Statistical Study of Relations Between the Induced Magnetosphere, Ion Composition, and Pressure Balance Boundaries Around Mars Based On MAVEN Observations

Abstract

Direct interaction between the solar wind (SW) and the Martian upper atmosphere forms a characteristic region, called the induced magnetosphere between the magnetosheath and the ionosphere. Since the SW deceleration due to increasing mass loading by heavy ions plays an important role in the induced magnetosphere formation, the ion composition is also expected to change around the induced magnetosphere boundary (IMB). Here we report on relations of the IMB, the ion composition boundary (ICB), and the pressure balance boundary based on a statistical analysis of about 8 months of simultaneous ion, electron, and magnetic field observations by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We chose the period when MAVEN observed the SW directly near its apoapsis to investigate their dependence on SW parameters. Results show that IMBs almost coincide with ICBs on the dayside and locations of all three boundaries are affected by the SW dynamic pressure. A remarkable feature is that all boundaries tend to locate at higher altitudes in the southern hemisphere than in the northern hemisphere on the nightside. This clear geographical asymmetry is permanently seen regardless of locations of the strong crustal B fields in the southern hemisphere, while the boundary locations become higher when the crustal B fields locate on the dayside. On the nightside, IMBs usually locate at higher altitude than ICBs. However, ICBs are likely to be located above IMBs in the nightside, southern, and downward ESW hemisphere when the strong crustal B fields locate on the dayside.

The Effects of Crustal Magnetic Fields and Solar EUV Flux on Ionopause Formation at Mars

“…This behavior is expected when one considers pressure balance across the interface. At Mars, similar trends are found in plasma boundaries such as the bow shock, MPB, ion composition boundary, and pressure balance boundary (Crider et al, ; Edberg et al, ; Gruesbeck et al, ; Halekas et al, ; Matsunaga et al, ; Ramstad et al, ; Vignes et al, ). However, as shown in Figure b, the flaring of the ionopause is much weaker, suggesting that pressure balance may not be the only mechanism that controls the formation of the ionopause at Mars.…”

Oxygen Ion Energization at Mars: Comparison of MAVEN and Mars Express Observations to Global Hybrid Simulation

“…In addition to the induced magnetosphere boundary several boundaries have been defined between the wake and the magnetosheath, which is the region where the shocked solar wind flows downstream of the bow shock (BS). These include the magnetic pileup boundary, the ion composition boundary, the protonopause, the planetopause, and the solar wind dropout boundary (see, e.g., Barabash et al, ; Kallio, ; Matsunaga et al, , and references therein).…”

Ion Composition Boundary Layer Instabilities at Mars

“…Within this layer, the strength of the magnetic field typically increases, its variance decreases, and it assumes a more draped configuration Crider et al, 2004). Over a comparable altitude range (Matsunaga et al, 2017) suprathermal electron fluxes decrease (Acuna, 1998) and the ion composition evolves from one dominated by light solar wind ions to one dominated by heavier ionospheric species (Breus et al, 1991;Halekas et al, 2018;Lundin et al, 1990;Vaisberg, 1992).…”