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ARRL Propagation Bulletin ARLP036 (2021)

SB PROP @ ARL $ARLP036
ARLP036 Propagation de K7RA

ZCZC AP36
QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 3, 2021
To all radio amateurs 

SB PROP ARL ARLP036
ARLP036 Propagation de K7RA

Solar activity is on the upswing this week.  Average daily sunspot
numbers increased from 21.7 to 50.6, with a high of 77 last
Saturday, August 28.  Average daily solar flux rose from 78.5 to 88.

Average daily planetary A index increased from 4.7 to 9.6, and
average daily middle latitude A index went from 5.7 to 10.7.
Geomagnetic activity peaked on August 27 and 28 due to a coronal
mass ejection.

New sunspot regions appeared on August 26 and 27, and on September 2
Spaceweather.com reported "New Sunspot, Rapidly Growing" to announce
the emergence of AR2863.

Predicted solar flux looks promising, particularly after
mid-September, at 85 and 82 on September 3 and 4, 80 on September 5
and 6, 78 on September 7, 75 on September 8 to 10, 80 on September
11 to 14, 85 on September 15, 90 on September 16 to 30, 85 on
October 1, and 80 on October 2 to 10.  Flux values rise to 90 again
after October 12 in this forecast from September 2.

Predicted planetary A index is 8, 5, 10 and 8 on September 3 to 6, 5
on September 7 to 10, then 10 and 8 on September 11 and 12, 5 on
September 13 to 20, 8 on September 21, 5 on September 22 to 25, then
a big jump to 25, 8, 18, 8, and 12 on September 26 to 30, and back
to 5 on October 1 to 7, then 10 and 8 on October 8 and 9.

Geomagnetic activity forecast for the period September 3 to 29,
2021, from F. K. Janda, OK1HH.

"Geomagnetic field will be
Quiet on September 7 and 8, 10, 14 and 15, 17 and 18, 28 and 29
Quiet to unsettled on September 4 and 5, 13, 16, 19, 22, 25, 27
Quiet to active on September 3, 6, 9, 11 and 12, 20 and 21, 26
Unsettled to active on September 23 and (- 24)
Active to disturbed, nothing predicted

Remarks:
- Parenthesis means lower probability of activity enhancement.
- The situation is confusing, the configuration of active regions
and coronal holes is variable, so this time it is not possible to
make a so-so reliable forecast.  Here and there it happens before
solar activity rises.
- F. K. Janda will travel next week, therefore next forecast will be
compiled on September 16."

The autumnal equinox will be on Wednesday, September 22 in the
Northern Hemisphere, always a welcome event for HF propagation.
Solar flux is forecast to be higher at that time, also a good sign.

For more information concerning shortwave 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 August 26 through September 1, 2021 were 47, 73,
77, 44, 41, 37, and 35, with a mean of 50.6.  10.7 cm flux was 88.6,
89.5, 89.9, 88.7, 90.6, 84.4, and 84.2, with a mean of 88.
Estimated planetary A indices were 6, 20, 14, 8, 7, 7, and 5, with a
mean of 9.6.  Middle latitude A index was 6, 19, 17, 9, 9, 9, and 6,
with a mean of 10.7.
NNNN
/EX