| 摘要: | 西北太平洋(WNP)地區全年會形成數個熱帶低氣壓(TD)，其中一些會增強為熱帶風暴(TS)，而有些最終會消散。因此，本研究旨在瞭解其發展過程中的雲微物理和降水特性。我們使用了向日葵八號(Himawari-8)衛星和全球降水測量任務(GPM)衛星的資料，對2015年7月7日至2021年12月31日期間的194個熱帶氣旋進行統計分析，並分為TD消散組和TS發展組。通過選擇從風暴中心延伸六倍最大風半徑(RMW)的區域來研究熱帶氣旋發展的環境條件。
向日葵八號衛星資料分析顯示兩組在臨界時間前48小時內有較顯著差異。具體而言，雲光學厚度(COT)、雲有效半徑(CER)和雲頂高度(CTH)在TS發展組均高於TD消散組，顯示TS發展組有更多水相粒子抬升凝結成冰相粒子，增加的COT表示雲發展得更高且更厚，伴隨強烈上升運動，使較大CER粒子能夠保持在一定高度。隨著臨界時間接近，TS發展組在風暴中心的對流活動更強烈，COT和CTH更高，伴隨較大降雨率，降雨範圍更廣。另外，我們將TS發展組依生成位置分為南海海盆區和西北太平洋海盆區進行區域分析。根據雲微物理特性的結果推測西北太平洋海盆區可能具有較大的雲凝結核，伴隨更強的上升氣流；動力環境場的結果則顯示南海海盆區存在較強的上升速度和低層渦度，更有利颱風發展。此外，西北太平洋海盆區具有較高的降雨率。;Several tropical depressions (TDs) form in the Western North Pacific (WNP) region throughout the year. While some of them intensify into tropical storms (TSs), others eventually dissipate. Therefore, the objective of this study is to analyze the characteristics associated with the development of TDs by investigating cloud microphysics and precipitation properties. The analysis is based on data obtained from the Himawari-8 and Global Precipitation Measurement (GPM) mission satellites. A total of 194 tropical cyclones (TCs) occurring between July 7, 2015, and December 31, 2021, are statistically analyzed in the study. Meanwhile, TCs are classified into two types based on their development: TD-dissipating cases and TS-developing cases. Environmental conditions for TC development are investigated by selecting an area extending six times the radius of maximum wind (RMW) from the storm center.
Analysis of Himawari-8 cloud properties reveals significant distinctions between the cases within 48 hours prior to the critical time. Within 24 hours prior to the critical time, TS-developing cases maintain their intensity, while TD-dissipating cases exhibit a decreasing trend. As the critical time approaches, the cloud optical thickness (COT), the cloud effective radius (CER), and the cloud top height (CTH) increase within 6 RMW, indicating thicker cloud layers and larger cloud droplet size throughout the entire region, with stronger updraft. While approaching the critical time, TS-developing cases display more vigorous convective activity with higher COT and CTH near the storm center, along with higher rain rate and wider precipitation range. To examine regional disparities in TS-developing cases, we divided the WNP region into the South China Sea Basin region and the Western North Pacific Basin region. Our analysis based on Himawari-8 cloud properties suggest that the Western North Pacific Basin region may have larger cloud condensation nuclei, along with more intense upward motion; the results of the dynamic fields reveal a more favorable environment for typhoon development in the South China Sea Basin region, which differs from the previous conclusions. In addition, the Western North Pacific Basin region has higher rainfall rates. |
