Studies on generation and propagation processes associated with magnetospheric substorms

在亚暴扩展初期，在以L = 9和LT = 22.5 h为中心的极光分裂区黎明和黄昏边缘，通过等离子体压力的增加，有效地产生了场向电流（FAC）扰动。这些扰动FACs沿磁力线传播并在极性电离层反射。因此，切变阿尔芬波的准周期场线振荡发生在极光纬度。与场线振荡相关的扰动FAC在破碎区黎明边缘的流动方向意义与在黄昏边缘的相反。这些具有相反感觉的扰动FACs通过电离层和交叉尾扰动电流关闭。这样就形成了一个时间尺度为1 ~ 2 min的准振荡电流楔，它是π 2脉动的主要来源。准振荡电流楔的横尾部分产生快速磁声波。磁声波在磁层内通过时，受介质不均匀性和曲线磁力线的影响，激发出剪切阿尔芬波。这些波是Pi2脉动的次级源。在此基础上建立了Pi2脉冲在磁层中的传播模型，并通过观测证实了该模型的有效性。三维MHD模拟也验证了上述场景和传播模型的有效性。

At the initial stage of a substorm expansion phase, the perturbations of field-aligned current (FAC) are generated efficiently around the dawn- and dusk-side edges of auroral breakup region centered at L = 9 and LT = 22.5 hour by an increase of the plasma pressure therein. These perturbation FACs propagate along magnetic field lines and reflect at the polar ionospheres. As a result, quasi-periodic field line oscillations of shear Alfven waves occur at auroral latitudes. The sense in flow direction of the perturbation FAC associated with the field line oscillation at the dawn-side edge of the breakup region is opposite to that at the dusk-side edge. These perturbation FACs with opposite senses are closed via the ionospheric and cross-tail perturbation currents. Thus, a quasi-oscillatory current wedge with a time scale of 1 to 2 min is formed and it is a main source of Pi 2 pulsations. The cross-tail portion of the quasi-oscillatory current wedge generates a fast magnetosonic wave. During its passage within the magnetosphere, the magnetosonic wave excites shear Alfven waves owing to the effects of inhomogeneous medium and curvilinear magnetic field line. These waves are secondary sources of Pi2 pulsations. On the basis of such a scenario a propagation model of Pi2 pulsations in the magnetosphere is constructed and its validity has been confirmed observationally. Three-dimensional MHD simulations also suggest the validity of the above scenario and propagation model.