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Quasi-periodic oscillations in LASCO coronal mass ejection speeds

Quasi-periodic oscillations in the speed profile of coronal mass ejections (CMEs) in the radial distance range 2–30 solar radii are studied. We considered the height–time data of the 307 CMEs recorded by the Large Angle and Spectrometric Coronagraph (LASCO) during 2005 January–March. In order to study the speed–distance profile of the CMEs, we have used only 116 events for which there are at least 10 height–time measurements made in the LASCO field of view. The instantaneous CME speed is estimated using a pair of height–time data points, providing the speed–distance profile.We found quasi-periodic patterns in at least 15 speed–distance profiles, where the speed amplitudes are larger than the speed errors. For these events we have determined the speed amplitude and period of oscillations. The periods of quasi-periodic oscillations are found in the range 48–240 minutes, tending to increase with height. The oscillations have similar properties as those reported by Krall et al., who interpreted them in terms of the flux-rope model. The nature of forces responsible for the motion of CMEs and their oscillations are discussed.

Sun: corona; Sun: coronal mass ejections (CMEs); solar wind

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