The K7RA Solar Update
SEATTLE, WA, May 13, 2005--Suddenly the sun is peppered with spots! While
it's true that the sunspot cycle is declining, that represents an
overall trend, and there is plenty of variation until
we later examine a moving average that smoothes out the bumps.
Average daily sunspot numbers this week rose nearly 22 points to 82.7, and
the average daily solar flux was up 10 points to 110.7. On Wednesday, May
11, the solar flux reached 125.3--the highest reported reading since
January 19, 2005. Also on May 11 the daily sunspot number was 117, the
highest value observed since November 4, 2004, although Valentine's Day,
February 14, was almost as high at 115.
On Sunday, May 8--Mother's Day--a big blast of solar wind sparked a
geomagnetic storm, and the planetary A index went all the way to 64,
Alaska's College A index went to 80, and the mid-latitude A index was 38.
This provoked some nice aurora displays over the weekend. Then sunspot 758
began to expand rapidly, and the sunspot count for Monday through
Wednesday, May 9-11 was 106, 106 and 117.
At 1040 UTC on May 11 a coronal mass ejection emerged from sunspot 758.
There is a good chance of aurora for Friday, May 13 as a result. The
predicted planetary A index for Friday through Monday, May 13-16 is 25,
10, 15 and 10. Predicted solar flux for those days is 120, 115, 110 and
105. So the sunspot count has been relatively high, and during days when
the A index is low, such as 10 or below, propagation should be good. If
you listen to WWV at 18 minutes past the hour (or call the recording at
303-497-3235) and hear that the K index is lower than three, this is also
a very good sign for HF propagation.
For more information concerning radio propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service Propagation page.
An archive of past
propagation bulletins also is on the ARRL Web site.
Sunspot numbers for May 5 through 11 were 50, 66, 55, 79, 106, 106 and
117, with a mean of 82.7. The 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.
Amateur solar observer Tad Cook, K7RA, Seattle, Washington,
provides this weekly report on solar conditions and propagation. This
report also is available via W1AW every
Friday, and an abbreviated version
appears in The ARRL Letter. Readers may contact the author via
e-mail.
Page last modified: 11:43 AM, 13 May 2005 ET
Page author: awextra@arrl.org
Copyright © 2005, American Radio Relay League, Inc. All Rights Reserved.
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