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ARRL Propagation Bulletin ARLP034 (2023)

ARLP034 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7RA
Seattle, WA  August 25, 2023
To all radio amateurs 

ARLP034 Propagation de K7RA

Five new sunspot groups emerged this week, one on August 17, another
August 18, two more on August 21 and another on August 22.

Average daily sunspot numbers rose slightly, while average daily
solar flux declined. Average daily sunspot numbers went from 95.7 to
105.9 and average daily solar flux declined from 154.2 to 149.4.

No big geomagnetic events this week, and average daily planetary A
index changed from 6 to 8.4 while average daily middle latitude
index went from 7.7 to 10.1.

Predicted solar flux is 145 on August 25-26, 150 on August 27, 155
on August 28-29, 160 on August 30-31, then 165, 163 and 160 on
September 1-3, 162 on September 4-5, 158 on September 6-7, then 160
and 162 on September 8-9, 158 on September 10-11, 155 on September
12, 152 on September 13-15, 153 on September 16-18, 155 on September
19, and 158 on September 20-23, 162 on September 24-25, 165 on
September 26-28, then 163 and 160 on September 29-30.

Predicted planetary A index is 8 on August 25, then 5, 10 and 8 on
August 26-28, 5 on August 29 through September 5, then 10, 8 and 8
on September 6-8, 5 on September 9-13, 12 on September 14, 10 on
September 15-17, and 5 on September 18 through the end of the month.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere August 25-31, 2023 from F. K. Janda, OK1HH.

Although solar activity has been rated as low over the last seven
days, let's not be misled by an assessment based mainly on the
number and importance of flares. Solar activity continues to
increase toward the peak of cycle 25, expected in two years.
Projected into the highest usable ionospheric F2 layer frequencies,
this means that we may finally be able to look forward to a wide
opening of the ten-meter band for DX shortwave contacts. If it
occurs during this fall, we can expect the 25th cycle maximum to be
quite high after all.

It was pretty quiet over the weekend as all eight sunspot groups had
stable magnetic fields. Despite another large sunspot appearing in
the meantime, apparently magnetically connected to another sunspot
on the other side of the solar equator, there was still not much
going on. Only the M1.1 0 class solar flare on August 22 at 2304 UTC
was an exception. But although it lasted long enough to carry a CME
out of the solar atmosphere, it evidently did not.

On August 23, a filament erupted near the southwest limb of the Sun.
If it envelops the Earth, it would likely not happen until August
27, with a possible G1 class storm.

Max White, M0VNG sent this about solar wind:

Reader Jeremy Gill of Seattle, WA contributed this article on aurora
and the ionosphere: .

Warnings about solar activity, some a bit shrill:

A new video from Tamitha Skov:

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

For more information concerning shortwave radio propagation, see and the ARRL Technical Information
Service at . For an
explanation of numbers used in this bulletin, see .

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 17 through 23, 2023 were 135, 112, 104,
93, 102, 96, and 99, with a mean of 105.9.  10.7 cm flux was 151.9,
150.6, 150.6, 146.3, 148.7, 150.9, and 147, with a mean of 149.4.
Estimated planetary A indices were 8, 11, 8, 11, 9, 8, and 4, with a
mean of 8.4.  Middle latitude A index was 10, 14, 8, 12, 10, 12, and
5, with a mean of 10.1.


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