Pressure and ion composition boundaries at Mars

Abstract

This study analyzes results from a multifluid MHD simulation to investigate the shape and structure of the pressure and composition boundaries at Mars, which can provide physical insight for the observational analysis. These boundaries are examined via the unity contours and gradients of the plasma β, as well as β∗, which includes the dynamic pressure in the numerator, and the ion mass and number density ratios. It is found that unity contours are well aligned with the gradient extrema, indicating that the unity contour is a topological boundary. In addition, these two transitions of pressure and composition are of a thickness of 0.05–0.1 RM near the subsolar region to 1–1.5 RM in the tail. The comparison of the pressure and composition boundaries indicates that the two are very similar and that not only the plasma sheet but also the full volume of the lobes are dominated by planetary ions. It suggests that the tail escape for ions not only concentrates in the central plasma sheet but also the magnetic lobes. It is also worthy pointing out that the ion number density ratio unity contour is found to be systematically smaller than other unity boundaries, which calls for attention when the ion number density is used to identify such boundaries. Finally, the comparison between the boundaries of this study and two analytical fittings is carried out. We found a good agreement with the Vignes fitting, with little flaring in the tail, in contrast to a larger flaring angle from the Trotignon fitting.

Statistical Study of Heavy Ion Outflows From Mars Observed in the Martian‐Induced Magnetotail by MAVEN

“…Using the values observed in +E hemisphere (the top row of columns 2 and 3 in the bottom part of Table ) and those observed in −E hemisphere (the top row of columns 4 and 5 in the bottom part of Table ), median (mean) escape rate of total O is calculated as 2.1 × 10 24 s (4.3 × 10 24 s). Suppose heavy ion outflows in the ion composition boundary are constant in all region, the area of the tail cross section becomes about 4 times larger around x MSO = −1.5 R M in comparison to that of the optical wake region (e.g., Xu et al, ), resulting in 4 times larger escape rate of total O, 8.3 × 10 24 s (1.7 × 10 25 s). Dong et al () showed that although the contributions of polar plumes to total heavy ion outflows change depending on solar EUV, several tens of percent of total heavy ion escapes are plume escape.…”

MAVEN and MEX Multi‐instrument Study of the Dayside of the Martian Induced Magnetospheric Structure Revealed by Pressure Analyses

“…Xu et al () used a Block‐Adaptive Tree Solar wind Roe‐type Upwind Scheme Mars Multifluid magnetohydrodynamic model to study the three‐dimensional shape and structure of the pressure boundaries and the ICB. They found that the thickness of the boundaries are 0.05–0.1 R M (170–340 km) near the subsolar region and 1–1.5 R M (3,396–5,094 km) in the magnetotail.…”

“…They showed that the process of the IMB formation is governed by the solar wind and that the solar wind/ionosphere interface only occasionally could be described with the previously stated definition of the MPB. Xu et al (2016) used a Block-Adaptive Tree Solar wind Roe-type Upwind Scheme Mars Multifluid magnetohydrodynamic model to study the three-dimensional shape and structure of the pressure boundaries and the ICB. They found that the thickness of the boundaries are 0.05-0.1 R M (170-340 km) near the subsolar region and 1-1.5 R M (3,396-5,094 km) in the magnetotail.…”

Ionospheric control of the dawn‐dusk asymmetry of the Mars magnetotail current sheet

“…Similarly, Xu et al . [] examined output from a multifluid MHD simulation of the Mars space environment and found a tail current sheet shift to the + Y direction. On the other hand, the multifluid simulation results presented and discussed in Najib et al .…”