The effects of crustal magnetic fields and solar EUV flux on ionopause formation at Mars

TL;DR

This study analyzes 11 years of Mars ionopause data to understand how crustal magnetic fields and solar EUV flux influence its formation and altitude, revealing that strong crustal fields inhibit ionopause development.

Contribution

It provides a comprehensive statistical analysis of ionopause characteristics at Mars and highlights the impact of crustal magnetic fields on ionopause formation.

Findings

Ionopause average altitude is 363 km.

Ionopause altitude varies weakly with solar zenith angle.

Strong crustal fields (>40 nT) prevent ionopause formation.

Abstract

We study the ionopause of Mars using a database of 6,893 ionopause detections obtained over 11 years by the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) experiment. The ionopause, in this work, is defined as a steep density gradient that appears in MARSIS remote sounding ionograms as a horizontal line at frequencies below 0.4 MHz. We find that the ionopause is located on average at an altitude of $363 \pm 65$ km. We also find that the ionopause altitude has a weak dependence on solar zenith angle and varies with the solar extreme ultraviolet (EUV) flux on annual and solar cycle time scales. Furthermore, our results show that very few ionopauses are observed when the crustal field strength at 400 km is greater than 40 nT. The strong crustal fields act as mini-magnetospheres that alter the solar wind interaction and prevent the ionopause from forming.