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ARRL Propagation Bulletin ARLP037 (2015)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 11, 2015
To all radio amateurs 

ARLP037 Propagation de K7RA

The Australian Space Forecast Centre issued a Geomagnetic
Disturbance Warning at 0132 UTC on September 8. They wrote, "The
effect of a high speed solar wind stream from a coronal hole is
keeping geomagnetic activity enhanced.

"Geomagnetic activity is expected to remain mostly enhanced to
Active levels on 8 September with the possibility of some minor
storm periods."

If you look at you can
see the effect, which is high numbers indicating geomagnetic
instability. What does this mean for performance on the air? For HF
it can mean higher absorption rates (meaning radio waves may be
absorbed more than they are reflected) but it can mean some
interesting propagation modes may occur on VHF.

The Australian Space Forecast Center issued another geomagnetic
disturbance warning at 0017 UTC on September 11: "A high speed solar
wind stream from a coronal hole is expected to arrive late on 11
September. This may result in the geomagnetic activity rising to
Active to Minor Storm levels. This rise in geomagnetic activity is
expected to continue on 12 September."

Frank Donovan, W3LPL sent a fascinating article about a rejuvenation
in solar magnetic strength toward the end of 2014, and an alternate
view from the recent news stories about a long term dearth of
sunspots. Instead, they propose that Cycle 25 (the next one) may be
similar to Cycle 24 (the one we are now in).

Read it at, .

Weak solar activity continued this week. The average daily sunspot
number for September 3-9 was only 37.3, down 11 points from the
previous seven days. Average daily solar flux was 85.3, compare to
97 for the previous week.

Geomagnetic activity was strong, with average planetary A index up
from 19.4 to 27.1. The most active day was Wednesday, September 9
when the planetary A index was 59.

The latest solar flux prediction from USAF/NOAA has readings of 85,
90 and 100 on September 10-12, 105 on September 13-14, 110 on
September 15-17, 115 on September 18-22, then 110, 105, 100 and 95
on September 23-26, 90 on September 27 to October 1, and 85 on
October 2-7. Flux values then rise to 115 on October 15-19.

Predicted planetary A index is 28, 16 and 27 on September 10-12,
then 16, 10 and 8 on September 13-15, 5 on September 16-17, then 8,
20 and 10 on September 18-20, 5 on September 21-23, then 15 and 10
on September 24-25, 5 on September 26-29, then 8 and 18 on September
30 through October 1, 12 on October 2-4, 8 on October 5, then 5 on
October 6-7, then 8, 12 and 8 on October 8-10, and 10 on October

Both the solar flux and planetary A index predictions are from
September 9. The new forecast appears every day after 2100 UTC, but
so far early on September 11 the September 10 forecast is not
available. You can catch up by checking, .

We do have a geomagnetic forecast from OK1MGW who predicts quiet to
active conditions September 11-13, (with September 11 conditions
perhaps at active to disturbed levels), quiet to unsettled September
14, quiet to active September 15-16 (with September 15 conditions
possibly at active to disturbed levels), quiet to unsettled
September 17-18, active to disturbed conditions September 19, then
mostly quiet on September 20-21, quiet to active September 22,
active to disturbed September 23-24, quiet to unsettled September
25, quiet on September 26-28, mostly quiet September 29, and quiet
to unsettled September 30. He expects increases of solar wind on
September 11-13, 15-16, 19, and 22-24.

Note that the mid-latitude A index for September 8 and 9 listed at
the end of this bulletin are wild guesses on my part, based on
tracking with the planetary A index. If you look at you will see there is no
data for those dates. This is probably because geomagnetic activity
was strong enough to knock the Fredericksburg and College (for the
high latitude number) magnetometers out of service.

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

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at, For an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at More good
information and tutorials on propagation are at

My own archives of the NOAA/USAF daily 45 day forecast for solar
flux and planetary A index are in downloadable spreadsheet format at and .

Click on "Download this file" to download the archive and ignore the
security warning about file format. Pop-up blockers may suppress
download. I've had better luck with Firefox than Internet Explorer.

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for September 3 through 9 were 27, 36, 24, 38, 47,
40, and 49, with a mean of 37.3. 10.7 cm flux was 86.5, 89.9, 85.4,
85.6, 83.7, 83.5, and 82.3, with a mean of 85.3. Estimated planetary
A indices were 9, 20, 13, 14, 46, 29, and 59, with a mean of 27.1.
Estimated mid-latitude A indices were 9, 18, 10, 12, 27, 24, and 31,
with a mean of 18.7.


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