Impacts of extended periods of low solar activity on climate

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Monday, 18 January 2010
Matthew J. Niznik, Rutgers, the State University of New Jersey, New Brunswick, NJ; and W. F. Denig

The present lull in solar activity which has persisted since early this decade has been a clear break from the more active cycles during the second half of the twentieth century. As a result, there has been some speculation that Solar Cycle 24 will be weak and perhaps even anomalous. Using data from NOAA's National Geophysical Data Center in Boulder, Colorado, the number of days each year that the sunspot number is relatively small can be examined in order to compare the current lull in solar activity to other historically low periods. Of particular interest is the number of days with a sunspot number less than ten since this non-zero upper bound makes discrepancies in observations less significant, accounting for human error to some extent. We introduce a new index, the Genesis Minimum Quiet Day Index, derived from this categorized data which shows a significant correlation between the inactivity of the sun preceding a solar cycle and its maximum average monthly smoothed sunspot number. This new index predicts that the current period of solar inactivity is not anomalous, and this finding allows for informed commentary on the implications of Solar Cycle 24, as well as more extreme solar minima, on Earth's climate and how these impacts relate to projected anthropogenic warming.