Long duration Pc 5 compressional pulsations inside

Authors: Sarafopoulos D V

Publish Date: 1995/09/30

Volume: 13, Issue: 9, Pages: 926-937

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Abstract

Abstract Pc 5type magnetic field pulsations are detected by the IMP8 spacecraft well inside the Earths magnetotail lobes The three studied events with an average duration of 3 h and mean amplitude of ΔB/B=66 show a strong longitudinal oscillation The clockwise polarization sense of the magnetic field arrowheads in the north lobe as well as the counterclockwise in the south lobe on the XZ plane is consistent with that expected when periodic solar wind lateral pressures squeeze the magnetotail axisymmetrically while moving tailward In the two case studies the latter property has been found to concur with quasiperiodic upstream density fluctuations detected by ISEE3 and/or ISSE1 The lobe magnetic field oscillations are classified in two distinct modes The manifestations of the first mode are tailwardtravelling waves detectable along the By and Bz magnetic field traces ie with regard to the Bz the spacecraft encounters constantly the same conspicuous signature of souththennorth tilting of field lines around each local compression region The second mode is associated with prolonged periods of extremely low geomagnetic activity and exhibits a signature along the By component inconsistent with travelling waves Thus the maxima of compressions occur simultaneously with the maxima of By excursions a feature that is explained in terms of tailaligned current density flowing at the boundary which separates the stable magnetic field in the tail lobe from the very irregular in the magnetosheath In this case the spacecraft was located in the vicinity of the highlatitude tail boundary and the observed By excursions are consistent with those anticipated by the tailaligned current polarity which is determined by the dominant Bycomponent of the interplanetary magnetic field IMF On the plane YZ we observe an almost linear and circular polarization sense of the vector magnetic field for the first and second mode respectively

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