Comparisons of electron energy deposition derived from observations of lower thermospheric nitric oxide and from X-ray bremsstrahlung measurements

Abstract

[1] Previous studies have shown the connection between electron precipitation and the excess amounts of nitric oxide at auroral latitudes. In this study the electron energy deposition derived from thermospheric nitric oxide (NO) measurements is compared with the electron energy deposition derived from X-ray bremsstrahlung measurements. The electron energy deposition is derived from nitric oxide densities by use of a photochemical model for nitric oxide and is referred to as the modeled energy deposition. The comparisons are made for the beginning of five geomagnetic storms in 1998: 21 March, 2 May, 14 June, 26 June, and 16 July. By using these quite different methods to derive the total electron energy deposition (4–100 keV), the results show that we have a generally good understanding of the physics and chemistry of the energy transfer from electron precipitation in the lower thermosphere. The comparisons also show some discrepancies. The modeled energy deposition is typically larger than the energy deposition derived from X-ray bremsstrahlung in the beginning of the storm period, whereas later on in the storm the energy deposition derived from X-ray measurements is largest. The cases where the modeled energy deposition is largest is probably due to production of NO occurring before the bremsstrahlung measurements. The systematic underestimate of the calculated energy deposition could be due to uncertainties in the reaction rates or in the characteristic electron energy used in the photochemical model. The effects from horizontal neutral wind on the NO gas from the production on the nightside to the observations on the dayside can also be a source of discrepancy.