SB PROP @ ARL $ARLP031
ARLP031 The ARRL Solar Report

ZCZC AP31
QST de W1AW
Propagation Forecast Bulletin 31 ARLP031

From ARRL Headquarters

Newington CT August 22, 2025
To all radio amateurs

SB PROP ARL ARLP031
ARLP031 The ARRL Solar Report

On August 22, Spaceweather.com [ http://Spaceweather.com ] reports a fast-moving Coronal Mass Ejection, or CME, left the Sun on August 21.
However, it is not Earth-directed, and is predicted to strike the planet
Mars.


Solar activity has decreased back to low levels with a few weak C-class
flares observed from areas located in the northeast quadrant of the solar
disk. There are currently three sunspot regions on the solar disk with the largest being Region AR4187. This region showed some weak leader spot growth. The remaining two regions were quiet and stable.


Solar wind parameters reflected negative polarity coronal hole high-speed stream (CH HSS) influences. A disturbed solar wind environment is likely to continue through August 22.


There is a slight chance for R1 (Minor) radio blackouts through August 23 due to the anticipated return of old active regions. Probabilities increase slightly to a chance for an isolated event, most likely from the east limb,
on August 24 as old active regions return to view.


Active conditions are likely again on August 28 due to negative polarity Coronal Hole High Speed Stream influences. Periods of G1 to G2
(Minor-Moderate) storming are likely on September 5, with active conditions likely on September 4 and 6, due to positive polarity Coronal Hole High Speed Stream influences. The remainder of the period is expected to be at quiet or quiet to unsettled levels.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, August 21, 2025, by F. K. Janda, OK1HH:


"Higher solar activity in the first half of August was caused mainly by two sunspot groups (out of a total of 11-13), whose magnetic configuration
allowed for the occurrence of moderately powerful eruptions (class M). After their disappearance, the number of groups dropped to three to five, while
only energetically insignificant eruptions sporadically occurred.

Changes in the speed of the solar wind and the concentration of particles in
it had a significant impact on the Earth's ionosphere.

As usual, the source on the Sun was the boundaries of coronal holes.

"After a brief calm in the geomagnetic field from August 13 to 15, turbulent developments followed from August 19. At the beginning, the speed of the
solar wind rapidly increased from 350 to 650 km/s, which was accompanied by a change in the polarity of the longitudinal component of the interplanetary magnetic field Bz to positive in a relatively long interval from 1130 to 1630 UT. Therefore, the deterioration of shortwave propagation conditions was only slight, while the MUF decline was delayed.

We are now likely to see a series of relatively calm days, probably until August 27.


Major disturbances are not expected to occur until around September 5, when
the Earth will enter the same stream of solar particles as it did around
August 9."


The latest video from Dr. Tamitha Skov, WX6SWW, can be found on YouTube at https://www.youtube.com/watch?v=brxIxVgiH_A [ https://www.youtube.com/watch?v=brxIxVgiH_A ] .


For more information concerning shortwave radio propagation, see www.arrl.org/propagation [ http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] and the ARRL Technical Information Service web page at www.arrl.org/propagation-of-rf-signals [ http://arrl.org/propagation-of-rf-signals ] . For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere [ http://arrl.org/the-sun-the-earth-the-ionosphere ] . Information and
tutorials on propagation can be found at http://k9la.us [ http://k9la.us/ ] .


Also, check this:
"Understanding Solar Indices" from September 2002 QST.
https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

The Predicted Planetary A Index for August 23 to 29 is 5, 5, 8, 8, 10, 12,
and 8, with a mean of 8. Predicted Planetary K Index is 2, 2, 3, 3, 3, 4, and 3, with a mean of 2.9. 10.7 centimeter flux is 120, 125, 120, 120, 125, 125, and 130, with a mean of 123.6.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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