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ARRL Propagation Bulletin ARLP036 (2015)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 4, 2015
To all radio amateurs 

ARLP036 Propagation de K7RA

The Australian Space Forecast Centre issued a geomagnetic warning at
0009 UTC on September 4:
"The IMF Bz has been strongly southward over the last 3 hours (2100
UTC on September 3 to present). However, the current solar wind
speeds are at moderate levels, which are unfavourable to cause any
major geomagnetic disturbance. If the solar wind speeds elevate in
the coming 24 hours, active to minor storm conditions are possible.
If this happens, there is chance that aurora would be visible during
the local night hours of the 4 Sep from Tasmania and other southern
most regions of Australia.
"Increased geomagnetic activity expected due to coronal hole high
speed wind stream for September 4, 2015."
The IMF Bz refers to the interplanetary magnetic field:
Over this reporting week, August 27 through September 2, the average
daily sunspot number was 48.3, which is 21.4 points lower than the
previous seven days. Similarly, average daily solar flux declined
22.7 points to 97.
New sunspot groups appeared on August 27, 29, 30, 31, September 1
and 3. But activity is still very weak and the sunspots are not
magnetically complex or strong.
Now that we are in early September, we can look at recent monthly
averages for sunspot numbers. For May through August monthly
averages of daily sunspot numbers were 83, 77.4, 68.5 and 61.7. As
you can see, there has been a steady decline in activity.
For our three-month moving average of daily sunspot numbers, the
past three months, June 1 through August 31 averaged 69.1. This is
centered on July, 2015. For the past 12 months, the three month
moving averages of daily sunspot numbers were 108.4, 107, 104.7,
107.8, 98.2, 78.1, 68.2, 72.4, 77.7, 76.3 and 69.1. According to our
same figures, the current sunspot cycle peaked between January and
April 2014, when the three month moving averages centered on those
months were 138.5, 146.4, 148.2 and 129.6.
The latest predicted solar flux values for the near term from
NOAA/USAF forecasters are 85 on September 4, 90 on September 5-8, 85
on September 9-10, then 95 and 105 on September 11-12, 115 on
September 13-22, then 110, 105 and 100 on September 23-25, 90 on
September 26-28, and then bottoming out at 85 on September 29
through October 7. Although this is a long way out, predicted flux
values then rise to 115 on October 10-18.
Planetary A index predictions show values of 8, 10 and 9 on
September 4-6, then 10, 12 and 9 on September 7-9, then 5 on
September 10-11, then 12, 15 and 10 on September 12-14, then 8, 10
and 5 on September 15-17, then 8, 20 and 10 on September 18-20, 5 on
September 21-23, and 15, 10, 5, 8, 20 and 22 on September 24-29. A
quiet period with planetary A index at 5 is predicted for October
Petr Kolman, OK1MGW of the Czech Propagation Interest Group predicts
geomagnetic conditions will be quiet to unsettled on September 4-5,
mostly quiet September 6-8, quiet on September 9-10, quiet to active
September 11-13 (with the possibility of disturbed conditions on
September 11), quiet to unsettled September 14, quiet to active
September 15-16 (possibly disturbed September 15), quiet to
unsettled September 17-18, active to disturbed September 19, mostly
quiet September 20-21, quiet to active September 22, active to
disturbed September 23- 24, quiet to unsettled September 25, quiet
September 26-28, mostly quiet September 29 and quiet to unsettled
September 30.
Petr expects increased solar wind on September 10-13, 15-16, 19, and
22-24. reports that 156 years ago this week, on
September 2, 1859 the huge Carrington Event occurred, the monster
geomagnetic storm in which a billion ton CME smashed into Earth,
setting fire to telegraph stations around the world. Check, using the archive feature in the upper right
corner of the site to select September 2, 2015.
David Moore sent a link to a dramatic video from the Solar Dynamics
Observatory of sunspot group 2403 breaking up in the past week:
David sent another link about solar activity and aurora over the
past week:
Slate has an animation created by stringing together a long series
of hand drawn sunspot maps:
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 August 27 through September 2 were 46, 52, 50,
50, 50, 49, and 41, with a mean of 48.3. 10.7 cm flux was 110.2,
109.1, 100.1, 91.6, 91, 89, and 88.2, with a mean of 97.  Estimated
planetary A indices were 53, 43, 16, 5, 6, 6, and 7, with a mean of
19.4. Estimated mid-latitude A indices were 26, 28, 13, 5, 5, 7, and
10, with a mean of 13.4.