of PEPU GPS station, the nearest GPS station near Hualien radiosonde station (the distance between these two stations is about 4.6km), in 2003 into the PWs estimation model made by Hualien radiosonde station and use the PW data estimated by PEPU GPS station to get the continuous time RHs at PEPU GPS station. Furthermore, use the data of automatic rainfall station (the distance between rainfall station and GPS station is about 1.3km) to get the change of RHs in front and behind the typhoons in each month at PEPU station indirectly. And then make sure that RHs has more sensitivity and accuracy in precipitation than RH.

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