MSE Budget Analysis of Strong and Weak MJO Events Using ERA5 and COSMIC RO Data: A Case-to-Case Comparison Study

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Title:	MSE Budget Analysis of Strong and Weak MJO Events Using ERA5 and COSMIC RO Data: A Case-to-Case Comparison Study
Authors:	林淑軒;Lin, Shu-Hsuan
Contributors:	大氣科學學系
Keywords:	馬登－朱利安振盪;Madden-Julian Oscillation
Date:	2022-08-10
Issue Date:	2022-10-04 10:47:56 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究選擇5個Madden-Julian Oscillation (MJO)事件，根據其在MJO index(MJOI)相位圖上之傳播特徵，將其分類成兩種(Type S和 W) MJO事件。前者在整個對流生命中維持一定的對流強度，而後者則是在離開印度洋(IO)地區後便會減弱。透過使用再分析ERA5資料來研究IO地區的濕靜能(MSE)收支及相關降雨趨勢得知，在MJO不同相位中，屬於Type S 的MJO事件皆呈現規律且顯著的充放電過程；相反地，Type W 的事件在特定的物理項及一些相位中，呈現較小的振幅。為更好的量化不同MJO事件的強度及其傳播潛力，我們制定一個新的指數為「recharge-discharge power」(RDP)，其代表gross moist stability (GMS) plane上橢圓所圍繞的面積。結果顯示，RDP指數和MJO的對流強度、東傳能力有正相關，擁有較大對流強度及傳播能力的MJO事件，其RDP值會較大。本研究也嘗試發展了一套使用福爾摩沙衛星無線電掩星衛星(COSMIC)資料的MJO事件監測系統，預期使用此系統來分辨MJO事件強度並在未來發展預報用途。本研究使用客觀分析將level-II資料轉換成level-III。經過確認格點化資料符合在時間及空間上呈現合理的分佈後，我們接著在MSE收支分析及GMS plane中，用COSMIC取代再分析資料，檢視該資料在MSE收支中，其能夠代表對流充放電過程的程度及表現。在熱帶地區，比起福衛三號(COSMIC-1)，福衛七號(COSMIC-2)提供更大量且精細的反演大氣溫度及比濕剖面，更能反應熱帶對流特徵。因此，利用COSMIC-2資料擁有高垂直解析度及近即時資料輸出的特性，我們設計新版本的GMS plane，替換MSE和乾靜能通量成gross moist stratification和gross dry stability來提供即時MJO事件的對流狀態。 ;In this study, five different Madden-Julian Oscillation (MJO) events are chosen and classified into two main groups (Type S and W) by their propagation characteristics as revealed in the MJO index (MJOI) phase diagram. The former shows a strong intensity during the entire life cycle; while the latter tends to decay after leaving the Indian Ocean (IO) region. From the evolution of moist static energy (MSE) budget conducted over the IO region and the associated precipitation change using the ERA5 data, Cases in Type S show a robust recharge-discharge cycle in different phases; in contrast, cases in Type W have a smaller recharge-discharge amplitude in certain terms in some phases. We define an index called “recharge-discharge power” (RDP)—an area enclosed by the elliptical orbiting cycle on the gross moist stability (GMS) plane—to measure the intensity and propagation potential of an MJO event. The result indicates that the RDP index is highly and positively correlated to the intensity of MJO, and an MJO event with a greater RDP index exhibits a greater intensity and propagation potential compared to a smaller one. By comparing strong and weak MJO events, we further develop an MJO monitoring system by using the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Radio Occultation data. As compared with COSMIC-1, COSMIC-2 provides abundant atmospheric temperature and moisture observations, especially in the Tropics. Firstly, we convert level-II COSMIC data into level-III by iterative correction objective analysis for computational purpose. After confirming the gridded data in spatial and temporal characteristic, we replace the reanalysis by gridded COSMIC in MSE budget analysis and GMS plane. Due to high resolution of layers and near-real time output in COSMIC-2, we expect that COSMIC-2 can offer instant temperature and moisture conditions for a new GMS plane using the gross moist stratification and gross dry stability.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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