Geometry of Coronal Mass Ejections in the Context of Recent Solar Cycle

Coronal mass ejections (CMEs) disrupt the flow of the solar wind and produce disturbances that strike the Earth with sometimes catastrophic results. These ejections are often associated with solar flares and prominence eruptions, but they can also occur in the absence of either of these processes. The frequency of CMEs varies with the sunspot cycle. At the solar minimum we observed about one CME a week. Near the solar maximum we could observe an average of 2 to 3 CMEs per day. We have studied different CME characteristics based on the observation with Large Angle and Spectrometric Coronagraph (LASCO) on board of the Solar and Heliospheric Observatory (SOHO) space craft during the period 1996-2006. It is noteworthy that the rate of occurrence of class B CMEs (with the measurement position angle (MPA) in the range 200°-360°) is greater than that for class A CMEs (the MPA in the range 50°-200°). The CME occurrence spectrum for both classes follows the trend of the phase of solar cycle, and the maximum number of both type CMEs seems to occur during the maximum solar activity. It is also observed that the maximum numbers of class A, class B CMEs are in a speed range of 0-500 km/s. We have observed that the maximum number of class A, class B CMEs occurred in the apparent angular width range 0°-90°. It is also found that the maximum numbers of class A and class B CMEs occur when the position angle ranges in 5°-100° and 250°-300° respectively.