Active Longitudes Over Three Solar Cycles
M. Snow and T. Woods, Laboratory for Atmospheric and Space Physics (LASP), University
of Colorado, Boulder; and O. R. White, Lazy FW Ranch, Mancos, Colorado, and LASP,
University of Colorado, Boulder
Prior observations of solar activity have shown that there are longitudes on the Sun which
produce active regions consistently for years at a time. Using the Mg II index record, we
have determined the relative activity on the Sun as a function of Carrington longitude for
each rotation since 1978. There is a longitude band of enhanced activity that persists not just
for a few years, but actually persists over multiple solar cycles. This longitude has an
apparent period of 26.4 days as seen from the Earth. At solar maximum, there is strong
activity at all longitudes on the Sun which masks the contribution from this band, but in the
declining phase, activity from this one longitude band is predominant. Time series data from
other wavelengths, such as He II, confirm this result.