兩種類型中尺度渦旋Rossby波的相速度及其物理機(jī)制

doi:10.3969/2012jms.00**

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兩種類型中尺度渦旋Rossby波的相速度及其物理機(jī)制
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                        10.3969/2012jms.00**
                    
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中圖分類號(hào):P456
基金項(xiàng)目:國(guó)家自然科學(xué)基金;江蘇省自然科學(xué)基金;江蘇省重點(diǎn)實(shí)驗(yàn)室基金;國(guó)家重點(diǎn)基礎(chǔ)研究發(fā)展計(jì)劃(973計(jì)劃);上海市臺(tái)風(fēng)研究基金

PHASE SPEEDS OF TWO KINDS OF MESO-SCALE VORTEX ROSSBY WAVE AND THEIR PHYSICAL MECHANISMS

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本文使用正壓淺水方程組以及緯向切變基流下二維中尺度橫波型擾動(dòng)的Bouss-inesq近似方程組,分析了這種沿著基本氣流方向傳播的中尺度擾動(dòng)的波動(dòng)傳播物理過(guò)程。研究結(jié)果表明,中尺度渦旋Rossby波劃分為兩種類型。由于緯向基本氣流的方向的二階水平切變或者基本氣流的垂直渦度在南北方向的變化(β*因子)所導(dǎo)致的渦旋Rossby波稱之為第一類渦旋Rossby波(正壓渦旋Rossby波),它產(chǎn)生的根本原因是β*因子的作用。這種第一類渦旋Rossby波相對(duì)于基本氣流-U0是單向傳播的,其傳播方向則與β*因子的正負(fù)符號(hào)有關(guān)?；練饬髟诖怪狈较蛏系娘L(fēng)速切變對(duì)于中尺度橫波型的擾動(dòng)起著不穩(wěn)定的作用。如果考慮基流的二次垂直切變時(shí),可以得到第二類渦旋Rossby波(斜壓渦旋Rossby波)的相速度表達(dá)式,第二類渦旋Rossby波產(chǎn)生的物理根源是基本流場(chǎng)的風(fēng)速-U的二次垂直切變或者基本流場(chǎng)y方向的平均渦度在空間z方向上的不均勻性(亦即β**因子)。第二類渦旋Rossby波相對(duì)于基本氣流-U0也是單向傳播的,其相速度與緯向波數(shù)k有關(guān),能量是頻散的,在緯向x方向存在群速度。在基本流場(chǎng)的風(fēng)速-U存在二次垂直切變時(shí),橫波型不穩(wěn)定可能是混合的渦旋Rossby-重力波的不穩(wěn)定;而當(dāng)基本流場(chǎng)的風(fēng)速-U僅僅存在線性切變,不存在二次垂直切變時(shí),此時(shí)根本不存在渦旋Rossby波,橫波型擾動(dòng)的不穩(wěn)定則僅僅是重力慣性波的不穩(wěn)定。最后利用橫波型擾動(dòng)的總渦度守恒方程對(duì)第二類渦旋Rossby波形成的物理機(jī)制做出了解釋。

Abstract:

In the context of a system of barotropic shallow-water equations and Boussinesq approximate equations for two-dimensional meso-scale transversal wave disturbance in zonally sheared base flow,study is performed of the physical process of the meso disturbance propagation along the flow,indicating that such vortex Rossby waves (VRW) are separated into two kinds.The first kind VRW (the barotropic VRW) is produced owing to the second-order horizontal shear in the flow or due to the meridional change in vertical vorticity of the flow，i.e.，the effect of β* as its central cause.This kind VRW travels unidirectionally with respect to base flow 0,depending on the plus or minus sign of β .The vertical windspeed shear of the base flow causes the transversal disturbance to be unstable.And the consideration of a second-order vertical shear of will lead to the expression for phase speed of VRW of second kind (the baroclinic VRW).This kind VRW has its physical mechanism lying in the second-order vertical shear of wind speed in the base flow or inhomogeneity of y-axis mean vorticity in the z direction,i.e.,the effect of β**.The second kind of VRW propagates unidirectionally with respect to 0,with its phase speed related to zonal wavenumber,its energy is dispersive and group velocity occurs in the x direction.When mean windspeed in the base flow experiences a second-order shear in vertical,the instability of transversal disturbance is likely to be that of mixed VRW and gravity wave.When experiences linear shear with no second-order shear in vertical available,no VRW happens at all,so that in this case the instability of transversal disturbance is that of internal inertial gravity waves only.Finally,the equation of total vorticity conservation for transversal disturbance is used to explain the physical mechanism for generating VRW of second kind.

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沈新勇.兩種類型中尺度渦旋Rossby波的相速度及其物理機(jī)制.氣象科學(xué),2006,(4):355-364 Shen Xinyong. PHASE SPEEDS OF TWO KINDS OF MESO-SCALE VORTEX ROSSBY WAVE AND THEIR PHYSICAL MECHANISMS. Journal of the Meteorological Sciences,2006,(4):355-364

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