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Possible generation mechanisms of the Pi2 pulsations estimated from a global MHD simulation

机译：通过全球MHD仿真估算的Pi2脉动的可能生成机制

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The plasmaspheric virtual resonance (PVR) and the transient Alfvén wave bouncing between the ionospheres in both hemispheres (the transient response,TR) are regarded as the possible generation mechanisms of the Pi2 pulsations. However,the global MHD simulation of a substorm (Tanaka et al.,2010) did not reproduce such wave modes because of insufficient ionospheric reflection of the Alfven wave,numerical transfer of the Alfven wave across the field lines,and no plasmasphere. Furthermore,it is noted that the substorm current wedge (SCW) which is a driver of the TR is not reproduced in the global MHD simulation. In this study,we search the sources of the Pi2 pulsations in the global MHD simulation,namely,the compressional wave in the inner magnetosphere for the PVR and the Alfvén wave injected to the ionosphere for the TR. In conclusion,there appears a compressional signal in the inner magnetosphere when the high-speed Earthward flow at the substorm onset surges in the inner edge of the plasma sheet. This simulation result suggests that this compressional wave would be trapped in the plasmasphere as the PVR if the model has the plasmasphere. As for TR,the global MHD simulation provides suddenly increasing field-aligned current (the Alfvén wave) associated with sudden appearance of the shear flow which comes from the high-speed flow in the plasma sheet at the onset of the substorm. If the global MHD simulation correctly lets the Alfvén wave be reflected in the ionosphere and transmitted along the field line,the TR would be established. As the ballooning instability is regarded as one of candidates of the Pi2 pulsation sources,we also briefly investigate whether the simulated plasma sheet in the growth phase is unstable or not for the ballooning instability.
机译：等离子层虚拟共振（PVR）和两个半球的电离层之间反弹的瞬变Alfvén波（瞬态响应TR）被认为是Pi2脉动的可能产生机理。然而，由于Alfven波的电离层反射不足，Alfven波在场线上的数值传递以及没有等离子层，因此对亚暴进行的全球MHD模拟（Tanaka等，2010）没有重现这种波模。此外，要注意的是，作为TR的驱动器的亚暴雨楔形（SCW）未在全局MHD模拟中重现。在本研究中，我们在全局MHD模拟中搜索Pi2脉动的来源，即，PVR的内部磁层压缩波和TR的电离层注入Alfvén波。总之，当子风暴开始时高速向地球流在等离子薄片的内边缘激增时，在内部磁层中就会出现压缩信号。该模拟结果表明，如果模型具有等离子层，则该压缩波将作为PVR被束缚在等离子层中。对于TR，全局MHD模拟提供了突然增加的场对准电流（Alfvén波），该电流与剪切流的突然出现有关，剪切流的出现是由于亚暴爆发时等离子板中的高速流动。如果全局MHD模拟正确地使Alfvén波在电离层中反射并沿磁力线传输，则TR将建立。由于气球膨胀不稳定性被认为是Pi2脉动源的候选者之一，我们还简要研究了在生长阶段模拟的血浆片对于气球膨胀不稳定性是否不稳定。

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