06/27/2025
Solar activity has been at low levels for the past 48 hours, with
low-level C-class flares.
ÿ
There was a narrow coronal mass ejection (CME), likely associated
with minor flaring from Regions AR4117 and AR4118 between 1439 UTC
and 1524 UTC on June 24. Initial modeling indicated a miss, south
and behind Earth's orbit. However, it should be noted that analysis
of this event is low confidence given the assumed source location.
ÿ
An enhanced solar wind environment is expected to continue through
June 28 under a negative polarity Coronal Hole High-Speed Stream
regime before beginning to trend towards a more nominal environment
on 29 June.
There is a chance for R1-R2 (Minor-Moderate) events through June 29.
There is also a slight chance for an R3 (Strong) or greater event
through June 29, as well as a slight chance for S1 (Minor) solar
radiation storm conditions through the reporting period.
Geomagnetic field activity is likely to reach active levels on July
1 to 3, 05 and 6, and 11 and 12, all due to recurrent CH HSS
influences. Quiet, and quiet to unsettled conditions are expected to
prevail throughout the remainder of the period through July 19.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - June 26, 2025, by F. K. Janda, OK1HH:
"The last significant solar flare was recorded on June 15, reaching
an X-ray brightness of M8.4, while ejecting a CME into space. The
particle cloud arrived at Earth on June 18, with the subsequent
increase in solar wind speed, which caused an improvement in
propagation conditions in the lower shortwave bands.
"Although eruptions with higher X-ray brightness were also recorded,
they only caused shorter attenuation in the lower layers of the
ionosphere on the illuminated part of the Earth.
"Overall solar activity declined steadily after June 15, with five
to six visible sunspot groups. At most two were capable of producing
larger eruptions.ÿ Their proximity to two of the three observable
coronal holes near the equator made it possible to predict an
intensification of the solar wind and the occurrence of geomagnetic disturbances for June 25-26 (or possibly also June 27).
"This was all the more likely given that it was the central meridian
region. Since then, however, the sunspot groups and coronal holes
have shrunk. The increase in solar wind speed (up to 700 km/s) and
geomagnetic activity (only G1) was therefore smaller. However, the
flux of electrons with energies above 2 MeV reached high values,
with a maximum flux of 1,260 pfu at 25/1355 UTC.
"Unfortunately, an increase in the concentration of free electrons
in the Earth's ionosphere is a relatively common phenomenon this
year and worsens the conditions for shortwave propagation.
"A return to background levels is expected from June 28. In July,
larger sunspot groups will return to the solar disk. Therefore, the
solar flux will rise slightly during the first ten days. Only a very
slight improvement in shortwave propagation conditions can be
expected in the summer ionosphere of the Earth's northern
hemisphere."
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.
The Predicted Planetary A Index for June 28 to July 4 is 15, 10, 5,
15, 15, 12, and 5, with a mean of 11.ÿ Predicted Planetary K Index
is 3,3, 2, 4, 4, 4, and 2, with a mean of 3.1.ÿ 10.7 centimeter flux
is 140, 145, 145, 140, 140, 140, and 145, with a mean of 142.1.
ÿ
[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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