  Although a variety of phenomena may create a geomagnetic storm on Earth, the
most severe geomagnetic storms arise from solar activity, and in particular,
coronal mass ejections (CMEs) and solar flares. CMEs and flares originate
primarily from sunspots. The "aa index" is a metric which ranks all of the
strongest geomagnetic storms between 1868 and 2010 based on a variety of
characteristics taken from several sources. This paper examines correlations
between the aa index of the most severe geomagnetic storms and the intrinsic
characteristics of the sunspots from which they originated. We find a
correlation between the total rank of the aa index of the storms and the "total
intensity" of the sunspot, where total intensity is defined as the sunspot's
mean intensity multiplied by its area. The correlation has an R-Squared = 0.690
and R-Squared = 0.855 when a potentially corrupted data point is removed.
