ON THE CONTRIBUTION OF THE THERMOSPHERIC NEUTRAL WIND TO HIGH-LATITUDE ENERGETICS

Although the neutral wind's contribution to ionospheric electrodynamics is well-established at low latitudes, this electrical energy source has been largely ignored at high latitudes, owing to the assumed dominance of the magnetospheric dynamo contribution. Yet, the potential for exchange of electrical energy between the neutral wind dynamo and the magnetospheric dynamo is a direct consequence of the coupling between the two regions by highly conducting magnetic field lines. The integral nature of this coupling precludes the direct separation of the neutral wind and solar wind contributions to the observed electrodynamics. Therefore, to gain some insight into their relative importance, we have performed a simple numerical experiment in which the two dynamos are individually connected to a fixed load and their energetics evaluated separately. To determine the electrical energy flux supplied by the magnetosphere, we treat it as a voltage generator and the ionosphere as a resistive load. The available electrical energy flux generated by the neutral wind dynamo is determined from the mechanical energy stored within an established neutral wind field. This exercise has led to a number of conclusions, including: i) The neutral wind dynamo contributes significantly to high-latitude energetics, particularly in the central polar cap; and ii) In the region near the plasma convection reversal boundary, the amount of energy flux available from the neutral wind dynamo can exceed that provided by the magnetospheric dynamo.