Circulation changes in the stratosphere and mesosphere during the stratospheric sudden warming event in January 2009

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Abstract

In this study, general circulation changes are investigated during the stratospheric sudden warming event in January 2009 by the use of Aura Earth Observing System Microwave Limb Sounder observations to show dynamical coupling of stratosphere and mesosphere. It is revealed that the reversal from westerly winds to easterly winds occurred earlier in the mesosphere in comparison with the stratopause level and suggested that the earlier reversal in the mesosphere may be caused by large-scale waves formed in the lower mesosphere due to barotropic and/or baroclinic instability there. Such instability is considered to be brought about by the intensification of the westerly jet with double maxima in the polar night stratosphere and subtropical mesosphere before the warming occurrence. Furthermore, it is shown that an independent meridional circulation cell might be formed by the earlier reversal of zonal winds in the mesosphere.

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