| SB PROP @ ARL $ARLP004
ARLP004 Propagation Update
ZCZC AP04
QST de W1AW
Propagation Forecast Bulletin 4 ARLP004
From ARRL Headquarters
Newington CT February 7, 2025
To all radio amateurs
SB PROP ARL ARLP004
ARLP004 Propagation Update
Spaceweather.com reports that sunspot 3981 has produced more than 20
M-class solar flares, including two that almost reached category X.
The activity is likely to continue today. The sunspot retains a delta-class magnetic field that harbors energy for frequent explosions.
The current solar forecast calls for there to be no G1 (Minor) or greater geomagnetic storms. A potential glancing blow is possible on February 7 and 8.
Solar radiation – as observed by NOAA GOES-18 over the past 24 hours – was below the S-scale storm level thresholds. (The S-scale is used to indicate the severity of energetic particles emitted from the Sun.) The scale ranges from S1 (minor) to S5 (extreme).
There is a chance for S1 (Minor) or greater solar radiation storms due to the complex cluster of sunspot groups in the Northwest Quadrant of the Sun.
Radio Blackouts are expected through February 8, with a chance for R3 (Strong) events due to several magnetically complex sunspot groups.
There is a chance for S1 (Minor) or greater solar radiation storms through February 9 as the complex cluster of sunspot regions in the north continues to rotate closer to the western limb.
The geomagnetic field activity is expected to be unsettled to active levels on February 10 to 19.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s Ionosphere, February 6, 2025, from F. K. Janda, OK1HH:
“The current 11-year solar cycle beautifully shows how little we still know about the universe we live in. Including the Sun, which is a relatively very stable star (otherwise we wouldn’t be here). Each ‘eleven year’ cycle is different from all the previous ones,
and all previous attempts to predict the next one have always failed. Better said – some of them have proven to be valid. But only some.
“The current developments do not appear to be complex. Coronal holes 11 and 12 were followed by the somewhat surprisingly active regions of AR3976 – 3971, where eruptive activity rose and fell irregularly. Occasionally including CMEs, which although they mostly did not hit the Earth, sometimes partially did.
“The ionospheric shortwave propagation conditions were therefore mostly above average, but at the same time very variable. There was no way to accurately predict their course, even if only for the next
24 hours. On the other hand, there was no major disturbance that would have made them significantly worse. There is only one thing to say about the future development: it will be relatively easy to predict at first sight. But only at first sight, the reality will probably be more different than usual.”
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Service web page at arrl.org/propagation-of-rf-signals.
For an explanation of numbers used in this bulletin, see
arrl.org/the-sun-the-earth-the-ionosphere.
An archive of past propagation bulletins is located at,
arrl.org/w1aw-bulletins-archive-propagation.
Check out this QST article about Solar Indices:
https://bit.ly/3Rc8Njt
The predicted Planetary A index for the period February 9 to 14 is 5, 10, 15, 15, 20, and 10. The predicted largest Kp index is 2, 3, 3, 4, 5, and 3. Predicted 10.7 cm flux is 200, 200, 195, 195, 195, and 190.
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