Stationary auroral current oscillations resulting from the magnetospheric generator

Abstract

An instance of steady state spatial current oscillations in auroral field‐aligned currents has been detected with the two Dynamics Explorer (DE) satellites. The oscillations are apparent in both the north–south electric fields and the east–west magnetic fields measured with DE 1 and DE 2 near a magnetic conjunction between the two satellites. Both satellites measured very similar large‐scale oscillations at the same location but separated in time by about 20 min. Three cycles with an average wavelength of approximately 266 km were detected. These waves, which consisted of alternating sheets of upward and downward currents, were imbedded within the region 2 current system near 13 hours local time, at 66° to 73° invariant latitude. An explanation for these oscillations has been developed in terms of a simple steady state model of the magnetosphere‐ionosphere current system. The wavelength of the oscillations is found to be dependent on the ionospheric height‐integrated Pedersen conductivity, the magnetic‐field‐aligned conductivity, and the conductivity of a generator at the magnetospheric equator. Stationary current oscillations may exist if the magnitude of the generator conductivity is less than the ionospheric Pedersen conductivity. There is good agreement between this model and the measurements from the DE satellites. The conductance of the magnetospheric generator is also found to be consistent with the magnetohydrodynamic equations.