Solar activity is likely to continue at low levels with isolated to
occasional C-class flare activity, along with a slight chance for
R1-R2 (Minor-Moderate) M-class flare events, through September 25,
according to NOAA’s Space Weather Prediction Center. The SWPC reports
that nine sunspot regions are on the visible disk, including a new
Region 4541. There were three solar flares observed in the past week,
none of which was directed toward Earth.
A disturbed solar wind environment was expected to arrive late
yesterday, followed by positive polarity coronal hole high-speed
stream (+CH HSS) influences continuing through September 25.
Unsettled to active geomagnetic field conditions levels are expected
as of today under early +CH HSS effects, including isolated periods
of G1 (Minor) geomagnetic storming today and tomorrow.
The Australian Space Weather Forecasting Centre’s global HF
propagation forecast for middle latitudes is for mild degradation
today due to forecast geomagnetic activity, followed by normal
propagation in the days that follow. We are currently in a period of
equinoctial propagation, during which conditions are relatively
uniform around the world.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s
Ionosphere, September 24, 2026, by F. K. Janda, OK1HH:
After a prolonged period of calm activity on the Sun as well as in
Earth’s magnetosphere—spanning the entire second third of
September—solar activity began to rise first, followed by an increase
in geomagnetic activity starting on September 24. On September 18
only, there were no sunspots on the Sun. The rise in solar activity
on the 24th was accompanied by an intensification of the solar wind,
while the geomagnetic disturbance began its so-called positive phase
(the critical frequencies f0F2 increased significantly between 9:00
and 13:00 UT). Improved shortwave propagation conditions were
observed on September 23–24.
Solar activity will remain at a higher level for several more days,
while the geomagnetic disturbance will continue only briefly in the
so-called negative phase of development. A calm period is expected to
follow during the last few days of the month. Recovery from the
disturbance will likely be rapid, while a return to improved
shortwave propagation conditions can be expected for most of the
remaining days of the month.
The Predicted Planetary A Index for September 25 to October 1 is 18,
12, 8, 5, 5, 5, and 5 with a mean of 8.3. The Predicted Planetary K
Index is 5, 3, 3, 2, 2, 2, and 2 with a mean of 2.7. 10.7 centimeter
flux is 105, 105, 100, 105, 110, 115, and 115 with a mean of 107.9.
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