Diamagnetic oscillations ahead of stopped dipolarization fronts

Abstract

It is well established that fast flows in the magnetotail plasma sheet which are separated from the ambient plasma by dipolarization fronts brake in the tail-dipole transition region. Flow/front braking is suggested to play an important role in generation of compressional waves in the inner magnetosphere and geomagnetic pulsations. Because of the paucity of multipoint observations in the tail-dipole transition region, however, details of wave generation during flow/front braking are unknown. Using comprehensive coverage of the near-Earth plasma sheet and geostationary orbit by six spacecraft, we explore the relationship between dipolarization fronts that propagated earthward at x=-11 to -9RE and stopped at x=-9 to -8RE and compressional oscillations observed at x≈-8RE. The oscillations, which were diamagnetic (i.e., exhibited antiphase variations in magnetic and plasma pressures), were observed about a minute prior to front detection. The amplitude of the magnetic oscillations at -8RE was ∼5 nT; the wavelength was ∼0.5RE. Enhancements of magnetic oscillations with different frequencies and amplitudes of 1 to 2 and 2 to 4 nT were detected at geosynchronous orbit and on the ground, respectively. Analysis of observations reveals that although the fast flow/front stopped a few RE beyond geosynchronous orbit, the plasma compression propagated farther inward and excited compressional diamagnetic oscillations in the tail-dipole transition region. Key Points Comprehensive coverage of the near-Earth plasma sheet by six spacecrafts Dipolarization front stopped between x=-9 and -8 RE Compressional diamagnetic oscillations were observed ahead of the stopped front © 2014. American Geophysical Union. All Rights Reserved.