A New Analysis Method for Determining Polar Ionosphere and Upper Atmosphere Characteristics from Esr Data: Illustration with Ipy Period

Abstract

The one-year incoherent scatter (IS) data set recorded at the EISCAT Svalbard Radar (ESR) during the International Polar Year (IPY) is an opportunity for studies on long-term variations in the ionosphere and neutral atmosphere. Such studies place severe requirements on the analysis of any IS observations which result in two major difficulties. First, concerning the ionosphere, the challenge is to make accurate measurements of the temperature profiles in the F₁-region, where the ion composition is changing, highly variable, and unknown. Changes in ion mass and temperature affect the received spectra in almost identical ways, and ambiguities in one present insurmountable difficulties in the determination of the other. The second difficulty, concerning the neutrals, is that it is necessary to separate the contributions from the neutral atmosphere and from frictional heating. In the F₁-region, differential drift induces differential heating of the atomic and molecular ions which can be used to distinguish between frictional and neutral atmosphere coupling. In this paper, we present in detail a method to solve these two difficulties: 13-moment, parallel, two-ion (atomic and molecular) energy equations are used to fit the full IS profile along the magnetic field. The molecular-atomic ion composition transition is assumed to follow an analytical hyperbolic tangent function, and the full altitude profile of the measured ion temperature is then used to fit the desired parameters. The results are validated against simulated data from a numerical model, and then against real measurements. A 36-hour data set was compared with the numerical model TRANSCAR, making some unknowns available from the numerical model (ion composition, frictional heating, neutral temperature), providing a convincing demonstration of the validity of the method. In particular, this “full profile” method is sufficiently robust for routine use, even for periods with relatively high convection electric fields. Finally, the application of the method to the IPY ESR data set is presented and some initial trends are identified.