SB PROP @ ARL $ARLP033
ARLP033 The ARRL Solar Report

ZCZC AP33
QST de W1AW
Propagation Forecast Bulletin 33 ARLP033

From ARRL Headquarters

Newington CT September 5, 2025
To all radio amateurs

SB PROP ARL ARLP033
ARLP033 The ARRL Solar Report

Spaceweather.com [ http://Spaceweather.com ] for September 5 reports that a total lunar eclipse occurs on September 7th. However, it will not be visible
in the Americas.


Solar activity will likely continue at moderate levels with isolated M-class flares through September 6 due to the combined flare potential of Regions AR4197 and AR4207. Probabilities decrease to just a chance for M-class flares on September 7 as AR4197 moves beyond the western limb.


An enhanced solar wind regime is anticipated to continue into September 6 due to a positive polarity coronal hole high-speed stream.


On September 7, High Speed Stream activity combined with the arrival of the September 4th CME is likely to cause further G1 (Minor) storming levels with
a chance for G2 (Moderate).


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, September 4, 2025, by F. K. Janda, OK1HH:


"As soon as we begin to think that we are starting to understand what is happening on the Sun and in its vicinity (where we and Earth are located), Mother Nature shows us that it is not that simple.

A small example: while we were observing the extensive active region 4197 on the Sun, an eruption occurred in another, much smaller and less conspicuous region, AR4199, which had a key influence on the events of the following
days.

It happened on the evening of Saturday, August 30, very close to the solar equator and the central meridian, so it was directed towards Earth.


"The forecasts of further developments from all forecasting centers were identical: the CME would arrive at Earth on September 1 in the late afternoon to evening hours and cause a G2-class magnetic storm, accompanied by auroras. And so, it happened.


"As predicted, the geomagnetic disturbance continued on September 2. This was followed by a relatively rapid calm, and by September 4, the state of the Earth's magnetosphere and ionosphere began to approach what we are used to at the end of summer and beginning of autumn - in other words, there was a noticeable improvement in the conditions for ionospheric shortwave
propagation.


"In further developments, the Earth will be affected by another surge of
solar wind on September 6. But this should come as no surprise, as it is a regularly recurring passage of the Earth through a stream of intensified
solar wind linked to active areas on the Sun. The entire system, together
with the Sun, rotates once every approximately 27 days. Therefore,
predictions of the onset of disturbances are relatively reliable."


The latest report from Dr. Tamitha Skov, WX6SWW, can be found at https://www.youtube.com/watch?v=XxbAzht2Eq0 [ https://www.youtube.com/watch?v=XxbAzht2Eq0 ] .


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 September 6 to 12 is 8, 12, 12, 12, 10,
5, and 5, with a mean of 9.1. The predicted Planetary K Index is 3, 4, 4, 4,
4, 2, and 2, with a mean of 3.3. 10.7 centimeter flux is 175, 160, 140, 130, 125, 125, and 120, with a

mean of 139.3.
NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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