Quiescent Prominence Dynamics Observed with the Hinode Solar Optical Telescope. II. Prominence Bubble Boundary Layer Characteristics and the Onset of a Coupled Kelvin-Helmholtz Rayleigh-Taylor Instability
Abstract
We analyze solar quiescent prominence bubble characteristics and instability dynamics using Hinode/Solar Optical Telescope data. We measure the bubble expansion rate, prominence downflows, and the profile of the boundary layer brightness and thickness as a function of time. The largest bubble analyzed rises into the prominence with a speed of about 1.3 {km} {{{s}}}-1 until it is destabilized by a localized shear flow on the boundary. Boundary layer thickness grows gradually as prominence downflows deposit plasma onto the bubble with characteristic speeds of 20{--}35 {km} {{{s}}}-1. Lateral downflows initiate from the thickened boundary layer with characteristic speeds of 25{--}50 {km} {{{s}}}-1, “draining” the layer of plasma. Strong shear flow across one bubble boundary leads to an apparent coupled Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) instability. We measure shear flow speeds above the bubble of 10 {km} {{{s}}}-1 and infer interior bubble flow speeds on the order of 100 {km} {{{s}}}-1. Comparing the measured growth rate of the instability to analytic expressions, we infer a magnetic flux density across the bubble boundary of ∼10-3 T (10 Gauss) at an angle of ∼ 70^\circ to the prominence plane. The results are consistent with the hypothesis that prominence bubbles are caused by magnetic flux that emerges below a prominence, setting up the conditions for RT, or combined KH-RT, instability flows that transport flux, helicity, and hot plasma upward into the overlying coronal magnetic flux rope.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2017
- DOI:
- 10.3847/1538-4357/aa95b6
- arXiv:
- arXiv:1707.05265
- Bibcode:
- 2017ApJ...850...60B
- Keywords:
-
- instabilities;
- magnetohydrodynamics: MHD;
- Sun: chromosphere;
- Sun: corona;
- Sun: filaments;
- prominences;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 17 pages, 7 figures