An Expansion on Solar Cycle Prediction

SC25 officially began as of December 2019, and was given a forecasted maximum sunspot number (SSN) of 115, predicted to take place around July 2025, as stated by NOAA. As the months passed, sunspot numbers quickly began to exceed the forecast for any given month in the middle of 2020, which then accelerated further in the beginning of 2021. As of March 2021, the sunspot number was regularly well above the forecasted amount, leading to a smoothed average over double what was predicted. Arrive at January 2023, NOAA had a forecasted average value of 63.4, whereas the measured value landed on 143.6!

As a comparison, this number is slightly higher than the first monthly average peak in SC24, and just barely under the second peak. More impressively in the numbers for January is the second index that is observed during the solar cycle, the Solar Flux Index, also denoted as the f10.7.

The Solar Flux Index (SFI) is a number that looks at how much light the sun emits specifically at a wavelength of 10.7cm, which translates to a radio frequency of 2800 megahertz, just within the Ultra High Frequency bands. This index generally increases and tonightsdecreases with sunspot number, but also increases as sunspot complexity increases, which leads to higher numbers during sunspot maximum. When January numbers were posted, the average SFI for January came out to 182.5, with several individual days sitting above 200!

These numbers are quite a bit higher than anything SC24 saw during its time and show a very sharp deviation even from the averaged numbers in SC25 thus far. This number can be attributed to the numerous amounts of sunspot regions present during January that also showed moderate-to-high level complexity in their forms. It’s clear the forecast set by NOAA back in 2019 will likely fall significantly short of the actual cycle strength we will see come solar maximum. How has McIntosh and his team’s forecast gone so far in comparison using the Hale Cycle Termination work?

The estimated maximum SSN ultimately finalized at a value of 184 with 95% confidence that the true value will lie between 121 and 247. Even the lower end of this estimate lies near the very top of the forecast set by NOAA. The chart below shows SSN values over time, with several of the forecasts and measured values superimposed on top. The measured daily values, and those values averaged month to month, are the thin green and bold black lines, respectively. These are then compared to the NOAA forecast with solar maximum 6 months early (blue line), and the McIntosh forecast (red line). When looking at this chart, the vast differences in recorded values and NOAA estimates are apparent, but what is more interesting is the much closer agreement to the McIntosh forecast. Similarly, the second photo below shows the current and forecasted solar flux values using the Hale Cycle Termination work.