SB PROP @ ARL $ARLP027
ARLP027 The ARRL Solar Report

ZCZC AP27
QST de W1AW
Propagation Forecast Bulletin 27 ARLP027

From ARRL Headquarters

Newington CT July 25, 2025
To all radio amateurs

SB PROP ARL ARLP027
ARLP027 The ARRL Solar Report

Solar activity was at low levels. The largest flare was a C7.6 from Region 4136. C-class activity was also observed from several other regions during
the highlight period. No Earth-directed CME activity was observed.


No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was at high
levels on 14-20 July in response to persistent positive polarity CH HSS influence.


Geomagnetic field activity reached Minor storm levels on 14, 15, and 17 July due to positive polarity CH HSS influence. Solar wind speeds were elevated to as high as 700 km/s on 15 and 17 July. The remaining days were at quiet to active levels despite enhanced solar wind parameters.


Forecast of Solar and Geomagnetic Activity 21 July-16 August 2025

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


No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is expected to
be at high levels on 21-22 July, 24-30 July, 5-6 August, and 10-16 August all due to recurrent CH HSS influences. Low to moderate levels are expected on
the remaining days.


Geomagnetic field activity is expected to be at active to Minor storm levels
on 23 July, 1-4 August, and 7-14 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 July 24, 2025 by F. K. Janda, OK1HH:


Less than a year has passed since the probable peak of the 25th eleven-year cycle, which means that we are still in a period of high solar activity.

This does not necessarily mean that there must be a high sunspot number, many eruptions, or a high level of solar radio noise power flux (or solar flux for short). Currently, there is mainly the high speed of the solar wind that alternately causes high concentrations of negatively charged free electrons
in the ionosphere, which quickly recombine with positively charged protons.

The result is irregular changes in shortwave propagation conditions, accentuated in the summer by the activity of the sporadic E layer.

From mid-July, sunspot activity initially increased, then declined significantly in the last third of the month as a result of the setting of larger sunspot groups.

No major eruptions were observed in the setting groups.
Therefore, the Earth's magnetic field calmed down, especially on July 20-21. The geomagnetic disturbance on July 23 was expected, as the Earth entered the co-rotating interaction region (CIR), where it was hit by solar wind and triggered a G1-class geomagnetic storm (CIRs are transition zones between
fast and slow solar wind streams and contain shock waves and amplified
magnetic fields similar to those in CMEs).


Forecasts of further developments from various sources now differ
considerably. If we look at the part of the far side of the Sun that is currently hidden behind the eastern limb of the solar disk, we can first
expect the current level of solar activity and, at the beginning of August, a slight decrease, accompanied by a slight increase in geomagnetic activity.


The latest solar report from Dr. Tamitha Skov, WX6SWW, can be found on
YouTube at https://www.youtube.com/watch?v=n1N58cOnedo [ https://www.youtube.com/watch?v=n1N58cOnedo ]


The Predicted Planetary A Index for July 26 to August 1 is 5, 5, 5, 5, 5, 5, and 15, with a mean of 6.4. Predicted Planetary K Index is 2, 2, 2, 2, 2, 2, and 4, with a mean of 2.3. 10.7 centimeter flux is 135, 135, 130, 130, 130, 130, and 130, with a mean of 131.4.


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

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