Register Account

Login Help

ARRL Propagation Bulletin ARLP039 (2023)

ARLP039 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 39  ARLP039
From Tad Cook, K7RA
Seattle, WA  September 29, 2023
To all radio amateurs 

ARLP039 Propagation de K7RA

Solar activity was up for this reporting week, September 21-27.
Eight new sunspot groups appeared, two on September 21, two more on
September 22, two more on September 25, another on September 26 and
another on September 27.

The average daily sunspot number jumped from 118.4 to 170.6, while
average daily solar flux went from 149.3 to 168.8.

The Autumnal Equinox was last weekend in the Northern Hemisphere, so
our Earth is bathed in equal amounts of solar radiation in both

The average daily planetary A index went from 20.4 to 17, while
middle latitude numbers changed from 18.1 to 13.7. Thursday had the
strongest geomagnetic activity, and Alaska's college A index was 68,
triggering a geomagnetic storm with aurora visible across the
northern tier of the United States. Activity peaked around 1200-1800
UTC, with planetary K index at 5.33.

Regarding solar flux predictions, the next predicted peak is at 168
on October 20-23.

Predicted flux values are 148 on September 29-30, then 145, 143 and
145 on October 1-3, 148 on October 4-5, 155 on October 6, 160 on
October 7-8, 155 on October 9, 150 on October 10-11, 145 on October
12-14, then 150, 155, 155, 160 and 165 on October 15-19, 168 on
October 20-23, then 164, 160, 160, 168 and 150 on October 24-28,
then 145 and 150 on October 29-30, 155 on  October 31 through
November 2, 160 on November 3-4, and 155 on November 5.

Predicted planetary A index is 5, 12, and 8 on September 29 through
October 1, then 8, 15, 12, 8 and 15, on October 2-5, then 5 on
October 6-21, then 10 and 8 on October 22-23, and 5 on October 24
through November 7, and 55 on November 8.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - September 27, 2023 from OK1HH:
"During September we saw nearly regular fluctuations in solar and
geomagnetic activity. M-class flares occurred nearly every day, some
accompanied by plasma eruptions (CMEs). On 24-25 September, the
fourth and strongest solar-origin proton cloud (G3) of the month
struck Earth.

"With such a large number of disturbances, each lasting several
days, there was a significant decrease in MUF and a general
deterioration of shortwave propagation (September 3-5, 13-15, 18-20
and since 25 September).

"After these disturbances, due to the high solar activity,
relatively rapid improvements followed, the best of which was
observed from 10 September onward. It culminated in a positive phase
of disturbance during the daytime hours of UTC on 12 September, with
the highest MUF values, and thus the best opening of the upper
shortwave bands. This also made the following deterioration, which
started already on the night of 13 September, even more noticeable.

"Given the number and duration of disturbances and despite several
improvements, overall propagation was below average. This pattern
began in August and given the trend in solar activity, looks set to
continue for the time being."

Gregory Andracke, W2BEE sent these two articles about Aurora

Check out his web site:

Here are more articles and videos about aurora:

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

An archive of past propagation bulletins is at . More good
information and tutorials on propagation are at .

Also, check this article from September, 2002 QST:

Instructions for starting or ending email distribution of ARRL
bulletins are at .

Sunspot numbers for September 21 through 27, 2023 were 159, 184,
198, 172, 164, 179, and 138, with a mean of 170.6. 10.7 cm flux was
168.1, 175.7, 173, 173.7, 170.2, 164.9, and 156, with a mean of
168.8. Estimated planetary A indices were 10, 8, 10, 21, 23, 32, and
15, with a mean of 17. Middle latitude A index was 10, 7, 9, 17, 15,
26, and 12, with a mean of 13.7.


Instragram     Facebook     Twitter     YouTube     LinkedIn