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Aims. Convective collapse, a theoretically predicted process that intensifiesexisting weak magnetic fields in the solar atmosphere, was first directlyobserved in a single event by Nagata et al. (2008) using the high resolutionSolar Optical Telescope (SOT) of the Hinode satellite. Using the same spacetelescope, we performed a statistical analysis of convective collapse events.  Methods. Our data sets consist of high resolution time series of polarimetricspectral scans of two iron lines formed in the lower photosphere and filterimages in Mg I b2 and Ca II H, spectral lines that are formed in the highphotosphere and the lower chromosphere, respectively. We were thus able tostudy the implication of convective collapse events on the high photosphericand the chromospheric layers. The physical parameters from the full Stokesprofiles were obtained with the MERLIN Milne-Eddington inversion code.  Results. We found that in all cases, the event was accompanied by a continuumbright point and nearly always by a brightening in the Ca II H images. Themagnesium dopplergram exhibits a strong downflow in about three quarters of theevents that took place within the field of view of the magnesium dopplergram.For each of the 49 events we determined the duration, maximum photosphericdownflow, field strength increase and size. We found event durations of about10 minutes, magnetic element radii of about 0.43 arcsec and 0.35 arcsec, beforeand after the event, respectively, and field strengths of up to 1.65 kG.

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