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

Abstract

Open and draped magnetic field topologies are important at Mars because they can provide ionospheric particles a path to escape to space. Four years of Mars Atmosphere and Volatile EvolutioN data are analyzed in this study, demonstrating that the altitude at which the ionospheric density drops below 10 2 cm −3 is essentially coincident with the altitude down to which open and draped magnetic field lines are observed in the ionosphere. During times of enhanced solar wind dynamic pressure, a greater fraction of the magnetic topology was observed as open or draped (as opposed to closed) above densities of 10 2 cm −3 . The altitudes at which the ionospheric density fell below 10 2 cm −3 , and the magnetic field topology transitioned from closed to open or draped, also decreased during higher dynamic pressure conditions. Times of enhanced solar wind dynamic pressure thus appear to drive greater penetration of draped magnetic field into the ionosphere, enhancing the rate of reconnection between draped and crustal magnetic fields and producing more open field. Such observations may have implications for the long-term evolution of the Martian ionosphere; the historic solar wind is thought to have been denser and faster than present-day conditions, and "quiet time" conditions may have been equivalent to extreme dynamic pressure events today. Depending on past atmospheric conditions at Mars, draped topology may have routinely penetrated deep into the ionosphere, and quiet time rates of ionospheric escape to space may thus have been much greater for early Mars than today.

Formation Mechanisms of the Molecular Ion Polar Plume and Its Contribution to Ion Escape From Mars

“…The localized source region of the CO 2 + plume (Figure 5) suggests that the molecular ion plume is facilitated by deep penetration of the solar wind-induced electric field into the ionosphere, which is caused by strong solar wind dynamic pressure. The deep penetration of the electric field under strong solar wind dynamic pressure conditions inferred by our statistical trajectory tracing (Section 3.2) is consistent with previous studies that show ionospheric compression (Dubinin et al, 2018;Girazian et al, 2019) and penetration of draped field lines into the ionosphere (Fowler et al, 2019;Xu et al, 2018Xu et al, , 2019.…”

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 crustal magnetic fields at Mars are also known to significantly affect the solar wind interaction and the structure of the ionosphere (Andrews et al, ; Brain et al, ; Flynn et al, ; Němec et al, , ; Nagy et al, ; Withers et al, ). Although recent work suggests that magnetic topology plays a significant role (Fowler et al, ), it is still an open question as to how the crustal fields affect the response of the topside ionosphere to variations in upstream solar wind conditions.…”

Mars’ plasma system. Scientific potential of coordinated multipoint missions: “The next generation”

“…Regarding water-species, the solar wind effects on atmospheric loss is beginning to be examined with MGS, Mars Express, and MAVEN, and space weather events have been shown to greatly enhance the escape rate of water-originating species from Mars (e.g., [87,50,33,116,89,88,70,26,85,94,49]). However, in-situ ionospheric observations are limited to a single swath every few hours from these missions.…”

“…These irregularities are characterized by quasi sinusoidal variations in the magnetic field strength at length scales of 5-20 km perpendicular to the local magnetic fields, and accompanied by large variations in the ionospheric electron density. These irregularities are observed primarily in the Martian dynamo region of the ionosphere (∼130 − 170 km altitude) at specific local times, solar zenith angles, and planetary latitudes and longitudes, during conditions when ions are unmagnetized due to frequent collisions with the neutral atmosphere, but electrons remain magnetized [49]. Such irregularities have been studied extensively at Earth since the 1930s [44,72,118] and are generated there primarily by the gradient drift and two stream instabilities at the magnetic equator where the magnetic field is horizontal.…”