Given that the number of sunspots is subject to large fluctuations on both daily and monthly time scales, aggregating a 13-month boxcar average with half-weights on the first and last month can be a helpful indication of the average number of sunspots over an extended period. This smoothing process is frequently used when charting solar activity over time, and it effectively tracks long-term changes in sunspot numbers over the entirety of a solar cycle.
The 13-month boxcar average is calculated using the monthly average numbers of sunspots, Rm (found using Wolf’s Number).
In addition to the extensive historical record of sunspots, there now exists a trove of data from modern solar observations, obtained both from the ground and by a flotilla of spacecraft. Moreover, astrophysical models of the Sun and its processes have reached a high degree of refinement. By combining all of this information, and by adopting a variety of forecasting methods, predictions of the intensity of upcoming solar cycles can be generated.
Accurate knowledge of the relative strength of the next cycle would have profound implications for satellite operations, radio communication, and power transmission. For example, if Cycle 25 generates a high sunspot number at solar maximum, it will be associated with increased upper-atmospheric drag. On the one hand, atmospheric drag can be beneficial, as drag removes dangerous space junk from orbit. With a strong maximum, however, satellite operators face increased risk of solar flares destroying satellite electronics and damaging solar panels. High levels of solar activity enhance long-range radio communication, but they are associated with coronal mass ejections (which generate geomagnetic storms) that can wreak havoc with terrestrial power grids.
At present (late Summer 2020) Solar Cycle 24 has reached its end, and solar activity is close to a minimum. Forecasts for the upcoming Solar Cycle 25, however, differ wildly. We thus ask:
What will be the 13-month mean sunspot number for the year of Solar Cycle 25’s maximum?
For context, the minimum of Cycle 24 occurred in December of 2008 with a total of 2.2 sunspots as a monthly average, and the maximum occurred in April of 2014 with a monthly average of 116.4. Data for this can be found here.
The Sunspot Index and Long-term Solar Observations (SILSO) site records the number of sunspots per month with individual and group numbers, as well as monthly means. Using the monthly numbers from this site the 13-month mean can be computed once sufficient time has elapsed.