Effect of solar wind density and velocity on the subsolar standoff distance of the Martian magnetic pileup boundary

Abstract

Using a 3D multispecies magnetohydrodynamic model, we investigated the effect of the solar wind dynamic pressure (Pd) with different densities and velocities on the subsolar standoff distance (r0) of the Martian magnetic pileup boundary (MPB). We fixed the solar maximum condition, the strongest crustal field located in the dayside region, and the Parker spiral interplanetary magnetic field at Mars. We simulated 35 cases with a Pd range of 0.1494 to 7.323 nPa (solar wind number density n ∈ [1, 9] cm−3, and solar wind velocity V ∈ [−258, −1344] km s−1). The main results are as follows. (1) r0 decreases with increasing Pd according to the power-law relations. For the same Pd, a higher solar wind velocity (lower density) results in a larger r0 of the Martian MPB. (2) A higher solar wind density leads to a lower ratio of the compressed magnetic field strength to the crustal field strength and a larger plasma β under the same Pd. This indicates that the thermal pressure at the Martian MPB plays a significant role for the compressed magnetic field. Because the magnetic pileup process is stronger for a higher solar wind velocity, the magnetic pressure at the Martian MPB is increased. As a result, the thermal pressure decreases and r0 of the Martian MPB increases. (3) We present a new formula of r0 with the parameters of the solar wind dynamic pressure, number density, and velocity.

A 3D parametric Martian magnetic pileup boundary model with the effects of solar wind density, velocity, and IMF

“…However, in their observational study, it was hard to remove the influence of other factors completely, such as the IMF and the crustal field. Recently, using a 3D multispecies MHD model, Wang et al (2021) confirmed the power-law relation between the subsolar standoff distance of the Martian MPB and P d . They further indicated that for the same P d , a higher solar wind velocity (lower density) can result in a larger subsolar standoff distance, which is explained by the stronger magnetic pileup process.…”

“…They further indicated that for the same P d , a higher solar wind velocity (lower density) can result in a larger subsolar standoff distance, which is explained by the stronger magnetic pileup process. However, Wang et al (2021) only focused on the subsolar point of the Martian MPB, and did not study the dependence of the whole geometry of the Martian MPB on the individual solar wind density and velocity.…”

The Dependence of the Venusian Induced Magnetosphere on the Interplanetary Magnetic Field: An MHD Study

“…, where P t is the thermal pressure, P b = B 2 /2μ 0 is the magnetic pressure, P d = ρv 2 is the dynamic pressure and MB denotes the magnetic barrier. Different methods give different IMB standoff distances (Wang et al 2021). Based on magnetic pressure, Zhang et al (1991) defined the upper boundary as the position where the local magnetic pressure equals half of the upstream solar wind dynamic pressure adjusted for the normal angle of the barrier,…”

A Two‐Spacecraft Study of Mars' Induced Magnetosphere's Response to Upstream Conditions

“…Importantly, however, no strong consensus yet exists regarding the physical parameters that specifically delineate the MPB. It has variously been defined as a pressure‐balance surface (Girazian et al., 2019; Holmberg et al., 2019), or by gradients in plasma and field pressures (Wang et al., 2021), and is also at least often well correlated with changes in the plasma composition from solar wind (H + ) to planetary ions (O + , $${\mathrm{O}}_{2}^{+}$$) dominated regimes (hence the occasionally used name, ion composition boundary, ICB; Halekas et al., 2018). Comparing these different definitions, it should be noted that the differences in location and behavior remain generally small compared to the intrinsic variability of the location of the MPB with upstream conditions.…”