High resolution observations and modelling of chromospheric spicules

With the recent advent of the Swedish 1-m Solar Telescope (SST), advanced image processing techniques, as well as numerical simulations that provide a more realistic view of the chromosphere, a comprehensive understanding of chromospheric jets such as spicules, mottles and fibrils is now within reach.

We will present results from a recent analysis of dynamic fibrils, short-lived spicule-like features that dominate the chromosphere (as imaged in H-alpha) of active region plage. Our analysis is based on a time series of extremely high-resolution (120 km) images taken in H-alpha linecenter at 1 second cadence, obtained by the Oslo group at the SST in October 2005. The 78 min long time series for the first time spatially and temporally resolves dynamic fibrils in active regions. Our analysis shows that most of the fibrils follow parabolic paths that are incompatible with ballistic flight at solar gravity. We compare our observations to advanced numerical 2D radiative MHD simulations, and find that fibrils are most likely formed by chromospheric shock waves that occur when convective flows and global oscillations leak into the chromosphere along the field lines of magnetic flux concentrations. We compare our results with observations of mottles and find that a similar mechanism is most likely at work in the quiet Sun.