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ARRL Propagation Bulletin ARLP042 (2015)

ARLP042 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 42  ARLP042
From Tad Cook, K7RA
Seattle, WA  October 16, 2015
To all radio amateurs 

ARLP042 Propagation de K7RA

The Australian Space Forecast Centre issued a geomagnetic
disturbance warning at 2345 UTC on October 15. The alert said "The
continued strengthening of the solar wind stream due to coronal hole
effect may lead to isolated periods of minor geomagnetic storms on
16 October."

Sunspot numbers over the past week (October 8-14) were nearly the
same as the previous seven days. Average daily sunspot numbers went
from 37 to 36.9, and average daily solar flux dropped from 93.8 to

Just as in previous solar cycles, geomagnetic indicators are high as
the cycle trends downward after the peak. Go to the bottom of the
page at and note the graph for
Ap (planetary A index) progression. If you look at the graph just
above that for solar flux, see how the Ap index is high after the
peak of solar flux or sunspot numbers.

From last week to this week, average daily planetary A index went
from 24.3 to 25.1, and average mid-latitude A index moved from 15.7
to 17.6.

Predicted solar flux is 105 on October 16, 110 on October 17, 120 on
October 18-21, 115 on October 22-23, 120 on October 24, 125 on
October 25-26, then 130, 120 and 110 on October 27-29, 100, 90 and
85 on October 30 through November 1, 80 on November 2-6, 85 on
November 7-8 and 90 on November 9-11. Solar flux then rises to 130
on November 23 and drops below 100 after November 26.

Predicted planetary A index is 18, 15 and 12 on October 16-18, 8 on
October 19-20, 5 on October 21-27, then 8, 12 and 10 on October
28-30, 8 on October 31 through November 2, 20 on November 3, 15 on
November 4-5, then 12, 8, 20, 15 and 18 on November 6-10, 20 on
November 11-12, 15 on November 13 and 8 on November 14-18.

OK1MGW of the Czech Propagation Interest Group says to expect a
quiet to active geomagnetic field on October 16-17, quiet to
unsettled on October 18, mostly quiet October 19-20, quiet to
unsettled October 21, quiet on October 22-26, mostly quiet October
27, quiet to unsettled October 28-30, quiet to active October 31
through November 1, active to disturbed November 2-5, quiet to
unsettled November 6, quiet to active November 7-9, and quiet to
unsettled November 10-11.

David Moore sent this: "The Sun has sprung a leak. A hole in the
topmost layer of the Sun and its magnetic field, the size of 50
Earths, is letting loose an ultra-fast solar wind that has kicked
off several nights of auroras down on Earth." See .

Check for a picture of that huge coronal hole.
Note you can click on the image to zoom in.  The white lines
represent magnetic lines of force. You can check current images of
the Sun at various wavelengths at .

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
the download.

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 October 8 through 14 were 24, 11, 22, 36, 51,
58, and 56, with a mean of 36.9. 10.7 cm flux was 79.7, 81.2, 81.4,
84.6, 89.1, 95.6, and 100.7, with a mean of 87.5. Estimated
planetary A indices were 56, 26, 12, 12, 22, 25, and 23, with a mean
of 25.1. Estimated mid-latitude A indices were 41, 15, 9, 8, 16, 18,
and 16, with a mean of 17.6.


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