Atmospheric Dynamical Coupling through Activity Changes of Gravity Waves during Stratospheric Sudden Warming Events

Stratospheric sudden warmings (SSWs) are caused by enhanced planetary waves propagating from the troposphere and bring about spectacular planetary-scale changes in the wintertime stratospheric circulation. The polar vortex is highly distorted and breaks down within a few days and the westerly polar night jet is quickly changed to easterlies with an accompanying large-scale warming of the circumpolar regions. In addition, poleward shifts of the polar night jet core are often observed prior to the occurrence of SSWs; such poleward shifts are known as the 'preconditioning' for SSWs. Thus, dramatic changes of wind and temperature fields during the course of SSWs would widely occur in mid- and high-latitudes of the stratosphere, which could bring about activity changes of gravity waves due to selective damping effects of the background atmosphere. Resultantly, gravity waves propagate vertically with specific phase velocities depending on the background atmospheric condition and may influence the circulation of the Mesosphere and Lower Thermosphere (MLT) region. In this study, observed changes of wind and temperature fields during the course of recent SSW events are shown and possible dynamical coupling processes due to gravity wave changes are discussed.