Ground based limb survey of the sun polar regions in the H alpha line

Evolutions of the cool component of the inner solar corona have an importan t part in the equilibria and energy transport processes in the sun atmosphe re. Since 1994, a numerical daily survey of the entire limb in the Hydrogen H alpha line is performed with the HACO coronagraph at Pic-du-Midi observa tory. This experiment is included in the general ground based support progr ams for the SOHO mission. Real and differed time data are available within the solar data base BASS2000. A statistical study using the data set obtain ed during the first four years of this program shows some important propert ies of the distribution of the polar ejection and surge events. An asymmetr y between North and South polar regions is well established. Its sign rever seal near the time of the apparition of the new solar magnetic activity cyc le is discussed.