Diamagnetic oscillations ahead of stopped dipolarization fronts

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 −9 R E and stopped at x =−9 to −8 R E and compressional oscillations observed at x ≈−8 R E . 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 −8 R E was ∼5 nT; the wavelength was ∼0.5 R E . 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 R E beyond geosynchronous orbit, the plasma compression propagated farther inward and excited compressional diamagnetic oscillations in the tail‐dipole transition region.