Interhemispheric Asymmetry of Large‐Scale Electron Density Gradients in the Polar Cap Ionosphere: UT and Seasonal Variations

Yaqi Jin,Chao Xiong

doi:10.1029/2019ja027601

Abstract

AbstractThe high‐latitude ionosphere is highly dynamical with significant irregularities and density gradients. However, the spatial and temporal distributions of density gradients and irregularities are very different between the Arctic and Antarctic. In this report, we study the interhemispheric asymmetry of the large‐scale (100 km) density gradients in both polar caps. Our results show that density gradients in the Arctic are enhanced during local winter (December solstice) with a peak around 19 UT. The UT and spatial distributions in the Antarctic local winter (June solstice) are similar to the Arctic except that they are reversed by 12 hr, which indicates a mirror symmetry between hemispheres. The 12‐hr difference in the peak density gradients can be explained by the displacements between the geographic and geomagnetic poles. The only asymmetry (anomaly) is the persistence of strong density gradients in the southern polar cap during local summer (December solstice).

Highlights

Ionospheric irregularities can be especially detrimental to satellite‐based communication and positioning systems that use trans‐ionospheric radio signals (Kintner et al, 2007)
We have presented the universal time (UT) and seasonal variations of the electron density and density gradient in the northern and southern polar caps
Due to the solar extreme ultraviolet (EUV) ionization, the electron density in both polar caps is high during equinoxes and local summer and low during local winter

Summary

Introduction

Ionospheric irregularities can be especially detrimental to satellite‐based communication and positioning systems that use trans‐ionospheric radio signals (Kintner et al, 2007). Polar cap patches have been studied using ground‐based measurements such as ionosondes, all‐sky imagers, coherent and incoherent scatter radars, and global positioning system (GPS) receivers (Buchau et al, 1985; Buchau et al, 1988; Carlson et al, 2006; Hosokawa et al, 2009; Rodger & Graham, 1996; Weber et al, 1986). Instruments, it is challenging to study polar cap patches and density gradients in the Antarctic, especially to obtain the long‐term statistics Polar orbiting satellites, such as the Swarm mission, provide an unprecedented opportunity to study electron density gradients in both hemispheres with good spatial coverages. We investigate the interhemispheric asymmetry of the large‐scale density gradient in the polar caps for the first time, and we focus on the seasonal and universal time (UT) variations

Data and Methodology

UT and Seasonal Variations

The Spatial Distribution of Density Gradients

Discussion and Summary