XPost: rec.radio.shortwave, rec.radio.info
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SB PROP @ ARL $ARLP034
ARLP034 The ARRL Solar Report

ZCZC AP34
QST de W1AW
Propagation Forecast Bulletin 34 ARLP034

From ARRL Headquarters

Newington CT September 12, 2025
To all radio amateurs

SB PROP ARL ARLP034
ARLP034 The ARRL Solar Report

Solar activity has been at very low to low levels this past week.

Low-level C-class flaring was observed from Regions AR4210 and AR4207. Slight growth was observed in Regions AR4213 and AR4214. The rest of the spotted regions were either stable or in decay. Solar activity is expected to remain
at low levels, with a chance for isolated M-class flares
(R1-R2/minor-moderate) through September 13.


A CME (Coronal Mass Ejection) was observed just beyond the Western limb on September 9. No impacts are expected, and no Earth-directed CMEs were
observed.


Solar wind parameters continued to be enhanced under positive polarity
coronal hole high-speed stream (CH HSS) influences. Solar wind speed
increased from approximately 450 km/s to nearly 550 km/s. Elevated solar wind conditions are expected to continue into September 12. Another enhancement is likely on September 14 with the onset of negative polarity CH HSS influences and the possible glancing effects of the September 11 CME.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, September 11, 2025, by F. K. Janda, OK1HH:


"During a seven-day interval (August 26 to September 1), when solar flux
values were above 200 s.f.u., there was a decline to below 120 s.f.u. during the first ten days of September, which also occurred during the previous
solar rotation, on August 17-19.


"Solar flare activity simultaneously decreased significantly, while all
sunspot groups moved to the western half of the solar disk. Instead, we are
now observing a large coronal hole, located mostly north of the solar
equator, whose boundary has already crossed the central meridian.


"The intensified solar wind, which is definitely blowing from its western
edge, is expected to reach Earth since September 13. It will likely
contribute to increased geomagnetic activity, which, combined with relatively low solar activity, will have negative consequences for the state of the ionosphere. MUF values will decrease, attenuation will increase, and
shortwave propagation conditions will deteriorate.


"Starting in the first half of September, however, solar activity will begin
to increase, although not as significantly as it did in August. In addition, geomagnetic activity appears to be declining at the same time. The
approaching Autumn Equinox will also have a significant impact on the state
of the ionosphere. These are already three reasons why shortwave propagation conditions should gradually improve."


The Predicted Planetary A Index for September 13 to 19 is 5, 12, 20, 15, 8,
8, and 8, with a mean of 10.9. Predicted Planetary K Index is 2, 4, 5, 4, 3,
3, and 3, with a mean of 3.4. 10.7-centimeter flux is 120, 125, 130, 135,
135, 140, and 145, with a mean of 132.9.


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 ]

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
Unsubscribe [ http://www.arrl.org/opt-in-out?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
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SB PROP @ ARL $ARLP034

ARLP034 Propagation Forecast

ZCZC AP34
QST de W1AW
Propagation Forecast Bulletin 34 ARLP034

From ARRL Headquarters

Newington, CT August 21, 2026
To all radio amateurs

SB PROP ARL ARLP034
ARLP034 The ARRL Solar Report

Solar activity has continued at low levels, with most of the C-class activity originating from Region 4507. The secondary source of C-class flares was
beyond the east limb and was responsible for the largest flare of the period,
a C5.0 on August 19.


There were four numbered regions on the visible disk. Most of them showed
some decay, losing intermediary/trailer spots or penumbra area. Region 4510 continued to rotate off the west limb. No Earth-directed coronal mass
ejection (CME) was observed in the available coronagraph imagery during the period.


Solar activity is expected to continue at low levels over through August 21 with a chance for M-class flares (R1-R2/minor-moderate).


Solar wind parameters reflected the waning effect of the co-rotating interaction region (CIR) and dominating influence of a negative polarity coronal hole high speed stream near Earth. Solar wind speeds increased from
400 km/s to about 550-600 km/s. Phi angle remained predominantly negative during the past 24 hours.


Solar wind parameters are likely to continue reflecting the presence of high speed streams associated with negative polarity coronal hole(s) through
August 21.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, August 20, 2026, by F. K. Janda, OK1HH:


Earlier this week, an active region referred to as AR 4499 during the
previous solar rotation was approaching the northeastern limb of the solar disk.

It emerged as AR 4513 on August 19. All four remaining active regions were located on the western side of the solar disk; therefore, had AR 4513 not emerged, there would have been a noticeable decline in overall solar
activity.

As it stands, however, solar activity will remain at its current level
through the end of August, although it remains lower than during the previous solar rotation.

Given the two larger coronal holes on the western half of the solar disk, it
is no surprise that the solar wind is intensifying intermittently,
contributing to slightly increased geomagnetic activity and, consequently, to intermittently deteriorating shortwave propagation conditions.


However, a decline in solar activity will eventually occur, as early as the first third of September. Even before then, however, we can tentatively
expect a decrease in the Earth s magnetic field activity. Given the current seasonal changes, as summer comes to an end in the ionosphere, we can expect calmer and more stable shortwave propagation conditions not only toward the
end of August but also throughout most of the first half of September.


The Predicted Planetary A Index for August 21 to August 27 is 12, 12, 10, 8,
5, 5, and 5 with a mean of 8.1. The Predicted Planetary K Index is 4, 4, 3,
3, 2, 2, and 2 with a mean of 2.9. Predicted 10.7 centimeter flux is 125,
125, 120, 115, 115, 110, and 110 with a mean of 117.1.


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://www.arrl.org/propagation-of-rf-signals?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] . For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere [ http://www.arrl.org/the-sun-the-earth-the-ionosphere?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] . 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 ]

NNNN
/EX

ARRL The National Association for Amateur Radio(R)


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