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ARRL Propagation Bulletin ARLP036 (2023)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 8, 2023
To all radio amateurs 

ARLP036 Propagation de K7RA

At 0046 UTC on September 8, the Australian Space Weather Forecasting
Centre issued this alert:

"A solar filament erupted from the north east quadrant of the Sun on
07-Sep. Event modeling shows an edge of the associated north east
directed CME may graze the Earth's magnetosphere on 10-Sep.

Eight new sunspot groups emerged this week, one on September 2, two
on September 3, two more on September 4, and one each on September
5-6, followed by another on Thursday, September 7.

Average daily sunspot number was up, from 78.7 to 95.4, while
average daily solar flux was less, from 140.9 to 137.6.

Geomagnetic activity was higher. On September 2 the planetary A
index was 38, when Earth moved through a high speed solar wind. In
Alaska, the college A index at Fairbanks was 59.

Average daily planetary A index increased from 7 to 15.4, and
average middle latitude A index rose from 8.9 to 16.3.

Predicted solar flux is 155, 158 and 155 on September 8-10, 150 on
September 11-16, then 155, 150, 155 and 150 on September 17-20, 145
on September 21-22, 150 on September 23-24, 145 on September 25, 140
on September 26-27, 135 on September 28-30, then 130, 135, 130 and
135 on October 1-4, then 140 on October 5-6, then 135, 135 and 140
on October 7-9, 145 on October 10-11, 150 on October 12-13, then
155, 150, 155 and 150 on October 14-17.

Predicted planetary A index 10 and 12 on September 8-9, 8 on
September 10-13, then 5, 8, and 12 on September 14-16, 8 on
September 17-18, 5 on September 19-22, 12 on September 23, 5 on
September 24-27, then 8, 12, 5 and 12 on September 28 through
October 1, then 12, 10, 12 and 10 on October 2-5, and 5 on October
6-10, then 10, 8 and 12 on October 11-13, and 8 on October 14-15,
and 5 over the following week.

I observed interesting 12 meter propagation using FT8 on September
4, at 1745 UTC with in which my 
signal was only received over a narrow 300 mile band hugging the East 
Coast from Maine to Florida, all signal reports between 2200 to 2500 
miles away, nowhere else.

Three hours later at 2045 UTC, the reports along the coast expanded
to 600 miles, 2000 to 2600 miles wide.

Later at 2300 UTC it was the same pattern, but a 200 mile band,
2300-2500 miles wide.

The next day at 1700 UTC it was an arc from Virginia to South Texas,
1700 to 2300 miles. At 1715 UTC it drifted to coverage of 1750 to
2600 miles.

Before FT8 and pskreporter, there was no practical way for me to
observe any of this. Who knew?

Rick Cochran, WO8L wrote:

"So, despite all of the indicators being pretty good, why are the
bands so terrible?

"In the nearly 60 years I've been a ham this Sun cycle has
consistently been a dud compared to past cycles, especially during
the day.

"So many of us would like to know why."

I replied:

"Good question. You aren't the only one to ask."

There is a theory that carbon in the atmosphere or a warming climate
contributes to this, but I do not understand the mechanism. K9LA
told me that models do not support this, but at the moment I cannot
recall what those models are. This issue was discussed in previous

Another theory is that this is a perception issue related to the
widespread adoption of FT8, in which users of traditional modes see
less activity on CW and SSB and perceive poorer propagation as a

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - September 7, 2023, from F.K. Janda, OK1HH:
"In late August, as AR3413 approached the northwestern limb of the
solar disk, its eruptive activity began to increase, even though its
size and magnetic configuration did not suggest it. However, we
observed it at a very low angle, so we may have missed details.

"Either way, it was the source of several C- and M-class flares, at
least two of which (on August 30 and September 1) ejected CMEs. Both
hit the Earth triggering a G2 class geomagnetic storm. For shortwave
propagation, this meant a significant improvement and increase in
MUF in the positive phase of the disturbance on 2 September
0900-1300 UTC, followed by a deterioration for the next few days.

"AR3413 meanwhile, continued with increased eruptive activity on the
Sun's far side, including a massive CME on 5 September, but it no
longer affected the Earth. It merely 'ripped off the tail' (a
disconnection event) of comet Nishimura (C/2023 P1), which is
approaching the Sun. Its closest approach will be on September 17.

"A relative improvement in shortwave propagation did not occur until
September 5, with a jump in solar wind speed at 1439 UTC. Meanwhile,
active region AR3421 began to grow significantly around the central

"The magnetic configuration points to the possibility of
geoeffective flares. This was followed by the growth of other active
regions in the northeast of the solar disk, so that solar activity
remains elevated. Since we expect the Earth's magnetic field to calm
down, shortwave propagation conditions should gradually improve.
Seasonal changes as the equinoxes approach will also contribute to

The Autumnal Equinox in the northern hemisphere is just two weeks

Here is a solar cycle prediction:

Nice video, once you get past the ads:

A "Solar Orbiter EUI" video from Max White, M0VNG and the European
Space Agency:

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

Also, check this article from September, 2002 QST:

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

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

Sunspot numbers for August 31 through September 6, 2023 were 77, 83,
77, 79, 100, 121, and 131, with a mean of 95.4  10.7 cm flux was
139.9, 135.8, 131.2, 130.5, 136, 142.9, and 147.1, with a mean of
137.6. Estimated planetary A indices were 6, 12, 38, 25, 8, 11, and
8, with a mean of 15.4. Middle latitude A index was 8, 15, 25, 28,
14, 14, and 10, with a mean of 16.3.


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