Observations of Magnetotail Interchange Heads' Signatures at Later Stage of Development

Abstract

<pre>The kinetic ballooning/interchange instability (BICI) was recently found to produce azimutally narrow interchange <br />heads extending from the near-Earth magnetotail into the dipole region. In their nonlinear evolution individual <br />heads were predicted to grow into transient earthward moving northward magnetic field intensifications <br />(dipolarization fronts; DFs). The distinguished signatures of such fronts would be their oblique propagation <br />and cross-tail localization due to the finite k$_y$ structure of the BICI modes. We compare DFs that were observed <br />by two THEMIS probes at 11 Earth's radii (R$_E$) downtail amidst previously identified interchange heads with a <br />simulated interchange head during later-stage BICI development. The comparison shows that the DFs propagated <br />dawnward at about 45$^{\circ}$ to the earthward direction. The leading edges and trailing tails of the DFs were <br />structured similarly to those of the simulated interchange head. The analysis evidences that BICI indeed releases <br />obliquely propagating azimuthally localized dipolarization fronts in the Earth's magnetotail. </pre>