Electromagnetic Fields of Magnetospheric Waves and Transients at Conjugate Antarctica-Greenland Arrays: Resolving the Current/Voltage Dichotomy

A circuit analogy for magnetosphere - ionosphere current systems has two extremes for drivers of ionospheric currents: the "voltage generator" and "current generator". We show with a simple box-field model with thin-layer asymmetric ionospheres that non-steady field-aligned currents (FACs) interact with the ionosphere in a different way depending on the ratio between the driver time scale and Alfven field line eigenperiod. A quasi-DC driving of FAC corresponds to a voltage generator, when the ground magnetic response is proportional to the ionospheric Hall conductance. Thus, according to the suggested conception, magnetic bays correspond to a voltage generator regime. The excitation of resonant field line oscillations corresponds to the current generator, when the ground magnetic response only weakly depends on the ionospheric conductance. Thus, Ultra-low-frequency (ULF) Pc5 waves should be considered as the result of the current generator regime. Sudden Commencements (SC/SI) at high latitudes, where a driver time scale is much less than an Alfven eigenperiod, correspond to any of those regimes only in the extreme situation of strongly asymmetric ionospheres. Theoretical predictions are compared with Traveling Convection Vortex (TCV)/SC/Pc5 wave observations at conjugate magnetometer arrays in Greenland and Antarctica.