(C) ARRL Letter
This story was originally published by ARRL Letter and is unaltered.
. . . . . . . . . .
The ARRL Solar Report [1]
[]
Date: 2025-05
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
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at,
http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at,
http://k9la.us/ .
Also, check this:
https://bit.ly/3Rc8Njt
"Understanding Solar Indices" from September 2002 QST.
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.
[END]
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