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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