Solar activity has been at low levels with only C-class flares
produced by Regions 4401, 4405, and 4409. There were 9 numbered
active regions on the solar disk, with 4409 showing the most
significant growth during the period and producing the largest flares
on April 1. A new region emerged but it has not yet been numbered.
Multiple filaments erupted during the day on April 1, producing
coronal mass ejections (CMEs) observed in coronagraph imagery, but
their propagation modeling did not suggest impacts to Earth. The
exceptions are the ejecta first observed at GONG H-alpha images on
April 1.
Solar activity is likely to reach moderate (R1/R2-minor/moderate)
levels, with a slight chance for X-class (R3-strong) flares through
April 4, due primarily to the flare potential of Regions 4404, 4405
and 4409.
Solar wind parameters were near nominal levels with solar wind speed
averaging around 440 km/s.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s
Ionosphere, April 2, 2026, by F. K. Janda, OK1HH:
The increase in overall solar activity during the third ten-day
period of March—albeit with a slight delay—led to a gradual rise in
MUF values, extending into the first days of April. An increase in
solar flare activity did not occur until April 30, beginning with a
flare at 0319 UT with an X-ray intensity of X1.4, which lasted a long
time and was accompanied by a CME. Since a large coronal hole No. 36
was located nearby, a significant increase in geomagnetic activity
was expected. This did not occur until April 2, but already during
several preceding active intervals, we could observe the effects of
electromagnetic wave scattering on ionospheric inhomogeneities,
clearly visible even on ionograms.
Active region NOAA 4405, located 27 degrees south of the solar
equator, has been clearly visible for a week as the largest on the
solar disk and appears to be stable. On April 3, it passes the
central meridian, and its proximity to coronal hole No. 36 is a
potential source of intensified solar wind. It also indicates higher
geomagnetic activity (at G2 level since April 2). This proximity will
likely be the cause of increased geomagnetic activity during the
first ten days of April. Consequently, this will lead to irregular
shortwave propagation conditions and more frequent drops in the MUF.
The next increase in solar activity will likely occur in the last
third of April. Daily MUF values will rise again, and at the same
time, a sporadic E layer will begin to appear occasionally in
mid-latitudes. Although it will not yet have a significant impact on
shortwave propagation, it will occasionally cause interesting DX
openings on the shortest shortwave bands.
The Predicted Planetary A Index for April 4 to April 10 is 22, 10,
15, 8, 7, 25, and 40 with a mean of 18.1. The Predicted Planetary K
Index is 5, 3, 4, 3, 2, 5, and 6 with a mean of 4. 145, 145, 135,
125, 118, 120, and 110 with a mean of 128.2
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.