Spectroscopic Detection of Turbulence in Post-CME Current Sheets

Details Spectroscopic Detection of Turbulence in Post-CME Current Sheets Spectroscopic Detection of Turbulence in Post-CME Current Sheets

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...689..572b&link_type=abstract

The Astrophysical Journal, Volume 689, Issue 1, pp. 572-584.

Astronomy and Astrophysics

Astronomy

20

Sun: Corona, Sun: Coronal Mass Ejections (Cmes), Sun: Uv Radiation, Turbulence

Scientific paper

Plasma in post-CME current sheets (CSs) is expected to be highly turbulent because of the tearing and coalescence instability and/or local microscopic instabilities. For this reason, in the last decade the inconsistency between the observed (~104-105 km) and the expected (~1-10 m) CS thickness has been tentatively explained in many MHD models as a consequence of plasma turbulence that should be able to significantly broaden the CS. However, from the observational point of view, little is known about this subject. A few post-CME CSs have been observed in UVCS spectra as a strong emission in the high-temperature [Fe XVIII] line, usually unobservable in the solar corona. In this work, published data on post-CME CSs observed by UVCS are reanalyzed, concentrating for the first time on the evolution of turbulence derived from the nonthermal broadening of the [Fe XVIII] line profiles. Derived turbulent speeds are on the order of ~60 km s-1 a few hours after the CME and slowly decay down to ~30 km s-1 in the following 2 days. From this evolution the anomalous diffusivity due to microinstabilities has been estimated, and the scenario of multiple small-scale reconnections is tested. Results show that the existence of many (~10-11 to 10-17 μCS m-3) microscopic CSs (μCSs) of small sizes (~10-104 m) could explain not only the high CS temperatures but also the much larger observed thickness of macroscopic CSs, thanks to turbulent broadening.

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