運用GPS獲取台灣地區大氣可降水量之分析

全球定位系統（Global Positioning System，GPS）的應用發展，除了工程領域外，在氣象科學上的應用也逐漸獲得肯定。透過GPS資料天頂濕延遲的分析，可以估計當時大氣的垂直總可降水量（Perceptible Water Vapor，PWV），其在天氣預測上的有效運用，業已受到各國氣象單位所重視。本研究運用2006-2012年GPS觀測量，反演對流層水氣資料，並與降雨站資料做比對，以探討台灣地區PWV與實際降雨量的特性，另分析該期間內之資料變化趨勢，以及PWV與高程之關係；本研究同時使用了調和分析法進行降雨趨勢的分析，以進一步瞭解豪大雨時，大氣中PWV之變化情形。由研究成果可知，GPS觀測站所在地之高程越高，其PWV估計值會越低，量級上呈現高程每上升100 m，水氣則會下降1.1 mm至1.8 mm之特性。另由2006-2012年期間之變化趨勢可知，台灣地區可降水量雖有逐年上升之線性趨勢，但實際降雨量卻變得更少，顯示大氣中需要更多的水氣含量才可能產生降雨，這也相對反映出台灣地區必須面對逐漸乾旱的事實。

關鍵字

全球定位系統；天頂濕延遲；可降水量；降雨量

並列摘要

The applications of Global Positioning System （GPS）are not only existed in the engineering field, but also extended to the scientific field of meteorology. Through the analysis of zenithal wet delay from GPS observation, it could be further applied to estimate the vertical total perceptible water vapor（PWV）in the atmosphere. This technique has been implemented worldwide by the meteorological societies for more efficiency in weather forecast. In this study, tropospheric water vapor derived by GPS data and rainfall recorded at the precipitation stations, both collected for the period of 2006-2012, are compared for further discussion. The trends of PWV and rainfall around Taiwan are analyzed, and the relationship between PWV and station elevation are also established. Moreover, the harmonic analysis is adopted to realize the trends of rainfall and tend to further explore the change of PWV in the atmosphere associated with the occurrence of heavy rainfall. The results show that the higher elevation of GPS station, the lower estimate of PWV, along with the function of the elevation increasing every 100 m, the water vapor falling 1.1 mm to 1.8 mm. The trends during the period of 2006-2012 can be found in Taiwan that the precipitation is increased linearly, but the recorded rainfall is decreased. This phenomenon indicates that more water vapor is needed to arouse rains; and it somehow reflects the fact that the drought might be more evident in the Taiwan area.