Flux transfer event observation at Saturn's dayside magnetopause by the Cassini spacecraft

Jamie M Jasinski,Andrew J Coates,James A Slavin,Geraint H Jones,Christopher S Arridge,Gangkai Poh,Nick Sergis,J Hunter Waite,Xianzhe Jia

doi:10.1002/2016gl069260

Abstract

AbstractWe present the first observation of a flux rope at Saturn's dayside magnetopause. This is an important result because it shows that the Saturnian magnetopause is conducive to multiple X‐line reconnection and flux rope generation. Minimum variance analysis shows that the magnetic signature is consistent with a flux rope. The magnetic observations were well fitted to a constant‐α force‐free flux rope model. The radius and magnetic flux content of the rope are estimated to be 4600–8300 km and 0.2–0.8 MWb, respectively. Cassini also observed five traveling compression regions (remote signatures of flux ropes), in the adjacent magnetosphere. The magnetic flux content is compared to other estimates of flux opening via reconnection at Saturn.

Highlights

Flux transfer events (FTEs) are twisted flux tubes first observed at Earth’s magnetopause by the ISEE 1 and 2 spacecraft [Russell and Elphic, 1978, 1979]
We have presented the first detection of an FTE-type flux rope at Saturn’s dayside magnetopause
The Cassini spacecraft passed from the magnetosphere, where it observed five TCRs and passed into an open flux region where energized magnetosheath plasma was observed as well as the FTE-type flux rope

Summary

Introduction

Flux transfer events (FTEs) are twisted flux tubes first observed at Earth’s magnetopause by the ISEE 1 and 2 spacecraft [Russell and Elphic, 1978, 1979]. The magnetopause position at Saturn was not found to depend upon the IMF direction [Lai et al, 2012], unlike at Earth and Jupiter [Aubry et al, 1970; Kivelson and Southwood, 2003] This is not to say that reconnection does not occur at all at Saturn, but it is not as common as at Earth, is not triggered under the same conditions, and that its effect on the dynamics of the Saturnian magnetosphere may not necessarily be analogous to the terrestrial system. We investigate a single dayside magnetopause crossing on 2 February 2007 at Saturn by the Cassini spacecraft This crossing contains evidence that an FTE-type flux rope was observed in a region of newly opened flux tubes adjacent to the magnetopause. We discuss the implications of these new observations for Saturn’s magnetosphere

Instrumentation

Observations

Discussion and Conclusions