Estimation of the Contribution of Different Mechanisms to the Phase Evolution of Quasi-Biennial Oscillation Using the Results of Climate Simulation

Abstract

For the evolution equation, a technique is proposed to estimate the contribution of different terms to a phase change during oscillations of different frequencies. The contribution is normalized such that a sum of contributions from all terms amounts to 1. This technique is applied to studying the quasi-biennial oscillation of the wind velocity in the equatorial stratosphere, which is retrieved from data of the 500-year preindustrial experiment using the climate model of the Institute of Numerical Mathematics of the Russian Academy of Sciences. The impacts of the nonorographic and orographic gravity-wave drags, as well as of the advection by a zonally averaged velocity, on the phase change of the model quasi-biennial oscillation are calculated. It is shown that the nonorographic wave drag is the main mechanism responsible for the phase change (impact is 1.58); the vertical advection slows down the phase change (impact is –0.74), while impacts of other terms are small.