斜压大气波动准共振与中高纬低频振荡

QUAST-RESONANCE OF BAROCLINIC ATMOSPHERIC WAVES AND MIDDLE AND HIGH LATITUDE LOW-FREQUENCY OSCILLATION

从准地转两层模式出发，可能产生两种情况准共振：（１）纯正压波；（２）两个斜压波和一个正压波。本文对（２）求得准共振三波振幅的解析解和波能量变化周期的近似式。此近似式和数值计算结果两者都表明，斜压情况能量变化周期比正压情况更容易趋于准共振频率偏离Δω自身周期，从物理上指出，波的位相与波振幅之间存在着一个反馈机制，由正压波与斜压波之间的慢变相差引起的动能与有效位能的互相转换，形成了正压波和斜压波交替增强和减弱的低频振荡，其振荡周期与上述近似式一致。当Δω～（０．１－０．０２）。（ωｊ）时，平均能量周期为１２－４３ｄ，而当Δω＝０时，平均周期为３６６ｄ．因此，频率偏离Δω出现仍可能是产生料压大气中高纬低频振荡的一种新的重要机制。

rom the quasi-geostrophic two-layer model, the quasi-resonance occurs possibly for two cases:(1) pure barotropic waves 1 (2) two baroclinic waves and one barotropic wave.For case(2), it is the analytic solution of triad amplitude of quasi-resonance and approximate expression for the variation period of wave energy which are found. Both the approximate expression and numerical calculation indicate that for the baroclinic atmosphere the period of energy variaton approaches the period 2 corresponding to the quasi-resonance frequency mismatch △ω itself more easily than for the barotropic atmosphere. It is pointed from physics that there is a feedback mechanism between the phase of wave and wave amplitude,the slowly varying phase difference between the barotropic wave and the baroclinic waves causes the transformation of the kinetic energy and the available potential energy, and formes the low-frequency oscillation alternately strengthening and weakening the barotropic wave and the baroclinic wave,which oscillation period is the same as above approximate formula. When △ω￣(0.1-0. 02)o (ωj),averaged energy period is 12-43 days and when △ω=0,it is 366 days. Therefore, the occurrence of frequency mismatch △ω is also probably a new important mechanism for the formation of middle and high latitude low-frequency in the baroclinic atmosphere.