Friday, February 11, 2011

Dalton or Maunder?

NASA lowers prediction for Solar Cycle 24 again

With the continued failure of solar cycle 24 to produce the expected levels of sunspot activity, NASA reduced their predictions for the maximum sunspot number to 58, less than half of the the recently passed cycle 23.

Why is this important?  You can hardly see a sunspot, right?  Sunspot cycles have been shown to have a strong correlation with climate in the past.  Two sunspot minimum periods have occurred in the historical past, the Maunder minimum, and the Dalton minimum, both of which were associated with extended periods cold climates world wide. 

As you can see from the chart below, the current prediction for Solar Cycle 24 is in the range of sunspot number observed during the Dalton minimum, which lasted 2-3 cycles.  So it would appear quite likely that we are going into at least a Dalton sized minimum.  But also note that the Maunder minimum, a much longer and more severe event,  seems to have been preceded by a few weaker cycles too.

The link between the sunspot minima and the climate is poorly understood.  While the sunspot activity reflects solar activity, the change in radiation from the sun itself is not sufficient to account for the cooling trends.  However,  during sunspot minima, the suns magnetic field is much weaker and one recent theory suggests that the reduced magnetic fields allow more cosmic rays to strike the earth's atmosphere, which help initiate cloud formation, and the increased clouds reflect more light, and cool the earth.

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