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ARRL Propagation Bulletin ARLP014 (2012)

ARLP014 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 14  ARLP014
From Tad Cook, K7RA
Seattle, WA  April 5, 2012
To all radio amateurs 

ARLP014 Propagation de K7RA

This bulletin appears a day early this week because ARRL
headquarters is closed for the Good Friday holiday.

Over the past week the average daily sunspot number and solar flux
values rose slightly, even though for both daily values, as the week
progressed each day had a lower number than the day before. The
daily sunspot number began the week at a high of 100 and ended at
60. Likewise, the daily solar flux started at 111.5 and the week
ended with 102.1.

The mild geomagnetic conditions made for a quiet week, with the only
unsettled conditions on April 1-2 in very high latitude regions,
with Alaska's College A index at 11 and 17.

From the April 4 USAF forecast, they see solar flux for April 5 at
105, April 6-7 at 110, 115 on April 8-10, followed by 110 on April
11, then 100 on April 12-22. The next predicted short-term peak for
solar flux is 130 on May 2-5.

This is a lower peak appearing sooner - when compared to the same
forecast six days ago - which had a peak of 140 over May 1-2. But
you can follow it yourself on a daily basis at The new daily
forecast is posted after 2100 UTC, recently appearing between
2110-2130 UTC.

Predicted planetary A index is 5 on April 5-7, then 10 and 8 on
April 8-9, followed by 5 on April 10-12, then 15 and 10 on April
13-14, and 5 again on April 15-23. Following the next peak at 15 on
April 13, the next predicted short term planetary A index peak is
also 15 on May 10, 27 days or the equivalent of one solar rotation
following April 13.

Do HF conditions seem a bit dull compared to Spring 2011?  They
should, because average daily sunspot numbers for the past eight
weeks were higher than the same weeks last year on only three out of
those weeks; the remaining five were lower.

From Propagation Forecast Bulletins ARLP007 to ARLP014 in 2012, the
weekly averages of daily sunspot numbers were 55.6, 55.7, 43.7,
69.4, 88.3, 75.1, 71.1 and 75.4.  In 2011 those same bulletins
numbers had average daily sunspot numbers at 69.9, 65, 50.9, 114,
69, 40.9, 102.1 and 68.3.

The differences are more extreme when compared to last Fall. Doing a
little data cherrypicking, the weekly averages of daily sunspot
numbers from October 13 through December 7, 2011 were 158.6, 156.6,
104.1, 153.4, 145, 124, 131.7, 124.7 and 133.9. Quite a difference!

Every month we see a slight tweaking in NASA's smoothed sunspot
number prediction for the peak of the current solar cycle.  On March
2, 2012 they predicted a smoothed sunspot number maximum "of about
59 in early 2013."  On April 2 the latest forecast predicted a
smoothed sunspot number "of about 61 in the spring of 2013."

Marv Bloomquist, N5AW sent some data about the T-Index used by the
Australian Government IPS Radio and Space Services. They say, "The T
index is an indicator of the highest frequencies able to be
refracted from regions in the ionosphere. The higher the T index,
the higher the frequencies able to be refracted from an ionospheric
region. The index is based on the measurement of ionospheric foF2
obtained from ionograms."

So this is data from ionospheric sounders, which beam a
swept-frequency radio wave straight up, and analyze the reflection
coming back. Marv points out that compared with their predictions,
they believe the T-Index peaked in November 2011.

The data is in a table at and
covers the T-Index from January 1938 through the present month and
into the future until December 2018.

After the story about in last week's
bulletin, Marv also recommended the tool at to get a prediction for
conditions over any path, over the current day.

Just click on any two points of interest on the map, watch the green
arc indicating the path, and then click on the "Do Prediction"
button. The result is a very basic rendering using plain ASCII
characters. The OWF figure represents "Optimum Working Frequency."

Patrick Dyer, WA5IYX wrote that the Texas FM signal into Mexico that
was mentioned in last week's bulletin was an example of tropospheric
propagation. He also said, "That morning I was getting somewhat rare
FM band signals from eastern New Mexico and the Texas panhandle for
several hours."  He included a link to a log at

Mike Carter, K8CN of Durham, New Hampshire sent in a link that
provides "an interesting example of using raw solar data from the
various solar imaging instruments and representing them in audible
form." He commented that "Perhaps it's just another way of hearing

Check it out at,
I found it most interesting to up the video resolution to 720p (just
click on the sprocket-shaped circle at the bottom to adjust) and run
it in full screen mode.  That way I could more clearly see the
passage of time represented.

It is certainly impressive, although it does bring to mind a much
cruder but still an unusual representation for data that Stan
Shankman, K7SJB told me about once. Several decades ago he found a
Hugo Gernsback popular science pulp magazine from the 1930s, and on
the cover was an illustration of men gathered around a microscope,
and the fellow peering into it was wearing headphones, and had a
shocked expression on his face.  The lurid headline said something
like "Scientists Hear Germs!"  Stan said the article described a
device which passed light through the microscope and onto a solar
cell, which was then modulating a sound in the headphones.

I just did a web search for that phrase, and must have found the
magazine on an auction site, although it is different from my memory
of his description.  It shows one fellow instead of a group, and the
headline says, "Scientists Hear Germs Die!"  The other headline
mentions what might be an early baby monitor, "Radio Guards the
Baby."  It is the July 1932 issue of Radio News.

Gregory Andracke, W2BEE reminded me to share a March 31 video, put
out by some smart folks who each year try to outdo their previous
year's wowee-zowie prank.  I saw it last week, and I must admit it
had me totally fooled for quite a while, or at least a fair number
of minutes.

Check it out at

What do you think?

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 Find more good
information and tutorials on propagation at

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 29 through April 4 were 100, 93, 96, 50,
67, 62, and 60, with a mean of 75.4. 10.7 cm flux was 111.5, 110.6,
110.1, 107.3, 105.9, 103.5, and 102.1, with a mean of 107.3.
Estimated planetary A indices were 4, 6, 4, 6, 8, 4, and 6, with a
mean of 5.4. Estimated mid-latitude A indices were 3, 6, 4, 6, 9, 4,
and 6, with a mean of 5.4.


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