The Latitudinal and Longitudinal Variations of the Thermospheric Density Caused by Aurora Heating

Abstract:

We use thermospheric mass densities measured by the accelerometers on satellites of GRACE at ~480 km and CHAMP at ~380 km from 2002–2010 to study the longitudinal and latitudinal distribution of the diurnally averaged thermospheric mass density. The result shows that there are strong longitude variations in the diurnally averaged thermospheric mass density. These variations are global and have the similar characteristics at the two heights under geomagnetically quiet conditions (Ap<10). The largest relative longitudinal changes of the diurnally averaged thermospheric mass density occur at high latitudes from October to February in the Northern Hemisphere and from March to September in the Southern Hemisphere. The positive density peaks locate always near the magnetic poles. The high density regions extend toward lower latitudes and even into the opposite hemisphere. This extension appears to be tilted westward, but mostly is confined to the longitudes where the magnetic poles are located. Thus, the relative longitudinal changes of the diurnally averaged thermospheric mass density have strong seasonal variations and show an annual oscillation at high and middle latitudes but a semiannual oscillation around the equator. Our results suggest that heating of the magnetospheric origin in the auroral region is most likely the cause of these observed longitudinal and latitudinal structures. Our results also show that the relative longitude variation of the diurnally averaged thermospheric mass density is hemispherically asymmetric and more pronounced in the Southern Hemisphere. To check how deep the auroral heating can affect the atmosphere, we analyze the diurnally averaged temperature observed by TIMED/SABER and MIPAS. Results indicate that there are similar structure in the lower thermosphere and the impact of auroral heating on the thermodynamics of the neutral atmosphere can penetrate down to about 105 km under geomagnetically quiet conditions.