# On the Response of Martian Ionosphere to the Passage of a Corotating Interaction Region: MAVEN Observations

## TL;DR

This study investigates how a Corotating Interaction Region (CIR) in June 2015 affected the Martian ionosphere, revealing compression on the dayside and depletion on the nightside linked to solar energetic particles and pickup ions, using MAVEN data.

## Contribution

It provides new insights into the ionospheric response to CIRs at Mars, highlighting the roles of solar energetic particles and pickup ions in ionospheric depletion.

## Key findings

- Dayside ionosphere compressed during peak solar wind pressure.
- Nightside electron density remained depleted longer after CIR passage.
- Enhanced fluxes of suprathermal heavy ions observed in the exosphere.

## Abstract

The response of Martian ionosphere to the passage of Corotating Interaction Region (CIR) of June 2015 is studied using observations from several instruments aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. An intense CIR arrived at Mars on 22 June 2015, during which the upstream solar wind and interplanetary conditions were monitored by the Solar Wind Ion Analyzer (SWIA), Solar Wind Electron Analyzer (SWEA), Magnetometer (MAG), and Solar Energetic Particle (SEP) instruments aboard MAVEN. The CIR event was characterized by enhancements in solar wind density, velocity, and dynamic pressure, and increased & fluctuating interplanetary magnetic field, and was associated with enhanced fluxes of solar energetic particles. The Langmuir Probe and Waves (LPW) instrument onboard MAVEN provided the ionospheric observations such as electron density and electron temperature during this period. The dayside ionosphere is significantly compressed only near the peak of solar wind dynamic pressure enhancement (~14 nPa). In contrast, on the nightside, the electron density remains depleted for a longer period of time. The electron temperatures are also enhanced during the period of electron depletion on the nightside. The STATIC (Suprathermal and Thermal Ion Composition) measurements show enhanced fluxes of suprathermal heavy ions in the Martian exosphere during CIR period, and evidences for enhanced tailward flow of these pickup ions. The analysis suggests that the nightside ionosphere is primarily controlled by the precipitating solar energetic particles and pickup ions transported across the Martian terminator, and depletes significantly when the heavy ion flux in the exosphere enhances.