Continued decline of South Pole neutron monitor counting rate

The counting rate of a neutron monitor at South Pole, Antarctica, displays a long-term decline over the 49year span from March 1964 to the present. The counting rate follows an 11year cycle with maxima at times of low solar activity. However, after adjusting for the unusually high overall cosmic ray fluxes in 2009, we find that the 2009 peak rate (based on 27 day averages) was approximately 10% lower than the 1965 peak rate. This change is much larger than that recorded by any other neutron monitor. We suggest that the South Pole monitor, owing to its unique position at both high latitude and high altitude may have a hitherto unsuspected sensitivity to secular changes in the magnetic field of the Earth.