Magnetic Topology Response to the 2003 Halloween ICME Event at Mars

Abstract

Understanding how the Mars plasma environment responds to space weather events provides insights into the early Sun‐Mars interaction and helps constrain the extrapolation of atmospheric loss back in time. The 2003 Halloween interplanetary coronal mass ejection (ICME) event is one of the most extreme space weather events encountered by Mars during the last two decades. Mars Global Surveyor's circular orbit at ∼400 km allows us to observationally study the magnetic topology response to this extreme event globally for the first time. We analyze the suprathermal electron data and magnetic field measurements from Mars Global Surveyor to infer magnetic topology before, during, and after this ICME event and quantify the variation of the topology over both weak and strong crustal regions and correlate the variation with the upstream dynamic pressure. Over weak crustal regions, more draped field lines and fewer closed field lines are observed under high dynamic pressures, implying a deeper interplanetary magnetic field penetration during the ICME event. Over dayside strong crustal regions, the dominant magnetic topology switches from closed field lines during quiet periods to open field lines during disturbed periods, suggesting more reconnection occurring between the crustal magnetic fields and interplanetary magnetic field. This mixed magnetic topological response is consistent with predictions from magnetohydrodynamic simulations for ICME events in previous studies.

Energetic Electron Depletions in the Nightside Martian Upper Atmosphere Revisited

“…Our analysis of the SWEA electron energy spectra, combined with the SWIA‐based estimates of the upstream SW condition, confirms the scenario proposed recently by Weber et al () that under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (see Figures 7–10). Our results, while obtained from a large data set mostly under quiet SW conditions, are also consistent with the reported SW modulation of magnetic connectivity near Mars under extreme SW conditions such as during the passage of an ICME (e.g., Xu et al, , ).…”

“…The SW control of electron depletions is presented in Figure in terms of the distribution of depletions with respect to altitude and SW dynamic pressure, including all SWEA measurements made at SZA>120°. The figure reveals a systematic decrease in the probability of observing electron depletions with increasing SW dynamic pressure, which is an expected trend because under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (e.g., Ma, Fang, Nagy, et al, ; Xu et al, ; Xu et al, ; Weber et al, ). Our result is also fully compatible with the observed SW control of the MGS‐based downward energetic electron flux (e.g., Lillis & Brain, ) and the MAVEN‐based electron impact ionization frequency (Lillis et al, ), both on the nightside of Mars.…”

“…Near strong crustal magnetic anomalies, the preferred formation of closed magnetic loops effectively shields the atmosphere from direct access of SW electrons at all altitudes examined here (e.g., Ma et al, , ). Such a shielding should also be strongly modulated by the upstream SW condition in that under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (e.g., Ma, Fang, Nagy, et al, ; Weber et al, ; Xu et al, , ). In weakly magnetized regions, it is likely that SW electrons are able to precipitate into the atmosphere unhindered, but their intensity is substantially reduced at low altitudes due to energy degradation via inelastic collisions with atmospheric neutrals.…”

The Effects of Solar Wind Dynamic Pressure on the Structure of the Topside Ionosphere of Mars

“…Interpretation of our findings is somewhat limited because MARSIS cannot measure vector components of the magnetic field, nor bulk properties of the topside ionospheric plasma. Nonetheless, it is well known that high solar wind dynamic pressures compress the Martian plasma environment (Crider et al, ; Edberg et al, ; Halekas et al, , ; Ma et al, ; Opgenoorth et al, ), allowing for stronger, and deeper penetrating, draped and open magnetic fields (Crider et al, , ; Fowler et al, ; Jakosky et al, ; Xu et al, , ). In such a scenario, the topside ionosphere can be depleted due to higher ion escape rates, driven by stronger magnetic tension and pressure gradient forces (Cravens et al, ; Halekas et al, ; Wu et al, ), increased pickup ion escape, and enhanced ion outflow.…”

The Penetration of Draped Magnetic Field Into the Martian Upper Ionosphere and Correlations With Upstream Solar Wind Dynamic Pressure

“…Because the upstream solar wind conditions drive the interaction with the Martian obstacle, “extreme” space weather events, such as coronal mass ejections (CMEs) and high pressure pulses from solar wind stream interactions, have been observed to drastically alter the Martian magnetosphere and drive substantial enhancements of ionospheric escape to space (Curry et al, ; Edberg et al, ; Futaana et al, ; Jakosky et al, ; Luhmann et al, ; Lundin et al, ; Ma et al, ; Ma et al, ; Opgenoorth et al, ). Recent studies by Xu et al () and Xu, Fang, et al () investigated the response of magnetic topology driven by the arrival of CMEs at Mars in 2003 and 2017, respectively, showing that draped magnetic field lines were observed at much deeper altitudes in the ionosphere compared to the quiet time conditions prior to the arrival of each CME. The authors postulated that extreme space weather events may thus expose a greater portion of the Martian ionosphere to open and draped field lines, contributing to the previously reported enhancements of ionospheric escape rates in the aforementioned studies.…”