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ARRL Propagation Bulletin ARLP036 (2020)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 4, 2020
To all radio amateurs 

ARLP036 Propagation de K7RA

I goofed last week and did not attribute that wonderful narrative
about solar cycle 19, which was written by Bill Hawkins, W5EC, who
is currently at the top of the DXCC Honor Roll.
As of Thursday night, no sunspots have appeared for the past 13
days.  I know we are all hoping for more sunspots, which I am sure
will return soon.  I have no special knowledge, but the trends for
this newly awakening solar cycle seem to favor it.  One event to
look forward to this month is the autumnal equinox on Tuesday,
September 22, which should favor worldwide HF propagation.
Average daily solar flux declined this reporting week (August 27
through September 2) from 70.4 to 69.6.
Geomagnetic indicators showed quite a bit more activity than they
have in some time now.  Average daily planetary A index rose from
5.1 to 13.1.  The most active day was August 31, when the planetary
A index reached 26.  The cause was a vigorous solar wind spewing
from holes in the solar corona.
Predicted solar flux is 70, forecast for every one of the next 45
days.  Predicted planetary A index is 5 on September 4 to 17, 8 on
September 18 and 19, 5 on September 20 to 22, then 8, 10 and 14 on
September 23 to 25, 10 on September 26 and 27, then 12 and 10 on
September 28 and 29, then 5 on September 30 through October 18.
This article says the solar minimum most likely occurred last
F. K. Janda, OK1HH has returned from vacation with his geomagnetic
activity forecast for the period September 4 to 29, 2020.
"Geomagnetic field will be 
Quiet on:  September 5 to 8, 10 to 13, 16 and 17, 20 and 21 
Quiet to unsettled on:  September 4, 9, 14, 29 
Quiet to active on:  September 15, 18 and 19, 22 to 24, 26 
Unsettled to active:  September 25, 27 and 28 
Active to disturbed:  Not expected 
Solar wind will intensify on:  September (4, 15, 19,) 22 and 23 
Parenthesis means lower probability of activity enhancement."
OK1HH wrote to us about his river cruise:
"As a captain, I sailed on the M / Y 'Daisy' (LOA 8 meters, 0.4
tons) on the Czech rivers Elbe and Vltava on the route Melnik -
Zernoseky Lake, Usti, Melnik, Luzec, Melnik, a total of 217.4 km.
And it was a beautiful week!"
Thanks to K9LA for this link to a fascinating and informative RSGB
lecture about sporadic-e propagation:
An article about Europe's most powerful solar telescope:
Tamitha Skov has a new video:
I love Dr. Skov's enthusiasm: "Whamo!"  And also of course her
expertise, which she shares so generously.
For more information concerning 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 August 27 through September 2, 2020 were 0, 0,
0, 0, 0, 0, and 0, with a mean of 0.  10.7 cm flux was 70, 70.1,
70.2, 70, 69.2, 69.5, and 68.3, with a mean of 69.6.  Estimated
planetary A indices were 8, 10, 14, 9, 26, 16, and 9, with a mean of
13.1.  Middle latitude A index was 7, 8, 14, 8, 19, 16, and 8, with
a mean of 11.4.


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