The motions of photospheric bright points

Photospheric magnetic bright points (PBPs) are considered reliable tracers of footpoints of magnetic flux tubes. Their evolution could demonstrate the behaviors of magnetic flux tube footpoints. In this work we firstly analyzed a PBP case in detail and found the magnetic flux inside the PBP moved fast in a short time with horizontal velocity of 8 km/s which is even faster than the footpoint traced by the PBP observed by imaging data at 388 nm wavelength. In this short moment, 60% of the magnetic flux move fast ahead, a few stood still. Continually, we identified another 35 isolated BPs and analyzed the instantaneous velocities calculated by vertical flux and by intensity. We obtained a total of 313 instantaneous velocities, and found that about 7% of measurements derived by vertical flux had values at least 1 km/s larger than those derived by intensity, and another 7% derived by intensity had speeds at least 1 km/s faster than calculated by magnetic flux for the same flux tubes. Whether this difference can excite MHD waves is still unclear and need more analysis in future.