Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...688..647l&link_type=abstract
The Astrophysical Journal, Volume 688, Issue 1, pp. 647-655.
Astronomy and Astrophysics
Astronomy
3
Sun: Activity, Sun: Coronal Mass Ejections (Cmes)
Scientific paper
We use the large database of coronal mass ejections (CMEs) observed by SOHO LASCO during solar cycle 23 to statistically obtain information about the source regions of CMEs. By determining the functional form of the position angle (P.A.) distribution, we are able to construct a random set of CME direction vectors (DVCME) under the following conditions: (1) assume a radial movement of the CME center of mass and (2) propose a latitude and longitude (λ, φ) photospheric position for the DVCME in such a way that (3) the distribution of the projected (on the plane of the sky) DVCME must be equal to the observed distribution of position angles. We iteratively adjust the proposed positions (λ, φ) until both distributions are equal, based on the Kolmogorov-Smirnov statistics. In this way, we obtain a set of DVCME that we use to study the relation between the CME source region and the overall coronal and photospheric magnetic field structures. We found that the CME activity has a small ``preference'' for the northern hemisphere during the first part of solar cycle, and for the southern hemisphere during the second part. This P.A. asymmetry is related to the overall magnetic field north-south asymmetry. We found also that most CME source regions are situated between high magnetic field regions, and are not necessarily associated to any one such region. For instance, during the minimum and ascending phase of the cycle, ~85% and ~60%, respectively, of the CME source regions are confined to the equatorial plane (λ=0deg), between the two active region belts (λ=+/-40deg). We conclude from this study that CME sources are in general high-altitude magnetic loops, or more precisely, transequatorial loops, occurring during the minimum and ascending phases of the cycle.
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