SB PROP @ ARL $ARLP012
ARLP012 The ARRL Solar Report
ZCZC AP12
QST de W1AW
Propagation Forecast Bulletin 12 ARLP012
From ARRL Headquarters
Newington CT April 4, 2025
To all radio amateurs
SB PROP ARL ARLP012
ARLP012 The ARRL Solar Report
Solar activity is likely to be moderate (R1-R2, Minor-Moderate) with a slight
chance for X-class flares through April 5.
The geomagnetic field is expected to be quiet to minor storm levels on April
4 and 5.
NOAA Geomagnetic Activity Probabilities for April 5 and 6 forecast a 15%
chance, and then a 1% chance, of a Moderate storm for the reporting period.
The forecast of solar and geomagnetic activity calls for a chance for R1-R2
(Minor-Moderate) effects throughout the outlook period due to multiple
complex regions on the visible disk as well as on the Sun's far side that are
likely to return.
A slight chance exists for R3 (Strong) events over the next three days
primarily due to the flare potential from complex regions in the Sun's
eastern hemisphere.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere -
April 3, 2025, by F. K. Janda, OK1HH:
"A harbinger of a somewhat more dramatic development in the Sun-Earth system
was the helioseismological observation of a larger active region on the far
side of the Sun. This region appeared on the northeastern limb of the solar
disk as AR4046. It was followed by the larger, more magnetically complex,
growing and eruptively active AR4048. Concurrent with the increase in solar
activity, the geomagnetic field remained quiet from March 29 to April 1, a
favorable combination for ionospheric evolution.
"The intensified solar wind from the coronal hole margins in the western half
of the solar disk was the cause of the geomagnetic disturbances, which caused
a significant decrease in the critical frequencies of the ionospheric F2
layer from 2 April onwards, together with an increase in the attenuation of
radio waves, to which the increased concentration of particles in the solar
wind - both electrons and especially protons - contributed.
"At the time of writing, the prediction of the onset of the recurrent
disturbance on the night of 4/5 April is valid. The cause is the passage of
the Earth through a region of enhanced solar wind in the corotating
interaction region (CIR) structure.
"In the next two weeks, the author of these lines will be in hospital. He
will send his next post after his return."
A greater electron flux at geosynchronous orbit is expected to be at high
levels on April 6 to 14 in response to multiple, recurrent, Coronal Hole
High-Speed Streams. The remainder of the outlook period is expected to be at
normal to moderate levels.
Geomagnetic field activity is expected to range from quiet to G2 (Moderate)
geomagnetic storm conditions. G2 conditions are likely on April 5 and 09, G1
(Minor) conditions are likely over April 8 and 10, active conditions are
likely over April 11 and 13, unsettled conditions are likely on April 6 and
7, 12, and April 14 and 15.
All increases in geomagnetic activity are anticipated in response to
multiple, recurrent Coronal Hole High-Speed Streams. The remainder of the
outlook period is likely to mostly quiet.
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: "Understanding Solar Indices" from September 2002 QST.
https://bit.ly/3Rc8Njt [
https://bit.ly/3Rc8Njt ]
The predicted Planetary A Index for April 5 to 10 is 35, 10, 12, 30, 35, and
25, with a mean of 24.5. The predicted Planetary K Index is 6, 3, 3, 5, 6,
and 5, with a mean of 4.7. The predicted 10.7 centimeter flux is 180, 180,
185, 185, 180, and 175, with a mean of 180.8.
NNNN
/EX
ARRL The National Association for Amateur Radio(R)
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ARLP012 The ARRL Solar Report