Geotail observations of low-frequency waves from 0.001 to 16 Hz during theNovember 24, 1996, Geospace Environment Modeling substorm challenge event

We present observations of low-frequency waves from 0.001 Hz up to the lowe r hybrid frequency during the time periods corresponding to the growth, exp ansion, and recovery phases of a substorm that occurred from similar to 210 0 to 2310 UT on November 24, 1996, while Geotail was located in the magneto tail at X-GSE similar to 25 R-E and 0100 LT. Large-amplitude waves near the lower hybrid frequency were observed when large-scale density and magnetic field gradients were present during thinning of the plasma sheet at substo rm onset and the beginning of the recovery phase. Later in the recovery pha se, waves near the lower hybrid frequency were observed close to the neutra l sheet in localized areas with strong small-scale density and magnetic fie ld gradients. Fluctuations of the electric and magnetic fields near the ion gyrofrequency were also observed during this event; however, the amplitude s were smaller than those often observed in the near tail in association wi th substorms. Compressional fluctuations of the magnetic field in the Pi2 f requency range were observed close to substorm onset. Although Geotail was not in the region considered in recent studies of Pi2 pulsations, it may st ill be possible that the magnetic field fluctuations observed by Geotail du ring the November 24, 1996, substorm are related to this phenomenon since l ittle is known about propagation of the compressional pulses and generation of the waves.