超长波的不稳定与发展的一个初步研究

A PRELIMINARY STUDY ON THE INSTABILITY AND DEVELOPMENT OF THE ULTRA-LONG WAVES

中文摘要:

      本文在绝热无摩擦的条件下,讨论了超长波的不稳定与发展。超长波不稳定的控制因子有静力稳定度的垂直差异及风的垂直切变。不稳定的出现要求高空静力稳定度要比低空大,平流层满足了这个要求。风的垂直切变愈大则愈不稳定。使扰动场对基本场反馈,求出了基本场的垂直切变与静力稳定度的变化方程。发现,扰动对垂直切变的反馈作用很大,而对静力稳定度则很小。根据d/dt(P+K=0(其中P'与K'分别是一个波长中的扰动位能和扰动动能)的条件,求出了扰动发展到极值的时间和振幅。所得扰动发展的时间和极大振幅与实况较为符合,同时扰动极大振幅对于初值振幅具有准保守性。影响超长波发展的因子除了风的垂直切变与静力稳定度垂直分布的作用外,还有波长。波长的改变对最后所要达到的极大振幅没有影响,而只是波长愈长扰动发展天数愈长。平流层的作用使扰动的振幅低空变小,高空增大。

英文摘要:

      This paper deals with the problem of the instability and development of the ultralong waves in frictionless and adiabatic motion.It is found that the controlling factors on the instability are the vertical distribution of the static stability and the vertical shear of the basic current.The occurrence of the instability requires that the upper layer of the atmosphere possesses higher static stability than the lower layer.The existence of the stratosphere provides this requirement.Further the degree of instability increases with the value of the shear.Taking the considerations of the feedback effect of the disturbances (ultra-long waves） on the basic field,equations concerning the variations of the static stability and the vertical shear of the basic westerlies are derived.From the condition that d/dt(P+K=0 the time required for the unstable disturbance to grow to its maximum intensity and the final amplitude (i.e.the maximum amplitude) are computed.[P'and K'are respectively the eddy potential (including internal) energy and the kinetic energy per wave length.The theoritical findings agree with the observations.It is further found that the final maximum amplitude of an unstable ultra-long wave depends only on the structure of the initial state of the basic field,but not on the initial state of the disturbance.