The role of inertial instability and the quasi 2-day wave in coupling wintertime planetary waves with the polar summer mesopause
Abstract
Recent work has documented the link between planetary waves in the winter stratosphere and the occurrence of polar mesospheric clouds (PMCs) through interhemispheric coupling. Breaking planetary waves in the winter hemisphere lead to warming in the low-latitude mesosphere and cooling in the stratosphere. These temperature anomalies lead to a weakening of the summer easterlies in the upper mesosphere and a strengthening of the summer easterlies in the stratosphere. These wind shifts can influence the occurrence of PMCs through a modification of gravity wave forcing in the upper mesosphere and subsequent weakening of the upper branch of the residual circulation. There is also a resulting enhancement to the wind shear near the equatorward flank of the summer jet, leading to enhanced baroclinic instability, and resulting growth of the 2-day wave. The 2-day wave can lead to a decline in PMCs by weakening the residual circulation, and forcing meridional advection and warming of the PMC region. The 2-day wave can also grow as a result of low-latitude inertial instability (negative EPV); inertial instability is associated with strong curvature of the mid-latitude summer easterlies, producing baroclinic and barotropic instability. This work considers inertial instability as a possible link between wintertime planetary waves and the growth of the summertime 2-day wave. Data from the Navy Global Environment Model (NAVGEM) and the Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) instrument are used to diagnose regions of inertial instability, identified as vertically stacked or "pancake" structures in temperature that occur in regions of anomalous EPV. Results suggest that low-latitude inertial instability may have contributed to the growth of the 2-day wave in 2014 which was responsible for the anomalous decline in PMCs in early August.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSA42A..04F
- Keywords:
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- 3334 Middle atmosphere dynamics;
- ATMOSPHERIC PROCESSESDE: 3369 Thermospheric dynamics;
- ATMOSPHERIC PROCESSESDE: 3384 Acoustic-gravity waves;
- ATMOSPHERIC PROCESSESDE: 3389 Tides and planetary waves;
- ATMOSPHERIC PROCESSES