Solar activity continued at low levels during the past 24 hours with
four active regions on the visible disk. The largest events were a
C1.0 on May 20 from the northeast limb and a C1.0/Sf, also on May 20,
from Region 4439 that was accompanied by Type-III radio sweeps. This
region was responsible for the majority of the period’s activity,
which otherwise included a B8.7 flare on May 20 from Region 4436.
Region 4441 showed some development during the period while 4443
remained stable. Coronal activity was observed in CCOR-1 imagery
after May 20, but additional data is needed for further analysis.
Solar wind parameters trended toward background conditions with
speeds reaching a peak of 542 km/s on May 20 and then decreasing
steadily throughout the reporting period, ending at ~450 km/s.
Weekly Commentary on the Sun, the Magnetosphere, and the
Earth’s Ionosphere May 22 – May 28, 2026 by F. K. Janda, OK1HH
The number of sunspot groups on the solar disk ranged from three to
seven over the past week; their total area was not large, while their
magnetic structure was relatively simple. Nevertheless, isolated
C-class flares were recorded. In addition, there was even an M-class
flare recorded on Sunday, May 17 (in AR 4435 near the northwestern
limb of the solar disk, peaking at 0339 UT). Thanks to the Solar
Orbiter probe, however, we know that the situation will change.
Because, in a location where there was no group of sunspots during
the previous solar cycle, not only is there a group now, but it is
also quite extensive. Its edge is already slowly beginning to appear
on the southeastern limb of the solar disk. While a week later, we
can expect the peak of activity within the current solar rotation.
The geomagnetic field will be mostly quiet to unsettled in the coming
days, after which its activity will rise, initially slightly—and a
disturbance can be expected toward the end of the month. This will
result in a generally favorable development for the ionosphere for
the remainder of May. This includes increases in geomagnetic
activity, during which, depending on the timing, MUF values may
temporarily rise.
The Predicted Planetary A Index for May 23 to May 29 is 5, 5, 5, 5,
12, 10, and 8 with a mean of 7.The Predicted Planetary A Index for
May 23 to May 29 is 5, 5, 5, 5, 12, 10, and 8 with a mean of 7.1. The
Predicted Planetary K Index is 2, 2, 2, 2, 4, 3, and 3 with a mean of
2.6. 10.7 centimeter flux is 112, 112, 115, 115, 115, 120, and 125
with a mean of 116.3.
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.