Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results

Z Vörös

doi:10.5194/npg-18-861-2011

Abstract

Abstract. On the basis of ARTEMIS two-probe mission magnetic reconnection (MR) outflow associated magnetic fluctuations and turbulence are analyzed on 19 February 2011. In the deep-tail, at distances between X = 45 – 51 RE, evidence for reconnection associated plasma sheet thinning was found, accompanied by heating of the plasma sheet. Correlated flow and field reversals and the large-scale Hall-effect signatures indicated the presence of the reconnection X-line. Within fast reconnection plasma outflows, magnetic fluctuations exhibit the same spectral scaling features and kinked spectra as magnetic fluctuations in the solar wind or in various parts of geospace. It was shown that the proton scale magnetic fluctuations are constrained by oblique firehose, proton cyclotron and mirror instability thresholds. For parallel plasma β|| > 1, where the thresholds converge, perpendicular magnetic fluctuations are enhanced. Magnetic compressibility decreases with the distance to the neutral sheet, however, near the instability thresholds it is comparable to the values obtained in the solar wind.

Highlights

Magnetic reconnection (MR) represents a multi-scale plasma process, in which the stored energy in the magnetic field is abruptly converted to plasma and particle energy, while the underlying system is usually embedded in a fluctuating and turbulent plasma environment
Evidence was found for plasma sheet thinning during MR, correlated flow and field reversals, including the Hall-effect
The kinked spectra were not routinely observed in the midtail plasma sheet (Voros et al, 2007). It has been found by Bale et al (2009) that magnetic fluctuation power near proton scales is constrained by temperature anisotropy instability thresholds

Summary

Introduction

Magnetic reconnection (MR) represents a multi-scale plasma process, in which the stored energy in the magnetic field is abruptly converted to plasma and particle energy, while the underlying system is usually embedded in a fluctuating and turbulent plasma environment. Deep-tail observations of the Geotail probe revealed an unsteady magnetotail at the distance of X ∼ −60 RE as well. It was found, that the tailward progression and retreat of MR associated activity is highly dynamic, turbulent, characterized by complex 3-D structures, multiple X-lines, appearance and dynamical evolution of acceleration centers (Angelopoulos et al, 1996). Strong magnetic turbulence has already been observed within MR outflows in the mid-tail (Voros et al, 2004). MR associated plasmoids and reconnection jets can evolve towards more relaxed states (Slavin et al, 1995) and the outflows on the earthward side are not experiencing the strong dipole-like field. The scaling properties of magnetic turbulence will be investigated jointly with gyroscale fluctuations constrained by pressure-anisotropy-driven instabilities

ARTEMIS data

Overview of reconnection observations

Findings

Conclusions