Sudden stratospheric warming effects on the light species and mass density of the thermosphere
Abstract
It is now widely established that sudden stratospheric warmings (SSWs) have a profound effect on the thermosphere-ionosphere (TI) system. Considerable progress has been made in monitoring, measuring, and modeling SSW effects on TI density and composition. However, the mechanisms responsible for driving the observed thermospheric mass density reduction during an SSW remain poorly understood. Since thermospheric mass density is determined by both thermospheric temperature and composition there are four mechanisms that could be responsible for driving upper thermospheric mass density reductions during an SSW: variations in thermospheric temperature, the mean meridional circulation, eddy diffusivity, and large-scale lower atmospheric wave forcing. We performed numerical experiments using the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) nudged by Navy Global Environmental Model a high-altitude version (NAVGEM-HA) analyses in the stratosphere and mesosphere, to quantify the relative contributions of these different mechanisms. The simulations cover the northern winter periods of 2012-2013, in which a major SSW occurred, and 2013-2014, in which a major SSW did not occur, assuming constant solar and geomagnetically-quiet conditions. Calculating the differences between the pre-SSW and SSW state in 2012-2013 northern winter and comparing these differences to the same time periods in the 2013-2014 northern winter period, allows us to separate out the seasonal versus the SSW-specific effects on the winter abundance of atomic oxygen (O), helium (He), atomic hydrogen (H), and thus thermospheric mass density. Prominent initial results to emerge from this study include: (1) A net reduction in the overall high northern latitude abundance of O, He, and H during the 2013 SSW event; (2) SSW driven differences in the zonal-mean thermospheric temperature and the thermospheric mean meridional circulation are small. These preliminary results, accompanied with previous research, suggest enhancements in large-scale lower atmospheric wave forcing and associated enhanced thermospheric mixing is the prominent mechanism responsible for reductions in O, He, H, and thermospheric mass density during an SSW event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSA11A..04J
- Keywords:
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- 0355 Thermosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0358 Thermosphere: energy deposition;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3369 Thermospheric dynamics;
- ATMOSPHERIC PROCESSES;
- 7949 Ionospheric storms;
- SPACE WEATHER