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ARRL Propagation Bulletin ARLP011 (2015)

ARLP011 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 11  ARLP011
From Tad Cook, K7RA
Seattle, WA  March 13, 2015
To all radio amateurs 

ARLP011 Propagation de K7RA

For the second week in a row, average daily sunspot numbers were
down. From ARRL Propagation Bulletins 6-10 the average sunspot
numbers were 139, 81.6, 54.6, 59, and 54.1. Over the past week the
number was all the way down to 32.

Also for the second week in a row, average daily solar flux had a
trend, but this one was up. Average daily solar flux from ARRL
Propagation Bulletins 6-11 were 151.1, 144.1, 121.4, 116.3, 122.9
and 127.8. These averages cover dates from January 29 through March

Predicted solar flux is 128 on March 13-14, 130 on March 15-16, 135
on March 17-19, 125 on March 20, 120 on March 21, 115 on March
22-23, 110 on March 24-27 and 115 on March 28-31. Solar flux then
goes to a high of 125 on April 2-15, then drops to a low of 110
again on April 20-23.

Predicted planetary A index is 30, 20 and 12 on March 13-15, then
10, 20, 15 and 10 on March 16-19, 5 on March 20-21, then 15, 20 and
8 on March 22-24, 5 on March 25-26, then 15, 30, 25, 12 and 10 on
March 27-31, then 8, 10, 15, 12, 18 and 12 on April 1-6, 8 on April
7-8, and 10 on April 9-10.  Going all the way out toward the end of
the 45 day forecast, planetary A index for April 24 is expected to
be 30. As you can see, forecasters predict similar active
geomagnetic conditions seen as previous solar cycles turned
downward. The current sunspot cycle peaked about a year ago.

OK1MGW of the Czech Propagation Interest Group predicts geomagnetic
conditions will be quiet to active March 13, mostly quiet March 14,
quiet to unsettled March 15, quiet to active March 16-18, mostly
quiet March 19-20, quiet to unsettled March 21, quiet to active
March 22, active to disturbed March 23, quiet to unsettled March 24,
mostly quiet March 25-26, quiet to unsettled March 27, active to
disturbed March 28-29, quiet to unsettled March 30 through April 2,
quiet to active April 3, quiet to unsettled April 4-5, quiet on
April 6, and mostly quiet April 7-8.

OK1MGW believes most increases in solar wind are unpredictable
during this period, but some peaks are expected March 16-17, 22-23
and 28-29.

Last Saturday, March 7 at 2222 UTC emerging sunspot 2297 produced a
strong solar flare. Although not aimed toward Earth, it produced an
extreme ultraviolet flash on our Sun's horizon, which ionized upper
layers of Earth's atmosphere and caused an HF radio blackout over
the Pacific below 10 MHz.

On March 8, reported, "It may seem strange, but
solar flares can be both good and bad for radio communications. It
all depends on the frequency. Below 10 MHz, signals were strongly
attenuated. At higher frequencies, however, the reflectivity of the
ionosphere was increased, allowing improved over-the-horizon
communications. Ham radio operator Bob MacKenzie of Ottawa, Canada,
shares this anecdote: 'Only minutes after the M9 flare on March 7th,
I was able to work three amateur stations in Japan using just 5
watts of single-sideband power and a single-element vertical antenna
in my backyard. It's a rare event to work Japan so easily with such
little power on phone and not Morse code. The annual ARRL
International DX Phone contest was on at the time so there were
plenty of DX stations on the air, making this observation of unusual
propagation possible."'

Unfortunately, the report did not say what frequency this occurred
on, or what Bob's callsign was, and searching a perhaps incomplete
database of Canadian hams turned up nothing, so I could not contact
him for more information. also reported a flare at 2353 UTC on March 9, which
produced an HF radio blackout over the South Pacific. They provided
this map showing the area of the blackout:

They provided another map for a brief March 11 blackout at 1622 UTC:

Reader David Moore sent this link, referring to the Wednesday, March
11 flare:

The Washington Post reported that high latitude aurora is possible

This month marks a special milestone for your author. It was 50
years ago this month, in March 1965 when the FCC issued callsign
WN7CSK to me at age 12. Back then, when I tried to interest some of
my fellow students at Kellogg Junior High School (near Seattle) in
amateur radio, a common response was, "Why would I want to go to all
that effort to talk with a bunch of old men?"  Well, now I am one of
those old men. But I still have a fascination for wireless
communications and HF radio propagation. Even back 50 years ago
there was the concern that the ranks of radio amateurs were aging,
and it was tough to attract young people.

One of the joys of starting back then was the easy access to old
timers who could tell me stories of the spark era. One amazing ham,
over 50 years my senior, was Howard S. Pyle, W7OE who lived on
Mercer Island. He was a prolific amateur radio author, and
encouraged me to write. When cleaning out my mom's house last year I
ran across a copy of a letter that W7OE wrote to Jim Fisk, W1DTY,
introducing me and encouraging him to publish an article I wrote in
73 Magazine, which Jim edited at the time.

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

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 5 through 11 were 31, 37, 20, 23, 29, 42,
and 42, with a mean of 32. 10.7 cm flux was 130, 127.4, 137.8,
124.2, 122.9, 120.9, and 131.7, with a mean of 127.8. Estimated
planetary A indices were 6, 13, 20, 11, 6, 5, and 9, with a mean of
10. Estimated mid-latitude A indices were 5, 9, 17, 7, 6, 4, and 8,
with a mean of 8.


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