| Popis: |
The Kelvin–Helmholtz instability (KHI) has been considered important in the energy transfer and momentum coupling between the solar wind and planetary magnetospheres. To explore this issue, we employ a two-dimensional magnetohydrodynamic simulation to study the nonlinear evolution of the KHI at Mercury’s magnetopause using the parameters derived from a global hybrid simulation of MESSENGER’s first flyby of Mercury. Due to the absence of comprehensive plasma observations of Mercury’s magnetosphere, two scenarios are considered: one with a heavily loaded magnetosphere and the other with a weakly loaded magnetosphere, to demonstrate the development of the KHI under distinct levels of magnetospheric plasma density. Our results indicate that the KHI with a heavily loaded magnetosphere leads to a significantly more turbulent magnetopause and grows into the nonlinear fast-mode plane waves expanding away from the magnetopause. The momentum and energy flux quantified from our simulations reveal that the KHI with a heavily loaded magnetosphere can efficiently transport momentum and energy away from the magnetopause in the presence of the fast-mode plane waves. In the cases with a heavily loaded magnetosphere, observed in the inner magnetosphere, the momentum flux can reach 10 ^−3 nP _a , i.e., about 0.5% of the initial solar-wind dynamic pressure; the energy flux can be $1{0}^{-2}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1},$ and the energy density is about 1.5%–3.0% of the initial solar-wind energy. In the cases with a very thin magnetosphere, observed away from the magnetopause, the momentum flux is negligible and the energy flux is smaller without the presence of the fast-mode plane waves in the magnetosphere. |
