The reconnection site of temporal cusp structures

K J Trattner,T K Yeoman,C P Escoubet,S A Fuselier,S M Petrinec,H Reme

doi:10.1029/2007ja012776

Abstract

The strong precipitating particle flux in the cusp regions is the consequence of magnetic reconnection between the interplanetary magnetic field and the geomagnetic field. Magnetic reconnection is thought to be the dominant process for mass, energy, and momentum transfer from the magnetosheath into the magnetosphere. Observations of downward precipitating cusp ions by polar orbiting satellites are instrumental in unlocking many questions about magnetic reconnection, e.g., their spatial and temporal nature and the location of the reconnection site at the magnetopause. In this study we combine cusp observations of structures in the precipitating ion‐energy dispersion by the Cluster satellites with Super Dual Auroral Radar Network radar observations to distinguish between the temporal and spatial magnetic reconnection processes at the magnetopause. The location of the cusp structures relative to the convection cells is interpreted as a temporal phenomenon caused by a change in the reconnection rate at the magnetopause. The 3‐D plasma observations of the Cluster Ion Spectrometry instruments onboard the Cluster spacecraft also provide the means to estimate the location of the reconnection site. While an earlier study of a spatial cusp structure event revealed bifurcated reconnection locations in different hemispheres as origins for the precipitating ions creating the cusp structures, the same method applied to the temporal cusp structures in this study shows only a single tilted reconnection line close to the subsolar point. Tracing the distance to the reconnection site provides not only the location of the reconnection line but can also be used to distinguish between spatial and temporal cusp structures.

Highlights

[1] The strong precipitating particle flux in the cusp regions is the consequence of magnetic reconnection between the interplanetary magnetic field and the geomagnetic field
Whatever process occurs at the magnetopause, a signature of the process can be found in the precipitating magnetosheath ions observed in the cusp [e.g., Lockwood and Smith, 1994; Onsager et al, 1993] as well as down to the ionosphere where the foot points of all magnetopause field lines converge to a relatively confined space [e.g., Frey et al, 2003]
[40] This study shows that temporal cusp structures originate at the same reconnection line as the result of significant changes in the reconnection rate, in agreement with the pulsed reconnection model [e.g., Cowley and Owen, 1989]

Summary

The reconnection site of temporal cusp structures

Observations of downward precipitating cusp ions by polar orbiting satellites are instrumental in unlocking many questions about magnetic reconnection, e.g., their spatial and temporal nature and the location of the reconnection site at the magnetopause. In this study we combine cusp observations of structures in the precipitating ion-energy dispersion by the Cluster satellites with Super Dual Auroral Radar Network radar observations to distinguish between the temporal and spatial magnetic reconnection processes at the magnetopause. While an earlier study of a spatial cusp structure event revealed bifurcated reconnection locations in different hemispheres as origins for the precipitating ions creating the cusp structures, the same method applied to the temporal cusp structures in this study shows only a single tilted reconnection line close to the subsolar point. Tracing the distance to the reconnection site provides the location of the reconnection line but can be used to distinguish between spatial and temporal cusp structures

Introduction

Summary and Conclusion