Numerical Simulation of QBO and ENSO Phase Effect on the Propagation of Planetary Waves and the Evolvement of Sudden Stratospheric Warming

The effects 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) are studied in numerical experiments with the nonlinear general circulation model of the middle and upper atmosphere (MUAM) for winter conditions of the Northern Hemisphere (January–February). The sensitivity of the model fields of zonal wind, temperature, and geopotential to ENSO and QBO phases is estimated. The statistics of observed SSWs and their evolution differ depending on the combination of phases, e.g., the largest number of SSWs is observed under the combination of El Niño and an easterly phase of QBO; major SSWs are not reproduced by the model under the combination of La Niña and a westerly phase of QBO. The fields of hydrodynamic parameters have been averaged for combinations of El Niño/easterly phase of QBO, El Niño/westerly phase of QBO, and La Niña/easterly phase of QBO to analyze the characteristic features of the model “climatic” SSWs. The analysis shows the maximal temperature rise in the stratosphere and cooling in the mesosphere in the model under El Niño and the eastern phase of QBO; wind weakening is maximal under El Niño and the western phase of QBO. The highest planetary wave amplitudes are modeled under easterly QBO phases regardless of the ENSO phase. The results can be used in climate forecasting on time scales from one month to decades.