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ARRL Propagation Bulletin ARLP038 (2021)

ARLP038 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 38  ARLP038
From Tad Cook, K7RA
Seattle, WA  September 17, 2021
To all radio amateurs 

ARLP038 Propagation de K7RA

On this reporting week, September 9-15, sunspot numbers started
strong at 124 but ended at 0. Average daily sunspot numbers went
from 64.6 to 58.3. Average daily solar flux declined from 92.9 to

Geomagnetic indicators remained moderate, with last week's average
daily planetary A index unchanged at 7, and average daily middle
latitude A index changed from 7.7 to 6.9.

Predicted solar flux is much lower than last week's bulletin
reported. Solar flux is predicted at 75 on September 17-23, 76 on
September 24-26, 78, 80 and 82 on September 27-29, 86 on September
30 through October 10, 82 on October 11-12, 80 on October 13, 78 on
October 14-17, and 76 on October 18-23. Solar flux is expected to
rise to 89 by the end of October.

Predicted planetary A index is 15 on September 17-18, 8 on September
19-20, then 5 and 8 on September 21-22, 5 on September 23 through
October 3, then 8 and 12 on October 4-5, and 5 on October 6-17, 8 on
October 18, and 5 on October 19 through the end of the month.

Geomagnetic activity forecast for the period September 17 to October
12, 2021 from F.K. Janda, OK1HH:

"Geomagnetic field will be:
quiet on: September 19, 29-30, October 9-10,
quiet to unsettled on: September 20, 28, October 1, 4, 7, 12,
quiet to active on: September 17-18, 22-23, 25-27, October 3, 8, 11,
unsettled to active on: September 21, 24, October (2,) 5-6,
Active to disturbed: Nothing predicted.
"Solar wind will intensify on October 11.

- Parenthesis means lower probability of activity enhancement.
- The confusing situation mentioned two weeks ago, together
  with the variable configuration of active areas and coronal
  holes, was a sign of the subsequent increase in solar activity."

Marty, KB0QZ in Tulsa was tuning 10 meters at noon on Sunday,
September 12 and heard no signals, not even any propagation beacons.
He called CQ on 28.040 MHz CW and received a 599 report from LU4HK,
who was also S9. The path distance was 5,094 miles. He continued to
tune the band and call CQ through the afternoon with nothing else
Page down in this article,, "Nevada County
Captures: Glorious sunrise" and page down for a great solar image in
a local California newspaper.

Go to your favorite search engine and enter this text:

mdpi: sunspot number and photon flux data

An interesting PDF is available for download.

At 2000 UTC on September 13 I (K7RA) called CQ on 15 meters with FT8
from my station in Seattle at CN87uq using a marginal end fed wire
antenna, about .72 wavelength long, partially indoors.

Typically I would see the map at light up with many
stations reporting my signal. But at that time only one station,
WA1SXK in North Carolina (EM95lf) heard me, reporting -19 dB, and
this continued through many attempts.

I switched to 17 meters and saw typical reports from stations in the
Midwest and East coast, 1500-2400 miles out.

Checked for flare activity and anything else unusual, but saw
nothing. But solar flux and sunspot numbers were declining, after
reaching a high several days earlier. Perhaps the MUF for this path
at that time was below 15 meters.

If you would like to make a comment or have a tip for our readers,
please email the author at, .

For more information concerning shortwave radio propagation, see and the ARRL Technical Information
Service web page 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 September 9 through 15, 2021 were 124, 99, 93,
47, 32, 13, and 0, with a mean of 58.3. 10.7 cm flux was 99.7, 96.3,
91.8, 87.7, 83.3, 78.1, and 75.2, with a mean of 87.4. Estimated
planetary A indices were 6, 9, 7, 6, 9, 6, and 6, with a mean of 7.
Middle latitude A index was 7, 9, 8, 6, 7, 5, and 6, with a mean of


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