QST de W1AW Special Bulletin 12 ARLX012 From ARRL Headquarters Newington CT December 30, 2019 To all radio amateurs New Solar Cycle 25 is on the way, but just when the transition from Solar Cycle 24 to Solar Cycle 25 will take place is not entirely clear. On December 24, two new sunspots - one in each hemisphere - emerged on the face of the Sun that exhibit the reversed magnetic polarity marking them as belonging to Solar Cycle 25. According to Hale's Law, sunspot polarities flip-flop from one solar cycle to the next, the National Center for Atmospheric Research explains. "The Sun is currently in solar minimum - the nadir of the 11-year sunspot cycle," Tony Phillips said in his article, "Reversed Polarity Sunspots Appear on the Sun" on the Spaceweather.com website. "It's a deep minimum, century-class according to sunspot counts." The remarkable sunspot scarcity has prompted discussion of a possible "extended minimum" akin to the Maunder Minimum in the 17th century, when no sunspots appeared for decades, Phillips said. "Such an event could have implications for terrestrial climate." This article can be found online at, https://spaceweatherarchive.com/2019/12/25/reversed-polarity-sunspots-appear-on-the-sun/ . "Today's new-cycle sunspots (along with isolated new-cycle spots earlier this year) suggest that the solar cycle is, in fact, unfolding normally," Phillips wrote, adding that a new Maunder Minimum does not appear to be in the offing. Earlier this month, the NOAA/NASA-co-chaired international Solar Cycle Prediction Panel released its latest forecast for Solar Cycle 25. The panel's consensus calls for a peak in July 2025 (+/- 8 months), with a smoothed sunspot number of 115 and the solar minimum between Solar Cycles 24 and 25 occurring in April 2020 (+/- 6 months). If this solar minimum prediction is correct, it would make Solar Cycle 24 the seventh longest on record at 11.4 years. The forecast can be found online at, https://www.swpc.noaa.gov/news/solar-cycle-25-forecast-update . Climate scientist David Archibald speculates that the Solar Cycle 24/25 minimum could occur as late as March 2021, and that Solar Cycle 25 maximum might not happen until 2027. "We are well into the Solar Cycle 24/25 minimum but [Cycle] 24 may not have ended yet," Archibald said in a December 22 update on the "Watts Up With That?" website. "A solar cycle isn't over until the heliospheric current sheet has flattened. And that could be as late as March 2021. Solar cycle amplitude does matter with respect to climate and the amplitude of Solar Cycle 25, from projecting trends from the last three cycles, looks like being about 80 in 2027." The Solar Cycle Prediction Panel agreed that Solar Cycle 25 will be of average intensity and similar to Solar Cycle 24. In an article posted on NOAA's Space Weather Prediction Center site, Scott McIntosh, the Director of the High Altitude Observatory at National Center for Atmospheric Research (NCAR - https://ncar.ucar.edu/ ), stresses that Solar Cycle 25 will happen, "but a sunspot cycle could be small." Predictability comes with some physical understanding of the underlying process, McIntosh asserts. "The sunspot cycle is erratic," he said in his presentation, "provocative of a chaotic, turbulent solar interior where sunspot progressions with time and latitude are the only tracers..." NNNN /EX
