Case studies of the mesospheric response to recent minor, major, and extended stratospheric warmings

Abstract

[1] We have studied the mesospheric response to two recent stratospheric warmings by performing short-term forecasts at medium (1.5°) and high (0.5°) spatial resolution under different gravity wave drag (GWD) scenarios. We validated our models with our highaltitude analysis that extends from 0 to 90 km. For the minor warming of January 2008, reduced upper-level orographic GWD weakened the downward residual circulation and cooled the mesosphere. Parameterized nonorographic GWD increased the simulated mesospheric cooling. For the prolonged major warming of 2006, heavily attenuated orographic GWD led to pronounced cooling near 50 km. During the extended phase of this event, an unusually strong westerly polar vortex reformed in the lower mesosphere, which allowed westward propagating nonorographic gravity waves to reach the mesosphere and break, with net westward accelerations of over 50 m s. This, in turn, forced a strong residual circulation, yielding descent velocities over 2 cm s −1 between 65°N and 85°N, consistent with previous reports of enhanced downward transport of trace constituents. The resulting adiabatic heating, as evidenced by the unusually vertically displaced stratopause at 80 km, is likely a direct consequence of this enhanced gravity wave driven descent. High-resolution simulations without parameterized GWD were closer to the analysis than medium-resolution simulations with parameterized orographic GWD only, but still did not fully simulate the mesospheric thermal response. Specifically, the 80 km temperature enhancement was still underestimated in these simulations. This suggests that higher spatial resolution is needed to adequately resolve extratropical gravity wave momentum fluxes.

Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings

“…Also the mesosphere (e.g., Labitzke, 1972;Jacobi et al, 2003;Siskind et al, 2005Siskind et al, , 2010Hoffmann et al, 2007;Yamashita et al, 2013;Zülicke and Becker, 2013), and even the thermosphere/ionosphere are affected (e.g., Goncharenko and Zhang, 2008;Fuller-Rowell et al, 2010;Yigit et al, 2014). The selective filtering of gravity waves by the anomalous winds during (major) SSWs is an important mechanism in these vertical influences.…”

The Antarctic ozone hole during 2010

“…In the Modern Era Retrospective-reanalysis for Research and Applications (MERRA) (Reinecker et al 2011) native resolution product, the zonal average zonal balanced winds above 65 km at 69°S showed a pronounced reduction coincident with the July-August stratospheric warming (not shown). Siskind et al (2010), has shown in a model study that mesospheric cooling and zonal wind reduction accompanying stratospheric warmings are potentially produced by a reduction of the residual downward circulation in the mesosphere due to stratospheric critical level filtering of orographic gravity waves.…”

On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016

“…Smith (1997) found that the first two mechanisms operate, however, the one that dominates depends on how favorable the conditions are in the middle atmosphere for vertical propagation. The third mechanism is well-known for the in situ generation of the quasi-2-day wave (e.g., Ern et al, 2013).…”

“…The third mechanism is well-known for the in situ generation of the quasi-2-day wave (e.g., Ern et al, 2013). A model study by Smith (2003) showed that vertical propagation of SPW dominates up to the lower mesosphere while in situ GW-generated SPWs dominate in the upper mesosphere. This result was confirmed by Lieberman et al (2013) using satellite observations.…”

“…There are three possible mechanisms for the occurrence of SPWs in the mesosphere: (1) the stratospheric SPWs propagate vertically into the upper mesosphere, (2) the SPWs are generated in situ by breaking or dissipation of gravity waves (GWs) that were filtered in a longitudinally variable fashion in the stratosphere by SPWs (e.g., Holton, 1984;Smith, 2003;Lieberman et al, 2013) or (3) by barotropic and/or baroclinic instabilities (e.g., Siskind et al, 2010). Smith (1997) found that the first two mechanisms operate, however, the one that dominates depends on how favorable the conditions are in the middle atmosphere for vertical propagation.…”