| 摘要: | 颱風和海平面溫度關係密切，而海平面溫度的年際變化又以聖嬰現象最為明顯。因此本研究用海平面溫度資料來區分兩種不同聖嬰：中太平洋聖嬰(後稱CP聖嬰)、東太平洋聖嬰(後稱EP聖嬰)，並使用各層流線場、高度場、颱風路徑以及生成位置來探討颱風和聖嬰的交互影響。
使用結合－經驗正交函數分析海平面溫度資料來區分出CP聖嬰和EP聖嬰，並以此兩種聖嬰來探討颱風和聖嬰的關係。以西北太平洋六至九月以及西南太平洋十一至二月來做分析，並用結合－經驗正交函數所分析出第一特徵模的指數來判斷是否為聖嬰，在四個月內有兩個月的指數超過正負一個標準差才會判斷為聖嬰或反聖嬰。通過此方法可以分類成CP聖嬰、CP反聖嬰、EP聖嬰、EP反聖嬰四類。
合成分析後發現：颱風在西北太平洋上由東向西的平均生成位置依序為CP聖嬰、EP聖嬰、EP反聖嬰、CP反聖嬰，西南太平洋的生成位置則依序是EP聖嬰、CP聖嬰、EP反聖嬰、CP反聖嬰。但在海平面溫度距平的表現上兩個半球並沒有明顯差別，因此使用海平面溫度來探討原因，發現因為在南北半球的夏季海平面溫度並不是對稱的，因此就算加上相似的距平後也是會呈現不同的狀況。而在海平面溫度的高溫範圍、低層季風槽位置和高層高壓位置都和颱風生成位置有相對應的排序。
而在颱風路徑的部分，西南太平洋因為無明顯導引氣流且數量較少在此研究中不討論。將西北太平洋的颱風分成兩類：直衝型颱風、轉彎型颱風，並在合成分析時使用此分類來做合成平均路徑。發現兩種颱風合成平均路徑都和生成位置的排序相同，由東向西為CP聖嬰、EP聖嬰、EP反聖嬰、CP反聖嬰，而使用每個颱風存在時間來做合成分析500hPa高度場，其中5880等高線範圍由西向東也是有相同的順序。
;Typhoon has a close relationship with sea surface temperature (SST). On the other hand, the most significant signal for the interannual variation of SST is the El Niño-Southern Oscillation (ENSO) phenomenon. Therefore, the SST data were used to identify two types of El Niño in this study first: east Central-Pacific El Niño (CP El Niño) and Eastern-Pacific El Niño (EP El Niño). Then, we will exam the influence of ENSO on the typhoon genesis location and typhoon track in terms of streamlines and geopotential high analysis at multi-levels.
First, we use combined regression–EOF analysis on SST data to help distinguish CP El Niño and EP El Niño modes. Based upon these two El Niño classifications, the mutual relationship between typhoon and ENSO is analyzed. The analysis time period for Northern Hemisphere is from June to September, while the Southern Hemisphere is from November to February. Using the first mode time series from combined regression–EOF analysis as an index together with its one standard deviation as a criterion, we are able to identify the cases either belong to El Niño or La Niña category. Finally, there are four type category determined: CP El Niño, CP La Nin ̃a, EP El Niño and EP La Niña.
Based upon the composite analysis, it is found that the sequential order of the averaged location for typhoon genesis in the Northwestern Pacific from west to east is CP El Niño, EP El Niño, EP La Niña, and CP La Niña. Meanwhile, the order in the Southwestern Pacific is EP El Niño, CP El Niño, EP La Niña, and CP La Niña. Due to their asymmetric summer SST distribution for Northern and Southern Hemispheres, it is better to exam the distinct features among ENSO episodes in separate Hemispheres although the anomalous SST distributions between them do not show much difference. It appears that the sequential locations order for both the lower level monsoon trough and upper level high pressure together with the high SST region are following that of typhoon genesis accordingly.
In regard to typhoon track issue, we might only focus on the Northwestern Pacific simply because there is no significant steering flow and less typhoon numbers for the Southwestern Pacific. Let us split the typhoons into two types: straight-moving typhoon and recurving typhoon, and then construct their composite mean typhoon tracks, respectively. It turns out that the sequential order from west to east for the typhoon track in both moving types are not only the same with each other but also similar to that of genesis location. The order still are CP El Niño, EP El Niño, EP La Niña, and CP La Niña. Interestingly, the composite contour line of 5880 gpm, generated from 500 hPa geopotential high during each typhoon’s lifetime, also exhibits the same order as that of typhoon track. |
