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

Abstract

Using global magnetohydrodynamic simulations, we construct a 3D parametric model of the Martian magnetic pileup boundary (MPB). This model employs a modified parabola function defined by four parameters. The effects of the solar wind dynamic pressure, the solar wind densities and velocities, and the intensity and orientation of the interplanetary magnetic field (IMF) are examined using 267 simulation cases. The results from our parametric model show that (1) the MPB moves closer to Mars when the upstream solar wind dynamic pressure (Pd) increases, the subsolar standoff distance decreases and the flaring degree of the Martian MPB increases with an increasing Pd according to the power-law relations. For the same Pd, a higher solar wind velocity (a lower density) leads to a farther location of the MPB from Mars, along with a larger flaring degree, which is explained by the higher solar wind convection electric fields and a stronger magnetic pileup process under these conditions. (2) Larger Y or Z components of the IMF, BY or BZ, result in a thicker pileup region and a farther MPB location from Mars, as well as a decrease in the flaring degree. The radial IMF component, BX, has little effect on the geometry of the MPB. (3) In most of the simulations used to derive the current parametric model, the strongest Martian crustal magnetic field is located on the dayside. However, for a larger value of the southward IMF, the Martian MPB is located farther away in the northern hemisphere instead of the southern hemisphere. The north-south asymmetry of the Martian MPB with the southern hemisphere being farther away is observed for other IMF directions. We suggest that the magnetic reconnection of the southward IMF with the crustal field that occurs at middle latitudes of the southern hemisphere results in different magnetic field topologies and the closer location of the MPB under these conditions. Our model results show a relatively good agreement with the previous empirical and theoretical models.

Interplanetary Magnetic Field Effect on the Location of the Martian Bow Shock: MAVEN Observations

“…First, as we mentioned above, the magnetic pileup dominated by the solar wind convection electric field controls the size of the Martian induced magnetosphere, affecting the location of the Martian BS. Generally, a stronger magnetic pileup process can lead to a larger region of the Martian induced magnetosphere, as well as a farther location of the BS (e.g., Wang et al , 2022. However, due to the solar wind convection electric field effect, the IMF can only be compressed in the direction perpendicular to the solar wind velocity (e.g., Crider et al 2004;Brain et al 2005).…”

The Dependence of the Location and Pressure Variations of the Martian Magnetic Pileup Boundary on the Interplanetary Magnetic Field: An MHD Simulation Study

“…We first studied the dependence of the MPB subsolar standoff distance (r 0 ), the solar wind pressure coefficient (k), and the magnetic compression factor ( f ) on the IMF components of B X , B Y , and B Z , as shown in 2, we can conclude that the Y-and Z-components of the IMF, B Y and B Z , mainly control the r 0 of the MPB, while the radial IMF component, B X , has little effect. This consists of the model results of Wang et al (2022). Moreover, the changing of r 0 due to B Y or B Z is largely caused by the magnetic compression factor, f, rather than the solar wind pressure coefficient, k. This result is partly inconsistent with that on the Earth (Wang et al 2014;Lu et al 2015), which will be discussed in detail.…”

“…The reason for the subsolar longitude effect on r 0 and f might be associated with the crustal field strength, as, on the one hand, a greater crustal field strength naturally causes a larger f, as well as a larger r 0 . On the other hand, the local magnetic reconnection may also play a role (Wang et al 2022). The reconnection can diminish the local magnetic pressure and result in a smaller r 0 , which is the same as the Earth (Shue & Chao 2013;Lu et al 2015).…”

“…In general, the dayside region is better served by methods based on the magnetic field magnitude gradient and pressure balance, while the nightside is better served by methods based on the flow speed gradient (Fang et al 2015). Recently, combining the methods of the pressure balance and the flow speed gradient to determine the location of the MPB, Wang et al (2022) constructed a threedimensional parametric model of the Martian MPB.…”

“…This model is implemented within the Block-Adaptive-Tree Solar wind Roe-type Upwind Scheme in the Space Weather Modeling Framework (Tóth et al 2012). Recently, we have utilized this model to investigate the Martian bow shock ) and the MPB (Wang et al 2021(Wang et al , 2022; the effectiveness and reliability of this model have also been verified by plenty of studies (e.g., Fang et al 2008Fang et al , 2015Fang et al , 2018Y. Ma et al 2014a; Y. J.…”