ARRL Propagation Bulletin ARLP015 (2016)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 8, 2016
To all radio amateurs 

ARLP015 Propagation de K7RA

All solar and geomagnetic indicators declined again last week.
Compared to the previous seven days, from March 31 through April 6
the average daily sunspot number slipped from 28.1 to 19.4. Average
daily solar flux sank from 88.8 to 83.1, while average daily
planetary A index went from 11.9 to 9.4. Average daily mid-latitude
A index went to 7.6 from 8.6.

The latest prediction (from April 7) has solar flux at 92 and 90 on
April 8-9, 95 on April 10-15, 78 on April 16-17, 80 on April 18-22,
78 on April 23, 80 on April 24-28, 82 on April 29 to May 1, 78 on
May 2-5, 82 on May 6-7, 80 on May 8-12 and 78 on May 13-14. Solar
flux then continues to dither between 78 and 80 over the remainder
of the 45 day forecast. You can find daily updates of this forecast
at .

Predicted planetary A index is 15 and 8 on April 8-9, 5 on April
10-12, then 12, 20, and 8 on April 13-15, 5 on April 16-20, 8 on
April 21-22, then 5 and 12 on April 23-24, 10 on April 25-26, 8 on
April 27, 5 on April 28-29, then 22, 8, 15 and 12 on April 30
through May 3, then 8 on May 4-5 and 5 on May 6-7.

The big factor in bringing the week's average sunspot number down
nearly 9 points was the fact that the daily sunspot number was 11 on
March 31 through April 2. 11 is the lowest sunspot number we can
possibly observe, unless there are 0 sunspots, then the sunspot
number is 0. Each sunspot group is counted as 10 points, and these
are added to the total number of sunspots which count as one each,
so a sunspot number of 11 is what you get with just one sunspot
visible. reported early Thursday that on April 7, Earth is
expected to cross a fold in the Heliospheric Current Sheet, which
could trigger unsettled geomagnetic conditions.

The Heliospheric Current Sheet separates regions of solar wind where
the magnetic field points toward or away from the Sun. See for a continuous animation of this effect from
2001 until 2009.

See for
more information.

Sure enough, early on April 8 at 0007 UTC the Australia's Space
Weather Services issued a geomagnetic warning:

"The geomagnetic conditions are currently at minor storm levels and
are expected to remain at these levels for the next 6-12 hours. This
is a combined effect of sustained strongly southwards IMF Bz (see ) starting from 07/1800 UTC but with stable,
weak solar wind speeds (380 km/s). However, the solar winds are
expected to gradually increase later today in response to a small
recurrent southern hemisphere coronal hole moving into a
geo-effective location on the solar disk. The aurora may be visible
from as low as some parts of the state of Victoria, Australia, on
the local night of 8 April.  Increased geomagnetic activity expected
due to a coronal hole high speed wind stream from 08-09 April 2016."

F.K. Janda, OK1HH reports:

Geomagnetic activity forecast for the period April 08-May 04, 2016

Geomagnetic field will be:
quiet on April 17-18, 21-22, 27-28, May 4
mostly quiet on April 19-20, 29, May 1, 3
quiet to unsettled on April 10, 14-16, 23-25, May 2
quiet to active on April 8-9, 13, and 26
active to disturbed on April 11-12, 30

Amplifications of the solar wind are expected on
April 9-10, (14,) 20, (24-25,) 28-30

Parenthesis means lower probability of activity enhancement.

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 March 31 through April 6 were 11, 11, 11, 38,
23, 27, and 13, with a mean of 19.1. 10.7 cm flux was 81.7, 82.1,
81.5, 82.3, 83.4, 83.4, and 87.1, with a mean of 83.1. Estimated
planetary A indices were 7, 3, 22, 15, 7, 5, and 7, with a mean of
9.4. Estimated mid-latitude A indices were 5, 2, 15, 13, 6, 5, and
7, with a mean of 7.6.