FIELD-ALIGNED POYNTING FLUX OBSERVATIONS IN THE HIGH-LATITUDE IONOSPHERE

We have used data from Dynamics Explorer 2 to investigate the rate of conversion of electromagnetic energy into both thermal and bulk flow p article kinetic energy in the high-latitude ionosphere. The flux tube integrated conversion rate E.J can be determined from spacecraft measu rements of the electric and magnetic field vectors by deriving the fie ld-aligned Poynting flux, S(parallel-to) = S.B(o), where B(o) is in th e direction of the geomagnetic field. Determination of the Poynting fl ux from satellite observations is critically dependent upon the establ ishment of accurate values of the fields and is especially sensitive t o errors in the baseline (unperturbed) geomagnetic field. We discuss o ur treatment of the data in some detail, particularly in regard to sys tematically correcting the measured magnetic field to account for atti tude changes and model deficiencies. S(parallel-to) can be used to ide ntify the relative strengths of the magnetosphere and thermospheric wi nds as energy drivers and we present observations demonstrating the do minance of each of these. Dominance of the magnetospheric driver is in dicated by S(parallel-to) directed into the ionosphere. Electromagneti c energy is delivered to and dissipated within the region. Dominance o f the neutral wind requires that the conductivity weighted neutral win d speed in the direction of the ion drift be larger than the ion drift , resulting in observations of an upward directed Poynting flux. Elect romagnetic energy is generated within the ionospheric region in this c ase. We also present observations of a case where the neutral atmosphe re motion may be reaching a state of sustained bulk flow velocity as e videnced by very small Poynting flux in the presence of large electric fields.