Ion composition measurements and modelling at altitudes from 140 to 350 km using EISCAT measurements

A Litvin,W Kofman,B Cabrit

doi:10.1007/s00585-998-1159-6

Abstract

Abstract. This work aims at processing the data of CP1 and CP2 programs of EISCAT ionospheric radar from 1987 to 1994 using the "full profile" method which allows to solve the "temperature-composition" ambiguity problem in the lower F region. The program of data analysis was developed in the CEPHAG in 1995–1996. To improve this program, we implemented another analytical function to model the ion composition profile. This new function better reflects the real profile of the composition. Secondly, we chose the best method to select the initial conditions for the "full profile" procedure. A statistical analysis of the results was made to obtain the averages of various parameters: electron concentration and temperature, ion temperature, composition and bulk velocity. The aim is to obtain models of the parameter behaviour defining the ion composition profiles : z50 (transition altitude between atomic and molecular ions) and dz (width of the profile), for various seasons and for high and low solar activities. These models are then compared to other models. To explain the principal features of parameters z50 and dz, we made an analysis of the processes leading to composition changes and related them to production and electron density profile. A new experimental model of ion composition is now available.Key words. Auroral ionosphere · Ion chemistry and composition · Instruments and techniques · EISCAT

Highlights

The ion composition analysis in the F region is one of the most dicult problems in incoherent-scatter data analysis
The incoherent-scatter spectrum depends on ®ve parameters in this region: ne: electron density, e and i: electron and ion temperature, p: ion composition, vi: ion velocity, but the determination of ®ve parameters simultaneously is very dicult, strongly depending on the signal-tonoise ratio and the method of measurements
We show the results of the analysis of 7 years of EISCAT data

Summary

Introduction

The ion composition analysis in the F region is one of the most dicult problems in incoherent-scatter data analysis. Kofman and 350 km, the transition between molecular and atomic ion composition occurs. The incoherent-scatter spectrum depends on ®ve parameters in this region: ne: electron density, e and i: electron and ion temperature, p: ion composition, vi: ion velocity, but the determination of ®ve parameters simultaneously is very dicult, strongly depending on the signal-tonoise ratio and the method of measurements. For these reasons, one of the parameters, usually the ion composition, is ®xed by the model. This study was started at the beginning of incoherentscatter work by Petit (1963) and Moorcroft (1964) and improved by LathuilleÁ re et al (1983)

Objectives

Findings

Discussion

Conclusion