Abstract
Abstract. The previously reported observation of anomalous eastward gravity wave forcing at mesopause heights around the onset of the January 2013 major sudden stratospheric warming (SSW) over Trondheim, Norway (63° N, 10° E), is placed in a global perspective using Microwave Limb Sounder (MLS) temperature observations from the Aura satellite. It is shown that this anomalous forcing results in a clear cooling over Trondheim about 10 km below mesopause heights. Conversely, near the mesopause itself, where the gravity wave forcing was measured, observations with meteor radar, OH airglow and MLS show no distinct cooling. Polar cap zonal mean temperatures show a similar vertical profile. Longitudinal variability in the high northern-latitude mesosphere and lower thermosphere (MLT) is characterized by a quasi-stationary wave-1 structure, which reverses phase at altitudes below ~ 0.1 hPa. This wave-1 develops prior to the SSW onset, and starts to propagate westward at the SSW onset. The latitudinal pole-to-pole temperature structure associated with the major SSW shows a warming (cooling) in the winter stratosphere (mesosphere) which extends to about 40° N. In the stratosphere, a cooling extending over the equator and far into the summer hemisphere is observed, whereas in the mesosphere an equatorial warming is noted. In the Southern Hemisphere mesosphere, a warm anomaly overlaying a cold anomaly is present, which is shown to propagate downward in time. This observed structure is in accordance with the temperature perturbations predicted by the proposed interhemispheric coupling mechanism for cases of increased winter stratospheric planetary wave activity, of which major SSWs are an extreme case. These results provide observational evidence for the interhemispheric coupling mechanism, and for the wave-mean flow interaction believed to be responsible for the establishment of the anomalies in the summer hemisphere.
Highlights
Sudden stratospheric warmings (SSWs) are dramatic dynamic events that influence the temperature, circulation and chemical composition of the winter polar middle atmosphere (e.g. Labitzke, 1981; Charlton and Polvani, 2007; Chandran et al, 2014; Gerber et al, 2012, and references therein)
The current paper uses Aura Microwave Limb Sounder (MLS) temperature observations to put the observations of de Wit et al (2014b) in a global perspective – de Wit et al showed the zonal wind over Trondheim (63◦ N, 10◦ E) to reverse from eastward to westward from the surface to 100 km around the onset of the major SSW on 7 January 2013, and mesopause gravity waves (GWs) forcing to peak eastward
Mesopause temperature observations obtained using meteor radar, OH airglow and MLS for the same location do not show a clear cooling in relation to the SSW
Summary
Sudden stratospheric warmings (SSWs) are dramatic dynamic events that influence the temperature, circulation and chemical composition of the winter polar middle atmosphere (e.g. Labitzke, 1981; Charlton and Polvani, 2007; Chandran et al, 2014; Gerber et al, 2012, and references therein). Labitzke, 1981) Due to their large effect on stratospheric zonal winds, SSWs are capable of altering filtering conditions for upwardpropagating gravity waves (GWs). Various modelling studies have shown eastward GW forcing anomalies at mesosphere and lower thermosphere (MLT) altitudes in relation to SSWs Yamashita et al, 2010; Chandran et al, 2011, 2014; Limpasuvan et al, 2012), a result that has been confirmed by radar observations of GW forcing at mesopause heights during the 2013 major SSW (de Wit et al, 2014b). Model studies have shown this departure away from climatological wintertime westward GW forcing to be associated with the weakening or reversal of the wintertime residual circulation and associated cooling of the mesosphere during. J. de Wit et al.: Atmospheric coupling during 2013 major SSW
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