On the Origin of Fluctuations in the Cusp Diamagnetic Cavity

<p> We have analyzed Cluster magnetic field and plasma data during high&hyphen;altitude cusp crossing on 14 February 2003. Cluster encountered a diamagnetic cavity (DMC) during northward interplanetary magnetic field (IMF) conditions, and as IMF rotated southward, the spacecraft reencountered the cavity more at the sunward side. The DMC is characterized by a high level of magnetic field fluctuations and high&hyphen;energy electrons and protons. Ultralow&hyphen;frequency turbulence has been suggested as a mechanism to accelerate particles in DMC. We demonstrate in this paper for the first time that many of the low&hyphen;frequency fluctuations in the cavity are back and forth motion of the DMC boundaries over the spacecraft and transient reconnection signatures. We also find examples of some isolated high&hyphen;amplitude waves that could possibly be nonlinear kinetic magnetosonic modes. The lack of strong wave power at the vicinity of local ion cyclotron frequency in the DMC suggests that perhaps a mechanism other than wave&hyphen;particle heating is a dominant source for ion heating in DMCs.</p>