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ARRL Propagation Bulletin ARLP032 (2023)

ARLP032 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 32  ARLP032
From Tad Cook, K7RA
Seattle, WA  August 11, 2023
To all radio amateurs 

ARLP032 Propagation de K7RA

Two new sunspot groups appeared on August 3, three more on August 7,
and another on August 9.

But solar activity was lower over our reporting week, August 3-9,
with average daily sunspot number dropping from 154.3 to 108.9 and
average solar flux from 173 to 166.4.

Average daily planetary A index rose from 8.3 to 12.3 and average
middle latitude A index from 9.3 to 10.1.

The middle latitude A index numbers on August 3-4 were not
available, and are my estimates, tracking with the planetary A index
and the remaining five middle latitude readings in the rest of the

Predicted solar flux is 150 on August 11-12, then 145, 140 and 130
on August 13-15, 135 on August 16-17, 162 on August 18, 164 on
August 19-20, 168 on August 21-23, then 172, 172 and 170 on August
24-26, 172, 172 and 174 on August 27-29, then 172, 172 and 170 on
August 30 through September 1, then 168, 168, 166 and 164 on
September 2-5, then 162, 162, 164 and 164 on September 6-9, then
162, 162 and 160 on September 10-12, 162 on September 13-14, 164 on
September 15-16, and 168 on September 17-19.

Predicted planetary A index is 5 on August 11 13, then 8, 12, 12 and
10 on August 14-17, 5 on August 18-25, 12 on August 26, then 5 on
August 27 through September 4, 12 on September 5, and 5 on September

On August 9 wrote about a geomagnetic storm in 1940
that sounds similar to the infamous Carrington Event. Two CMEs hit
Earth 109 minutes apart. Here is a recent scientific paper on the
event: .

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere August 11-17, 2023 from OK1HH.

Sometimes you need to take a break and that's why this time the
commentary covers the last two weeks instead of one. During these
weeks, solar activity was often elevated.

M and X class flares and CMEs occurred frequently. The Earth was
lucky not to be hit by the fiery loop that ejected from the Sun from
AR3372 during the M4-class eruption on October 28 at 1558 UTC.
Energetic protons from the Sun were hitting Earth's atmosphere for a
significant part of the period (a "radiation storm" - class S1). The
source this time was beyond the northwestern edge of the solar disk
and was most likely an X-class flare. The consequence was also
absorption in the polar cap (PCA).

On August 1, the CME was very likely to hit the Earth's magnetic
field, but instead we only registered a hint of a near-Earth flyby
around 1600 UTC. We expected another CME arrival and a smaller G1
class geomagnetic storm on August 4-5. It happened, and the magnetic
filament connecting the two sunspots exploded on August 5 around
0500 UTC, hurling the CME into space.

An X1.6 class eruption was observed in AR3386 on August 5 at 2221
UTC. The CME did not head directly toward Earth, so there were fewer
disturbances than expected with the current solar activity. But the
opposite was true for shortwave propagation conditions - they were
mostly worse.

The proton flux higher than 10 MeV began to rise at 2146 UTC on
August 7 and exceeded the 10 MeV warning threshold at 0110 UTC. This
proton event followed the X1.5 eruption observed on August 7 with a
peak at 2046 UTC. Thereafter, the proton flux above 10 MeV started
to slowly decrease and remained close to the threshold.

F. K. Janda OK1HH

In the past, I've noted odd 10 meter propagation observed with using FT8 in which my signals (from Seattle) were
only received in Florida, about 2300 to 2700 miles away.

On Thursday, August 10 at 2200 UTC on 12 meters FT8 the only reports
from North America I saw were in Florida, 2500-2700 miles away, plus
NH6V in Hawaii, and VK5HW and VK4TUX in Australia at 8367 and 7402
miles. I have no idea what causes this seemingly restricted
propagation. The antenna at my end was an end fed 32 foot wire,
about .85 wavelength, partially indoors.

Solar mysteries.


Tamitha Skov:

You can always catch the latest video from Dr. Skov on Youtube at:

This weekend is the Worked All Europe DX Contest:

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 3 through 9, 2023 were 124, 122, 100, 97,
101, 115, and 103, with a mean of 108.9. 10.7 cm flux was 162.9,
170.8, 175.8, 173.5, 169.7, 158.9, and 153.4, with a mean of 166.4.
Estimated planetary A indices were 6, 13, 36, 4, 12, 8, and 7, with
a mean of 12.3.  Middle latitude A index was 5, 12, 24, 4, 11, 7,
and 8, with a mean of 10.1.


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