Mesoscale simulations of gravity waves during the 2008–2009 major stratospheric sudden warming

A series of 24 h mesoscale simulations (of 10 km horizontal and 400 m vertical resolution) are performed to examine the characteristics and forcing of gravity waves (GWs) relative to planetary waves (PWs) during the 20082009 major stratospheric sudden warming (SSW). Just prior to SSW occurrence, widespread westward propagating GWs are found along the vortex's edge and associated predominantly with major topographical features and strong near-surface winds. Momentum forcing due to GWs surpasses PW forcing in the upper stratosphere and tends to decelerate the polar westerly jet in excess of 30 m s⁻¹ d⁻¹. With SSW onset, PWs dominate the momentum forcing, providing decelerative effects in excess of 50 m s⁻¹ d⁻¹ throughout the upper polar stratosphere. GWs related to topography become less widespread largely due to incipient wind reversal as the vortex starts to elongate. During the SSW maturation and early recovery, the polar vortex eventually splits and both wave signatures and forcing greatly subside. Nonetheless, during SSW, westward and eastward propagating GWs are found in the polar region and may be generated in situ by flow adjustment processes in the stratosphere or by secondary GW breaking. The simulated large-scale features agree well with those resolved in satellite observations and analysis products.