SB PROP @ ARL $ARLP024
ARLP024 The ARRL Solar Report

ZCZC AP24
QST de W1AW
Propagation Forecast Bulletin 24 ARLP024

From ARRL Headquarters

Newington CT June 27, 2025
To all radio amateurs

SB PROP ARL ARLP024
ARLP024 The ARRL Solar Report

Solar activity has been at low levels for the past 48 hours, with low-level C-class flares.


There was a narrow coronal mass ejection (CME), likely associated with minor flaring from Regions AR4117 and AR4118 between 1439 UTC and 1524 UTC on June 24. Initial modeling indicated a miss, south and behind Earth's orbit.
However, it should be noted that analysis of this event is low confidence
given the assumed source location.


An enhanced solar wind environment is expected to continue through June 28 under a negative polarity Coronal Hole High-Speed Stream regime before beginning to trend towards a more nominal environment on 29 June.


There is a chance for R1-R2 (Minor-Moderate) events through June 29. There is also a slight chance for an R3 (Strong) or greater event through June 29, as well as a slight chance for S1 (Minor) solar radiation storm conditions
through the reporting period.


Geomagnetic field activity is likely to reach active levels on July 1 to 3,
05 and 6, and 11 and 12, all due to recurrent CH HSS influences. Quiet, and quiet to unsettled conditions are expected to prevail throughout the
remainder of the period through July 19.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - June 26, 2025, by F. K. Janda, OK1HH:


"The last significant solar flare was recorded on June 15, reaching an X-ray brightness of M8.4, while ejecting a CME into space. The particle cloud
arrived at Earth on June 18, with the subsequent increase in solar wind
speed, which caused an improvement in propagation conditions in the lower shortwave bands.


"Although eruptions with higher X-ray brightness were also recorded, they
only caused shorter attenuation in the lower layers of the ionosphere on the illuminated part of the Earth.


"Overall solar activity declined steadily after June 15, with five to six visible sunspot groups. At most two were capable of producing larger
eruptions. Their proximity to two of the three observable coronal holes near the equator made it possible to predict an intensification of the solar wind and the occurrence of geomagnetic disturbances for June 25-26 (or possibly
also June 27).


"This was all the more likely given that it was the central meridian region. Since then, however, the sunspot groups and coronal holes have shrunk. The increase in solar wind speed (up to 700 km/s) and geomagnetic activity (only G1) was therefore smaller. However, the flux of electrons with energies above
2 MeV reached high values, with a maximum flux of 1,260 pfu at 25/1355 UTC.


"Unfortunately, an increase in the concentration of free electrons in the Earth's ionosphere is a relatively common phenomenon this year and worsens
the conditions for shortwave propagation.


"A return to background levels is expected from June 28. In July, larger sunspot groups will return to the solar disk. Therefore, the solar flux will rise slightly during the first ten days. Only a very slight improvement in shortwave propagation conditions can be expected in the summer ionosphere of the Earth's northern hemisphere."


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 June 28 to July 4 is 15, 10, 5, 15, 15,
12, and 5, with a mean of 11. Predicted Planetary K Index is 3,3, 2, 4, 4, 4, and 2, with a mean of 3.1. 10.7 centimeter flux is 140, 145, 145, 140, 140, 140, and 145, with a mean of 142.1.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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