SB PROP @ ARL $ARLP029
ARLP029 The ARRL Solar Report

ZCZC AP29
QST de W1AW
Propagation Forecast Bulletin 29 ARLP029

From ARRL Headquarters

Newington CT August 8, 2025
To all radio amateurs

SB PROP ARL ARLP029
ARLP029 The ARRL Solar Report

Solar activity was at low levels on 28 July to 02 August and moderate levels
on 03 August. The largest flare of the period was an M2.9/2b event observed from Region 4168 on 03 August. The region also produced numerous C-class events. Numerous C-class activity was observed from Regions 4153, 4155, and 4167. No Earth-directed CME activity was observed.


No proton events were observed at geosynchronous orbit.

Geomagnetic field activity was at quiet to unsettled levels the entire highlight period. A single active period was observed late on 03 August. A majority of the unsettled periods was due to weak negative polarity CH HSS influence. Solar wind speeds were at mostly 400 km/s from 28 July through midday on 30 July and 475-500 km/s from midday 30 July through 03 August with
a peak velocity observed at 600 km/s late on 03 August.


Solar activity is expected to be at mostly low levels with a chance for
M-class flares for the outlook period.


Geomagnetic field activity is expected to be at active to G1 storm levels on
11 to 15 August, 18 to 22 August, and 25 to 30 August due to recurrent CH HSS effects. Quiet to unsettled levels are expected on the remaining days of the outlook period.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere
for August 7, 2025 by F. K. Janda:


Overall solar activity has not changed much in recent days, but it has been higher than on the same days of the previous solar cycle.

However, eruption activity increased in the northwestern part of the solar disk.

The M4.4 eruption on May 5, with a maximum at 1553 UTC, was of greatest significance for further development, as it was accompanied by a CME, part of which is heading toward Earth.

It is expected to arrive on August 8, at the same time as a co-rotating interactive region (CIR), should cause an intensification of the solar wind blowing from a large coronal hole in the southern hemisphere of the Sun.


The combination of these two phenomena will cause an increase in geomagnetic activity on August 8. Thanks to the intensified solar wind, the geomagnetic field will remain active on May 9. On the first day, there will likely be a positive phase of development, accompanied by an increase in the highest
usable frequencies of the F2 ionospheric region, while on the second day, the development will transition to a negative phase, with a decrease in usable frequencies and an overall deterioration in shortwave propagation conditions due to increased attenuation.


After that, rather turbulent developments can be expected until approximately August 12, followed by a calming down from August 13. Overall solar activity should remain only slightly elevated.


The latest report from Dr. Tamitha Skov can be found on YouTube at https://www.youtube.com/watch?v=SItdIe1X7RU [ https://www.youtube.com/watch?v=SItdIe1X7RU ]


The Predicted Planetary A Index for August 9 to 15 is 5, 5, 25, 18, 20, 12,
and 8, with a mean of 13.2. Predicted Planetary K Index is 2, 2, 5, 5, 5, 4, and 3, with a mean of 3.7. 10.7 centimeter flux is 135, 135, 130, 130, 130, 135, and 135, 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. Information and tutorials on propagation can be found at http://k9la.us [ http://k9la.us/ ] .


Also check "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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