| SB PROP @ ARL $ARLP041
ARLP041 The ARRL Solar Report
ZCZC AP41
QST de W1AW
Propagation Forecast Bulletin 41 ARLP041
From ARRL Headquarters
Newington CT, October 31, 2025
To all radio amateurs
SB PROP ARL ARLP041
ARLP041 The ARRL Solar Report
Solar activity has decreased to very low levels. Region 4266 exhibited signs of slight development as it gained asymmetric penumbra surrounding its trailing spots. Meanwhile, Region 4267 underwent decay, losing several leading spots. Additional activity included a coronal mass ejection (CME) off the NE limb on October 29.
An associated Type II radio sweep was reported with the CME; however, SUVI 195 imagery revealed the CME to have originated on the far side. Also, an approximate 12-degree filament eruption, centered near N27W24, was observed becoming unstable beginning on October 29. Most of the material of this event appeared to have been reabsorbed, with perhaps a faint and narrow CME escaping. Modeling of this event revealed a possible glancing blow to the north of Earth by late on November 2, but confidence is low in both the analysis of this event and the modeling outcome.
Solar wind parameters continued to reflect positive polarity coronal hole high-speed stream (CH HSS) influences. Solar wind parameters are expected to continue to reflect positive CH HSS influences through November 1.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s Ionosphere, October 30, 2025, by F. K. Janda, OK1HH:
“It is very rare for the situation on the Sun and between it and Earth to be as relatively simple and clear as it has been in recent days. This is one of the reasons why it was possible to make a fairly accurate prediction of further developments. Although there were concerns that an intensified solar wind could hit Earth as early as October 26, the original forecast ultimately proved accurate, and the disturbance began on October 28. The last weekend in October was thus marked by relatively good conditions for radio wave propagation on all shortwave bands.
“Regular helioseismological observations of the far side of the Sun are closely monitoring the only two currently active regions on the Sun. They will begin to emerge on the eastern edge of the solar disk in the first half of next week, which will immediately be reflected in an increase in solar flux. This may peak around October 10, but it seems that it will happen sooner.
“The increase in solar activity during the usual favorable seasonal changes alone will result in improved conditions for shortwave propagation. With a little luck, the improvement could peak around November 8, when the next increase in geomagnetic activity can be expected.”
Solar activity is expected to be at moderate levels until November 15 due to the return of Region 4246. Low levels are expected to prevail from November 14 to 22 as multiple regions depart the visible disk.
A greater than 2 MeV electron flux at geosynchronous orbit is expected to be at high levels until November 15 due to responses from recurrent CH HSS influences. Moderate levels are expected from November 16 to 22.
Geomagnetic field activity is expected to be at quiet to unsettled levels on November 1 to 6, 10 to 14, and November 16 to 22. Active conditions are expected from November 7 to 9 and November 15.
The latest video report from Dr. Tamitha Skov, WX6SWW, can be found on YouTube at https://www.youtube.com/watch?v=y8uEPcivbQ8.
Spaceweather.com for October 31 reports on “Halloween Fireballs” and the rapid brightening of Comet 3I/ATLAS.
The Predicted Planetary A Index for November 1 to 7 is 8, 5, 5, 5, 5, 5, 8, and 12, with a mean of 6.9. Predicted Planetary K Index is 3, 2, 2, 2, 2, 3, and 4, with a mean of 2.6. 10.7-centimeter flux is 130, 130, 135, 140, 140, 140, and 140, with a mean of 136.4.
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Service web page at www.arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere. Information and tutorials on propagation can be found at http://k9la.us.
Also, check this: “Understanding Solar Indices” from September 2002 QST. https://bit.ly/3Rc8Njt
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