Subj : The ARRL Solar Update To : QST From : ARRL de WD1CKS Date : Fri Sep 26 2025 22:41:45 09/26/2025 Solar activity reached moderate levels this past week. An impulsive M1.0 flare was observed on September 24 from Region AR4217. Slight growth was observed in Region AR4226 with an increase in spots near the leader. New Regions AR4229 and AR4230 were numbered this period. All other regions were either stable or in decay. No Earth-directed CMEs were observed. Solar activity is expected to return to low activity. Solar wind parameters were indicative of the arrival of a negative polarity Coronal Hole High Speed Stream (CH HSS). Solar wind speed increased from approximately 310 km/s to near 530 km/s. Total field showed an increase beginning on September 22. The CH HSS influence persisted through September 23 and diminished to background levels on September 25. A trend towards nominal solar wind conditions is expected through September 26 as Earth moves out of a geoeffective position with the CH HSS. Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, September 25, 2025, by F. K. Janda, OK1HH: "A study published on September 8 in the Astrophysical Journal Letters states that solar activity will increase after approximately sixty years of decline (following the high Solar Cycle No. 19). The next solar cycles should be even higher than the current one and, in particular, higher than the previous one (i.e., than Solar Cycles 24 and 25). "Short-term developments in the second half of September are in line with forecasts. Overall solar activity has increased, although eruptive activity is slightly lower than expected. In line with the forecast, on September 21, the Earth's magnetic field entered the common rotation interaction (CIR) region and the solar wind intensified. After a two-day increase that began on September 24, geomagnetic field activity declined again. Although the forecasts are based primarily on the expected increase in the speed of the solar wind flowing from the edges of coronal holes, while should therefore be less accurate than forecasts based on observed eruptions and CMEs, they are still relatively reliable. "Most sunspot groups are now on the solar disk (the visible part of the Sun), but they will gradually begin to set. Solar activity should therefore decline by the end of September, with the decline likely to stop in mid-October. In the Earth's ionosphere, the decline in maximum usable frequencies (MUF) will begin with a slight delay, similar to the expected rise in the second half of the month." There is a chance for isolated R1-R2 (Minor-Moderate) radio blackouts until September 28. Unsettled to active levels are likely on September 29 and 30, October 3 to 7, October 11 to 13, and on October 18 due to recurrent CH HSS influences. Quiet to unsettled levels are likely for the remaining days in this outlook period. The geomagnetic field is expected to be quiet to unsettled levels on September 27, and quiet to active levels on September 28. The latest video report from Dr. Tamitha Skov, WX6SWW, can be found on YouTube at, https://www.youtube.com/watch?v=xzoxXGTDLyM[1] . The Predicted Planetary A Index for September 27 to October 3 is 5, 5, 15, 8, 5, 5, 5, and 15, with a mean of 8.3.ÿ Predicted Planetary K Index is 2, 2, 5, 3, 2, 2, and 5, with a mean of 3.ÿ 10.7 centimeter flux is 175, 170, 170, 170, 160, 150, and 140, with a mean of 162.1. For more information concerning shortwave radio propagation, see http://www.arrl.org/propagation[2] and the ARRL Technical Information Service web page at, http://arrl.org/propagation-of-rf-signals[3]. For an explanation of numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere[4] . Information and tutorials on propagation can be found at, http://k9la.us/[5] . Also, check this: https://bit.ly/3Rc8Njt[6] "Understanding Solar Indices" from September 2002 QST. ÿ [1] https://www.youtube.com/watch?v=xzoxXGTDLyM [2] http://www.arrl.org/propagation [3] http://arrl.org/propagation-of-rf-signals [4] http://arrl.org/the-sun-the-earth-the-ionosphere [5] http://k9la.us/ [6] https://bit.ly/3Rc8Njt --- þ Synchronet þ Whiskey Lover's Amateur Radio BBS .