Coronal electron density over a full solar cycle - Implications for the solar wind velocity
Abstract
In January 2008, the LASCO-C2 coronagraph aboard SOHO has completed 12 years of quasicontinuous observations of the solar corona from 2 to 6 solar radii, that is over a full solar cycle. We study the temporal evolution of the electron density derived from the calibrated pB images over this unsurpassed time span, first globally, and then by distinguishing different latitude intervals so as to characterize the the equatorial and polar regions. The local density moderately increases with activity (factor 2), as the bulk of the increase essentially results from the development of new sources associated to emerging neutral or current sheets. We extensively study different typical structures of the corona, polar and trans-equatorial holes and the streamer belt to constrain the velocity profiles of different regimes of solar wind. Finally we combine LASCO-C2 density profiles, SWAN mass flux data and interplanetary solar wind velocities derived from ground-based Interplanetary Scintillation Observations (IPS) to conclude that the fast solar wind reaches its terminal velocity about 6 solar radii, and expands with constant velocity beyond this distance, while the slow solar wind reaches only half its terminal velocity value at this distance and thus continues its acceleration further out.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.1687L