ARRL

ARRL Propagation Bulletin ARLP016 (2010)

SB PROP @ ARL $ARLP016
ARLP016 Propagation de K7RA

ZCZC AP16
QST de W1AW  
Propagation Forecast Bulletin 16  ARLP016
From Tad Cook, K7RA
Seattle, WA  April 23, 2010
To all radio amateurs 

SB PROP ARL ARLP016
ARLP016 Propagation de K7RA

A Sun with no sunspots!  The quiet Sun returned -- and through
Thursday, April 22 there have been eight days straight with no
sunspots.

A new spot began to emerge on Wednesday, but it quickly faded.  For
the next ten days NOAA/USAF predict solar flux at 78, 78, 80, 80,
80, 78, 76, 80, 80 and 80.  Solar flux values above 80 aren't
predicted until May 20-23, with a value of 85, but that is too far
into the future to predict accurately.  They also predict the return
of sunspot group 1061 on April 23-25.  That sunspot group was
previously visible on April 5-10.

Planetary A index for April 23 through May 2 is predicted to be 8,
6, 5, 5, 5, 8, 8, 5, 5 and 5.  Geophysical Institute Prague predicts
quiet to unsettled conditions for April 23, then quiet April 24-26,
quiet to unsettled April 27, and back to quiet for April 28-29.

Carl Luetzelschwab, K9LA has a new propagation column about sunspot
Cycle 24 in the current issue of WorldRadio online at
http://www.worldradiomagazine.com.  Carl's columns are always
worthwhile, and a new issue of WorldRadio appears on the twentieth
day of each month.

We've seen some reports of 10 meter activity over the past couple of
weeks.  Julio Medina, NP3CW of Puerto Rico reports that on April 9
he saw an opening to the Pacific on 10 meters.  He writes, "H44MS at
2122z SSB, KH6CE Henry, ZL4IV Rick at 2159z, HR1RJF, KC5JAR from TX,
and LU5FCI at 2255z."  Around the start of the month he had 6 meter
openings to South America.

Pat Dyer, WA5IYX sent in a report generated by "DX Sherlock," which
automatically collects propagation data from a network of WSPR
stations.  WSPR stands for Weak Signal Propagation Reporter.  Pat
said that on April 12, 10 meters opened up to the Pacific, which is
normal after a geomagnetic storm.  You can go to
http://www.vhfdx.net/spots/index.php to generate your own
propagation snapshots, including maps.

Peter Sils, KD0AA of Nixa, Missouri wrote that there was "a
wonderful 10 Meter opening on Wednesday, April 14 at 8:30 PM CDT. I
was alerted by Mark, K0ABC via Nixa ARC email that there was a
Tahiti station on. I proceeded to work FO8RZ, ZL1BYZ and VK7ZE on a
NB6ZEP antenna up 30' with 100 watts. What a wonderful opening it
was!"

Bill Alsup, N6XMW of San Francisco wrote, "I read years ago that
there was a correlation between how closely the planets aligned and
the sunspot cycle, the idea being that the more intense the
gravitational pull on the Sun, the more sunspots would appear.
Evidently, they more or less align every 11 yrs. I have never seen
any other reference to that concept."

That was by J.H. Nelson, a forecaster at RCA who wrote about it in
the 1950s.  The reason you never heard of it since the 1970s
(although astrologers like it) is that it didn't work, and it proved
to be no better than chance at predicting anything.

What Nelson worked out was a system in which certain planetary
alignments were thought to put some sort of tidal influence on the
Sun, and that there were more solar flares at those times, causing
HF radio disruption.  He kept records for many years, and worked out
a system that when these alignments occurred, there was a three-day
period in which these events were likely to occur.  So if the
alignment is on Wednesday, the disruption could occur Tuesday
through Thursday.

In the early 1980s the "Skeptical Inquirer" published an article in
which they went over his records, and counted the number of
occurrences per year.  Then they randomly distributed the same
number of dates over each calendar year, and used the three-day
rule.  The correlation was no worse than Nelson's predictions.

So it had zero prediction value, because you could just as easily
toss dice.  A stopped clock is correct twice per day.  Check this
article at http://www.rudolfhsmit.nl/d-arti2.htm which mentions
Nelson's work.  It also talks about false correlations.  I dug up an
interesting thread on Nelson at http://www.eham.net/articles/8828,
and the best comments are by N3AIU, who also is a reader of our
propagation bulletin.

Several people wrote in to comment about volcano ash and
propagation, and this is from Tom Segalstad, LA4LN of Oslo, Norway.

"Some countries have allowed radio amateurs to use the 70 MHz (4 m)
band. A number of contacts are being made every day on this band
between radio amateurs in some European countries via meteor scatter
using the K1JT digital modes JT6M and FSK441.  On 14 April this year
the Icelandic volcano Eyjafjallajokull started an explosive
eruption, which produced a high column of volcanic ash. With
westerly winds, the ash cloud was blown towards Europe in the
stratosphere.

"In the NRAU (Nordic Radio Amateur Union) Nordic Activity Contest on
70 MHz Thursday 15 April we experienced fairly poor propagation on
70 MHz meteor scatter (MS). Being a geologist (with a degree in
volcanology) I wondered if the poor MS propagation could be due to
volcanic ash attenuation. The very fine ash grains would not be
expected to be large enough to cause reflections of radio signals at
4 m, being a fairly large VHF wavelength.

"During the days after the start of the volcanic eruption -- with
continued ash eruption from the volcano -- airplanes were grounded
at airports all over Western Europe for several days, and passengers
were not allowed to travel. Continued experiments between LA4LN and
G4DEZ (and others) on 70 MHz found that the signals (bursts and
pings) via meteor scatter were weaker, less frequent and shorter
than experienced during normal conditions, and what would be
expected from meteor data from the Virgo satellite:
http://www.dl1dbc.net/Meteorscatter.

"A complete MS QSO with JT6M on 70 MHz, which usually would take
some 15 minutes between G4DEZ and LA4LN (distance about 1000 km),
now took about 3 times longer. We see no other explanation to this
attenuation than the presence of the thick, fresh volcanic ash
clouds between Iceland and Western Europe.

"After some days, with reduced ash eruption from the volcano, the
air traffic started again, and the MS propagation on 4 m seemed to
go back to normal. The 6 m MS reflections did not seem to be
affected to the same degree as the MS attenuation experienced on the
4 m band. But this may also be because radio amateurs generally have
better antennas and more transmitting power on 6 m than on 4 m.

"It would be interesting to hear if other radio amateurs had
experiences with peculiar radio propagation associated with volcanic
eruptions."

Thanks, Tom!
 
If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at,
http://arrl.org/propagation-of-rf-signals. For an explanation of the
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.

Monthly propagation charts between four USA regions and twelve
overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL
bulletins are at http://arrl.org/bulletins.

Sunspot numbers for April 15 through 21 were 0, 0, 0, 0, 0, 0, and 0
with a mean of 0. 10.7 cm flux was 74.5, 74.8, 73.9, 74.7, 75.4,
75.6 and 76.1 with a mean of 75. Estimated planetary A indices were
8, 4, 2, 2, 5, 5 and 6 with a mean of 4.6. Estimated mid-latitude A
indices were 5, 2, 1, 1, 3, 4 and 4 with a mean of 2.9.
NNNN
/EX