场向电流驱动下电离层电场的时间演变

本文以Senior-Blanc的驱动电位随时间阶跃变化的简单模式为基础,讨论了随时间阶跃变化的场向电流驱动下电离层电场的时间演变。结果表明,场向电流驱动和电位驱动的总体过程是一致的。在两种情况下,有关物理量都经约50分钟的弛豫时间而趋向于稳定态。但两者也有一定的差异。这主要表现在,电流驱动下极盖区边界上的电位不再是常量,而是一个随时间作指数衰减的函数,最后趋于稳态值;极光区的稳态和初态电场相差不大。此外,电流驱动下场向电流2的稳态值小一些,似乎更接近于观测值;各区电位随纬度的变化更快些,最大电位出现的时间也更早一些。对屏蔽因子和屏蔽时间常数的计算表明,电流驱动比电位驱动的屏蔽要强些。这些都反映了电流驱动和电位驱动的不同特点。

THE TEMPORAL EVOLUTION OF THE IONOSPHERIC ELECTRIC FIELD DRIVEN BY THE FIELD-ALIGNED CURRENT

On the basis of simple Senior-Blanc's time-dependent model and by using a step-varying field-aligned curret instead of potential as driving force, the temporal evolution of the ionospheric electric field was discussed. It is shown that configurations in both cases are similar; the relaxation time toward the steady state is about fifty minutes in both cases. But there are some differences between them: under current driving situation, the potential at the boundary of the polar cap is not constant but decreases exponentially toward the steady state; at the auroral zone the difference between the steady state and the initial time electric fields is very small. Furthermore, the steady state value of the field-aligned current 2 calculated from our model is even closer to the observed value. The latitudinal variation of the potential is steeper, and the maximum potential appears earlier. The calculated shielding factor and the shielding time c-aligned current driving.onstant show that the shielding effect under the current driving situation seems stronger than that in the potential driving case.