The roles of planetary and gravity waves during a major stratospheric sudden warming as characterized in WACCM

Abstract

The roles of planetary waves (PWs) and gravity waves (GWs) are examined during a realistic major stratospheric sudden warming (SSW), simulated in the National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM). This major SSW event is characterized by a well-separated polar stratopause during a wind-reversal period. Formed by adiabatic warming induced by westward GW drag, the early-winter stratopause layer appears at its climatological level. With the incipient wind reversal and SSW onset, this layer plunges ∼20km in time, as the amplified PW interacts with the mean flow. The SSW recovery starts in the upper mesosphere as GW drag becomes eastward due to the filtering effects of the underlying wind. During this recovery, the stratopause reforms at an elevated altitude due to adiabatic warming induced by strong upper mesospheric PW forcing. Intensified downward motion from the mesosphere then ensues as the stratopause descends toward its climatological position.