Study On The Response Of Mesosphere-lower Thermosphere High-latitude Temperature To Magnetic Storm

The Mesosphere and lower thermosphere(MLT)is an important region of the Earth’s atmosphere,and its temperature state has a profound effect on the stability of the middle and upper atmosphere.During geomagnetic storms,a large number of particles and energy are poured into the Earth’s upper atmosphere,causing temperature perturbations in the highlatitude MLT region through processes such as Joule heating and thermal convection,etc.The MLT temperature has important effects on the material state,orbital altitude,and flight attitudes of aircraft operating in this region,so the study of MLT temperature perturbations during storms is of great application.However,the storm-time variation of MLT temperature at high latitudes is very drastic,in which the complex physical and chemical processes make the study extremely difficult.The coverage of traditional observations cannot meet the research needs,so it is necessary to combine it with numerical simulation methods to gain a deep understanding of the storm-time perturbation phenomenon of high-latitude MLT temperature.In this paper,we first simulate the September 10-11,2005 geomagnetic storm event using the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model(TIMEGCM),and use the thermodynamic diagnostic analysis module of the model to elucidate the storm-time variation pattern of the temperature in the mesosphere and low thermosphere.Besides,the contribution of each mechanism to the temperature perturbation in different regions was compared.After that,we investigate the variation of the high-latitude temperature in the MLT region observed by the SABER(Sounding of the Atmosphere using Broadband Emission Radiometry)on the TIMED(Thermosphere Ionosphere Mesosphere Energetics and Dynamics)satellite to investigate the difference in the response of highlatitude temperature to two moderate geomagnetic storms with different durations on April 20,2018 and April 10,2022 in the MLT region.Finally,the two events are simulated using TIMEGCM to explore the physical causes of the difference in temperature variation through thermodynamic diagnostic analysis and dynamic diagnostic analysis.The main results and conclusions of this paper are as follows:(1)In the initial and main phases of the geomagnetic storm,a positive temperature perturbation appears on the dusk side and a negative temperature perturbation appears on the dawn side in the high-latitude MLT region.With the development of the magnetic storm,the cooling region gradually disappears and all time zones show warming.These temperature perturbations are dominated by adiabatic heating/cooling,vertical thermal convection,and Joule heating,the specifics of which vary with altitude and latitude.(2)Adiabatic heating/cooling is the main cause of temperature perturbations in the 90 km to 100 km altitude range in the sub-auroral region,and above 105 km vertical convection becomes more important than adiabatic heating/cooling.Within the auroral oval,the contribution of Joule heating is significant and its influence can penetrate below 95 km.Within the auroral oval,Joule heating below 110 km is comparable to that caused by vertical convection and adiabatic heating/cooling,and above 110 km Joule heating becomes more important.Also,horizontal advection contributes to the total heating above 105 km.The situation in the polar cap region is similar to that in the sub-auroral region,although horizontal advection also contributes to the total heating rate in the MLT region,and its contribution becomes even larger than that of adiabatic heating/cooling above 105 km.In addition,other heating and cooling processes do not vary much during the storm and do not contribute significantly to the temperature perturbation.(3)The temperature increase is stronger in the high-latitude MLT region during long events compared to magnetic storms with larger Kp maximum but shorter durations.The adiabatic heating/cooling and vertical thermal convection responsible for this difference in temperature increase are caused by downward vertical winds of different velocities.(4)More particles and energy are input to the Earth’s atmosphere in geomagnetic storm events with longer duration for large Kp values,resulting in stronger ion drag and pressure gradient forces in the lower thermosphere.Then,the faster horizontal winds near 130 km in longer duration event cause greater horizontal wind dispersion in this layer and produce faster downward vertical winds in the same pressure level.This pulls the vertical winds at lower altitudes and eventually leads to stronger vertical wind disturbances below 110 km.