Determination of neutral density in the upper thermosphere using the EISCAT Svalbard Radar
Dr. Hannah Vickers
The Auroral Observatory
Department of Physics and Technology
University of Tromsø
9037 Tromsø
Norway
Abstract
Global studies of the Earth’s upper thermospheric density are often conducted using satellite drag data, a method which has proven to be a highly effective tool in observing short and long-term changes in the neutral density at a quasi-constant height. These changes are associated with a number of factors that include solar and geomagnetic activity, secular variations in the Earth’s magnetic field and increased greenhouse gas concentration in the lower and middle atmosphere, amongst others. In contrast, incoherent scatter radars probe the ionosphere from bottomside to topside altitudes. Coupling of the ionized and neutral atmosphere through particle collisions therefore permits an indirect study of the neutral atmosphere through measurements of ionospheric plasma parameters. Through special considerations of the ion momentum equation, we utilise a large database of observations made by the EISCAT Svalbard Radar (ESR) during the International Polar Year (IPY) to infer estimates on the atomic oxygen density at altitudes from between 250 to 400 km during intervals of low geomagnetic activity. Our estimates are parameterized according to local magnetic perturbations and by season, and compared with the NRLMSISE-00 neutral atmosphere model. Optimum agreement between MSIS and the radar measurements is found at two heights near to 285 and 350 km, but the model is typically 1.25 times greater at heights near the F region peak and up to 2 times smaller than the ESR estimates at 400 km where the signal to noise ratio of the radar becomes low. In addition we verify the radar technique by comparing with CHAMP satellite measurements at 350 km during intervals when CHAMP passed close to the ESR location. Three examples where both ESR and CHAMP data were available indicate that the CHAMP measurements are within ± 40% of the radar estimates. These early results provide strong support to suggest that incoherent scatter radar measurements may become a very useful alternative for continuous monitoring of the upper thermospheric density for a single location.
Created 2012-05-24 12:10:34 by Mats Holmström Last changed 2012-05-30 13:19:01 by Mats Holmström
