A coronal mass ejection is an expulsion of plasma and embedded magnetic field from the solar corona into interplanetary space. It carries matter as well as magnetic structure. A solar flare instead denotes a rapid atmospheric energy-release event observed through enhanced radiation; the two phenomena can accompany the same eruption without being interchangeable.[ref]
Coronal Mass Ejections by NOAA Space Weather Prediction Center. Definition and distinction between expelled plasma/field and associated solar activity
A coronagraph suppresses the bright solar disc so that much fainter coronal structures can be followed outward. A sequence of images gives projected size, motion and morphology. SOHO's LASCO observations provide an important example of the instrument-based diagnosis used in space-weather analysis.[ref]
Coronal Mass Ejections by NOAA Space Weather Prediction Center. Coronagraph imagery, LASCO observations and inferred size, speed and direction
For an illustrative measurement, suppose an apparent front moves from projected radius to in one hour. Using givesThis is a plane-of-sky speed, not automatically the true radial speed. Projection, the choice of visible front and evolution between frames affect the inference. Motion mainly towards the observer can produce a surrounding halo in projection rather than a simple sideward trajectory.
A passing interplanetary disturbance can also be studied through local solar wind density, velocity and magnetic-field measurements. A leading shock wave and the magnetized ejecta are different parts of that disturbance. Combining remote imaging with local measurements is more informative than treating brightness or apparent speed alone as a complete description of the eruption.
Articles by others on the same topic
A Coronal Mass Ejection (CME) is a significant release of plasma and magnetic fields from the solar corona, which is the outer layer of the Sun's atmosphere. CMEs are often associated with solar flares and active regions, but they can occur independently as well. During a CME, large quantities of solar material (primarily electrons and protons) are expelled into space at high speeds, sometimes reaching millions of kilometers per hour.