| 摘要: | 隨著全球暖化的加劇，熱浪的發生頻率逐漸增加，而熱浪的發生和高壓系統有關。臺灣在夏季時受到西北副熱帶太平洋高壓(Western North Pacific Subtropical High, WNPSH)的影響，經常會有連續性的高溫事件發生。因此探討WNPSH的變化對於臺灣熱浪的分析是至關重要的。
透過EOF分析850百帕的重力位高度，以及針對各模態進行氣象場的回歸分析之後，前三個影響WNPSH的模態分別為熱帶大西洋暖化、P-J pattern的負相位、以及ENSO。在暖化的影響下，WNPSH的強度在東亞區域增強，且在熱帶大西洋暖化的影響下，位置相對西伸；在P-J pattern的負相位影響下，臺灣有一氣旋式距平，此距平回歸使得在降水距平增加，不利於WNPSH的增強；在ENSO的影響之下，在西北太平洋有一反氣旋式的系統增強，主要是和ENSO消退其間所引發的Kelvin wave所引發之負渦度切變造成WNPSH增強有關。綜上所述，在熱帶大西洋暖化、P-J pattern正相位、ENSO消退期間為對於WNPSH的增強有利的情境。
在探討有利於WNPSH發展的模態後，本研究針對過去43年的觀測資料進行分析，將天氣型態分為四類，分別為弱西南季風(C1)、強西南季風(C2)、弱WNPSH (C3)、及強WNPSH (C4)，探討出在水氣量較少的條件下，較有利於熱浪事件的發展。接續，本研究針對在三個模態當中的4個分類下的熱浪天數進行分析，在熱帶大西洋海溫增加、P-J pattern正相位、以及反聖嬰年時的熱浪持續天數以及頻率都相較正常年多，而強度則並沒有明顯差異，因此臺灣熱浪主要是透過多天數以及高頻率的條件所造成。最後探討各天氣型態天數統計上與三個模態的關聯，其中在C4的天數上和PC1有著顯著正相關，C1及C2有著顯著的負相關，表示在暖化的情境下，西南季風有所減弱以及WNPSH的天數有所增加，因而使得臺灣在過去43年的熱浪天數有所增加。透過上述分析，整合了在暖化中以及年際變化下的大尺度環流對於WNPSH的影響，並探討如何影響臺灣的熱浪事件。
;As global warming intensifies, the frequency of heatwaves is gradually increasing, and heatwaves are associated with high-pressure systems. During the summer, Taiwan is influenced by the Western North Pacific Subtropical High (WNPSH), which often leads to prolonged high-temperature events. Therefore, investigating the changes in WNPSH is crucial for analyzing heatwaves in Taiwan.
Through EOF analysis of the 850 hPa geopotential height and regression analysis of meteorological fields for each mode, the first three modes influencing the WNPSH are identified as tropical Atlantic warming, the negative phase of the Pacific-Japan (P-J) pattern, and ENSO. Under the influence of warming, the intensity of the WNPSH strengthens in the East Asia region, and under the impact of tropical Atlantic warming, its position shifts westward. In the negative phase of the P-J pattern, a cyclonic anomaly develops over Taiwan, and the regression of this anomaly leads to increased precipitation anomalies, which are unfavorable for the strengthening of WNPSH. During ENSO′s decay phase, an anticyclonic system strengthens in the Northwest Pacific, primarily related to the negative vorticity shear caused by the Kelvin wave triggered by the ENSO decay, resulting in the enhancement of WNPSH. In summary, conditions that favor WNPSH strengthening occur during tropical Atlantic warming, the positive phase of the P-J pattern, and the decay phase of ENSO.
After exploring the modes favorable for WNPSH development, this study analyzes observational data from the past 43 years, classifying weather patterns into four types: weak southwest monsoon (C1), strong southwest monsoon (C2), weak WNPSH (C3), and strong WNPSH (C4). The analysis shows that heatwave events are more likely to develop under conditions with less water vapor. Further analysis of the heatwave duration in the four categories under the three modes indicates that during tropical Atlantic sea surface temperature increases, the positive phase of the P-J pattern, and El Niño decaying years, the heatwave duration and frequency are higher than in normal years, while the intensity does not show significant differences. Therefore, Taiwan′s heatwaves are primarily caused by prolonged duration and high frequency. Finally, the correlation between the number of days in each weather pattern and the three modes is explored. In C4, the number of days shows a significant positive correlation with PC1, while C1 and C2 show significant negative correlations. This suggests that under warming conditions, the southwest monsoon weakens, and the number of WNPSH days increases, leading to an increase in heatwave days in Taiwan over the past 43 years. Through this analysis, the study integrates the influence of large-scale circulation changes due to warming and interannual variations on WNPSH and investigates how it affects Taiwan′s heatwave events. |
