GPS and in situ Swarm observations of the equatorial plasma density irregularities in the topside ionosphere

Irina Zakharenkova,Elvira Astafyeva,Iurii Cherniak

doi:10.1186/s40623-016-0490-5

Abstract

Here we study the global distribution of the plasma density irregularities in the topside ionosphere by using the concurrent GPS and Langmuir probe measurements onboard the Swarm satellites. We analyze 18 months (from August 2014 till January 2016) of data from Swarm A and B satellites that flew at 460 and 510 km altitude, respectively. To identify the occurrence of the ionospheric irregularities, we have analyzed behavior of two indices ROTI and RODI based on the change rate of total electron content and electron density, respectively. The obtained results demonstrate a high degree of similarities in the occurrence pattern of the seasonal and longitudinal distribution of the topside ionospheric irregularities derived from both types of the satellite observations. Among the seasons with good data coverage, the maximal occurrence rates for the post-sunset equatorial irregularities reached 35–50 % for the September 2014 and March 2015 equinoxes and only 10–15 % for the June 2015 solstice. For the equinox seasons the intense plasma density irregularities were more frequently observed in the Atlantic sector, for the December solstice in the South American–Atlantic sector. The highest occurrence rates for the post-midnight irregularities were observed in African longitudinal sector during the September 2014 equinox and June 2015 solstice. The observed differences in SWA and SWB results could be explained by the longitude/LT separation between satellites, as SWB crossed the same post-sunset sector increasingly later than the SWA did.

Highlights

After recent reentry of the C/NOFS satellite on November 28, 2015, the Swarm becomes the only one satellite mission providing the in situ measurements of the ionospheric plasma density for altitudes below 550 km
The highest occurrence rates for the post-midnight irregularities were observed in the African longitudinal sector during the September 2014 equinox and June 2015 solstice
In this paper, we present first results on the joint comparison of the ionospheric irregularities occurrence detected by two independent instruments onboard the Swarm mission

Summary

Introduction

After recent reentry of the C/NOFS satellite on November 28, 2015, the Swarm becomes the only one satellite mission providing the in situ measurements of the ionospheric plasma density for altitudes below 550 km. In situ plasma probe measurements represent the very important data source for ionosphere research, development and validation of the empirical ionospheric models. Special attention focuses on the plasma density irregularities occurring in the topside ionosphere (above the ionospheric F2 peak), as only in situ measurements onboard low-earth-orbit (LEO) satellites can be used to study the global distribution of these. Statistical distribution of the plasma density irregularities using the in situ measurements has been studied for many years (e.g., Basu et al 1980; Aggson et al 1996; Burke et al 2004; Huang et al 2014). In the conditions of the decrease or lack of the actual in situ data it is important to consider additional information on the properties of the plasma density irregularities, derived from other instruments onboard LEO satellite. Zakharenkova and Astafyeva (2015) proposed an “additional” use of the precise orbit determination

Methods

Results

Conclusion