Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward-southward angle of 45 degrees, continuous formation of cavitons is found up to ~ 11 Earth radii (R_E) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ~ 2 R_E from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that the transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.

中文翻译：

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前额空洞和自发热流异常：全球混合-Vlasov模拟的统计研究

摘要。位于地球弓激波上游的前震具有多种现象，这些现象与弓激波反射太阳风粒子以及随后形成的超低频（ULF）波有关。在这项工作中，我们研究前兆空洞，它们是由ULF波的非线性演化和自发的热流异常（SHFA）引起的瞬态结构，自发热流异常是由于空洞在累积超热离子的同时被弓形激波携带而产生的。太阳风。使用全局混合Vlasov仿真模型Vlasiator，我们进行了一项统计研究，在其中跟踪单个空洞和SHFA的运动，以检查它们的特性和演化。在我们的模拟运行中，行星际磁场（IMF）指向太阳向南和向南的45度角，_E）（从船首冲击（沿IMF方向）），并且鱼子酱向SHFA的演化发生在2 R _E以内从震惊。在我们的实验中，三分之一的空洞演变成SHFA，并且我们发现在弓形冲击附近有相当数量的SHFA独立形成。我们将空洞体和SHFA的特性与先前的航天器观测和模拟进行了比较，发现了很好的一致性。我们还研究了前震中位置随位置变化的特性变化，表明靠近弓形激波的瞬变与等离子体密度和磁场强度的更大耗竭以及等离子体温度和电磁场的较大增加有关。大流量挠度水平。我们对空洞和SHFA传播速度的测量结果与早期研究一致，表明瞬变在太阳风静止框架中向太阳传播。