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熱帶太平洋地區大氣與海洋年際變異度研究:海溫、低層大氣與颱風

The Interannual Variability of the Atmosphere and Ocean in the Tropical Pacific Region: Sea Surface Temperature, Low-Level Atmosphere, and Typhoons

摘要


本文利用ECMWF/TOGA BASIC大氣網格點資料、中央氣象局西太平洋颱風資料、COADS海溫資料分析低層大氣、颱風與海溫年際變化間之關係。結果顯示,赤道太平洋海溫之年際變化基本上以160°E為界,呈東西反相位分佈,最大之海溫年際變異量發生在赤道東太平洋地區。另外透過海溫之波譜分析顯示,赤道太平洋海溫年際變化是由多重時間尺度現象所組成,其主要週期有二:一個是25個月左右的「準兩年週期震盪」;另一個則為43~54個月左右的「準四年週期震盪」。大氣低層緯向風場、渦度場、輻散場、濕度場與海溫變化有密切之關係。當赤道太平洋海溫上升時,我們發現赤道太平洋上空之低層將產生西風異常;渦度場則以赤道為界,以北產生正渦度環流,以南產生負渦度環流;150E以東之赤道及副熱帶地區低層大氣大多為輻合區所籠罩,主要輻散區則位於澳洲北部、印尼附近之西太平洋地區。另外低層大氣濕度明顯增加之區域基本上與年際海溫上升最大區域一致,亦即在赤道中太平洋和東太平洋地區。我們也發現,中或強度El Nino之海溫增溫對於西太平洋強烈颱風之發生頻率與持續日數有顯著之影響,「El Nino年」平均強烈颱風次數由氣候值之9.5個上升到13個,持續日數也由氣候值之90日上升到142日。然而,強度在中度以下之颱風年際變化受到El Nino海溫增溫影響極為有限,且較弱的海溫增溫(如弱和極弱El Nino個案)對颱風發生頻率和持續日數也沒有顯著影響。

關鍵字

年際變異 海面溫度 颱風

並列摘要


Long period of the ECMWF/TOGA BASIC atmospheric grid data, CWB typhoon reports, and COADS sea surface temperature (SST) data are used to study the relation between low-level atmosphere, typhoon activities and the tropical Pacific SST. Our study indicates that the interannual pattern of SST exhibits opposite phase relation between eastern and western Pacific. Spectra of SST indicate multiple time scale characteristics in the eastern Pacific, with two dominant periods: the 25 months ”quasi-biennial oscillation” and the 43-54 months ”quasi-quadrennial oscillation”.The zonal wind, voracity, divergence, and specific humidity of the low-level atmosphere are highly related to the SST variations. The warming of the equatorial Pacific SST induced low-level westerly wind anomaly over warm SST, along with positive low-level voracity anomaly to the north of the equator and negative to the south. The eastern Pacific SST warming also causes significant low-level convergence anomaly and low-level moisture increase over warm SST, while results in low-level divergence anomaly in the equatorial western Pacific.Our study also confirms that the frequency and duration days of strong typhoons in the western Pacific are strongly influenced by moderate and strong El Nino warming episodes. The number of strong typhoons increases from 9.5 time per year on the average to 13 times per year during the ”El Nino years”; while the related to the SST variations. The warming of the equatorial Pacific SST induced low-level westerly wind anomaly over warm SST, along with positive low-level voracity anomaly to the of the equator and negative to the south. The eastern Pacific SST warming also causes significant low-level convergence anomaly and low-level moisture increase over warm SST, while results in low-level divergence anomaly in the equatorial western Pacific.Our study also confirms that the frequency and duration days of strong typhoons in the western Pacific are strongly influenced by moderate and strong El Nino warming episodes. The number of strong typhoons increases from 9.5 times per year on the average to 13 times per year during the ”El Nino years”; while the duration days of strong typhoons increase from 90 days on the average to 142 days per year during the ”El Nino years”. Moderate and weak typhoons, however, are much less influenced by the SST, and the weak El Nino episodes do not show significant impact on the occurrence frequency and duration days of any typhoon activities.

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