Horizontal component of photospheric plasma flows during the emergence of active regions on the Sun

The dynamics of horizontal photospheric plasma flows during the first hours after the emergence of active regions in the solar photosphere have been analyzed using SOHO/MDI data. Four active regions emerging near the solar limb have been considered. It has been found that extended regions of high Doppler velocities with different signs are formed as the magnetic flux emerges in the horizontal velocity field. The flows appear when active regions start emerging and exist for a few hours. The peak values of the mean (inside the ±500 m/s isolines) and maximum Doppler velocities are up to 800-970 and 1410-1700 m/s respectively. The asymmetry has been detected between velocity structures of the leading and following polarities. Velocity structures located in the region of leading magnetic polarity are more powerful and exist for a longer period of time than those in theregions of following polarity. The asymmetry for the mean and maximum Doppler velocities is up to 240-460 and 710-940 m/s respectively. An interpretation of the observable flows of photospheric plasma is given.