ARRL

ARRL Propagation Bulletin ARLP018 (2013)

SB PROP @ ARL $ARLP018
ARLP018 Propagation de K7RA

ZCZC AP18
QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 3, 2013
To all radio amateurs 

SB PROP ARL ARLP018
ARLP018 Propagation de K7RA

Solar activity made a healthy jump over the past week, with average
daily sunspot numbers up over 30 points to 120.9, and average daily
solar flux increasing over 27 points to 136.5.

The most active day for geomagnetic indices was May 1, when the
planetary A index reached 21 and the high-latitude college A index
(measured near Fairbanks, Alaska) was a whopping 57. That number has
been higher, but only twice in the past six months, when it was 64
on March 1 and 79 on March 17.

The latest forecast has solar flux at 155 on May 3-4, 150 on May
5-6, 145 on May 7-9, then 140, 125 and 120 on May 10-12, 125 on May
13-15, 120 on May 16-17, then 125, 120, and 130 on May 18-20, 135 on
May 21-22 and 130 on May 23-24.

Predicted planetary A index is 8 on May 3-4, 12 on May 5, 8 on May
6, 5 on May 7-20, then 15, 10 and 15 on May 21-23, and then 5
forever after that. This is from a 45 day forecast, so we won't
really see quiet conditions forever, but the forecast ends on June
16 with planetary A index of 5 until then.

F.K. Janda, OK1HH has another short forecast for geomagnetic
conditions, like last week. He sees the geomagnetic field quiet to
unsettled May 3-10, quiet to active May 11-12, and quiet to
unsettled May 13-19. That's it!

NASA released a new solar cycle prediction on May 1, but it wasn't
really new. These arrive at the start of every month, and remain the
same since March 1. On March 1, 2013 the prediction for the smoothed
International Sunspot Number at the cycle peak shifted from 69 to 66
for Fall 2013. The 2013 Autumnal Equinox begins in about four months
and three weeks. This week the May 2013 issue of CQ Magazine
arrived, and across the top of the cover was this headline: "Another
Double-Peak Sunspot Cycle?" We certainly hope so.

Time to review our 3-month moving average of sunspot numbers, which
has increased. The average daily sunspot number for February, March
and April was 85.2. The average daily sunspot number for the three
month periods centered on September 2012 through March 2013 were
81.2, 82.3, 74.4, 82.8, 73.6, 80.7 and 85.2. This is a moving
average, so 81.2 was the average for August through October 2012,
82.3 was September through November 2012 and so on. But this
involves a bit of cherry picking of the data, as the three previous
period's averages were 96.5, 91.9 and 89.9.

The average sunspot number for the month of April was 112.8, for
March it was 81.1 and February was 60.1.

Eric Ferguson, VE3CR of Burlington, Ontario sent his father-in-law
Bruce Jones an article about solar flares, and they both wondered
why there are no solar flares at the Sun's poles.

I passed this question on to Robert Steenburgh, KA8JBY who is a
Senior Space Weather Forecaster at the NOAA Space Weather Prediction
Center.

Robert wrote, "Flares are thought to originate from the deformation
of magnetic field lines which break and reconnect. There is a
latitudinal band in which this magnetic flux emergence (and hence
sunspot formation) and deformation occurs.

"Sunspots typically form at mid-latitudes (equatorward of around 40
degrees) at the beginning of the solar cycle, and the breeding
grounds drift towards the equator over the course of the cycle. This
behavior is attributed to the solar dynamo.  See
http://solarscience.msfc.nasa.gov/dynamo.shtml.

"A cartoon depiction of the dynamo process is here:

http://www.nasa.gov/images/content/144061main_CycleDiagramLG.jpg

"You can find a paper on flare distribution for Solar Cycle 23 here:

http://www.ias.ac.in/jaa/junsep2006/JAA10.pdf

"There were 4 flares identified poleward of 50 degrees latitude in
that paper, out of a total of 20,186.

"The poles are usually dominated by coronal holes and 'open'
magnetic field lines that extend out into the heliosphere. So the
mechanisms for flare formation are generally absent."

David Moore sent a link to a NASA video showing ten coronal mass
ejections over five days in April:

http://www.nasa.gov/multimedia/videogallery/index.html?media_id=162261751

Mike Snyder, KN8J who lives a few miles south of Harrisville, West
Virginia in EM99lf wrote this morning, May 3: "My wife and I are
early risers. I mean real early. We're up about 3AM. Generally
speaking, 3 to 5AM produces some fair DX for me.

"Lately it's been getting a bit better on the 20 and 30 meter bands.
The South Pacific is usually open at these hours. I've managed a
couple QRP contacts with Hawaii. I've noticed parts of Europe open
as well. I had a solid QSO with OK1HB from the Czech Republic on
14.062MHz. I was running 100 watts barefoot for this one.

"This morning I finally worked a new one: A35JP in Tonga on 14.003
MHz running up two at 0736 UTC.

"Well, gotta go...someone just spotted FO/KH0PR!"

Mike runs a Cushcraft A4 antenna on a 40 foot tower with the two
rear elements askew due to high winds last month. On 160 and 30
meters he uses a fan inverted vee dipole at 35 feet.

He sent this final note: "Just worked A35UD on 10.108 MHz at 1010
UTC. Too bad I gotta go to work now!"

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. More good
information and tutorials on propagation are at http://k9la.us/.

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 25 through May 1 were 93, 104, 100, 97,
136, 165, and 151, with a mean of 120.9. 10.7 cm flux was 119.2,
121.9, 127, 131.7, 142.4, 154.4, and 159.2, with a mean of 136.5.
Estimated planetary A indices were 8, 17, 6, 5, 5, 7, and 21, with a
mean of 9.9. Estimated mid-latitude A indices were 14, 18, 6, 4, 5,
6, and 16, with a mean of 9.9.
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