Propagation Forecast Bulletin #12 de K7RA:
W1AW Bulletin via the ARRL
March 22, 2013
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Propagation Forecast Bulletin #12 de K7RA:
QST de W1AW
Propagation Forecast Bulletin 12 ARLP012
From Tad Cook, K7RA
Seattle, WA March 22, 2013
To all radio amateurs
SB PROP ARL ARLP012
ARLP012 Propagation de K7RA
Average daily sunspot numbers over the past week (March 14-20) were
up 16.2 points to 101.1, while average daily solar flux remained
about the same, rising from 118.5 to 119. An eruption on March 15
caused a CME (Coronal Mass Ejection) which struck Earth on March 17,
causing the planetary A index to jump to 46.
The predicted solar flux is 105 on March 22, 100 on March 23-27, 105
on March 28, 100 on March 29-30, 105 on March 31, 110 and 120 on
April 1-2, 125 on April 3-6, 120 on April 7-8, 115 on April 9, 110
on April 10-11, then 105, 100, 120, 115 and 110 on April 12-16.
The planetary A index is predicted to be 8 on March 22-23, 5 on
March 24-26, 12 on March 27-28, 10 on March 29, 5 on March 30
through April 16, and 8 on April 17.
F.K. Janda, OK1HH of the Czech Propagation Interest Group predicts
the geomagnetic field will be quiet to active March 22, quiet to
unsettled March 23, quiet March 24, mostly quiet March 25, quiet
March 26, active to disturbed March 27-28, quiet to active March 29
and mostly quiet March 30-31.
He continues with quiet April 1-3, mostly quiet April 4, quiet April
5, quiet to unsettled April 6, quiet April 7, quiet to unsettled
April 8, quiet April 9, mostly quiet April 10, quiet to unsettled
April 11 and active to disturbed April 12.
Last weekend on March 16-18 the planetary A index was 10, 46 and 7.
How well did our sources of geomagnetic forecasts foresee this?
From late January through March 11, NOAA/USAF predicted a planetary
A index value of 5 for all three days. This seems to be their
default predicted value for low activity. I've never seen them issue
a prediction for an A index value below 5, even though since the
first of the year the planetary A index has been below this value on
January 1-12, 15, 21-24, 28-31, February 1, 3-6, 9-12, 15, 18,
24-25, 27, March 4-8, 10 and 13.
Their forecast was revised on March 12, when the values changed to
10, 5 and 5. That changed to 12, 5 and 5 on March 13-14, and on
March 15, the forecast for March 16-18 was 12, 39 and 20. So two
days prior to the event, they predicted 39 for March 17, which is
What did OK1HH predict for those dates? On February 28 the
prediction was quiet to unsettled on March 16, and mostly quiet
March 17-18. The March 7 prediction was quiet to unsettled on March
16-17 and quiet March 18. The March 14 prediction was quiet to
unsettled March 16-17 and mostly quiet March 18, echoing the
prediction from two weeks prior. Of course, the U.S. government
source has the advantage of releasing a new prediction every day.
Spaceweather.com issued an alert about the event on Friday, March 15
at 2355 UTC. The message titled "Geomagnetic Storm Warning" said, "A
magnetic eruption on the Sun during the early hours of March 15th
hurled a coronal mass ejection (CME) directly toward Earth. NOAA
forecasters estimate a 70% chance of polar geomagnetic storms when
the CME arrives on March 17th."
Jack Kelley, K4WY of Fairfax Station, Virginia had an unusual
experience on a seemingly dead band on Sunday. He wrote, "I had some
interesting propagation in the wake of the CME last weekend. After
checking the bands (160-10) the sole station I found was 5T0JL at S9
on 30 meters - we worked each other easily - and after listening to
Jean's following QSOs I found he was working W6s almost exclusively.
Again no other signal, anywhere. So how did this occur? The path was
assumed to be east-west, and in darkness, but all the W6 QSOs
stumped me, particularly after the worst of the CME effects. A
similar scenario happened with 6V7S later that same evening as he
plowed through the extremely high QRN."
This was Sunday night local time, 0130-0200z Monday. We ran this by
Carl Luetzelschwab, K9LA, who indicated that the path through low
latitudes was the key to success.
He wrote, "The effects from elevated K indices due to a CME include
modification to the worldwide F2 region ionization. Generally the
mid and high latitudes see a depletion of electrons, whereas low
latitudes aren't affected too much (or even see an enhancement)."
He ran some numbers using the Space Weather Prediction Center STORM
model, and said, "In both hemispheres the F2 region ionization was
depleted significantly around 0200 UTC on 18 March. But the
ionization at low latitudes in both hemispheres fared much better.
"Additionally, was there perhaps some 'spotlight' propagation going
on? Could be. The ionosphere is very dynamic, especially under
The day after the big blast, the New York Times ran an interesting
article on solar flares and possible effects on the power grid,
satellites and communications. Check it out at
and don't forget to click on the link, "Related Article," which
takes you here:
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 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. Find more good
information and tutorials on propagation at
Monthly propagation charts between four USA regions and twelve
overseas locations are at
Sunspot numbers for March 14 through 20 were 133, 105, 90, 126, 116,
68, and 70, with a mean of 101.1. 10.7 cm flux was 122.8, 123.1,
126, 125.7, 117.6, 110.4, and 107.6, with a mean of 119. Estimated
planetary A indices were 5, 6, 10, 46, 7, 5, and 9, with a mean of
12.6. Estimated mid-latitude A indices were 4, 5, 8, 32, 6, 4, and
7, with a mean of 9.4.
Source: W1AW Bulletin via the ARRL.
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