Modulation of type Pi waves by temporal variations in ionospheric conductivity in a three-dimensional magnetosphere-ionosphere current system

It is suggested that Pi ULF waves are generated from magnetosphere-ionosphere current systems. This current system is modeled by an R (resistance), C (capacitance) and L (inductance) circuit loop in which R = R(t). We studied three cases of modification of ULF waves by variations in ionospheric conductivity: (1) ω ? ω', (2) ω ≈ ω' and (3) ω ? ω', where ω and ω' are the frequency of the driving electric field and ionospheric conductivity variations, respectively, assuming that both variations are sinusoidal. The characteristics of the modification are very different in these three cases. In case 1, the envelope of the ULF wave intensity correlates with the variations in ionospheric conductivity. In case 2, the wave form of the ULF waves is slightly modified from a sinusoidal wave. In case 3, high frequency components are generated in the ULF wave form due to rapid oscillations in ionospheric resistance. We present observational evidence for the existence of the three types of modifications.