NCEP GSM的夏季下墊面熱通量與環流特性：氣候與年際變化

The Characteristics of NCEP GSM on Lower Boundary Heat Flux and Circulation in Summer: The Climate and Interannual Variability

郭漱泠(Shu-Ling Kuo) ； 呂芳川(Fang-Chuan Lu) ； 陳昭銘(Jau-Ming Chen) ； 莊漢明(Hann-Ming H. Juang) ； 王金慶(Jim Chihing Wang)

《大氣科學》 30卷1期 (2002/03) Pp. 35-59

摘要

本研究的主要目的在了解美國國家環境預報中心(NCEP)全球波譜模式(GSM)的氣候特性，可藉此評估運用該模式於氣候研究等之適宜方式，本文選取之分析標的是模式的夏季熱源與環流，探討的重點為模式對氣候海溫與Nino3.4區海溫變化之反應特性，此分析結果可供下游的區域模式使用GSM的模擬結果從事夏季區域氣候預報時的參考。因此，吾人分別設計了氣候實驗與年際變化實驗，並將實驗結果與NCEP的逐月分析資料以及Xie和Arkin所分析的全球月降水資料作比對。
氣候實驗結果顯示，NCEP GSM對夏季的下墊面熱源收支各項皆能有效掌握。在熱帶地區，潛熱通量是夏季下墊面的主要熱源，並將明顯影響降水的模擬，而模式降水的强度與空間分布將進一步影響模式對環流系統的模擬。整體而言，模式的模擬能力不錯，下墊面熱源與低層大氣環流的模擬結果與NCEP分析場間的相關係數大都高達0.9以上，但對亞洲夏季季風的降水之模擬仍有待加強。
年際變化實驗結果分析顯示，模式對Nino3.4區海溫年際變化的反應，不論是下墊面熱源、降水與環流都有相當正面的模擬能力。當Nino3.4區海溫偏暖時，觀測分析顯示，其主要的作用是增加該區的潛熱通量，導致該區偏西側的熱帶中太平洋上的降水強度加强，但在模式中的作用則是直接加強了該區的降水強度。模擬結果與分析結果皆顯示，Nino3.4區海溫的年際變化主要影響的是東太平洋上的環流系統，較高緯度太平洋上的環流系統因受到熱帶環流的動力驅動，間接地亦受到Nino3.4海溫變化的影響，但西太平洋至印度洋等地區的環流受到Nino3.4海溫變化的影響間接而不明確。

關鍵字

下墊面熱源收支 ； 潛熱通量 ； 海溫

並列摘要

The main purpose of this study is to investigate the characteristics of NCEP GSM on climate and interannual variability during summer. We take the aim upon how the surface heat sources and the lower level circulation respond to the Nino3.4 SST. The climate and interannual experiment are designed. The results are compared with the NCEP monthly data and the global precipitation estimates compiled by Xie and Arkin. We hope this study is helpful to assess the way to downscale to the regional climate forecast.
The results of climate experiment show that NCEP GSM can simulate the surface heat budget components well. In the tropic, the latent heat flux is the main heat source and plays a key role to affect the precipitation simulation. The intensity and the spatial distribution of precipitation will, in turn, affect the simulation of circulation. Most of the correlation coefficient of the heat budget components and the lower level circulation patterns between the model output and analysis data have the value more than 0.9. The skill to simulate the precipitation of Asian summer monsoon needs to improve further.
The results of interannual experiment show that NCEP GSM can positively reflect the Nino3.4 SST variability on the surface heat sources and circulation. There somewhat defect is noticed. When Nino3.4SST is above normal, the latent heat flux is enhanced over Nino3.4 area and the precipitation is enhanced over the west of Nino3.4 area in analysis data whereas the precipitation is enhanced directly over Nino3.4area in the model. The model results as well as the analysis data also show that the Nino3.4 SST variability directly affect the tropical circulation around middle to east Pacific. Also, The middle to high latitude circulation is affected by Nino3.4 SST variability indirectly via the dynamic drive. But, the effect of Nino3.4 SST variability on the circulation around west Pacific and Indian Ocean is not evident, especially in the model.

並列關鍵字

Surface heat budget ； Latent heat flux ； SST