Patrick Antolin: A rainy day on the Sun


The tropical wisdom that when it is hot and dense we can expect rain might also apply to the Sun. Indeed, observations and numerical simulations have showed that strong heating at the base of coronal magnetic field structures, such as coronal loops, leads to the loss of thermal equilibrium, a phenomenon usually known as catastrophic cooling. Pressure drops locally in the corona leading to a rapid condensation of plasma, which dramatically cools down to chromospheric temperatures. These blobs become bright in lines such as H-alpha and Calcium II H in time scales of minutes, and their dynamics seem to be more subject to pressure changes inside the loops rather than to gravity. They thus become trackers of the magnetic field, which results in the spectacular "coronal rain" that is observed falling down coronal loops in solar active regions.

In this talk I will report on high resolution observations of coronal rain with the Solar Optical Telescope of the Hinode satellite, and with the CRISP spectropolarimeter of the Swedish Solar Telescope. A statistical study is performed in which properties such as velocities, accelerations, occurrence frequencies and shapes of coronal rain are derived. Results suggest that coronal rain is a far more common phenomenon than previously thought, and which can help in the understanding of the magnetic field morphology of the corona. Furthermore, I will discuss the important role coronal rain can play as a helioseismology tool, and in determining the coronal heating agents.

Publisert 14. jan. 2011 15:28