切變基流中赤道Kelvin波及緯向對稱擾動的穩(wěn)定性

doi:10.3969/2012jms.00**

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切變基流中赤道Kelvin波及緯向對稱擾動的穩(wěn)定性
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                        10.3969/2012jms.00**
                    
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中圖分類號:P432
基金項目:江蘇省自然科學基金;國家重點基礎研究發(fā)展計劃(973計劃);國家自然科學基金;南京信息工程大學校科研和教改項目

THE STABILITY OF EQUATORIAL KELVIN WAVE AND ZONAL SYMMETRICAL DISTURBANCES IN SHEAR FLOW

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摘要:

本文使用赤道β平面下的熱帶大氣Boussinesq近似方程組,分析了緯向切變基流中的赤道Kelvin波以及緯向對稱擾動的穩(wěn)定性。研究結果表明,在緯向基本氣流只具有y方向水平切變的情況之下,基本氣流在y方向的切變并不能導致Kelvin波發(fā)生不穩(wěn)定,只能導致不同的緯度上對應于Kelvin波傳播的相速度有所不同。擾動位勢和擾動風速等物理量在y方向的分布特征與基本氣流無關。在只考慮垂直切變基流時,要存在穩(wěn)定的相對于平均基流向東傳播的Kelvin波必須要滿足Richardson數(shù)Ri>2的條件?；練饬髟诖怪狈较虻那凶円膊荒軐е翶el-vin波發(fā)生不穩(wěn)定,只能導致Kelvin波的相速度發(fā)生Doppler頻移效應。擾動位勢以及擾動速度在y方向的分布特征與基本氣流在垂直方向的切變有關。當風的垂直切變大于零時,對流層低層的擾動位勢和擾動速度沿y軸的正反方向衰減較快;而當風的垂直切變小于零時,對流層高層的擾動位勢和擾動速度沿y軸的正反方向衰減較快。對于沿緯圈方向的對稱天氣系統(tǒng),只要風的垂直切變較大,滿足Ri<1時,低緯重力慣性內波一定會發(fā)生不穩(wěn)定。而當基本氣流的垂直切變較小(Ri>1)時,本文則給出了該擾動發(fā)生不穩(wěn)定的判據(jù)條件。只要風的水平切變足夠大,大于某一臨界值(該臨界值與垂直波數(shù)m,β因子,靜力穩(wěn)定度N2以及Richardson數(shù)Ri有關),在赤道y—z平面上的重力慣性內波也會發(fā)生不穩(wěn)定,從而引起這種沿x軸對稱擾動的激發(fā)產生與發(fā)展。

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Using the equatorial β-plane Boussinesq approximate equations for the tropical atmosphere,study is performed of the stability of Kelvin wave and zonal symmetric disturbances in zonal shear flow.Results show that only the meridional horizontal shear,when available in the basic flow,doesn't lead to unsteadiness of Kelvin wave but leads to somewhat differing phase velocity of the wave propagation at different latitudes.The physical variables,e.g.disturbance geopotential and disturbance windspeed ,have their y-direction distributions independent of basic flow.Only with vertical shear flow considered，the Richardson number (Ri>2) must be satisfied to produce stable Kelvin wave propagating east with respect to mean flow.The vertical shear in the basic flow does not lead to the instability of Kelvin wave but to Doppler frequency shifting of its phase velocity.Disturbance geopotential and velocity have their meridional distributions dependent on the vertical shear.For wind vertical shear>0(<0),the lower (higher) troposphere disturbance geopotential and velocity are attenuated swiftly in the meridional direction.For weather systems symmetric about a latitude circle,low-latitude internal inertial gravity wave is bound to display instability as long as wind vertical shear is big enough to meet Ri< 1.The present work presents the criterion of unsteadiness of the disturbance for smaller vertical shear of basic flow (Ri>1).Horizontal windspeed shear,if bigger than a critical value associated with vertical wavenumber m,factor β,hydrostatic stability N2 and Richardson number Ri,leads to instability of equatorial internal inertial gravity wave on the y-z plane,which thus causes zonally symmetric disturbances to emergence and development.

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沈新勇,何金海,蘇銀蘭,周偉燦.切變基流中赤道Kelvin波及緯向對稱擾動的穩(wěn)定性.氣象科學,2006,(6):605-611 Shen Xinyong, He Jinhai, Su Yinlan, Zhou Weican. THE STABILITY OF EQUATORIAL KELVIN WAVE AND ZONAL SYMMETRICAL DISTURBANCES IN SHEAR FLOW. Journal of the Meteorological Sciences,2006,(6):605-611

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收稿日期:2005-08-16
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