Slow modes in the Hermean magnetosphere: effect of the solar wind hydrodynamic parameters and IMF orientation

TL;DR

This study uses MHD simulations to analyze how solar wind parameters and IMF orientation influence slow mode structures in Mercury's magnetosphere, revealing conditions that favor or inhibit their formation.

Contribution

It provides the first detailed simulation-based analysis of slow mode formation in Mercury's magnetosphere considering various solar wind and IMF conditions.

Findings

Slow modes form near the poles depending on IMF orientation.

Higher solar wind density and velocity suppress slow mode formation.

Increased solar wind temperature widens slow mode structures.

Abstract

The aim of this study is to simulate the slow mode structures in the Hermean magnetosphere. We use a single fluid MHD model and a multipolar expansion of the Northward displaced Hermean magnetic field, to perform simulations with different solar wind parameter to foreseen the most favorable configuration for the formation of slow modes, attending to the solar wind density, velocity, temperature and the interplanetary magnetic field orientation. If the interplanetary magnetic field is aligned with the Mercury-Sun direction, the magnetic axis of Mercury in the Northward direction or the planet orbital plane, slow mode structures are observed nearby the South pole. If the orientation is in the Sun-Mercury or Northward directions, slow mode structures are observed nearby the North pole, but smaller compared with the structures near the South pole. Increase the density or the solar wind velocity avoids the formation of slow modes structures, not observed for a dynamic pressure larger than $6.25 \cdot 10^{-9}$ Pa in the case of a Northward interplanetary magnetic field orientation, due to the enhancement of the bow shock compression. If the solar wind temperature increases, the slow mode structures are wider because the sonic Mach number is smaller and the bow shock is less compressed.