The response of Martian magnetotail to interplanetary coronal mass ejection events: joint observations of Tianwen-1 and MAVEN

The Martian magnetotail serves as an important channel for the escape of planetary ions, with abundant dynamic processes. After Tianwen-1 successfully entered the scientific orbit around Mars, the sun is becoming increasingly active. With the orbital apoapsis ~10,760 km, Tianwen-1 completed its first magnetotail phase from March to July 2022, providing a good opportunity to investigate the response of the Martian far magnetotail to interplanetary coronal mass ejections (ICMEs). We made a preliminary analysis of the dynamic tail under an ICME impact on 16 May 2022, with Tianwen-1 monitoring magnetotail and Mars Atmosphere and Volatile EvolutioN (MAVEN) providing upstream measurements. Based on MAVEN observations, the arrival of the ICME was determined to be around 05:10 UT on 16 May 2022. Subsequently, a significant increase in the energy levels of H⁺ and O⁺ ions was seen when Tianwen-1 entered the magnetotail about one and a half hours later. Tianwen-1 continuously detected a subset of O⁺ ions with energies exceeding 1 keV. Accordingly, the escape rate of O⁺ became ~6.2 times greater during this ICME, and the highest O⁺ enhancement happened between 1 keV and 3 keV. The disturbance lasted 39 hours before returning to a quiet level. Furthermore, we conducted a statistical analysis on the escape rate of O⁺ in the far magnetotail (attitude higher than 2 Mars radius) during 11 ICME events from March to July 2022. The ion loss rates substantially increased during ICME events, especially for O⁺ with energy above several keV. This observation suggests the presence of effective acceleration processes in the Martian tail under ICME conditions.