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ARRL Propagation Bulletin ARLP039 (2021)

ARLP039 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 39  ARLP039
From Tad Cook, K7RA
Seattle, WA  September 24, 2021
To all radio amateurs 

ARLP039 Propagation de K7RA

Last week's Propagation Forecast Bulletin ARLP038 reported a big
increase in activity with the daily sunspot number going to 124, but
by the end of that week all sunspots disappeared. The Sun was blank
for several days, but sunspots returned on September 19.

Average daily sunspot numbers were 28.7 this week, below the 58.3
average reported a week earlier.

Average daily solar flux was down nine points from 87.4 to 78.4.

Geomagnetic indicators were higher, with the highest activity on
September 17 when planetary A index was 24 due to a minor
geomagnetic storm triggered by a weak Coronal Mass Ejection. Average
daily planetary A index for the week increased from 7 to 9.1, and
average middle latitude A index went from 6.9 to 8.4.

Predicted solar flux for the next month is 90 and 92 on September
24-25, 95 on September 26-29, 92 on September 30, 84 on October 1-5,
82 on October 6, 80 on October 7-8, 78 on October 9-11, 75 on
October 12-20, 80 on October 21-22, 82 on October 23-25, 84 and 82
on October 26-27, and 84 on October 28 through November 1.

Predicted planetary A index is 15, 8 and 20 on September 24-26, then
35, 20 and 12 on September 27-29, 5 on September 30 through October
3, 8 and 12 on October 4-5, 5 on October 6-9, 12 on October 10, 5 on
October 11-17, 8 on October 18-19, then 10, 8 and 12 on October
20-22, 10 on October 23-24, and 5 on October 25-30, then 8 and 12
again on October 31 through November 1.

The northern Autumnal Equinox occurred at 1920 UTC on September 22.
Earth is bathed in approximately equal amounts of solar radiation
over the northern and southern hemispheres, always a good sign for
HF propagation. reported on September 23 that at 0442 UTC sunspot
group AR2871 produced a strong M3 class solar flare. A coronal mass
ejection is headed our way, but not directly toward Earth. "A
glancing blow might be possible on September 26-27." If so, then the
predicted planetary A index of 35 on September 27 may turn out to be
a lower number.

Geomagnetic activity forecast for the period September 24 to October
19, 2021 from F.K. Janda, OK1HH.

"Geomagnetic field will be,
quiet on: September 29, October 13, 16-18
quiet to unsettled on: September 24, 27-28, October 1, 3-4, 7, 9, 12
quiet to active on: September 25 (- 26), 30, October 2, 8, 10-11
unsettled to active on: October 5 (- 6), 14-15, (19)
Active to disturbed: Nothing predicted.

"Solar wind will intensify on October (3, 8,) 11, (19).

- Parenthesis means lower probability of activity enhancement.
- Contradictory indications currently reduce the accuracy of the

Last week N8II sent this update from West Virginia:

"During the period when the SFI (10.7 cm Solar Flux Index) was near
or over 100, conditions to Europe were somewhat disappointing on
15M; most of the time a short opening of about an hour at 1400 UTC.
Yesterday and today, September 16-17, the SFI was only 73, but there
is now a minor to moderate solar storm in progress at 2400 UTC.

"As the storm was beginning there was definitely enhanced high band
propagation to the higher latitudes. Around 1400 UTC, I easily
worked 4S7AB, Sri Lanka on 15M CW who was peaking S7, my first QSO
with central Asia on 15M in a long time. Also, I worked OH0V, Aland
Islands around 1500 UTC who was about S5. Geoff, GM8OFQ in the
Orkney Islands, north of Scotland (mainland) was easily 20 dB over
S9 on 17M SSB about 1500 UTC on my dipole antenna. I also worked
HB0/DL5YM and YL on 15M CW peaking S9. 7V7V portable on the beach in
Algeria called about S5. By 1600 UTC band conditions had drastically
declined, but EU signals were very loud again on 20M around 2000 UTC
including OH0V on CW about 20 dB over S9."

N0JK wrote on September 17, "In your last propagation report you
mentioned KB0QZ working LU4HK on 10M CW. I think I know what was up.

"I neglected to send a report of the September VHF contest
conditions. Sunday afternoon September 12 there were reports of
sporadic-E on 6 Meters. I worked WA8QYJ (EL96) on 50.313 MHz FT8 at
2109z on Es. KF0M (EM17) and WQ0P (EM19) also worked Florida
stations on 6M Es at that time. I think it is plausible KB0QZ had a
sporadic-E link to afternoon TEP on 10 Meters. I also saw WW1L
(FN54) spotted HC2FG at 2115z on 50.313 MHz. I suspect double hop
Es. There was single hop 6M Es from the Gulf Coast to HC2FG."

Here is a new forecast from Dr. Tamitha Skov, WX6SWW:

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 16 through 22, 2021 were 0, 0, 11, 13,
51, 50, and 76, with a mean of 28.7. 10.7 cm flux was 73.2, 73.4,
73.7, 75, 80, 84.9, and 88.5, with a mean of 78.4. Estimated
planetary A indices were 3, 24, 11, 3, 3, 8, and 12, with a mean of
9.1. Middle latitude A index was 3, 19, 14, 2, 4, 6, and 11, with a
mean of 8.4.


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