Studies on generation and propagation processes associated with magnetospheric substorms

在亚暴扩展相的初始阶段，场向电流（FAC）的扰动是在极光破裂区的黎明和黄昏边缘附近产生的，其中心位置为L = 9和LT = 22.5h，扰动产生的原因是等离子体压力的增加。这些扰动FAC沿着磁场线传播并在极电离层反射。因此，剪切阿尔芬波的准周期场线振荡发生在极光纬度。与分裂区黎明侧边缘的场线振荡相关的扰动FAC的流向与黄昏侧边缘的方向相反。这些具有相反意义的扰动FAC通过电离层和交叉尾扰动电流闭合。因此，一个准振荡电流楔的时间尺度为1至2分钟的形成，它是一个主要的源Pi 2脉动。准振荡电流楔的交叉尾部分产生快速磁声波。磁声波在磁层中传播时，由于受到非均匀介质和曲线磁力线的影响，激发出剪切阿尔芬波。这些波是Pi2脉动的次要来源。在此基础上，建立了磁层中Pi2脉动的传播模型，并从观测上证实了模型的正确性。三维MHD模拟也表明了上述方案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.