The development of the solar polar field strength throughout a solar sunspot cycle can be used to predict the magnitude of the next cycle and the peak of the current cycle. Polar field reversals typically occur within a year of sunspot maximum. It is not uncommon for the northern and southern polar fields to have significant differences in field strength and develop asynchronously over time. The Wilcox Solar Observatory has been collecting solar polar field data since 1975. Non-filtered data can be viewed in this plot. Below you will find a plot where only the filtered (by a 20 nHz lowpass filter) field strength data is displayed. Vertical lines representing field reversals and sunspot cycle min/max have been added to increase the potential usefulness of the plot.
There is some interest in when solar cycle 24 will peak. The current data indicates that the northern polar field could reverse polarity in June or July 2011 while the southern polar field reversal is many months into the future. Current projections are that both fields will have reversed sometime between February 2012 and December 2012. Based on previous solar cycles and the current polar field situation, the maximum for cycle 24 could be reached earlier than expected, probably sometime in 2012.
Wilcox Solar Observatory data used in this study was obtained via the web site http://wso.stanford.edu courtesy of J.T. Hoeksema.