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ARRL Propagation Bulletin ARLP050 (2023)

ARLP050 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7RA
Seattle, WA  December 15, 2023
To all radio amateurs 

ARLP050 Propagation de K7RA


"Two predominately westward CMEs were observed on 14-Dec and
component arrivals are expected on 17-Dec.


"MAJOR X-CLASS SOLAR FLARE: The Sun just unleashed the strongest
solar flare of Solar Cycle 25 (so far), an X2.8-class explosion from
unstable sunspot AR3514. The blast caused a deep shortwave radio
blackout over the Americas and may have hurled a fast CME toward

Solar activity declined this week. Average daily sunspot numbers
dropped from 121.1 to 110.3, and average daily solar flux from 146.5
to 129.8.

With such low geomagnetic activity, conditions were good for last
weekend's ARRL 10 Meter Contest, although some wished for more

Six new sunspot groups appeared this week. The first two on December
8, another two on December 11 and 12, and two more on December 13.

Geomagnetic conditions were quieter, with planetary A index dropping
from 14.1 to 5.6, and middle latitude numbers from 7.3 to 4.6.

Predicted solar flux shows some expected improvement, with values
peaking at 160 on December 20-22, and 155 on January 23.

Predicted solar flux is 135 on December 15-16, then 145, 150 and 155
on December 17-19, 160 on December 20-22, but dropping back to 140
on December 23-24, 150 on December 25-26, then 155, 150 and 145 on
December 27-29, then 140 on December 30 through January 2, 2024, and
135 on January 3-5, then 130, 125, 120, 118, and 120 on January
6-10, 122 on January 11-12, then 124, 125, and 130 on January 13-15,
135 on January 16-18, 140 on January 19-20, and 150 on January

Predicted planetary A index is 18 and 22 on December 15-16, 12 on
December 17-18, then 18, 8, 8, 20 and 10 on December 19-23, 5 on
December 24-29, 8 on December 30-31, then 10 and 8 on January 1-2,
2024, 5 on January 3-6, 12 on January 7-9, 8 and 5 on January 10-11,
12 on January 12-13, then 15, 25, 8, 5, 20 and 10 on January 14-19,
and 5 for at least the following few days.

"Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere December 15-21, 2023 from F.K. Janda, OK1HH:

"Solar activity has been gradually decreasing over the last seven
days, broadly in line with the forecast.

"Most of the flares came from the active region AR3514, which was
moving from the northeast to the northwest.

"Eventually, most of the sunspots were in the northwest of the solar
disk, and as they gradually set over the next few days, solar
activity should continue to decrease.

"While activity on the Sun's receding half does not appear to be
great, there is definitely a larger active region beyond the Sun's
northeastern limb. This observation is likely the basis for the
latest forecast from the U.S. Air Force, which predicts a rise in
solar flux initially to 160, and after a slight drop back above 150
around Christmas.

"Shortwave propagation conditions, which have suffered particularly
in the Earth's northern hemisphere from the decline in solar
activity, should improve.

"But developments may be more complicated. Just as a CME originating
from the solar flare of 11 December with a peak at 2243 UT arrived
at Earth before midnight UTC on 13 December, triggered a geomagnetic
disturbance in the first hours UTC on 14 December and significantly
worsened propagation, we can expect something similar from the
stronger flare of 14 December with a peak at 0744 UTC. However,
subsequent geomagnetic disturbances should be no more intense than

Reader David Moore sent this article from "SpaceNews":

On Wednesday morning announced:

"The best meteor shower of the year is expected to peak on December
13-14 with no Moon to spoil the show. Rural observers could see
hundreds of Geminid meteors and more than a few fireballs."

From Angel Santana, WP3GW in Trujillo Alto, Puerto Rico:

"The 10 meter contest in my view was pretty nice on average,
although did notice this:

"During 0000 UTC on Saturday got always South America for about 3
hours before the band closed. Then before 1200 UTC got to work
VR2XAN which was a surprise as my antenna was pointing to Europe (he
said he was beaming the South Pole) and it's been 10 years since I
worked Hong Kong for the first time.

"But then, could not work a few Europeans, and the band likely
closed to them by 1500 UTC, and the US was pretty strong.

"Then it closed at 2230 UTC, so SA predominated again. It repeated
for Sunday.

"Also noted that there was a lot of fading as some stations
disappeared for a few seconds to a minute. And the SFI dropped to
130 which could have been a factor.

"But for what I am happy is that I accumulated 600 points for the
VOTA event, and I delivered 35."

Did you know India has a solar observatory in space?  Here is an
article from "The Times Of India":

From WBZ news, a story about a Massive Solar Flare:

Bil Paul, KD6JUI wrote:

"The solar flux wasn't optimal for the ARRL 10-meter contest last
weekend, but it was good enough. There was a lot of activity on the
voice part of the band.

"Operating from my kayak with 10 watts and a small homebrew loop, I
gathered 38 contest exchanges on Saturday and Sunday, around 3-1/2
hours of operating in total.

"On Saturday, South and Central America, and Caribbean stations were
coming in as well as the usual Canadian stations for
out-of-the-country exchanges. I managed to snap up one Brazilian
station for DX.

"On Sunday, I heard Australian stations coming in, but couldn't get
them to hear me. There were also more Brazilian stations plus a few
from Argentina.

"I was operating around noontime. QSB was evident."

Dr. Tamitha Skov, WX6SWW, put out a new video this week:

A couple of interesting pages to check out: KS7ROH for his
astrophotography and other projects, and W6BSD for links to his
propagation pages.

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

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

Also, check this article from September, 2002 QST:

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

Sunspot numbers for December 7 through 13, 2023 were 121, 125, 125,
120, 87, 80, and 114, with a mean of 110.3. 10.7 cm flux was 134.6,
132.6, 127.9, 126.6, 125.9, 126.2, and 134.8, with a mean of 129.8.
Estimated planetary A indices were 5, 5, 3, 4, 3, 10, and 8, with a
mean of 5.6. Middle latitude A index was 4, 4, 2, 4, 3, 8, and 7,
with a mean of 4.6.


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