Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near‐simultaneous occurrence of two types of the whistler‐mode waves in the magnetotail Hall reconnection region. The first type is observed in the magnetic pileup region of downstream and propagates away to downstream along the field lines and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type, propagating toward the X line, is found around the separatrix region and probably is generated by the electron beam‐driven whistler instability or Čerenkov emission from electron phase‐space holes. These observations of two different types of whistler waves are consistent with recent kinetic simulations and suggest that the observed whistler waves are a consequence of magnetic reconnection.

[1] Magnetic reconnection is a crucial physical process in laboratory and astrophysical plasmas. Plasma waves are believed to provide the dissipation mechanism in magnetic reconnection. In this paper we analyze the properties of low-frequency waves in a magnetotail reconnection diffusion region with a small guide field and high b. Using the k-filtering method on the magnetic field data measured by Cluster spacecraft, we found that low-frequency waves in the diffusion region were highly oblique propagating mode. We compared the measured dispersion relation with theoretical ones calculated using the linear (hot) two-fluid and Vlasov-Maxwell theory. It is found that the observed waves in the diffusion region (with high plasma b) follow the dispersion relation of the Alfvén-Whistler wave mode. Comparisons with previous simulations and observational results are also discussed.

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