The K7RA Solar Update
Average daily sunspot numbers were up a little, rising more than five points to 12.4. After a short period of no sunspots, we are back to seeing a spot or two every day. Expect these conditions to continue, possibly falling back to zero spots again around August 16-20. Today (August 10), expect some unsettled to active geomagnetic conditions due to a solar wind stream. Planetary A index predicted for August 10-16 is 25, 15, 5, 5, 5, 5 and 10. Geophysical Institute Prague predicts unsettled to active conditions August 10, quiet to unsettled August 11, quiet August 12-14, quiet to unsettled August 15 and unsettled August 16. Sunspot numbers for August 2 through 8 were 0, 11, 11, 11, 16, 13 and 25 with a mean of 12.4. The 10.7 cm flux was 69.4, 70.4, 69.4, 68.9, 70, 69 and 69, with a mean of 69.4. Estimated planetary A indices were 5, 4, 2, 2, 12, 23 and 6 with a mean of 7.7. Estimated mid-latitude A indices were 5, 4, 0, 2, 8, 23 and 5 with a mean of 6.7.
New predictions for smoothed sunspot numbers in coming months seem to appear almost monthly from the Space Environment Center (SEC). Now the estimate for smoothed sunspot number in December 2007 has risen from 21 to 24. You can see the prediction from last month and the current one at the SEC Web site. Look on page 9 of both issues.
Bob Wertz, NF7E, was operating in Alaska last month, and he wrote asking about some strange conditions he observed on the air. "Recently, while on a mini DXpedition on Ushagat Island (located off the coast of Homer, Alaska), we encountered some strange lulls in operating. We landed on the island on July 12, and after about three hours, we were on the air and doing great. Then on the following few days, we almost lost all communications with the world. At first we thought it was rig problems, then antenna problems, but then realized it must be poor propagation. Can you give me some input about conditions those days?"
Yes, we can. Looking at data from the magnetometer at University of Alaska, we see that the A index (called the College A index) on July 11-16 was 32, 10, 2, 39, 19 and 7. The cause was solar wind and the disturbance tends to concentrate toward the poles, so the absorption in Alaska from this activity can lead you to believe your radio is dead. Folks operating at high latitudes have had a respite from this activity, because during a lull in the solar cycle, the chance of geomagnetic storms is much less. But old Alaska hands will tell you of times in years past when geomagnetic storms seemed to last for months and HF was mostly unusable. That is the downside of higher solar activity. We like sunspots because of the accompanying increase in reflection and refraction in the ionosphere. But along with that comes greater chance of geomagnetic storms.
For more information concerning radio propagation, see the ARRL Technical Information Service. A detailed explanation of the numbers used in this bulletin can be found here. An archive of past propagation bulletins can be found here. Monthly propagation charts between four USA regions and 12 overseas locations are available at http://www.arrl.org/qst/propcharts/.
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: 09:12 AM, 10 Aug 2007 ET
Page author: awextra@arrl.org
Copyright © 2007, American Radio Relay League, Inc. All Rights Reserved.
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