How long to the 24/25 solar minimum?

Guest post by David Archibald

Climate has real world consequences, and those operating in fields that will be affected by changing climate bring a different perspective to the problem of predicting what will happen. Bill Fordham, advising the grain industry in the Midwest, kindly sent me a copy of the advice he provides to his clients. Following are two of his charts:

In Bill’s words,” Here is a chart of the 11-Year Sunspot Cycle you have probably never seen before! It is an 11-Year Average of the Monthly Sunspot Data. Why do I think it is important to look at an 11-Year Average? Because I am interested in how the ongoing 11-Year Average acts as we go forth in time with the droughts in the 1930’s and 1906.

I am also greatly interested in how the ongoing 11-Year Average acts as we go forth in time with the “Little Ice Age” that bottomed in 1816, the “Year Without A Summer”! The 1816 Eleven-Year Average Bottom was 327 months from the 1788 Eleven-Year Average Peak. If Sunspot history repeats similar to the 1788-1816 cycle, 327 m onths from the April 1990 Eleven-Year Average Peak will be in July 2017. For what it’s worth, the rate of decline since the 60 level was broken in April 1990 projects an 1816 level of 14.2 in just 44 more months from now, or by October 2016. If the current rate-of-decline in the 11-Year Average stays on track for another 44 months, we may need a few more blankets!”

This graph of Bill’s plots Solar Cycles 22 to 24 over Solar Cycles 3 to 6. What is interesting about this graph is that it suggests that the Sun has a limited playbook. Solar Cycles 22 and 23 are very similar in size and shape to Solar Cycles 3 and 4. But we are now coming up to big departure from how Solar Cycle 5 played out. To put that into context, let’s revisit the last prognostications of the Solar Cycle 24 Prediction Panel of 8^th May, 2009. Four years ago, they said that,”solar maximum is now expected to occur in May, 2013.” They got it right, possibly to the month, or at least very close. As solar cycle length is more important in controlling climate than solar cycle amplitude, it doesn’t matter so much that they got the amplitude wrong.

The above figure of the heliospheric current sheet from the Wilcox Observatory tells us that we are at the peak of the solar cycle, even though peak sunspot number was some time ago.

Now that we are at solar cycle maximum, there is only one prediction of future solar activity extant from the solar physics community. That is Livingstone and Penn’s estimate of Solar Cylce 25 maximum amplitude of 7. But the important number from here, the parameter that tells us what climate is going to do, is the time to the flattening of the heliospheric current sheet at the 24/25 minimum. So far the monthly sunspot number of Solar Cycle 24 has tracked Solar Cycle 5 very closely. Solar Cycle 5 was 12 years long. If Solar Cycle 25 is also to be 12 years long, the year of 24/25 minimum would be 2020. The climate implication of that is no net cooling over Solar Cycle 25 relative to Solar Cycle 24.

But there is a parameter which tells us exactly how long Solar Cycle 24 will be. That is the green corona emissions diagram produced by Richard Altrock, manager of the USAF coronal research program at Sacramento Peak, New Mexico. This is that diagram from June 2011:

I have annotated it to show the solar cycles over the same period. In his public statement, Altrock noted that Solar Cycle 24 was 40% slower than the average of the previous two cycles. That means that it is going to be 40% longer and that is borne out by the diagram. Solar minimum for the last four minima has occurred when emissions are exhausted at 10°. The latitude of 10° is shown as the red line on the diagram. Further to that, the last two solar cycles show that the month of minimum can be predicted by drawing a line between solar maximum (the point at which the rush to the poles intersects 76°) and the point of exhaustion at 10°. The bulk of activity is bounded by this line. On this line of evidence, Solar Cycle 24 will be 17 years long and the longest solar cycle for 300 years. We have a long wait ahead of us – half a generation.

While we are waiting for minimum, someone could do the world a very good service and take Bill Fordham’s interest in the droughts of the 1930’s and 1906 a bit further and calculate, on a year by year basis, what the Corn Belt would produce if the climate of the period 1800 to 1850 was repeated. Then we would know with enough certainty what we are in for – both the quantum and the volatility.