熱帶氣旋（TCs）是自然風險，尤其是在最活躍的西北太平洋（WNP）地區，對生態系統和人類社會產生巨大的影響。颱風是指持續最大風速≥64節的熱帶氣旋，通常在夏季發生，但現在在西北太平洋幾乎全年都會出現。雷伊颱風是2021年12月的冬季超級颱風，也是繼2013年11月超級颱風海燕之後菲律賓第二個造成經濟損失最嚴重的颱風。雷伊颱風在登陸菲律賓前快速增強（RI）；它在南海經歷了另一次快速增強，並成為南海記錄中第三個5級強度颱風。本研究調查了雷伊颱風的環境條件，以確定哪些因素對颱風的強化最為顯著。本研究使用JTWC的最佳路徑數據來描述颱風的位置和強度等特徵，分別使用ERA5和CMEMS全球海洋物理再分析的數據來描述雷伊颱風的大氣和海洋環境，並且量化分析影響熱帶氣旋強度變化的變數，例如垂直風切（VWS）、相對濕度（RH）、海表溫度（SST）、T100和海洋熱含量（OHC），還使用地球同步氣象衛星—向日葵八號（Himawari-8, H-8）的紅外線影像來補充熱帶氣旋最佳路徑和再分析數據的分析。結果顯示，雷伊颱風的大氣和海洋條件對西北太平洋的快速增強時期1非常有利；同時，其條件對於南海的快速增強時期2相對不利，尤其是在海洋組成部分。儘管環境條件不利，雷伊颱風仍能經歷快速增強並在南海增強為超級颱風的強度。這些結果表明，內核過程可能在發生快速增強時有著更重要的作用。雖然以前的研究聲稱有利的大範圍環境條件並不能保證快速增強的發生，本研究的結果表示反之亦然，不利的大範圍環境條件並不能排除快速增強的可能性。;Tropical cyclones (TCs) are natural hazards that greatly impact ecosystems and human society especially in the western North Pacific (WNP), which is the most active region in the world. Typhoons, TCs with maximum sustained winds ≥64 knots (kts), typically occur during summer but now occur almost year-round in the WNP. Typhoon Rai was a winter super typhoon event in December 2021 and became the 2nd most economically damaging typhoon in the Philippines after Super Typhoon Haiyan in November 2013. Typhoon Rai experienced rapid intensification (RI) shortly before it made landfall in the Philippines. It experienced another RI event in the South China Sea (SCS) and became the 3rd recorded category 5 intensity typhoon in the SCS. This study investigates the environmental conditions of the Typhoon Rai event to determine which factors are the most significant for the intensification of the typhoon. This study uses the best track data from JTWC to describe the TC characteristics such as location and intensity. Data from ERA5 and CMEMS global ocean physics reanalysis are used to describe the atmospheric and oceanic environments, respectively, of the Typhoon Rai event. Variables affecting the intensity change of TCs such as VWS, RH, SST, T100, and OHC were quantified. IR imagery from Himawari-8 geostationary satellite was also used to supplement the analysis of TC best track and reanalysis data. Results show that atmospheric and oceanic conditions of Typhoon Rai were favorable for the RI1 period in the WNP. Meanwhile conditions were less favorable for the RI2 period in the SCS, particularly the oceanic component. Despite the unfavorable environment, Typhoon Rai was still able to experience RI and strengthen into super typhoon intensity in the SCS. These results indicate that inner-core processes may play a more significant role for RI to occur. While previous studies have claimed that favorable large-scale environment conditions do not guarantee the occurrence of RI, the results of this study suggest the inverse is also true, that unfavorable large-scale environment conditions do not exclude the possibility of RI.
