Numerical simulation of QBO and ENSO phase effect on the propagation of planetary waves and the evolvement of sudden stratospheric warming
V.D. Lifar1, K.A. Didenko1,2, A.V. Koval1,3, T.S. Ermakova1,3
1St. Petersburg State University, St. Petersburg, Russia
2N.V. Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences, Troitsk, Russia
3Russian State Hydrometeorological University, St. Petersburg, Russia
Keywords: numerical simulation, El NiГ±o - Southern Oscillation, quasi-biennial oscillation, planetary wave, sudden stratospheric warming
Abstract
The purpose of the present investigation is to evaluate the effect of tropical oscillations on the polar stratosphere. The influence of the quasi-biennial oscillation (QBO) of the zonal wind in the equatorial stratosphere and the El Niño Southern Oscillation (ENSO) on the dynamic state of the stratosphere in winter and the evolvement of sudden stratospheric warming (SSW) is studied. A number of numerical experiments were carried out using the nonlinear general circulation model of the middle and upper atmosphere (MUAM) for the winter conditions of the Northern Hemisphere (January-February). They made it possible to estimate the sensitivity of the fields of zonal wind, temperature, and geopotential to taking into account certain ENSO and QBO phases in the model. Depending on the combination of phases, the statistics of observed SSWs and their evolution differ. For example, the largest number of SSWs is observed under the combination of El Niño and the easterly QBO phase, while major SSWs are not reproduced by the model under the combination of La Niña and the westerly QBO phase. For combinations of El Niño/easterly QBO, El Niño/westerly QBO, La Niña/easterly QBO, the fields of hydrodynamic parameters were averaged to investigate the characteristic features of the model “climatic" SSWs. It is shown that the largest temperature increase in the stratosphere and cooling in the mesosphere are modeled under El Niño conditions and the eastern phase of QBO, but the wind weakening is maxumal during El Niño and the western phase of QBO. The largest amplitudes of planetary waves are modeled during the QBO eastern phase regardless of the ENSO phase. The results can be used in climate forecasting on time scales from one month to decades.
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