07/24/2026
Solar activity continued at moderate levels as Region 4493 produced an M3.6
flare on July 22, which was the largest event of the period and was associated
with a 10.7-centimeter radio burst of 200 solar flux units (sfu). Additionally,
4493 produced a C3.4 flare on July 22, which was associated with another 10.7-cm
radio burst of 150 sfu.
Region 4493 continued to undergo consolidation in its leading and trailing
spots, but showed signs of new flux emergence in its intermediate area during
the early hours of the reporting period. Region 4494 developed new, simple
spots, but remained uni-polar. The remaining two numbered active regions were
relatively stable and quiet.
A filament eruption NW of Region 4493 on July 21 was modeled and assessed to be
at least partially Earth-directed. While modeling efforts suggest that a bulk of
the material should pass north and ahead of Earth s orbit, this is low
confidence given the faintness of this event in Sun-Earth line-focused
coronagraph imagery and compounded by likely interaction with the coronal hole
in the vicinity of the source location.
Additional M-class flare activity (R1-R2 radio blackouts) is likely through July
25 primarily due to the flare potential currently exhibited by AR 4493.
Solar wind parameters were mildly enhanced under a sustained negative polarity
coronal hole high-speed stream (CH HSS) regime and a possible secondary
Co-rotating Interaction Region (CIR). Solar wind speeds were roughly between 400
and 482 km/s.
The current regime is expected to largely continue through July 25. Additional
enhancements are possible beginning late on July 23 due to a coronal mass
ejection (CME) that left the sun on July 20, with stronger enhancements arriving
by early on July 24 with the arrival of the aforementioned CME event from July
21.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere,
July 23, 2026, by F. K. Janda, OK1HH:
A relatively large sunspot group, which was already very conspicuous in images
from the SOLAR ORBITER spacecraft, was designated NOAA 4493 after its discovery
as an active region on the northeastern limb of the solar disk. It produced
class C and M flares on a daily basis. It is currently located in the northwest
of the solar disk. As it grew, it disrupted a long north-south coronal hole and
remains the largest and most complex sunspot group on the visible disk,
accounting for most of the observed eruptive activity. The eruption observed
within it on July 20 was accompanied by a CME. The ejected particles triggered a
geomagnetic disturbance on the afternoon of July 23.
As a result of this activity, the ionosphere is currently undergoing variable
conditions, characterized albeit irregularly by a pronounced presence of the
summer sporadic E layer in the Earth s northern hemisphere. In the coming days,
geomagnetic activity should begin to gradually decline (no earlier than July
25). Increased solar activity will likely persist almost until the end of the
month. Conditions for ionospheric radio propagation will therefore remain
variable, with irregular occurrences of relatively very favorable days.
The predicted Planetary A Index for July 25 to 31 is 5, 5, 5, 5, 5, 5, and 5,
with a mean of 5.0. The predicted Planetary K Index is 2, 2, 2, 2, 2, 2, and 2,
with a mean of 2.0. The predicted 10.7 centimeter flux is 125, 125, 120, 118,
118, 115, and 112, with a mean of 119.0.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation[1] and the ARRL Technical Information Service
web page at, http://arrl.org/propagation-of-rf-signals[2]. For an explanation of
numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere[3] . Information and
tutorials on propagation can be found at, http://k9la.us/[4] .
Also, check this:
https://bit.ly/3Rc8Njt[5]
"Understanding Solar Indices" from September 2002 QST
[1] http://www.arrl.org/propagation
[2] http://arrl.org/propagation-of-rf-signals
[3] http://arrl.org/the-sun-the-earth-the-ionosphere
[4] http://k9la.us/
[5] https://bit.ly/3Rc8Njt
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