Cluster observations of waves in the whistler frequency range associated with magnetic reconnection in the Earth's magnetotail

On 21 August 2002 the Cluster spacecraft encountered a quasi-collisionless magnetic reconnection event when it crossed the plasma sheet. Prior to the southward turning of magnetic field in the tailward flow, the weak whistler waves were first observed. The burst of whistler waves appeared about 30 s earlier than the southward turning. During magnetic reconnection event, the waves in the whistler frequency range were greatly enhanced. For the waves in the reconnection process, those in the higher- frequency range are mainly quasi- parallel propagating right- hand polarized whistler waves, while those in the lower-frequency range are quasi- perpendicular propagating linear polarized waves, which may be a superposition of several linearly polarized waves. The combined observations of energetic electrons and waves show that after the southward turning of magnetic field, the waves in the reconnection process are greatly enhanced by energetic electron beams.