Physics Dept Seminar
March 11th, Monday
Alfven Wave Damping and Heating in Coronal Holes
Dr. Michael Hahn, Columbia Univ.
(Solar Physics, Host: Wang)
Time: 11:45 am - 12:45 pm with 11:30 am tea time
Room: ECE 202
One theory for heating coronal holes is that energy is carried by Alfven waves into the corona where the waves are damped, thereby converting their energy into plasma heating. Using spectroscopic observations, we have found evidence suggesting that Alfven waves do carry enough energy for the heating and indeed damped at low heights in the corona, as required by wave heating models. However, the physical processes that cause the wave damping are unknown. We are now investigating the cause of this damping through both observations and laboratory experiments. Recently, we studied intensity fluctuations in EUV images obtained by the Sun Watcher with Active Pixels (SWAP) instrument on the Proba2 satellite. These intensity fluctuations are proportional to density fluctuations, and show that density fluctuations grow in amplitude at heights similar to where the Alfven waves are damped. This suggests that the density fluctuations promote Alfven wave dissipation through increasing reflection or through instabilities. We have also been carrying out laboratory experiments using the Large Plasma Device at the University of California Los Angeles. There, we have studied the propagation of Alfven waves through Alfven-speed gradients similar to those in the corona. Our results show that the transmission of Alfven wave energy is significantly reduced by the gradient. Surprisingly, though, we have not observed any reflection of the Alfven waves from the gradient, which is the mechanism predicted by theory to be responsible for the reduced transmittance.