A Comparison of the Location of the Mid‐Latitude Trough and Plasmapause Boundary

J M Weygand,I Zhelavskaya,Y Shprits

doi:10.1029/2020ja028213

Abstract

AbstractWe have compared the location of the mid‐latitude trough observed in two dimensional vertical total electron content (vTEC) maps with four plasmapause boundary models, Radiation Belt Storm Probes (RBSP) observations, and IMAGE extreme ultraviolet (EUV) observations all mapped to the ionosphere pierce point using the Tsyganenko (1996) magnetic field line model. For this study, we examine four events over North America: one just after the October 13, 2012 storm, one during the April 20, 2002 double storm, another during a large substorm on January 26, 2013, and one quiet event on May 19, 2001. We have found that in general, the equatorward edge of the mid‐latitude trough is within several degrees in geographic latitude of the mapped model plasmapause boundary location, the plasmapause boundary identified with IMAGE EUV, and the location identified by the RBSP spacecraft. When the mid‐latitude trough is mapped to the inner magnetosphere, the observed boundary agrees with the plasmapause boundary models within two Earth Radii at nearly all local times in the nightside and the observed mid‐latitude boundary is within the uncertainty of the observations at most local times in the nightside. Furthermore, during dynamic solar wind conditions of April 20, 2002, the mid‐latitude trough observed in the vTEC maps propagates equatorward as the plasmapause boundary identified with IMAGE EUV moves earthward. Our results indicate that the mid‐latitude trough observed within the vTEC maps represents an additional means of identifying the plasmapause boundary location, which could result in improved plasmapause boundary models.

Highlights

The plasmasphere plays an important role in modulating energetic particles fluxes (e.g., Kozyra et al, 1995) and influences the propagation of ULF waves (e.g., Takahashi & Anderson, 1992; Webb & Orr, 1975a, 1975b)
We have compared the location of the mid-latitude trough observed in two dimensional vertical total electron content maps with four plasmapause boundary models, Radiation Belt Storm Probes (RBSP) observations, and IMAGE extreme ultraviolet (EUV) observations all mapped to the ionosphere pierce point using the Tsyganenko (1996) magnetic field line model
We have found that in general, the equatorward edge of the mid-latitude trough is within several degrees in geographic latitude of the mapped model plasmapause boundary location, the plasmapause boundary identified with IMAGE EUV, and the location identified by the RBSP spacecraft

Summary

Introduction

The plasmasphere plays an important role in modulating energetic particles fluxes (e.g., Kozyra et al, 1995) and influences the propagation of ULF waves (e.g., Takahashi & Anderson, 1992; Webb & Orr, 1975a, 1975b). Chen et al (2017) used electron density measurements to find the mid-latitude trough and whistler signals from ELF/VLF observations, to identify the plasmapause where both measurements were performed on the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite They found that the mid-latitude trough was about 2° poleward of the plasmapause ionospheric location (or about 0.5 L further away from the Earth in the magnetosphere) for low values of ap, but the mid-latitude trough was equatorward of the plasmapause location for more active ap conditions. This study presents evidence that vTEC observations of the mid-latitude trough can potentially provide measurements of the plasmapause boundary and can help identify the location of the plasmasphere.

Observations

Discussion and Conclusions

Data Availability Statement