Scale analysis of equatorial plasma irregularities derived from Swarm constellation

Chao Xiong,Guram N Kervalishvili,Jaeheung Park,Hermann Lühr,Claudia Stolle,Bela G Fejer

doi:10.1186/s40623-016-0502-5

Abstract

In this study, we investigated the scale sizes of equatorial plasma irregularities (EPIs) using measurements from the Swarm satellites during its early mission and final constellation phases. We found that with longitudinal separation between Swarm satellites larger than 0.4°, no significant correlation was found any more. This result suggests that EPI structures include plasma density scale sizes less than 44 km in the zonal direction. During the Swarm earlier mission phase, clearly better EPI correlations are obtained in the northern hemisphere, implying more fragmented irregularities in the southern hemisphere where the ambient magnetic field is low. The previously reported inverted-C shell structure of EPIs is generally confirmed by the Swarm observations in the northern hemisphere, but with various tilt angles. From the Swarm spacecrafts with zonal separations of about 150 km, we conclude that larger zonal scale sizes of irregularities exist during the early evening hours (around 1900 LT).

Highlights

At the low-latitude ionosphere, the equatorial plasma irregularities (EPIs), often called equatorial plasma bubbles (EPBs) or equatorial spread-F (ESF), have been a subject of intense research for several decades
A correlation less than 1.0 between Swarm B/A reveals that the EPI had fine structure with zonal extent less than 0.1° or that the plasma density structure did change within the 27 s leading time between Swarm B/A
The positive values of Δt result from the EPI inverted-C shell structure

Summary

Introduction

At the low-latitude ionosphere, the equatorial plasma irregularities (EPIs), often called equatorial plasma bubbles (EPBs) or equatorial spread-F (ESF), have been a subject of intense research for several decades Their morphology, including the generation and evolution processes, spatial structures, global distribution, as well as their effects on the global navigation satellite system (GNSS) have widely been investigated by ground-based radars and in situ satellite observations (Tsunoda 1980; Huang et al 2001; Burke et al 2004; Kil et al 2004; Su et al 2006; Stolle et al 2006; Yokoyama et al 2007; Xiong et al 2010, 2012; Huang et al 2014; Park et al 2015a). In the meridional (north–south) direction, the 50-Hz magnetic field data from the CHAMP satellite revealed EPI structures with scale size as small as 50 m (Stolle et al 2006)

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