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ARRL Propagation Bulletin ARLP030 (2023)

ARLP030 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 30  ARLP030
From Tad Cook, K7RA
Seattle, WA  July 28, 2023
To all radio amateurs 

ARLP030 Propagation de K7RA

Average daily sunspot numbers declined slightly over the past week
(July 20-26) to 128.1, compared to 130.6 over the previous seven

Average daily solar flux declined significantly from 190.5 to 172.2.

The solar flux forecast sees values at 165 and 162 on July 28-29,
158 on July 30-31, then 155 on August 1-3, then 165, 170 and 175 on
August 4-6, 180 on August 7-10, 175 on August 11-13, 180 on August
14-15, 175 on August 16-18, 170 on August 19, then 165, 165 and 160
on August 20-22, and 155 on August 23-26, 160 on August 27, 165 on
August 28-30, 170 and 175 on August 31 through September 1, and 180
on September 2-6.

Predicted planetary A index is 5 on July 28-29, 15 and 10 on July
30-31, 5 on August 1-3, 8 on August 4, 5 on August 5-9, 10 on August
10, 8 on August 11-13, 5 on August 14-19, then 10, 8 and 5 on August
20-22, 12 on August 23-24, 10 on August 25-26, 5 on August 27-29, 10
and 8 on August 30-31, and 5 on September 1-5.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere -- July 27, 2023 from OK1HH.

"The likelihood of more massive solar flares has slowly decreased in
recent days as large groups of spots have fallen behind the western
limb of the solar disk and the magnetic configuration of the 
remaining regions has become increasingly simple over the past few

On July 20 and 21, two CMEs struck Earth's magnetic field in
accordance with the prediction. However, both impacts were weak and
did not produce even a minor geomagnetic storm.

Another weak halo CME was expected to leave the Sun on 23 July at
about 1530 UTC in a C5 class flare in spot group AR3376, coinciding
with the outburst of a relatively nearby magnetic filament. The
Earth's magnetic field detected its arrival at 0200 UTC on 26 July.
The result was an increase in geomagnetic activity and a
deterioration of shortwave propagation conditions. The disturbance
actually started on 25 July at 2235 UTC, but it was not clear
whether it was an early arrival of the same CME or another one that
we did not detect.

Note: since I will be abroad next week, I will not post the next
comment on August 3, but on August 10."

Sunspots, flares and aurora.

Mars Rover sees the far side of the sun.

Rocket punches hole in ionosphere.

Nearly five decades ago I witnessed the same thing, viewed from
Marin County, California. It was a huge dramatic display, My friend
had seen it before, and said it was created by a rocket launch from
Vandenberg AFB in Southern California.

Another CME.

On July 27, sent this alert:

just got hit by the kind of CME that may have once caused a major
power blackout on Earth. This time, Earth was not in the line of
fire. It was a farside eruption that flew away from our planet.
Maybe next time?"

Massive flare?

Latest from Dr. 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 July 20 through 26, 2023 were 131, 121, 103,
117, 141, 137, and 147, with a mean of 128.1  10.7 cm flux was
184.3, 172.8, 174.4, 172.5, 165.1, 169, and 167.4, with a mean of
172.2. Estimated planetary A indices were 10, 13, 9, 6, 7, 11, and
21, with a mean of 11. Middle latitude A index was 10, 11, 9, 5, 8,
12, and 23, with a mean of 11.1.


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