Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsh53a..05h&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SH53A-05
Physics
7513 Coronal Mass Ejections
Scientific paper
Calculating the total mass of a CME is a standard technique that has been used for several decades and which SOHO/LASCO has refined and automated. The total mass of a CME is only that material that arises from below the occulting disk. It doesn't consider any mass that has been swept up from within the field of view and moved, since we always consider a "pre-event" coronal state. In this paper we turn to the question of swept up material and investigate the evolution in height of the volume density of the region at the CME front. Often the post-CME corona is "cleaned out", meaning that it is very dim compared to the pre-event and general background. We thus assume that the material has been swept up by the CME expansion through that volume. Can LASCO detect that swept up mass? To investigate this we have selected only events that have a clearly defined leading and trailing edge to the CME front, and which in an ideal sense are examples of the "three-part" CME. We calculated the mass of those LASCO events, which also gives the column electron density. We convert that electron content to a volume density in a narrow region at the center of the front, by approximating the shape as a small section of a sphere. This enables us to say that the depth along the line of sight is the same as the angular latitudinal span, which we take to be on the order of a few degrees. We find that the volume density in such events decreases with increasing height by a simple power law with an exponent of -3. This is exactly what would be expected for purely radial expansion and no pileup of material in the front. We will discuss why the pileup isn't observed by LASCO and where implications for the height origin of these CMEs. We will also discuss the implications for the upcoming STEREO mission.
Howard Russ A.
Vourlidas Angelos
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