长期天气过程中的长波不稳定問題的探討

本文中采用二层线性模式讨论了地面摩擦,水平热量交换和动量交换,以及长波辐射冷却等因子对长波稳定状况的影响.并且给出了相应的温压场结构,由理论上证实了当温度波还落后于气压波时,运动就已经开始阻尼的这个事实.

A STUDY FOR THE INSTABILITY OF LONG WAVE IN THE LONG-PERIOD WEATHER PROCESS

In the long-period numerical forcast models, many factors, such as non-adiabatic heating and friction, must be considered. The object of this paper is to study the stability of long wave under the influence of these factors. A two-level quasi-geostrophic model including the effect of non-adiabatic heating, friction and horizontal austausch （1）-（3） is used. The instability criterion is given as （10）. In the case of baroclinic atmosphere without these factors the criterion agrees with that of Phillips'（fig. 1）. It is found that in barotropic atmosphere the friction and horizontal austausch are purely damping factors. In baroclinic atmosphere it is, however, not so simple. With the parameter A_T=A_v=0.00213 arc² day^-1,k=0.26 day^-1,ε=1.05 arc^-2 day^-1, A₁²=30.4 arc^-2, the curves of stability criterion are given in fig. 2. We notice in the figure that for sufficiently short wave or for small wind shear, these parameters are damping factors; but for long waves （m, n<3） the minimum baroclinity for initia'e instability is smaller than that for the case without these factors. Finally, the structure of the unstable wave.is shown in fig. 4a-b. Fig. 4a is without damping factors and the other is with these factors under the same baroclinity. It may be seen that these factors decrease the instability. In the case without damping factors the disturbance starts to damp when the temperature wave and pressure wave are in phase, but in the case with damping factors the disturbance starts to damp when the phase of temperature wave is still left behind the pressure wave （fig. 4c）. This is because when the phase of temperature wave is left behind the pressure wave, there is release of potential energy and this energy is used to compensate the frictional loss.