Response of the Temperature in the Mesosphere and Lower Thermosphere during the Recovery Phase of the Storm

Using Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM), the nature and causes of MLT temperature variations at high latitudes during the 10 September 2005 storm were elucidated, which were caused by Coronal Mass Ejection (CME). At the beginning of the recovery phase of the geomagnetic storm, the temperature decreased in the dusk region but increased in the other regions. As the recovery phase evolved, the temperature decreases at high latitudes disappeared and the temperature increases were distributed throughout the whole high-latitude north hemisphere. The storm-time temperature changes at high latitudes were closely correlated with vertical wind changes. When the vertical wind was upward, the total heating was negative, corresponding to the decreased temperature variations, vice versa. In the thermosphere, radiative cooling, especially NO cooling, was "natural thermostat", which is the most important cooling mechanism. The radiative cooling contributes about 80% temperature reduction due to Joule heating enhancement during the storm. However, the NO radiative cooling has little effect on the temperature changes during the recovery phase of the storm, which was only a tenth of total heating. Therefore, the NO radiative cooling was a minor cause of MLT high-latitude temperature changes during the recovery phase of the storm.