Solar activity was quiet over the past week, but geomagnetic numbers
were way, way up.

Average daily sunspot numbers dropped from 178.4 to 120, and average
daily solar flux from 223.7 to 175.7.

Average daily planetary A index rocketed from 7.9 to 35.7, and
middle latitude numbers from 11.1 to 23.4.

Six new sunspot groups emerged over the past week; one each on
September 13 and 14, two on September 16, and two each on September
17 and 18.

Predicted solar flux is 160 and 155 on September 20-21, 150 on
September 22-26, then a huge leap to 230 and 225 on September 27-28,
240 on September 29 through October 2, 230 on October 3, 220 on
October 4-5, then 215, 205 and 207 on October 6-8, 201, 186 and 172
on October 9-11, 173 and 175 on October 12-13, 170 on October 14-16,
165 on October 17-18, 170 on October 19, 225 on October 20-21, then
230, 225, 230 and 225 on October 22-25, then 240 on October 26-29.

Predicted planetary A index is 5, 10 and 8 on September 20-22, 5 on
September 23-26, then 25, 15 and 10 on September 27-29, then 5 on
September 30 through October 4, 10 on October 5-6, and 5 on October
7-9, 10 on October 10, 20 on October 11-13, 15 on October 14, 10 on
October 15-16, then 5 on October 17-22, 25 on October 23-24, and 15
and 10 on October 25-26.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - September 19, 2024 from F.K. Janda, OK1HH:

"Overall solar activity has decreased slightly in recent days, but
before that AR3825 produced energetic flares, including two of the
largest: X1.3 on September 12th and a very strong X4.5 on September
14th. The arrival of the CMEs and the onset of the disturbance,
expected on the afternoon of UT Sept 16th, was delayed and
registered as an influx of protons in the solar wind at 22:44 UT
Sept 16th. After that, a geomagnetic disturbance started to develop,
which significantly affected the shortwave propagation conditions,
especially on 17 September.

"A more pronounced upsurge in solar flux can be expected once the
large active regions known to be present through helioseismology
start to reappear at the eastern limb of the solar disk. This should
happen around 26 September. However, a repeat of the August 28-29
disturbance is expected in the same period. Therefore, an
improvement in propagation conditions can be expected before
September 26, or better yet, shortly during the onset of the
disturbance-after which a deterioration will occur."

New STCE newsletter:

https://www.stce.be/newsletter/newsletter.php

The latest video from Dr. Tamitha Skov, WX6SWW:

https://youtu.be/o0HWm0W-YRw

Send your tips, reports, observations, questions and comments to
[email protected]. 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 12 through 18 2024 were 160, 127, 136,
68, 103, 140, and 106, with a mean of 120. 10.7 cm flux was 201.2,
185.8, 172.4, 172.8, 169.2, 165.4, and 163.3, with a mean of 175.7.
Estimated planetary A indices were 67, 37, 21, 19, 23, 71, and 12,
with a mean of 35.7. Middle latitude A Index was 36, 22, 22, 16, 19,
39, and 10, with a mean of 23.4.