熱源驅動Gill模型解與熱帶年際震盪的比較;An evaluation of tropical interannual circulation as heat-induced solution by Gill model

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Title:	熱源驅動Gill模型解與熱帶年際震盪的比較;An evaluation of tropical interannual circulation as heat-induced solution by Gill model
Authors:	郭品秀;Kuo,Pin-Hsiu
Contributors:	大氣物理研究所
Keywords:	Gill模式;熱帶年際震盪;熱源驅動;Gill model;tropical interannual circulation;heat-induced
Date:	2015-08-31
Issue Date:	2015-09-23 10:12:00 (UTC+8)
Publisher:	國立中央大學
Abstract:	Gill (1980)所提出的簡單模式，被廣泛的用來解釋熱帶大氣在非絕熱加熱下的強迫反應。此模式也被與簡單的海洋模式耦合，廣泛的用在聖嬰現象的研究。但Gill的簡單模式是否足以解釋觀測的流場、質量場與熱源等的年際變化，是我們所好奇的。因此本研究應用GPCP v2.2月平均降水、輻射資料以及乾位能對流項導出伴隨El Nino演化的大氣熱源項，並依據拋物柱面函數將熱源分解成對稱及反對稱於赤道的分量，以Gill模式計算出風場及重力位高度，並與ERA-interim中對應的風場與重力位結果進行比較，據以量化熱帶大氣（對稱、反對稱結構）熱源對自由大氣環流的影響。以1997年12月為例，大氣的風與質量距平場的第一斜壓分量顯示為對稱赤道的結構。若僅考慮降水對稱結構分量為熱源，代入模式所得解為對稱赤道的南北氣旋環流，其位置跟觀測結果相比偏西且向高緯度擴張，若加入降水在反對稱結構分量，模式解與觀測特性差異更大。接著我們將乾位能對流項視為熱源，發現可以增強對稱赤道的熱源強度、減少熱源的不對稱性，導致模式對稱赤道解的強度增強，使模式環流更接近觀測場的量值與局限熱帶的空間分佈。至於輻射項的作用相較於前兩者來說值小很多，影響較小。上述模式與觀測場的比較，顯示在聖嬰最強的冬季，降水與海溫距平高溫區互相對應，主要分佈於中部及東太平洋赤道區，但第一斜壓環流為對稱赤道的兩個氣旋環流，模式解偏弱約50%，熱源以西的兩個氣旋環流偏西，熱源以東的東風過強等。這樣的情形可能與平流項的忽略、模式的損耗項、熱源的垂直分佈、由邊界層向上激發的大氣剩餘反應均有相關；這些部分也顯示Gill 模式過於簡化的特徵。 ;For an equilibrium adiabatic atmosphere and rest basic state, the shallow water model provides a fundamental framework for studying tropical waves. Using such a model on the equatorial beta plane, analytic solution for free equatorial waves can be derived. (Matsuno 1966; Lindzen 1967) Then, Gill (1980) designed a simple model to show solutions for steady tropical motion forced by imposed heating to elucidate basic features of the response of tropical atmosphere to diabatic heating. Several simple atmospheric models were developed later for simulating atmospheric response to SST anomalies after Matsuno and Gill, e.g. Lindzen and Nigam (1987) ; Wang and Li (1992). Observation data can be used to explore the forced response by tropical heating, e.g. to evaluate tropical interannual circulation in free atmosphere in response to perturbation condensational heating in Gill model. We used ECWRF Interim data U,V,ϕ as the first baroclinic mode, and used GPCP perturbation precipitation, -ω ̅ (∂s^′)/∂p term, and perturbation radiation term of 1997 December as heating in free atmosphere. We put these heating in the function of Gill model, and estimate the circulation with the observation first baroclinic mode. Then we find that if we only use perturbation condensational heating on Gill model, the symmetric features Rossby wave spread to the high latitude, and the simulation would be similar to the observation when we combine the -ω ̅ (∂s^′)/∂p term with perturbation condensational heating. -ω ̅ (∂s^′)/∂p is important to let the heating become more symmetrical, and make the symmetric result of circulation become similar to the observation for putting the center of Rossby wave closer to the equator. Its asymmetric result also make the features of circulation more similar to the observation though the value is 0.2 times to the perturbation condensational heating. And the radiation term is an important part of the heating in mean flow, however its influence in eddy is much smaller than others that can be ignored.
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