摘要
利用线性理论模型进行解析和模拟是大气科学的重要基础研究方法之一,其简单明了,解释了如Rossby波形成等重要的环流现象。近年,有研究(Chenetal.,2001)运用定常线性准地转模型研究副热带高压的形成,在相似加热强迫下,其结果与理论研究和GCM的研究不同。本文运用该模型系统研究了由季风降水产生的潜热加热所激发的副热带定常波的结构特征,以理解其结果与GCM不一致的原因。研究表明基本流对热强迫的定常波的结构有重要的影响:(1)当基本流为东风或为零时,定常波在垂直方向上表现为第一斜压结构,波动振幅随东风的增大而减小;(2)当基本流为西风时,呈现向上的传播特征,振幅随高度的升高而增大。而且存在一个临界风速Uc(约3m/s),此时,波动振幅最强;基本流的平流作用具有非对称性,西风时平流作用远远强于东风。由此揭示了该线性模型解的本质:加热在热源区所激发的经向地转涡度输送必须能够平衡加热的位涡制造和纬向位涡平流;基本流的经向和垂直方向的变化使得气旋和反气旋中心偏向热源中心北侧,并进一步发现当基本流为夏季亚洲季风区纬向平均的纬向风场时,线性模型的解中位于中低层的反气旋中心显著抬升,而不出现在地面上,与完整的大气环流模式的结果接近。说明即使在线性模式中,洋面副高的形成也不能完全用季风潜热加热来解释;另外,静力稳定度对热强迫的副热带环流的影响也很重要,使热源的强迫作用放大。
Simulation and analysis by using linear quasigeostrophic models is one of the important basic methods in the atmospheric field. It is simple and easy to understand and explains some vital phenomena of circulation, such as the formation of Rossby waves. In recent years, the formation of subtropical anticyclones was studied based on the linear stationary quasigeostrophic model （Chen et al., 2001）. The results are different from those from the general circulation model and theoretical studies responding to the similar heating. In this paper, the characteristics of sub- tropical stationary waves forced by the latent heating released from Asia summer monsoon precipitation are studied using a linear quasigeostrophic model in order to understand the reason of the difference. Results show that basic flow is very important to the thermally forced stationary waves. （1） When zonal flow is easterly or at rest, the sta- tionary waves are trapped in the vertical and exhibit a baroclinic structure. The amplitude becomes smaller with the increasing of easterly wind. （2） When zonal flow is westerly, the waves are propagating upward and the amplitude increases with height. There is a critical westerly basic flow Uc （about 3 m/s）. For U=Uc, the amplitude is the strongest. It is also shown that advection is much stronger with westerly basic states than with easterly basic states and shows asymmetry. As a result, the essence of solutions in this linear model is revealed： the meridional geo- strophic vorticity transportation forced in the heating field must be balanced by thermally created potential vorticity and by zonal potential vorticity advection. In addition, it is found that the center of the subtropical circulation will be located on the north of heating area when there is the meridional and vertical shear of the basic flow. It is also found that when the basic zonal flow is the zonal-mean wind of the Asia monsoon area in summer, the center of anticyclone in the lower troposphere lifts significantly instead of appearing at the surface, which is similar to the result of C, CM. Therefore, the formation of surface anticyclone cannot be explained by latent heating totally even if a linear model is use＆ Moreover static stability is also important to the thermally forced subtropical circulation by intensifying the external thermal forcing.
出处
《大气科学》
CSCD
北大核心
2009年第4期868-878,共11页
Chinese Journal of Atmospheric Sciences
基金
国家重点基础研究发展规划项目2006CB403607
国家自然科学基金资助项目40575028
40221503
40523001
关键词
线性准地转模型
潜热加热
副热带环流
纬向平流的非对称性
静力稳定度
linear quasigeostrophic model, latent heating, subtropical circulation, asymmetry of zonal advection, static stability
