On thermonuclear convection: I shellular instability     

Sandip Ghosal  Edward A. Spiegel 《地球物理与天体物理流体动力学》2013,107(1-4):161-178

Abstract

As the sun evolves, a sharp compositional peak of He ³ builds up in the core. Nuclear reactions involving He ³ are very temperature sensitive, as a result, this He ³ layer is susceptible to thermal instability. The small horizontal wavenumber g-modes have large time scales, comparable to the thermal time scale. Using a two-layer model, we find that such “shellular modes” are the most unstable. As a result of nuclear heating, these modes may be excited in the solar core in a shallow layer confined to the He ³ zone. A possible effect of such shellular convection on the solar neutrino problem is discussed. In this paper we discuss the linear theory; the nonlinear effects will be treated in a subsequent paper.  相似文献   

Barotropic unstable modes in zonal and meridional channel on the beta-plane     

Sumito Kobayashi  Satoshi Sakai 《地球物理与天体物理流体动力学》2013,107(1-4):73-103

Abstract

The linear stability of a non-divergent barotropic parallel shear flow in a zonal and a non-zonal channel on the β plane was examined numerically. When the channel is non-zonal, the governing equation is slightly modified from the Orr-Sommerfeld equation. Numerical solutions were obtained by solving the discretized linear perturbation equation as an eigenvalue problem of a matrix. When the channel is zonal and lateral viscosity is neglected the problem is reduced to the ordinary barotropic instability problem described by Kuo's (1949) equation. The discrepancy between the stability properties of westward and eastward flows, which have been indicated by earlier studies, was reconfirmed. It has also been suggested that the unstable modes are closely related to the continuous modes discretized by a finite differential approximation. When the channel is non-zonal, the properties of unstable modes were quite different from those of the zonal problem in that: (1) The phase speed of the unstable modes can exceed the maximum value of the basic flow speed; (2) The unstable modes are not accompanied by their conjugate mode; and (3) The basic flow without an inflection point can be unstable. The dispersion relation and the spatial structure of the unstable modes suggested that, irrespective of the orientation of the channel, they have close relation to the neutral modes (Rossby channel modes) which are the solutions in the absence of a basic shear flow. The features mentioned above are not dependent on whether or not the flow velocity at the boundary is zero.  相似文献   

The instability in relativistic,plane parallel,compressible shear flows     

Sanjiv Kumar 《地球物理与天体物理流体动力学》2013,107(1-4):191-202

Abstract

The growth rates of instabilities in these shear flows are bounded by the rate of shear and the relativistic y factor. It is also shown that (i) the Howard Semi-Circle theorem is still valid, and (ii) the critical layer lies in the flow. Beaming effects are taken into account.  相似文献   

An experimental investigation of spin-up from rest of a stratified fluid     

Jan Bert Flor  John W.M. Bush  Marius Ungarish 《地球物理与天体物理流体动力学》2013,107(4):277-296

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Nonlinear internal waves in the upper atmosphere     

P. Caillol 《地球物理与天体物理流体动力学》2013,107(4):271-308

To investigate the mechanism of mixing in oscillatory doubly diffusive (ODD) convection, we truncate the horizontal modal expansion of the Boussinesq equations to obtain a simplified model of the process. In the astrophysically interesting case with low Prandtl number (traditionally called semiconvection), large-scale shears are generated as in ordinary thermal convection. The interplay between the shear and the oscillatory convection produces intermittent overturning of the fluid with significant mixing. By contrast, in the parameter regime appropriate to sea water, large-scale flows are not generated by the convection. However, if such flows are imposed externally, intermittent overturning with enhanced mixing is observed.  相似文献   

山东地区一次台风降水事件的干侵入特征分析     

刘会荣  李崇银  周育锋 《气候与环境研究》2011,16(3):289-300

利用NCEP/NCAR再分析资料对2008年7月17～21日发生在山东地区的强降水事件进行了分析,发现这次强降水是在中低纬度系统相互作用下产生的.对干侵入特征的分析表明,这次强降水事件中干空气主要以纬向侵入为主,这与济南“7.18”暴雨不同.通过对假相当位温(θx)的诊断分析发现,干空气侵入一方面有利于锋区的形成和维持...  相似文献   

Richardson Number in a Moist Atmosphere and Its Application in the Analysis of Heavy Rainfall Events          下载免费PDF全文

ZHAO Yu  CUI Xiaopeng  GAO Shouting 《Acta Meteorologica Sinica》2010,24(1):95-103

To better describe the stability of a moist atmosphere,a new Richardson number,the Richardson number in a non-uniformly saturated moist atmosphere(Ri~*),is defined in this paper.Ri~* is the same as the Richardson number(Ri) except that the generalized potential temperature introduced by Gao et al.in 2004 is used to calculate the Brunt-Vaisala frequency.Then,with outputs from simulations of two heavy rainfall events,Ri~* is applied to diagnosing instabilities of rainfall areas.The results show that convec...  相似文献   

九华山区下垫面对局地降水的影响分析   总被引：4，自引：1，他引：3  

丁仁海  周后福 《气象》2010,36(3):47-53

利用安徽中尺度自动气象站的探测数据和多年统计数据,对九华山区下垫面影响降水的地理分布及强度进行讨论,分析下垫面物理过程在降水天气中的作用。结果表明:山区的湿热条件及不稳定能量均强于周边地区,非均匀下垫面的热力作用和山区地形作用形成地面中尺度风场辐合线及其所造成的上升运动对低空急流起加强作用,这些均影响强对流天气的形成和发展。山区降水地理分布受地形影响很大,山区的降水量、降水日数及降水强度均明显多于周边丘陵地区,并有迎风坡降水明显及在一定高度内山体越高降水量越大的特点。逐小时地面自动站资料分析对山区强降水的形成、发展和消散具有很好的临近预报指示作用。  相似文献   

2009年5月9—10日华北南部强降水天气分析   总被引：1，自引：0，他引：1  

杨晓霞  周庆亮  郑永光  刘鑫华  周晓霞 《气象》2010,36(6):43-49

应用常规天气图、地面加密降水观测资料、探空资料和NCEP/NCAR 1°×1°再分析资料,对2009年5月9—10日华北南部大范围持续性强降水天气过程进行分析研究。结果表明,强降水是在冷空气与西南暖湿气流交汇的过程中产生的。500 hPa为槽前西南气流,850～700 hPa为东北—西南向切变线,地面冷锋转变为静止锋,之后生成弱的气旋波向东南方向移动消失。大气高温高湿,中层为弱的对流不稳定和对称不稳定。冷空气从底层锲入,一方面与暖湿气流汇合产生辐合上升,另一方面抬升暖湿气流,使上升运动加强,降水增幅。中高层空气暖湿,0℃层较高,以强降水天气为主,伴有雷电。由于暖湿气流较强,冷空气在南下过程中逐渐减弱,速度减慢,冷暖空气在黄河下游长时间对峙,强降水持续时间长。  相似文献   

登陆台风环流内的一次中尺度强对流过程   总被引：2，自引：2，他引：0       下载免费PDF全文

徐文慧  倪允琪 《应用气象学报》2009,20(3):267-275

2005年05号台风“海棠”登陆福建后,在外围云系里有1个明显发展的中尺度对流云团经过温州东部及北部地区,引起了强降水。通过分析这次中尺度对流系统的环流形势,得到该次中尺度对流系统的垂直结构特征,并对中尺度强对流系统的形成和发展机制进行研究。结果表明:台风东南急流在温州附近冷区边缘处低层受地形影响发生强烈辐合引起的垂直上升运动和冷暖空气相汇产生的对流不稳定性是台风环流内中尺度对流系统的主要形成机制;对流系统在暖湿空气和冷空气中心交汇处发展,西北侧的冷空气堆迫使暖湿东南气流沿西北倾斜的等熵面爬升,有利于倾斜对流系统的发展;低层条件不稳定区与中层条件对称不稳定区叠加,产生对流对称不稳定,在湿等熵面倾斜引起的涡旋发展的强迫机制下在中层产生范围较广的倾斜上升对流;由于等熵面的倾斜,大气水平风垂直切变或湿斜压性增加,进一步加强涡度的发展,使得对流系统向西北方向发展;另外,源于东南沿海,由台风东南气流输送的水汽为特大暴雨的产生提供了有利的热力条件。  相似文献