Message:20649 In: PROP.ARL
From: NC8QDate: Sat, 11 Apr 26 08:44:00 Z
Newsgroups: PROP.ARL
Subject: ARLP015 Propagation Forecast
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R:260411/0844Z 28148@DK0WUE.#BAY.DEU.EU LinBPQ6.0.25
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ZCZC AP15
QST de W1AW
Propagation Forecast Bulletin 15 ARLP015
>From ARRL Headquarters
Newington, CT April 10, 2026
To all radio amateurs
SB PROP ARL ARLP015
ARLP015 The ARRL Solar Report
Solar activity remained at low levels this week. Most of the C-class activity came from either Region 4414 or Region 4409, whic
h has developed a delta spot in its intermediary area. All remaining spots were either stable or in slight decay, with Region 4
406 rotating over the west limb by the end of the reporting period.
Coronal activity was observed in CCOR-1, LASCO, and STEREO available imagery during the period. Of the four eruptions, one was
far-sided, one was too narrow plus too far north of the ecliptic to have any Earth-directed component, and two had the potentia
l for Earth-directed components. The first was associated with a C2.4 flare from Region 4414, while there was no clear source f
or the second. Modeling indicates these eruptions will pass behind Earth's orbit, and no impact is anticipated. Eruptions poten
tially associated with the C8.9 are currently being analyzed. Radio blackouts reaching the R1 levels were observed over the pas
t 24 hours. The largest was on Apr 9th 2026, at 08:45 UTC.
Solar activity is expected to be at low levels over April 9 to 11, with a chance for M-class (R1-R2/minor-moderate) flares and
a slight chance for X-class (R3/strong or greater) flares, driven primarily by the flare potential of Regions 4409 and 4414.
A brief description of Sunspots can be found on the Space Weather Prediction Center website at www.swpc.noaa.gov/phenomena/suns
potssolar-cycle.
Solar wind parameters reflected the transition out of a waning negative polarity coronal hole high-speed stream (CH HSS) into n
ominal conditions. Wind speeds continued to decline from a peak of ~500 km/s to near 400 km/s by the end of the period.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 9, 2026, by F. K. Janda, OK1HH:
Perhaps the biggest surprise in recent days was that, following the geomagnetic disturbance of April 2 3 (which had been expect
ed, albeit a day earlier and with lower intensity), there were no further major surprises. Solar activity declined as predicted
, whereas because it declined over a relatively long period, there was a greater-than-expected drop in critical frequencies in
the F2 ionospheric region at mid-latitudes.
For forecasting developments in the second third of April, the 27-day cycle could serve as a relatively reliable guide this tim
e. First of all, one might expect a one- to two-day increase in geomagnetic activity (which is also indicated by the presence o
f solar coronal holes near the central meridian), followed by relative calm. This is despite the short time that has elapsed si
nce the eleven-year peak of solar activity.
The Predicted Planetary A Index for April 4 to April 10 is 5, 4, 3, 2, 2, 2, and 2 with a mean of 2.8. The Predicted Planetary
K Index is 18, 10, 8, 7, 5, 4, and 7 with a mean of 8.4. 10.7 centimeter flux is 106, 105, 108, 110, 115, 115, and 120 with a m
ean of 111.2.
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Se
rvice web page at www.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. Information and tutorials on propagation can be found at http://k9la.us.
Also, check this: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt
NNNN
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