Seven sunspot groups emerged this week. The first was on September
19, three on September 20, one each on September 22 and 23, and the
last on September 25.

Average daily sunspot numbers increased from 120 to 137.2, and
average daily solar flux shifted from 175.7 to 164.3.

Geomagnetic numbers were much quieter. Average daily planetary A
index changed from 35.7 to 14.3, and middle latitude A index from
23.4 to 10.7.

Predicted solar flux is 180 September 27 to October 1, 190 on
October 2-6, 185 on October 7-9, 180 on October 10, 175 on October
11-16, 170 on October 17-18, 165 on October 19, 160 on October
20-23, 165 on October 24-26, then 170 and 175 on October 27-28, 180
on October 29-30, and 190 on October 31 through November 2.

Predicted planetary A index is 5 on September 27-28, 8 on September
29-30, 5 on October 1-4, 10 on October 5-6, 5 on October 7-9, then
10, 20 and 19 on October 10-12, and 5 on October 13-21, 8 on October
22-23, 5 on October 24-31, and 8 on November 1-2.

"Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - September 26, 2024 from OK1HH:

"Solar flare activity is generally lower than it was in the first
half of September, when M-class solar flares were common and X-class
flares also occurred. The last significant M-class flare, including
a CME, was observed on September 22. However, the Earth's magnetic
field activity increased on September 25-26, incidentally in good
agreement with the forecast.

"Propagation conditions, especially in the shorter half of the
shortwave range, have understandably improved, but not as much as we
might have expected in the run-up to the equinox. This was
influenced by a decrease in solar activity (compared to August
levels) - and of course an increase in geomagnetic activity.

"Unlike in times relatively recently past, any of us can monitor not
only total solar activity, but also changes in solar wind
parameters. Both its speed and the concentration of free electrons
and protons ejected by flares. Changes in the ionosphere follow
quickly, but not always in the same way. It is also always the
result of previous developments."

Latest report from Dr. Tamitha Skov, WX6SWW:

https://youtu.be/B9jWbAVEpZw

Send your tips, reports, observations, questions and comments to
k7ra@arrl.net. When reporting observations, don't forget to tell us
which mode you were operating.

For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals . For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere .

An archive of past propagation bulletins is at
http://arrl.org/w1aw-bulletins-archive-propagation . More good
information and tutorials on propagation are at http://k9la.us/ .

Also, check this article:

https://bit.ly/3Rc8Njt "Understanding Solar Indices" from September
2002 QST.

Instructions for starting or ending email subscriptions to ARRL
bulletins are at http://arrl.org/bulletins .

Sunspot numbers for September 19 through 25 2024 were 109, 113, 117,
114, 224, 123, and 160, with a mean of 137.1. 10.7 cm flux was
161.2, 153.8, 158, 162.8, 167.4, 172.4, and 174.2, with a mean of
164.3. Estimated planetary A indices were 20, 7, 6, 5, 13, 17, and
32, with a mean of 14.3. Middle latitude A Index was 15, 6, 6, 3, 9,
12, and 24, with a mean of 10.7.