Abstract
We look at some simple theoretical considerations relevant to the origin of Pi 2 geomagnetic pulsations observed on the ground with the onset of geomagnetic activity. Using a basic model, we examine how subsidiary current flows are created by auroral ionospheric conductivity enhancements in the electrojet regions. These current flows, which include field‐aligned currents, are associated with reflected shear Alfvén waves localized to the field lines which thread ionospheric conductivity gradients. Thus the ionosphere can create distinct latitudinal structure in the signal. We discuss the origin of the observed polarization pattern and predominantly westward phase propagation of Pi 2 pulsations in the light of our results. We conclude that a superposition of two travelling waves of differing amplitude is required to produce these characteristics.
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