A numerical study of the middle-latitude neutral temperature and wind responses to geomagnetic storms in the mesosphere and lower thermosphere region
Abstract
Observations from lidars and satellites have shown that large neutral temperature changes occur in the middle and low latitudes of the mesosphere and lower thermosphere (MLT) region during geomagnetic storms. Here, we undertake first-principles simulations of the MLT temperature and wind response to storms using the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) to elucidate the nature and causes of these changes. Temperatures increased in some places/times and decreased in others. The model captured most of the observed storm-time temperature variations in the MLT region. As the simulation behaves similarly to observations, it provides an opportunity to understand physical processes that drive the observed changes. The origin of these changes is found to be the storm-time variations of the thermospheric wind pattern. Global wind circulation is changed due to enhancements in both the pressure gradients associated with Joule heating-induced temperature increases and ion drag at high latitudes. The upper thermospheric wind changes are greater and move faster toward lower latitudes than those in the MLT region. The disturbance winds are divergent at high latitudes and convergent at middle and low latitudes, which produce upward vertical winds in the high latitudes and downward winds at lower latitudes. The changes in vertical winds in the upper thermosphere are then transmitted into the MLT region. Therefore, storm-time MLT temperature variations at middle latitudes are produced mainly by adiabatic heating/cooling that is associated with vertical winds resulting from general circulation changes, with additional contributions from vertical heat advection.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSA31C3450W
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0340 Middle atmosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3303 Balanced dynamical models;
- ATMOSPHERIC PROCESSESDE: 3332 Mesospheric dynamics;
- ATMOSPHERIC PROCESSES