STUDY ON NEUTRAL WIND CONTRIBUTION TO THE ELECTRODYNAMICS IN THE POLAR IONOSPHERE USING EISCAT CP-1 DATA

Energy coupling between the thermosphere, ionosphere and magnetosphere is studied quantitatively through an analysis using the European Inco herent Scatter (EISCAT) Common Program (CP) - 1 version H data obtaine d on May 3, 1988. A negative excursion of the H component in the Troms o magnetogram occurred during the experiment period, which involved th e following two features: (1) the electric potential across the polar cap was expected to be reduced abruptly in association with a sudden c hange of the interplanetary magnetic field (IMF) B-z polarity from sou thward to around null and (2) the negative excursion had a relatively long duration of development (about 4 hours), which may drive neutrals to move significantly through ion drag. In order to investigate the e nergy coupling between the thermosphere and ionosphere, we evaluate qu antitatively the electromagnetic energy flux J.E, the Joule heating ra te J.E' (E' = E + U x B), and the mechanical energy transfer rate U.(J x B), where U is the neutral wind velocity. The CP-1-H experiment pro vides directly or indirectly all quantities above at altitudes of 101 km, 109 km, 119 km, and 132 km. The results are summarized as follows. (I) The amplitude of the neutral wind related electric field U x B va ried greatly with altitude, i.e., at altitudes above 119 km it often b ecame larger than 50% of the amplitude of the observed electric field; (2) during the late recovery phase of the negative excursion of the H component of the Tromso magnetic field, the neutral wind related elect ric field tended to be canceled with the observed electric field; (3) in the E region the neutral wind mechanical energy transfer rate U (Jx B) is not negligible but is comparable to the Joule heating rate J.E'; and (4) in particular, at higher altitudes (132 km high) the conversi on from the neutral wind mechanical energy to the electromagnetic ener gy occasionally may occur.