Periodic Oscillations in Coronal Mass Ejection Kinematics

Solar coronal mass ejections (CMEs) are large scale eruptions of plasma and magnetic field which are propelled into the heliosphere and can interact with the Earth causing adverse space weather. Typical CMEs have velocities between ~200-3500 km s-1, masses in range 1013- 1016 g and magnetic field strengths of tens of nT. The average daily CME rates varies with the 22-year solar cycle from ~5 CMEs per-day at solar max to less than one per-day at solar min.

Extensive coronagraph observations have been used to study the kinematics of CMEs < 30 RSun and more recently to 1 AU with heliospheric imagers. A number of studies have shown some evidence of CME quasi-periodic oscillations, that is the derived kinematic profiles (height, velocity, acceleration) appear to contain an oscillatory component. Two possible mechanisms which could cause these apparent oscillations are bursty reconnection and MHD waves. In bursty reconnection, the reconnection rate is modulated, which in turn modulates the magnetic forces accelerating the CME resulting in oscillatory kinematic profiles. Most CMEs are believed to contain magnetic flux ropes which can support MHD waves. Such waves have been observed in prominence structures, which can erupt as CMEs. Waves excited during the CME’s eruption would persist and evolve due to changes in the CME properties, density, magnetic field and size. As such these waves could provide interesting diagnostics about CMEs such as their magnetic field strengths.

Synthetic CME data sampled from known distributions was created and analysed using a number of techniques. The results indicated that methods previously used may over estimate the number of CMEs containing oscillations and their magnitude.

Presented at the INAM 2018 http://astrophysics.ie/inam2018/