| 摘要: | 對流系統對於全球氣候扮演著重要的角色，除了影響水文循環、地球輻射收支與水氣及化學物質垂直傳輸混合等，而對流系統中的大氣深對流亦常在地面造成豪大雨、強風等劇烈天氣現象，致使快速發展的深對流系統常為災害天氣的主要原因。由於大氣對流生命週期十分短暫且發展快速，因此本研究使用地球同步衛星向日葵八號(Himawari-8)觀測，針對2017年6月於南海與臺灣地區發展中大氣對流雲頂特性進行分析。
利用對流雲頂高度於衛星觀測區間內的改變，可以估算雲頂垂直發展速度，發現其主要集中在0-4 m s -1，於對流系統發展最強時，可達到10 m s -1以上，且當雲頂高度低於10公里時，隨著雲頂高度向上發展垂直速度也增強。此外對流發展時雲光學厚度發展集中在0-20之間，隨著雲頂高度發展，雲光學厚度值分佈減小，南海相較臺灣對流雲更有機會發展大的光學厚度。兩區域雲滴粒徑都主要分佈在20-30微米，其中南海地區當雲頂高度發展尚在8公里以下時，雲滴粒徑分佈相對較大顆。進一步探討雲參數間的關係，雲頂垂直速度越強，對流雲越不易發展大的雲光學厚度，且不利於大顆雲滴生成。
於所區分對流雲發展的三階段中，無論是臺灣或南海地區，在對流肇始後(Post-CI)階段，大的垂直速度分佈頻率最高，此階段是對流發展最強的時候。而在對流雲生成初期，南海與臺灣地區光學厚度值都集中在20以下，至Post-CI 階段，南海相較於臺灣，光學厚度大於30的對流雲發生頻率會較高。此外南海在對流發展初期，相較臺灣地區整體雲滴粒徑較大，而進入Post-CI階段後隨著雲頂高度增加雲滴粒徑減小，而在臺灣地區雲滴粒徑都集中在20-30微米區間，直到Post-CI階段大顆(>60微米)雲滴的出現頻率才增多。
;Convective system plays an important role in the global climate, including hydrological cycle, radiative budget and vertical energy transportation. It is usually associated with severe weather hazards, particularly deep convective clouds. Due to the fast development and short lifecycle, it is hard to understand the characteristics of convections. The research studies development of the deep convective cloud in South China Sea (SCS) and Taiwan during June 2017 from high spatial-temporal geostationary satellite Himawari-8. We track and select convective cases by detecting minimum brightness temperature from 11 µm infrared channel as the cumulus center. Besides, to investigate the difference in the characteristics of the cloud top from generation to mature, we could separate developing convective lifetime into three stages, including Pre-CI, CI and mature stages by using convective initiation signal.
The cloud top vertical velocities (CTW) estimated by calculating the change of the cloud top height (CTH) are found to be clustered 0-4m s -1 and could reach more than 10 m s -1. Besides, the value of CTW tends to increase with height when CTH below 10 km. On the mature stage, no matter in SCS or Taiwan, the frequency of large value of CTW is highest. The cloud optical thickness (COT) is mainly distributed between 0-20, and with the increase of CTH, the higher occurrence frequency shows lower value of COT. Compared in Taiwan, the higher value of COT (> 30) occurs frequently in SCS. Furthermore, the cloud effective radius (Re) is mainly distributed between 20-30 µm. When the CTH is lower than 8 km, the Re in SCS would be larger than in Taiwan, and on mature stage, the Re decreases with development of CTH. In Taiwan, the larger Re more than 60 µm is frequently. Further analysis, the stronger the CTW, it is hard for convective clouds to develop larger COT and RE. |
