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The K7RA Solar Update
After five days of no sunspots from May 24-28, spots returned on May 29, and have increased since in number and size. There are currently several sunspots visible, and the sunspot number for the past five days (Sunday through Thursday) was 58, 58, 63, 47 and 59. Coupled with quiet and stable geomagnetic indicators, this is good for HF propagation. Our reporting week for this bulletin (the numbers reported at the end) runs from Thursday through Wednesday, and the average daily sunspot number for May 31 to June 6 rose nearly 43 points to 46.1 when compared to the prior seven days. Average daily solar flux rose nearly 15 points to 83.7.
Last week's bulletin mentioned ARRL Field Day, now just two weeks away. The bulletin reported (in some uncorrected versions) that the event is always held on the last full weekend in June, but Don Jackson, AE5K of Marion County, Arkansas pointed out that the rules specify the fourth full weekend. Both fourth and last are on the same weekend this year (June 23-24), which is usually the case, but not always. In 2002, the fourth full weekend was June 22-23, but the last full weekend was June 29-30. This occurs whenever June 1 is a Saturday, as it will be again in 2013 and 2024.
Last week the latest projection looked like no sunspots around Field Day with a declining geomagnetic disturbance, but this week the forecast looks a little better. Including the Friday before (the event doesn't begin until Saturday) the projected solar flux last week for June 22-24 was 65 for all three days, with a planetary A index of 20, 12 and 5. This week's prediction for those dates shows the same A index, but a solar flux ten points higher, at 75 for all three days.
A check of recent sunspot numbers alongside solar flux values on the same dates at http://www.sec.noaa.gov/ftpdir/indices/DSD.txt shows no sunspots when the solar flux was down around 65, but at 75 the sunspot number can be in the forties.
For the next few days expect continued quiet geomagnetic activity, with the same moderate (for the low point of the sunspot cycle) sunspot count.
Alex Mendelsohn, AI2Q in Kennebunk, Maine sent a link to an article about a solar burst last December 6, which caused problems for GPS receivers. You can read it here. We reported the same flare here. Our bulletin shows that the solar flux observatory in British Columbia also had problems from that event.
If you would like to make a comment or have a tip for our readers, email the author.
For more information concerning radio propagation, see the ARRL Technical Information Service Web page.. Another TIS Web page has a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins is at W1AW Propagation Bulletins for 2007. Monthly propagation charts between four USA regions and twelve overseas locations are at http://www.arrl.org/qst/propcharts/.
Sunspot numbers for May 31 through June 6 were 11, 41, 45, 58, 58, 63 and 47 with a mean of 46.1. 10.7 cm flux was 74.6, 79.4, 83.2, 87, 85.7, 88.8, and 87.1, with a mean of 83.7. Estimated planetary A indices were 4, 6, 7, 10, 8, 3 and 2 with a mean of 5.7. Estimated mid-latitude A indices were 2, 5, 5, 7, 8, 2 and 2, with a mean of 4.4.
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: 04:00 PM, 08 Jun 2007 ET
Page author: awextra@arrl.org
Copyright © 2007, American Radio Relay League, Inc. All Rights Reserved.
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