04/10/2026
Solar activity remained at low levels this week. Most of the C-class activity
came from either Region 4414 or Region 4409, which has developed a delta spot in
its intermediary area. All remaining spots were either stable or in slight
decay, with Region 4406 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 potential for Earth-directed components. The first was associated with a
C2.4 flare from Region 4414 while there was no clear source for the second.
Modeling indicates these eruptions will pass behind Earth's orbit and no impact
is anticipated. Eruptions potentially associated with the C8.9 are currently
being analyzed. Radio blackouts reaching the R1 levels were observed over the
past 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. The greatest expected 3 hr Kp for Apr 09 through Apr 11
2026 is 5 (.33NOAA scale G1).
A brief description of Sunspots can be found on the Space Weather
Prediction Center website at,
https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle[1] .
Solar wind parameters reflected the transition out of a waning negative polarity
coronal hole high speed stream (CH HSS) into nominal 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 expected, 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 time. First of all, one might
expect a one- to two-day increase in geomagnetic activity (which is also
indicated by the presence of solar coronal holes near the central meridian),
followed by relative calm. This is despite the short time that has elapsed since
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 mean of 111.2.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation[2] and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals[3]. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere[4] . Information and
tutorials on propagation can be found at, http://k9la.us/[5] .
Also, check this:
https://bit.ly/3Rc8Njt[6]
"Understanding Solar Indices" from September 2002 QST.
[1] https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle
[2] http://www.arrl.org/propagation
[3] http://arrl.org/propagation-of-rf-signals
[4] http://arrl.org/the-sun-the-earth-the-ionosphere
[5] http://k9la.us/
[6] https://bit.ly/3Rc8Njt
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