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ARRL Propagation Bulletin ARLP020 (2005)

ARLP020 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 16, 2005
To all radio amateurs 

ARLP020 Propagation de K7RA

This is a special edition of the Propagation Forecast Bulletin.

On Friday the Thirteenth (May 13, 2005) at 1650z a tremendous
explosion near sunspot 759 blasted toward earth. The impact on the
earth's magnetic field was felt at 0230z on May 15, producing an
extreme geomagnetic storm.

I use a service from called
"SpaceWeather PHONE." I can set parameters for alerts, and the
service calls my cell phone when events occur, such as the planetary
K index rising above a set value. The service rang me up so many
times this weekend that I finally shut the phone off. I could have
gone to the web and shut it off or raised the parameters, but at the
time I just wanted to roll over and go back to sleep.

On Sunday, May 15 the planetary K index reached 9. This is huge.
The middle latitude, high latitude and planetary A indexes for
Sunday were 44, 77 and 105 respectively, all very high values. The
planetary A index predicted for Monday, May 16 is 40. Solar flux is
expected to stay around 100 for Monday through Wednesday, May 16-18.

Michael Shaffer, KA3JAW is currently in Tampa, Florida. On Friday,
May 13 Michael began to scan low VHF television channels because of
the possibility of aurora from a coronal mass ejection on May 11.
He emailed several photos he took of his television displaying KGAN,
channel 2, in Cedar Rapids, Iowa. He received both audio and video
for about 30 minutes after 5:00 PM local time. The distance was
about 1,100 miles.

Steven Smith, K6BZ of Carmichael, California wrote to ask if "in the
early period of a new solar cycle, sunspot groups tended to form in
the higher latitudes on the solar disk and towards the end, favored
more equatorial latitudes." This is true, and the greater emergence
of sunspots toward the sun's equator later in the cycle heightens
the probability that the energy from those spots will be

If you would like to comment or have a tip, email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
bulletins is found at,

Sunspot numbers for May 5 through 11 were 50, 66, 55, 79, 106, 106
and 117 with a mean of 82.7. 10.7 cm flux was 109.1, 110.4, 99.9,
101.3, 110, 119.2 and 125.3, with a mean of 110.7. Estimated
planetary A indices were 6, 4, 10, 64, 11, 10 and 11 with a mean of
16.6. Estimated mid-latitude A indices were 3, 3, 10, 38, 10, 6 and
7, with a mean of 11.


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