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ARRL Propagation Bulletin ARLP050 (2020)

SB PROP @ ARL $ARLP050
ARLP050 Propagation de K7RA

ZCZC AP50
QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7RA
Seattle, WA  December 11, 2020
To all radio amateurs 

SB PROP ARL ARLP050
ARLP050 Propagation de K7RA

Solar activity quieted this week, with average daily sunspot number
declining from 57.6 to 28.9, and average daily solar flux softening
from 108.1 to 91.9. On December 8 to 10, the sunspot number was 11
on each day, which is the minimum non-zero sunspot number.

Sunspot group 2786 gave us some great activity, but is about to
rotate off our sun's visible surface. But a look at
https://stereo.gsfc.nasa.gov on Thursday night shows some magnetic
complexity about to became geo-effective from the sun's southern
hemisphere, which could mean more great conditions.

Average daily planetary A index went from 6.4 to 4.4, and average
daily middle latitude A index went from 5.6 to 3.1.

Predicted solar flux for the next 45 days is 82 on December 11 and
12, 84 on December 13 and 14, 80 on December 15 to 18, 92 on
December 19 to 24, 94 on December 25 to 28, 96, 94 and 92 on
December 29 to 31, 90 on January 1, 2021 to January 4, 88 on January
5 to 7, 86 on January 8 to 11, then 84, 85 and 88 on January 12 to
14, 92 on January 15 to 20, and 94 on January 21 to 24.

The forecast for planetary A index shows 12, 8, and 8 on December 11
to 13, 5 on December 14 to 18, then 20 and 8 on December 19 and 20,
5 on December 21 and 22, then 8, 10 and 8 on December 23 to 25, 5 on
December 26 through January 5, 2021, then 10 and 8 on January 6 to
7, 5 on January 8 to 13, then 12, 20 and 8 on January 14 to 16, 5 on
January 17 and 18, then 8, 10 and 8 on January 19 to 21, and 5 on
January 22 to 24.

You can get daily updates of these numbers, usually after 2120 UTC,
from ftp://ftp.swpc.noaa.gov/pub/forecasts/45DF/ .

A coronal mass ejection on December 7 was expected to spark a
geomagnetic storm on December 10 and 11, which is why the planetary
A index was predicted at 40, 25, 8 and 8 on December 10 to 13. But
this was revised to the forecast of December 10 shown above.

Check https://bit.ly/2KbZsI7 for a story from Minnesota Public Radio
on what happened, and how we missed the storm.

The ARRL 10 meter contest is this weekend, much anticipated because
of recent increased solar activity. I was concerned about the
forecast from earlier in the week, but now it looks like good
conditions are expected. Around this time each December, there is
possible sporadic-E activity, and enhancement from the Geminids
meteor shower. This year the shower does not peak til the day after
the contest, December 14. But it is already underway.

Geomagnetic activity forecast for the period December 11, 2020 to
January 5, 2021 from F. K. Janda, OK1HH.
 
"Geomagnetic field will be 
Quiet on: December 13, (29,) January 12, 14 
Quiet to unsettled on: December 14 to 16, 21, January 5 
Quiet to active on: December 12, 17 and 18, 22 and 23, 26, 30 
Unsettled to active: December (11, 24,) 25 and 26, (27,) 31,
(January 3) 
Active to disturbed: December 19 (-20,) 28 
 
Solar wind will intensify on: December (11, 19,) 20 to 22, (23,) 27
(28 and 29, January 5)

Parenthesis means lower probability of activity enhancement."

Max White, M0VNG shared this article about the European Space
Agency's Solar Orbiter: https://bit.ly/342Qvbd

Tony Dixon, G4CJC compiles a weekly ten meter report. See
https://bit.ly/3oIxGlC for the most recent offering.

Tamitha Skov, WX6SWW and her latest forecast:

https://www.youtube.com/watch?v=bgB8JxYcQFE

Another article about that optimistic Cycle 25 forecast:

https://bit.ly/37ZqKtI

Big sunspots:

https://bit.ly/374XEK6

Great images showing transition of sunspot group 2786:

https://skyandtelescope.org/online-gallery/transition-of-sunspot-ar2786/

For more information concerning radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service at http://arrl.org/propagation-of-rf-signals. For an
explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere.

An archive of past propagation bulletins is at
http://arrl.org/w1aw-bulletins-archive-propagation. More good
information and tutorials on propagation are at http://k9la.us/.

Instructions for starting or ending email distribution of ARRL
bulletins are at http://arrl.org/bulletins .

Sunspot numbers for December 3 through 9, 2020 were 40, 38, 42, 25,
35, 11, and 11, with a mean of 28.9. 10.7 cm flux was 102.9, 95.8,
99.9, 90.9, 89.5, 82.4, and 82.1, with a mean of 91.9. Estimated
planetary A indices were 3, 2, 5, 6, 3, 5, and 7, with a mean of
4.4. Middle latitude A index was 1, 1, 4, 4, 2, 4, and 6, with a
mean of 3.1.
NNNN
/EX