Guest essay by David Archibald
The following is a series of graphs that depict the current and past state of the sun.
Figure 1: Solar Cycle 24 relative to the Dalton Minimum
Solar Cycle 24 had almost the same shape as Solar Cycle 5, the first half of the Dalton Minimum, up to about six months ago and is now a lot stronger.
Figure 2: Monthly F10.7 Flux 1948 to 2014
The strength of the current solar cycle is confirmed by the F10.7 which is not subject to observer bias. Solar Cycle 24 is now five and a half years long.
Figure 3: Ap Index 1932 to 2014
The biggest change in solar activity for the current cycle is in magnetic activity which is now at the floor of activity for the period 1932 to 2007.
Figure 4: Heliospheric Tilt Angle 1976 to 2014
Peak of the solar cycle has occurred when heliospheric tilt angle reaches 73°. For Solar Cycle 24, this was in February 2013. It is now heading down to the 24/25 minimum.
Figure 5: Interplanetary Magnetic Field 1966 to 2014
This looks like a more muted version of the Ap Index. The main difference between them is that the IMF was a lot flatter over Solar Cycle 20 than the Ap Index.
Figure 6: Sum of Solar Polar Field Strengths 1976 to 2014
This is one of the more important graphs in the set in that it can have predictive ability. The SODA index pioneered by Schatten is based on the sum of the poloidal fields and the F10.7 flux. This methodology starts getting accurate for the next cycle a few years before solar minimum. If Solar Cycle 24 proves to be twelve years long, as Solar Cycle 5 was, then the SODA index may start being accurate from about 2016. In terms of solar cycle length, the only estimate in the public domain is from extrapolating Hathaway’s diagram off his image. Hathaway’s curve-fitting suggests that the Solar Cyce 24/25 minimum will be in late 2022. If so, Solar Cycle 24 will be thirteen years long, a little longer than Solar Cycle 23.
It seems that Livingstone and Penn’s estimate of Solar Cycle 25 amplitude of 7 remains the only one in the public domain. The reputational risk for solar physicists in making a prediction remains too great.
David Archibald, a Visiting Fellow at the Institute of World Politics in Washington, D.C., is the author of Twilight of Abundance: Why Life in the 21st Century Will Be Nasty, Brutish, and Short (Regnery, 2014).