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 nPa, i.e., about 0.5% of the initial solar-wind dynamic pressure; the energy flux can be 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.

中文翻译：

---

水星开尔文-亥姆霍兹不稳定性对太阳风-磁层的耦合


开尔文-亥姆霍兹不稳定性 （KHI） 被认为在太阳风和行星磁层之间的能量传递和动量耦合中很重要。为了探索这个问题，我们采用二维磁流体动力学模拟，使用来自 MESSENGER 首次飞越水星的全球混合模拟得出的参数，研究水星磁层顶处 KHI 的非线性演变。由于缺乏对水星磁层的全面等离子体观测，因此考虑了两种情况：一种是重负载磁层，另一种是弱负载磁层，以证明 KHI 在不同磁层等离子体密度水平下的发展。我们的结果表明，具有重负载磁层的 KHI 会导致明显更湍流的磁层顶，并发展成从磁层顶向外扩展的非线性快模平面波。从我们的模拟中量化的动量和能量通量表明，在快模平面波存在的情况下，具有重负载磁层层的 KHI 可以有效地将动量和能量从磁层顶传输出去。在内磁层中观察到的重负载磁层的情况下，动量通量可以达到 10-3 nPa，即大约是初始太阳风动态压力的 0.5%;能量通量可以是初始太阳风能的能量密度约为 1.5%–3.0%。在远离磁层顶的地方观察非常薄的磁层的情况下，动量通量可以忽略不计，并且磁通量较小，而磁层中不存在快模平面波。