Energetics of Solar Coronal Mass Ejections

Coronal mass ejections (CMEs) from the sun are now recognized to be the primary progenitors
of near-earth space weather disturbances. The overall energetics of these structures
involve the amount of energy required to initiate it by disrupting an originally stable
magnetic structure and lift it against the gravity of the sun, and the energy required
to propagate it through the heliosphere. Using mass images obtained from the LASCO instrument
aboard the SOHO Satellite (Fig 1) and data from a variety of other sources, it has recently been
realized that a significant fraction of CMEs are clearly driven, for their
mechanical energy increases with time. Subramanian & Vourlidas (2007, to appear in Astronomy &
Astrophysics, astro-ph/0701160) seek to address the origin of the driving power for such
CMEs from approximately 2 to 30 solar radii. They find that the magnetic fields associated
with the CME are a viable source of driving power for these CMEs. They also find no evidence
to suggest that the driven CMEs are "dragged" along by the ambient solar wind.

(Prasad Subramanian)

A montage of mass images for a structured CME propagating outwards from
the sun. The circular structure is envisaged to be the cross-section of a magnetic
flux rope. These images give the surface density (g per square cm) at each pixel, and
enable us to easily calculate the mechanical energy of the CME as it evolves in time.