DYNAMO期間，季內震盪之濕化過程診斷

Abstract

在本研究中，利用熱帶季內震盪觀測實驗 Dynamics of Madden Julian Oscillation (DYNAMO) 期間，所搜集的探空資料、經過探空同化的作業用網格資料以及衛星資料等，對於季內震盪(MJOs)低層大氣濕化過程進行探討。對於MJOs的濕化過程，我們利用時間尺度分離的水氣方程，與季內尺度(intraseasonal)的水氣趨勢項(tendency term)和水氣異常(moisture anomaly)求取內積，並利用相關係數探討在MJOs不同相位時，各種濕化機制所扮演角色。在研究的結果顯示，背景場與季內震盪的水氣和風場交互作用，是促使MJOs水氣移動以及成長的主要來源，同時對流貢獻(-Q2)則為主要的水氣耗散項 。更進一步將MJO生命期分成四個階段：對流抑制相位(suppressed phase) 、對流成長相位(cloud developing phase) 、 對流相位(convective phase) 、對流消散相位(decaying phase)，我們發現十月份 (MJO1) 與十一月份的MJO(MJO2)在對流抑制相位到對流成長相位這段過程(pre-moistening stage)，呈現不同特徵 。在MJO1，背景場的沉降作用限制了對流的發展，Q2呈現負值代表透過海面蒸發以及非降水性淺對流再蒸發影響濕化低層大氣；而在MJO2，背景場的上升運動，使得對流活動相對活躍，伴隨的Q2呈現正值，顯示對流降水有效的移除大氣中的水氣。這個結果也指出，低頻系統(如：季節變化或年際變化)對於MJO生成都有顯著影響。而先前研究所注重的低層水氣輻合則在對流成長相位較為顯著；除此之外由天氣尺度(synoptic eddies)所貢獻的水氣平流項，則為水氣混合擴散的效果，此項在MJO1 pre-moistening為濕化低層大氣效果，在ＭJO2則為耗散水氣效果。

Low-tropospheric (1000~700 hPa) moistening processes of the two Madden-Julian Oscillations (MJOs) over the Indian Ocean during Dynamics of the MJO (DYNAMO) are investigated by using soundings, operational assimilation and satellite data. Through the life cycles, the moistening processes responsible for MJO evolution is investigated by projecting the scale-separated moisture budget terms onto intraseasonal moisture anomaly and its time tendency change and by checking their correlation over their life cycles using time-decomposed wind and moisture fields. Results indicate that broad-scale advection by low-frequency and MJO flow and moisture fields are dominant moisture sources, while residual of moisture budget (−Q2) as dominant sink contributing to tendency term (propagation) and intaseasonal moisture anomaly (growth and decay). Dividing their life cycles into four phases (suppressed, cloud developing, convective, and decaying phase), the two MJOs exhibit different budget balances in pre-moistening stage from the suppressed phase to cloud developing phase when low-frequency vertical motion is downward in MJO1 but upward in MJO2. The corresponding drying and moistening are balanced by negative Q2 (re-evaporation in non-raining cloud) in MJO1 and positive Q2 in MJO2. The result implies that seasonal cycle and interannual oscillations can affect the initiation of MJOs. The pre-moistening in the low-troposphere by boundary-layer moisture convergence leading the deep convection is observed but only in the cloud developing to convective phase of MJOs. Nonlinear moisture advection by synoptic disturbances and by MJOs always acts as diffusive terms. They are dominant moisture sources (sinks) in the suppress phase of MJO1 (MJO2).