Solar Cycle Trends and The Gleissberg Cycle


This month's Sky & Telescope magazine mentions an interesting study presented in a press release from the International Astronomical Union's 29th General Assembly held this past summer.

Frederic Clette (Royal Observatory of Belgium) and colleagues analyzed the past 400 years of sunspot records and found that the (previously believed) upward trend in solar activity is really a calibration error. They found instead, that solar activity has been relatively stable since the 1700s.

The IAU's summer press release goes on to say ...

" The Sunspot Number, the longest scientific experiment still ongoing, is a crucial tool used to study the solar dynamo, space weather and climate change. It has now been recalibrated and shows a consistent history of solar activity over the past few centuries. The new record has no significant long-term upward trend in solar activity since 1700, as was previously indicated. This suggests that rising global temperatures since the industrial revolution cannot be attributed to increased solar activity.

The results ... make it difficult to explain the observed changes in the climate that started in the 18th century and extended through the industrial revolution to the 20th century as being significantly influenced by natural solar trends.

The apparent upward trend of solar activity between the 18th century and the late 20th century has now been identified as a major calibration error in the Group Sunspot Number. Now that this error has been corrected, solar activity appears to have remained relatively stable since the 1700s

The newly corrected sunspot numbers now provide a homogeneous record of solar activity dating back some 400 years. Existing climate evolution models will need to be reevaluated given this entirely new picture of the long-term evolution of solar activity. This work will stimulate new studies both in solar physics (solar cycle modelling and predictions) and climatology, and can be used to unlock tens of millennia of solar records encoded in cosmogenic nuclides found in ice cores and tree rings. This could reveal more clearly the role the Sun plays in climate change over much longer timescales. "

courtesy: World Data Center - SILSO
The graph above shows the Group Sunspot Numbers (GSN) measured over the past 400 years following the new calibration. The Maunder Minimum, between 1645 and 1715, when sunspots were rare and winters harsh, is clearly evident.

I found this graph particularly interesting with regards to long-term affects on propagation as it illustrates the upcoming predicted Gleissberg Cycle, the 'cycle within the Cycle' ... a period of several weak 11-year cycles in a row and lasting from 80-90 years ... great news for low-frequency fans but not so good for 6m diehards

Maybe we'll get one more humdinger before it arrives!

Steve McDonald, VE7SL, is a regular contributor to and writes from British Columbia, Canada. Contact him at [email protected].

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