Antarctic gravity wave variations during the 2019 stratospheric sudden warming in GEOS-5

Abstract:

Stratospheric sudden warmings (SSWs) drastically change the temperature and wind in the stratosphere. Consequently background wind variation during SSWs can significantly influence gravity wave (GW) generation and propagation. Observations and high-resolution general circulation models have revealed the enhancement of GWs associated with the location of the polar night jet before the onset of northern SSWs, and reduction of GW activities after SSW onsets (Wang and Alexander, 2009; Wright et al., 2010: Yamashita et al., 2010). However, most previous studies examined Arctic SSWs events, because Antarctic SSWs are very rare.

In September 2019, a minor SSW occurred in the Southern Hemisphere for the first time since 2002. In this study, we examine temporal and spatial variations of Antarctic GW activities during the 2019 SSW simulated by the GEOS-5 FP (Goddard Earth Observing System Model, Version 5, forward process). First, temperature perturbations of gravity waves in the GEOS-5 FP data are compared with the AIRS/Aqua observation. The locations and time variation of gravity waves are very consistent between both data. Next, we investigate the temporal variation of the gravity wave absolute momentum flux before/after the SSW. We find that the zonal mean momentum flux in 50-70°S decreased following the weakened zonal mean zonal wind moving downward (Figure 1). In terms of local spatial variation, GW momentum flux was large around the polar night jet before the SSW onset and decreased after the onset, accompanied by the polar night jet weakening at 10-0.1 hPa. Mountain waves over the Andes above 1 hPa were also suppressed due to the weak zonal wind.