The Sun's Polar Magnetic Flux from 1996-2006 Observed With SOHO/MDI
Abstract
Observations of the Sun's magnetic field using nearly 10 years of full-disk SOHO/MDI data are used to investigate the net flux and total flux of the polar regions.The northern pole above 78 degrees changed polarity in April 2001 (CR 1974), five rotations before the southern pole (August, 2001, CR 1979). These dates are a little earlier than those found by Durrant and Wilson (2003): CR 1975 in the north and CR 1981 in the south.Solar cycle changes in the total polar magnetic flux are more difficult to determine. Most of the polar measurements are near the noise level due to the extreme reduction in the line-of-sight component due to projection effects near the limb. Determination of the total flux is highly sensitive to changes in noise due to the different MDI observing modes, to systematic errors in the instrument, and to the exact method of processing the data (e.g. spatial and temporal averaging). Periodic orientation changes of the SOHO spacecraft in recent years allow better characterization of the systematic errors. Observations taken at different inclinations of the solar rotation axis also help characterize the known errors to provide a better estimate of the solar polar flux with time.
- Publication:
-
AAS/Solar Physics Division Meeting #37
- Pub Date:
- June 2006
- Bibcode:
- 2006SPD....37.0702H