SB PROP @ ARL $ARLP026
ARLP026 The ARRL Solar Report

ZCZC AP26
QST de W1AW
Propagation Forecast Bulletin 26 ARLP026

From ARRL Headquarters

Newington, CT, July 18, 2025
To all radio amateurs

SB PROP ARL ARLP026
ARLP026 The ARRL Solar Report

Spaceweather.com [ http://Spaceweather.com ] reports solar activity was
ranged from low to moderate levels. Minor events were observed on 08 and 09 July and 12 July. The largest was an M2.4 flare at 08/0417 UTC from Region 4136. Region 4140 produced a similarly powerful M2.3/1f flare at 12/0834 UTC. The other 15 numbered active regions on the visible disk were either quiet or only produced C-class activity. No Earth-directed CMEs were observed in available coronagraph imagery.


No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit reached high levels on 09 and 10 July following elevated wind speeds from a coronal hole. The remainder of the summary period was at normal to moderate levels.


Geomagnetic field activity was varied from quiet to minor geomagnetic storm levels.

G1 conditions were observed early on 07 July, with a slow decrease to active levels on 08 July and unsettled levels on 09 July due to influence from a negative polarity coronal hole.

Active conditions were observed on 11 July and unsettled conditions on 12
July were in response to the onset of a positive polarity coronal hole.

G1 conditions observed on 13 July followed a pronounced increase in solar
wind speeds from a mildly elevated 500 km/s on 12 July to a peak just over
700 km/s on 13 July.


Forecast of Solar and Geomagnetic Activity 14 July - 09 August 2025

Solar activity is likely to be at low levels, with a chance for Minor to Moderate radio blackouts, over next 27 days due to several complex active regions on the visible disk and the anticipated return of multiple active regions from the Sun's farside.


No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is expected to reach high levels on 20 to 28 July and 05 and 06 August following activity
from recurrent coronal holes. The remainder of the outlook is likely to be at normal to moderate levels.


Geomagnetic field activity is likely observed mild elevations, mostly in response to recurrent coronal hole features. Active conditions are likely on
14 July, 22 to 24 July, 02 to 04 August, and 07 to 09 August. Unsettled conditions are likely on 15 to 17 July, 25 July, and 01 August. The remaining days of the outlook period are expected to be mostly quiet.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere
for July 17, 2025 by F. K. Janda, OK1HH


The lowest solar activity during the last solar turnaround (i.e., during the last approximately 27 days) was recorded between July 4 and 8, whereupon it
has been increasing since then. The number of sunspot groups has increased
from five to eleven. The same applies to the number of solar flares, although most of them were energetically insignificant. So far, developments have been in line with forecasts.


However, geomagnetic activity did not match the assumptions. Although it was significantly increased only on July 13 and 15, the last relatively calm days were July 9 and 10. After July 14, a calming was expected, but this forecast was pushed further and further forward day by day. Therefore, we did not see the expected improvement in shortwave propagation conditions.


One solar turnaround back (on June 21), activity had already begun to
decline, but in previous turns it continued to increase, so it is better not
to rely on recurrence, but to give preference to the latest observations.

There are six sunspot groups on the western half of the solar disk and five
on the eastern half.

Thanks to helioseismological observations, we know of another three to four spots beyond its eastern limb.

Therefore, solar activity will most likely begin to decline slowly.
But above all, the massive coronal hole in the southern half of the solar
disk, responsible for a series of solar wind bursts and thus geomagnetic disturbances, will begin to set.

Therefore, shortwave propagation conditions should slightly improve.

The Predicted Planetary A Index for July 19 to 25 is 5, 5, 5, 12, 20, 18, and 8, with a mean of 10.4. Predicted Planetary K Index is 2, 2, 2, 4, 4, 4, and
3, with a mean of 3. 10.7 centimeter flux is 122, 118, 120, 125, 125, 128,
and 128, with a mean of 123.7.


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 "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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