Evidence for Rayleigh-Taylor Plasma Instability at the Front of Solar Coronal Mass Ejections

Daniele Telloni,Francesco Carbone,Ester Antonucci,Alessandro Bemporad

doi:10.3390/atmos10080468

Abstract

This work focuses on the interaction of a Coronal Mass Ejection (CME) with the ambient solar corona, by studying the spatial and temporal evolution of the density fluctuations observed by the SOHO/UV Coronagraph Spectrometer (UVCS) during the CME. The investigation is performed by applying a wavelet analysis to the HI Ly α 1216 Å line intensity fluctuations observed with UVCS during the CME occurred on 24 December 2006. Strong and coherent fluctuations, with a significant spatial periodicity of about 84 Mm ≃ 0.12 R ⊙ , are shown to develop in about an hour along the front of the CME. The results seem to indicate the Rayleigh-Taylor (RT) instability, susceptible to the deceleration of the heavier fluid of the CME front into the lighter surrounding coronal plasma, as the likely mechanism underlying the generation of the observed plasma fluctuations. This could be the first inference of the RT instability in the outer solar corona in UV, due to the transit of a CME front in the quiet coronal plasma; this interpretation is also supported by a linear magnetohydrodynamic analysis of the RT instability.

Highlights

During Coronal Mass Ejections (CMEs) coronal plasma is expelled against the gravitational field of the Sun into the interplanetary space, over the course of minutes to hours
This paper presents evidence for non-stationary density fluctuations induced at the interface of a CME with the surrounding plasma during its outward propagation, and provides further information on the dynamic and energetic interaction of CMEs with the ambient corona
The wavelet technique, increasingly adopted in astrophysical studies, was used for instance to detect (i) outward propagating perturbations with periods of 180–420 s at a footpoint of an active region bright loop [18], (ii) a sporadic oscillation with periods of 7–8 min in the quiet solar corona [19], (iii) coherent fluctuations within a weak solar magnetic network region [20] and (iv) magnetic and cross-helicity events in the solar wind [21,22]. This method is applied to explore the region of interaction between a CME and the surrounding corona in order to investigate the existence of oscillatory signals associated with the transit of the ejected plasma

Summary

Introduction

During Coronal Mass Ejections (CMEs) coronal plasma is expelled against the gravitational field of the Sun into the interplanetary space, over the course of minutes to hours. It is worth noting that during the primary dissipation processes (associated to magnetic reconnection) most of the free magnetic energy (about 68%) is used to accelerate electrons and ions (nonthermal energy), while only a relatively small portion of the magnetic energy (about 7%) goes into CME kinetic and gravitational potential energies (see the review by [3], and references therein). During CMEs expansion, magnetic reconnection events can occur e.g., [10,11], in particular, along their flanks with the surrounding coronal magnetic field, causing secondary small-scale plasma ejections [12]

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