Distinct Propagating Behaviors of Madden-Julian Oscillation over Indian Ocean and Maritime Continent

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题名:	Distinct Propagating Behaviors of Madden-Julian Oscillation over Indian Ocean and Maritime Continent
作者:	蔡雨虔;Tsai, Yu-Cian
贡献者:	大氣科學學系
关键词:	馬登－朱利安振盪;Madden-Julian Oscillation
日期:	2021-07-15
上传时间:	2021-12-07 11:06:18 (UTC+8)
出版者:	國立中央大學
摘要:	本研究探討Madden-Julian Oscillation（MJO）在暖池地區（15°N -15°S, 60-180°E）上的不同傳播行為，並且著重在北半球冬季（11月至4月）的印度洋（IO）和海洋大陸（MC）區域。透過使用ERA-Interim再分析資料和高解析度大氣模式（HiRAM）產出的850百帕緯向風（u850）、200百帕緯向風（u200）、外逸長波輻射（OLR）場，配合多重經驗正交函數（EOF）分析的主分量1（PC1）和主分量2（PC2）時間序列將 MJO 事件分類為向東衰減（ED）和向東傳播（EP）類型，後者能進一步分為強傳播（SP）和弱傳播（WP）兩種類型。本研究主要內容分為兩大章，第一章研究利用再分析資料檢驗MJO東傳和維持的物理機制。與 ED MJO事件相比，EP MJO事件產生了更強的深對流以及顯著的第二斜壓模結構，特別是在海洋大陸的發展階段。此外，在較強的初始對流之後伴隨著較慢的MJO相速度特徵。濕靜能（MSE）收支分析表明水平平流的經向分量對促進MJO傳播至關重要。大氣淨輻射和表面熱通量在提供能量以維持MJO對流方面也起著關鍵作用。另一方面，標轉化的粗濕穩定度（NGMS）平面分析呈現各種MJO事件中的充電–放電和濕化–乾化（RDMD）過程。第二章研究透過水平解析度約25公里的HiRAM 模式探討全球暖化下EP和ED MJO事件的變化。在RCP8.5全球變暖情景下，MJO有更快的傳播相速與更短的週期為特徵。此外，在 HiRAM 預測（2076-2100）中，EP MJO事件的數量略有減少，而ED MJO事件的數量顯著增加，這意味著在暖化下，全球MJO的活動正在減少。垂直速度的空間剖面隨時間變化進一步表明，IO區域中的MJO對流結構將會隨著暖化而加深，特別是在EP MJO事件中。隨著臨界NGMS的下降，RDMD過程變得更加激烈，這說明需要更多的能量輸入才能在全球暖化下產生相同強度的對流。 ;This study investigates the distinct behaviors of Madden-Julian Oscillation (MJO) propagation over the warm pool region (15°N -15°S, 60-180°E), focusing on the Indian Ocean (IO) and Maritime Continent (MC) during the boreal winter (November – April). The multivariate EOF PC1 and PC2 time series of u850, u200, OLR fields from ERA-Interim reanalysis and High-Resolution Atmospheric Model (HiRAM) data are utilized to categorize MJO events into Eastward Decaying (ED) and Eastward Propagating (EP) types, with the latter further dividing into two subtypes of strong propagating (SP) and weak propagating (WP) events. Major contents of this study are divided into two Chapters. In Chapter 1, we examine the physical mechanism for MJO eastward propagation and maintenance with reanalysis data. The EP MJO events generate a more robust deep convective structure along with a significant second baroclinic structure, particularly during the developing phase over the Maritime continent compared to the ED MJO events. In addition, a slower MJO phase speed is identified following stronger initial convection. The moist static energy (MSE) budget analysis demonstrates that the horizontal MSE advection′s meridional component is crucial to promoting MJO propagation. Atmospheric net radiation and surface heat fluxes also play a critical role in providing energy to maintain the MJO convection. On the other hand, the Normalized Gross Moist Stability (NGMS) plane analysis nicely pictures the recharging-discharging and moistening-drying (RDMD) processes in all kinds of MJO events. In Chapter 2, we examine the potential changes of EP and ED MJO events under global warming based on two time-sliced HiRAM simulations with about 25-km horizontal resolution. Faster phase speed is distinguished by shortened MJO period under the RCP8.5 global warming scenario. Furthermore, the number of EP MJO events decreases slightly, whereas the number of ED MJO events increases significantly in the HiRAM projection (2076-2100), implying declining MJO activities around the globe in a warming world. The time-height diagram of omega further suggests that the MJO convection in the IO domain is projected to be deeper under global warming, especially for the EP MJO events. The RDMD processes turn more drastic with a declined critical NGMS, implying that more energy inputs are required to generate the same intensity of convection under global warming.
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