Statistics of convective collapse events in the photosphere and chromosphere observed with the HINODE SOT

Abstract

Convective collapse, a theoretically predicted process that intensifies existing weak magnetic fields in the solar atmosphere, was first directly observed in a single event by Nagata et al. (2008) using the high resolution Solar Optical Telescope (SOT) of the Hinode satellite. Using the same space telescope, we observed 49 such events and present a statistical analysis of convective collapse events. Our data sets consist of high resolution time series of polarimetric spectral scans of two iron lines formed in the lower photosphere and filter images in Mg I b2 and Ca II H. We were thus able to study the implication of convective collapse events on the high photospheric and the chromospheric layers. The physical parameters from the full Stokes profiles were obtained with the MERLIN Milne-Eddington inversion code. For each of the 49 events we determined the duration, maximum photospheric downflow, and field strength increase. We found event durations of about 10 minutes and field strengths of up to 1.65 kG.