Upstream Proton Cyclotron Waves at Mars During the Passage of ICMEs

Abstract

AbstractThe presence of proton cyclotron waves (PCWs) upstream from Mars indicates picked up protons originating from the Martian extended hydrogen (H) exosphere by the solar wind and loss of H to interplanetary space. The occurrences and properties of PCWs associated with normal solar wind conditions have been extensively investigated since their initial detection about 32 years ago, but little attention has been paid to PCW activity under extreme space weather conditions. Here we characterize PCWs during the passage of interplanetary coronal mass ejections (ICMEs) through the Martian environment using the measurements by the Mars Atmosphere and Volatile EvolutioN spacecraft from December 2014 to February 2019. It is found that PCWs occur more frequently during perihelion periods (Ls = 180°–360°) than during aphelion periods (Ls = 0°–180°) for disturbed times of ICME passage. In the perihelion season, the PCW occurrence rate is increased on average by a factor of about 2 during the ICME phase relative to the pre‐ICME and post‐ICME phases. Moreover, PCWs reveal more pronounced wave characteristics with larger amplitudes, higher ellipticity, and smaller propagation angle with respect to the ambient magnetic field direction during the ICME phase.