K-GRAINS AS A 3-DIMENSIONAL PHENOMENON .1. STATISTICS AND SPATIAL EVOLUTION

We present new data concerning the statistics and motion of chromosphe ric K-grains, in order to verify possible excitation mechanisms. We ha ve analysed a time-series of Ca K-2v filtergrams obtained with the VTT at Observatorio del Teide, Tenerife. K-grains are not only characteri sed by their brightness but also by their pointlike appearance and in some cases by a horizontal motion. Our statistical analysis of the spa tial distribution of bright point emission reveals no significant clus tering at particular areas in the internetwork. Some of the observed g rains travel through the chromospheric internetwork cells with a speed comparable to the phase speed of the solar p-modes. Both results seem to be inconsistent with a causal relation between Ca K bright points and magnetic flux tubes, and rather favour a mechanism related to p-mo de interference. Finally we present statistical evidence showing that bright points do not dominate the emission of the quiet chromosphere b ut rather contribute only about 9 percent of the K-2v intensity emitte d from the internetwork areas in our data.