SB PROP @ ARL $ARLP025
ARLP025 The ARRL Solar Report
ZCZC AP25
QST de W1AW
Propagation Forecast Bulletin 25 ARLP025
From ARRL Headquarters
Newington CT July 11, 2025
To all radio amateurs
SB PROP ARL ARLP025
ARLP025 The ARRL Solar Report
Spaceweather.com [
http://Spaceweather.com ] reports solar activity was at
low levels with only C-class flares observed. The largest flare during the period was a C8.9 from an unnumbered region beyond the east limb at S13. This region was also responsible for the majority of the remaining flares
alongside Regions 4136 and 4137.
An approximate M2 was observed by Solar Orbiter at 10/1326 UTC just beyond
the east limb, brightening can be seen in the SUVI-94 channel at this time. A slow moving CME was observed in coronagraph imagery, modelled and was determined to not have any impact.
Solar activity is expected to be low with a chance for M-class flares, minor
to moderate, through 13 July, primarily due to the flare potential of Region 4136.
Solar wind parameters remained at nominal conditions. Total field was 2-5 nT with the Bz component between +/-4 nT. Solar wind speeds were between 350-400 km/s. The phi angle was variable after 10/0500 UTC.
Nominal solar wind conditions are expected through 11 July. The co-rotating interacting region associated with a positive polarity CH HSS is expected to arrive 12 July, an enhancement of the solar wind parameters will follow the arrival and remain enhanced thereafter.
Mostly quiet conditions are expected 11 July. Unsettled to active conditions are likely starting 12 July as Earth moves into a geoeffective position with
a positive polarity CH HSS.
There is a decreased chance for minor to moderate radio blackouts on 11 July with most regions on the visible disk rotating off and no appreciable spot groups rotating on. Conditions could increase on 12 or 13 July as old Regions 4117, 4118, 4120, and 4121 rotate back onto the visible disk.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere July 6 and 10, 2025
Although solar activity is lower this year than it was last year, it is still at the maximum level of the eleven-year cycle. Moreover, it is quite possible that it will increase further this year.
This is indicated by the continuing slight predominance of activity in the northern half of the solar disk, while in the southern half, we more often observe relatively large coronal holes.
The active regions are mostly simple (magnetic type alpha or beta) and therefore, with a few exceptions, do not show significant eruptive activity.
Although solar flares have not been powerful recently, they are quite often accompanied by CMEs. When ejected particles hit Earth, it is often three to four days after the CME is observed, instead of the usual two to three days. This is one reason why the error in predicting the arrival time of the
particle cloud is slightly increasing. This is especially true when their source is on the far side of the Sun.
The solar wind has finally slowed down in recent days (from speeds of over
800 km/s observed not long ago to less than 400 km/s now) and the
interstellar magnetic field has weakened, which has finally had a positive effect on the state of the Earth's ionosphere, as well as the shortwave propagation conditions.
Although the arrival of a high-speed stream from a recurring coronal hole
with negative polarity can be expected from July 4, causing unstable geomagnetic conditions, the phenomenon should not last long.
In addition, the low flux of electrons with energies greater than 2 MeV is likely to remain, so a return to fairly favorable conditions can be expected.
In connection with the occurrence of a large coronal hole in the southeastern part of the solar disk, slightly increased geomagnetic activity can be expected. In the coming days (starting July 13-14), it may reach level G1.
On the above-mentioned days (July 13 to 14, or 1 to 2 days later), the
negative impact on the ionosphere could be intensified by declining solar activity. Further developments cannot be predicted with greater accuracy, but the probability of disturbances will be higher in the last third of July.
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 July 12 to 18 is 10, 8, 8, 12, 12, 10,
and 10, with a mean of 10. Predicted Planetary K Index is 4, 3, 3, 4, 4, 4,
and 4, with a mean of 3.7. 10.7 centimeter flux is 105, 105, 110, 115, 120, 125, and 125, with a mean of 115.
NNNN
/EX
ARRL The National Association for Amateur Radio(R)
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