Viggo Hansteen: Hinode and the dynamic chromosphere: Spicules and Alfven waves

Fredagskollokvium

Abstract

High-resolution, high-cadence Ca II and H-alpha observations of the solar chromosphere obtained with the Solar Optical Telescope (SOT) onboard Hinode provide an unprecedented view of the dynamics of the chromosphere. We find that there are at least two types of spicules with very different dynamic properties. We show that the first type is driven by the same mechanism that forms dynamic fibrils: shock waves that form when global oscillations and convective flows leak into the chromosphere along magnetic field lines on on 3-7 minute timescales. The second type of spicules is much more dynamic: they form rapidly (in ~10s), are very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem to be rapidly heated to (at least) transition region temperatures, sending material through the chromosphere at speeds of order 50-150 km/s. The properties of Type II spicules suggest a formation process that is a consequence of magnetic reconnection.

Our analysis of chromospheric Hinode data also indicates that the chromosphere is permeated by strong Alfven waves. Both types of spicules are observed to carry these Alfv\'en waves, which have significant amplitudes of order 20 km/s, transverse displacements of order 500-1,000 km and periods of 150-400 s. Estimates of the energy flux carried by these strong Alfven waves and comparisons to advanced radiative MHD simulations indicate that these waves most likely play a significant role in the acceleration of the solar wind, and possibly the heating of the quiet Sun corona. We will discuss the implications of these waves on the energy balance of the lower atmosphere.

Publisert 11. aug. 2009 14:26 - Sist endret 15. juni 2011 13:49