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ARRL Propagation Bulletin ARLP018 (2023)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 5, 2023
To all radio amateurs 

ARLP018 Propagation de K7RA posted the following report on May 4:

sunspot exploded today, producing a long-lasting M-class solar flare
and a CME that might hit Earth. Geomagnetic storms are possible this
weekend if/when the CME arrives."

Sunspot activity and solar flux increased over the past reporting
week, April 27 through May 3.

Average daily sunspot numbers climbed from 91.4 to 114, while
average daily solar flux grew from 139.4 to 151.5.

Average daily planetary A index dropped from 26.9 to 13.6, and
average daily middle latitude A index declined from 15.6 to 11.9.

Predicted solar flux over the next month is 162 on May 5-6, 164 on
May 7, 162 on May 8-9, 164 on May 10-11, 170 on May 12-13, then 165,
160, 155, 150, 145 and 140 on May 14-19, 135 on May 20-21, then 130
and 125 on May 22-23, 120 on May 24-25, then 125, 130 and 135 on May
26-28, 140 on May 29 through June 2, then 145, 150 and 155, 160 and
165 on June 3-7, 170 on June 8-9, then 165, 160, 155, 150, and 145
on June 10-14.    .

Predicted planetary A index is 5 on May 5, then 12, 8, 5 and 5 on
May 6-9, 5 on May 10-11, 8 on May 12, 5 on May 13-22, 12 and 20 on
May 23-24, 15 on May 25-26, 8 and 12 on May 27-28, 10 on May 29-30,
then 8, 5, 12 and 10 on May 31 through June 3, 5 on June 4-6, 8 on
June 7-8, and 5 on June 9 through mid-month and beyond.

On Wednesday, May 3 posted, "INTENSIFYING SOLAR
ACTIVITY: Sunspot complex AR3293-3296 is crackling with strong
M-class solar flares--six of them today so far."

It looks like we face continued favorable HF propagation.

Recently I wrote of my bafflement at 10 meter propagation I observed
using FT8 and, in which my signals were only being
reported in Florida. I now have a better understanding of this.

On May 1 from 1930-2030 UTC I saw the same thing, with reports from
2,200-2,700 miles away, which suggests a 500 mile wide skip
distance. Mexican stations also reported me, over that same distance
in a 500 mile band. So, this suggests that it isn't just Florida,
and that the same signal is stretching out into the Gulf of Mexico
and the Atlantic Ocean, but I don't see it because there are no
stations there to receive my signal.

Later I saw multi-hop reports from ZL4KYH at 7,246 miles, 5W1SA at
5,230 miles, LU8EX at 6,893 miles and LU4FTA at 6,750 miles.

Jon N0JK wrote on April 29:

"I was able to work LU9DO, LU8EX and PY2XB that afternoon. The South
American signals popped up on what was otherwise a dead band. Later
some station in Florida came in. I was running 50 watts and a 3
element Yagi portable in EM28, northeast Kansas. May 1 - D2UY worked
stations in Florida and W3LPL in Maryland on was likely Es -- TEP.

"There will likely be more of these Es -- TEP openings in early

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere May 05-11, 2023 from OK1HH:

"While long-term forecasters are beginning to come to terms with the
possibility that the growth in solar activity could slow this year
and the current 25th cycle may not be one of the high ones, solar
activity has begun to increase. Already last week, sunspot group
AR3288 in the southwest with an unstable delta class magnetic field
was the source of an M7 class solar flare on May 1 at 1309 UTC. But
another M7 class eruption occurred on May 3 in the newly emerged
AR3293 in the northeastern part of the solar disk.

"Interestingly, a new group of spots, AR3296 in the northwest,
violates Hale's Law, as it has the opposite magnetic polarity that
is appropriate in the current 11-year cycle (polarity should be
negative on the left and positive on the right).

"The solar wind speed and Earth's magnetic field activity have
finally begun to decrease after a long active period, and the
conditions for shortwave propagation have finally improved, although
not to the extent we had hoped."

A story from Sky & Telescope about the Sun:

Two stories about massive solar flares, one from about 400 years

Some nonsense about flares:

More Aurora in our future:

A story about Radio Blackout:

More about Aurora Australis:

This weekend is the 10-10 CW QSO Party, on 10 meters of course:

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 .

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 April 27 through May 3, 2023 were 136, 111, 82,
105, 87, 134, and 143, with a mean of 114. 10.7 cm flux was 140.8,
149.8, 155.8, 153.5, 147.9, 156.8, and 156.2, with a mean of 151.5.
Estimated planetary A indices were 23, 19, 20, 10, 10, 9, and 4,
with a mean of 13.6. Middle latitude A index was 20, 16, 18, 8, 8,
9, and 4, with a mean of 11.9.


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