SB PROP @ ARL $ARLP016
ARLP016 The ARRL Solar Report
ZCZC AP16
QST de W1AW
Propagation Forecast Bulletin 16 ARLP016
From ARRL Headquarters
Newington CT May 2, 2025
To all radio amateurs
SB PROP ARL ARLP016
ARLP016 The ARRL Solar Report
On May 2, Spaceweather.com reported: "Astronomers are monitoring a very large
sunspot now turning toward Earth. Sunspot AR4079 stretches more than 140,000
km from end to end and has two dark cores each large enough to swallow Earth.
Moreover, it is surrounded by a ring of Ellerman Bombs.
"Ellerman bombs are a sign of magnetic complexity in a sunspot. Opposite
polarities bump together, reconnect, and--boom! A full-fledged flare may not
be far behind."
Solar activity increased to moderate levels this past week. The largest flare
was on April 30 from an area where there was a major M-class flare producer
on its previous rotation last week.
No Earth-directed Coronal Mass Ejections (CMEs) were observed. Solar activity
is expected to be low with a chance for M-class flares (R1-R2,
minor-moderate), and a slight chance for X-class flares (R3-strong) through
May 2.
Radio blackouts reaching the R1 levels were observed over the past 24 hours.
The largest was on April 30.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere -
May 1, 2025, by F. K. Janda, OK1HH:
"In the past few weeks I have allowed myself to take a break because I have
been under the care of excellent doctors and caring nurses in a top Prague
hospital. Fortunately, I had a receiver available and could and did use it
occasionally, but the computer was at home, QRB 53 km away. Now I'm back and
continuing my usual activities: observing the events between the Sun and the
Earth, analyzing the context and trying to predict the future developments
(yes, I know that more accurate predictions are not possible, while I can
well justify why - but why not take science a bit as a sport too, right...?).
"In the last few days of April, AR4079 rose on the northeastern limb of the
solar disk, while soon increased in area to over 1000 millionths. Already
during the early months of this year, the Sun had subtly hinted that the
centre of gravity of activity might shift from its southern to its northern
hemisphere, but only now can we see this trend more clearly. So, it's
possible that we're in for another upward swing within the current 11-year
cycle, with active regions mostly north of the equator. This could hold the
promise of improved ionospheric shortwave propagation conditions this Autumn.
"During this April, we experienced a really large number of geomagnetically
disturbed days and mostly low MUF values. The calm and improvement occurred
only in the last decade of April, when we witnessed all six geomagnetically
quiet days of the whole April.
"Going forward, although we do not expect a major increase in solar activity
for the time being, it will not be important during the Northern Hemisphere
ionospheric Summer. Solar activity will more or less remain at the current
level, the geomagnetic field will be calmer compared to the past weeks - and
the situation in the ionosphere will be more favourable."
Solar wind parameters remained slightly enhanced due to waning positive
polarity of the Coronal Hole High-Speed Stream (CH HSS) influences. A return
to a mostly ambient-like state is expected for May 1, but by May 2, an
enhancement in solar wind parameters is likely with the arrival of a
recurrent, negative polarity CH HSS.
Unsettled to active levels will likely persist into May 4 as an additional
negative polarity CH HSS moves into place.
Geomagnetic field activity is likely to reach G1 (Minor) storm levels on May
5 and 6 due to negative polarity CH HSS influences, and again on May 18 due
to positive polarity CH HSS influences.
Periods of active conditions are likely on May 07 to 10, and on May 16 and 17
in response to CH HSS influences. Quiet and quiet to unsettled levels are
expected to prevail throughout the remainder of the period.
For more information concerning shortwave radio propagation, see
www.arrl.org/propagation [
http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL] and the ARRL Technical Information Service web page at,
www.arrl.org/propagation-of-rf-signals [
http://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 [
http://arrl.org/the-sun-the-earth-the-ionosphere ] . Information and
tutorials on propagation can be found at:
http://k9la.us [
http://k9la.us/ ]
.
Also, check this out: "Understanding Solar Indices" from September 2002 QST.
https://bit.ly/3Rc8Njt [
https://bit.ly/3Rc8Njt ]
The Predicted Planetary A Index for May 3 to 9 is 10, 8, 18, 18, 15, 15, and
15, with a mean of 14.1. Predicted Planetary K Index is 3, 3, 5, 5, 4, 4, and
4, with a mean of 4. Predicted 10.7 centimeter flux is 140, 140, 150, 160,
160, 165, and 165, with a mean of 154.3.
NNNN
/EX
ARRL The National Association for Amateur Radio(R)
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ARLP016 The ARRL Solar Report