Subj : The ARRL Solar Update To : QST From : ARRL de WD1CKS Date : Fri Oct 10 2025 23:17:06 10/10/2025 Solar activity has been at moderate levels for the past 24 hours. Solar activity is expected to be low with a chance for M class flares. Solar wind speed reached a peak of 1124 km/s. Solar activity reached moderate levels following an M2.0 flare (R1-Minor) at from a region just around the Northwestern limb. Only low-level C-class activity was observed from the remaining spotted regions on the visible disk. New Regions 4248 and 4249 were numbered as they emerged late in the period, but were otherwise unremarkable. A chance for R1-R2 (Minor-Moderate) radio blackouts exists over October 10 to 12 due to flare potential from several active regions returning from the Suns far side. Spaceweather.com[1] reports on October 10, a hole has opened in the sun's atmosphere, and it is venting a stream of solar wind directly toward Earth Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - October 10,2025 Solar activity has been declining since the beginning of October, as expected. The last slightly larger sunspot group, designated as active region AR 4236, disappeared behind the northwestern limb of the solar disk in the middle of the present week. Almost immediately after it became invisible to us, a moderately strong eruption occurred. This happened on Thursday, October 9, peaking at 12:31 UTC. However, the decline in solar activity will continue, followed by an increase that should last for almost the entire second half of October. This will include a positive effect on the state of the F2 ionospheric layer. Although this did not bring such good conditions for shortwave propagation, precisely because of the decline in solar radiation, there were interesting improvements here and there - especially at the beginning of geomagnetic disturbances, most recently on the afternoon of October 7. However, another phenomenon played a major role in the surprising improvement in shortwave propagation conditions between Europe and the Antipodes on October 8 - the rare and rather unusual occurrence of a sporadic E layer at this time of year... Official forecasts of increased solar activity for the second half of October are rather skeptical for the time being. This is probably because the activity on the far side of the Sun, as measured by helioseismological methods, is not high. However, this may change. A surprise in the form of faster growth cannot be ruled out. The latest report from Dr. Tamitha Skov, WX6SWW, can be found on Youtube. The predicted Planetary A Index for October 11 to 17 is 15, 12, 10, 8, 5, 5, and 5 with a mean of 8.5. The Predicted Planetary K Index is 5, 4, 3, 3, 2, 2 and 2 with a mean of 3. Predicted 10.7 centimeter flux is 140, 135, 135, 140, 135, 140 and 145 with a mean of 137.1. 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] http://Spaceweather.com [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 .