Register Account

Login Help


The K7RA Solar Update


Sunspot numbers and solar flux declined this week, with the average daily sunspot numbers down more than 15 points to 20.3, and the average daily solar flux down nearly 4 points to 81.4. These are the numbers from last Thursday through this Wednesday, July 29-August 5. A new sunspot group emerged Wednesday, and three more appeared on Thursday. Sunspot numbers for Wednesday and Thursday were 27 and 54. Sunspot numbers for July 29-August 4 were 31, 29, 12, 13, 17, 13 and 27, with a mean of 20.3. The 10.7 cm flux was 84.6, 83.2, 81.5, 79.7, 79.1, 80.6 and 80.8, with a mean of 81.4. The estimated planetary A indices were 7, 7, 6, 4, 5, 20 and 42, with a mean of 13. The estimated mid-latitude A indices were 5, 5, 4, 2, 5, 14 and 26, with a mean of 8.7.

Geomagnetic activity has been high, due to a coronal mass ejection which hit Earth at 1710 on Tuesday, sending Wednesday’s planetary A index to 42, but Thursday’s (August 5) only to 10. The predicted planetary A index for August 6-7 is 12 and 8, then 5 on August 8-10, then back to 8 on August 11, and 5 again for August 12-21. Geophysical Institute Prague expects active geomagnetic conditions August 6, quiet to unsettled August 7, quiet August 8-9, unsettled August 10-11 and quiet August 12.

In last week’s ARRL Letter, we promised a comparison of sunspot activity during sporadic-e seasons in recent years. Steve Daniel, NN4T, had a question about comparing sunspot levels during June and July since the turn of the century. The average sunspot numbers for those months from 1999-2010 were 188.4, 213.9, 160, 165, 125.8, 82.5, 64.3, 23.5, 18.1, 2.7, 5.8 and 20.6. You can see they were highest of all in 2000, and have increased a bit since 2007. Since July has passed, we can take another look at our three-month moving averages for sunspot numbers. The averages for the past year, centered on July 2009 through June 2010 were 4, 4, 4.6, 7.1, 10.2, 15.2, 22.4, 25.7, 22.3, 18.5, 16.2 and 20.4. The monthly average sunspot numbers for January through July of this year were 21.3, 31, 25.2, 11.2, 20, 18 and 23.1.

In recent activity, Bob Karpinski, WB8B, of Clinton Township, Michigan, reports that with 5 W CW, he worked ZL2IFB on 10 meters at 0040 on August 4.

Marty, K3PBU brought to my attention the fact that on the recent propagation chart at the bottom of the page it says the prediction is based on a solar flux of 123. This is not right, and should be corrected soon.

Mike Schaffer, KA3JAW, likes to chase broadcast television DX in Tampa, Florida. He posted a video showing an August 4 1725-1805 signal from Ontario on Channel 2, about 1300 miles away. He feels the coronal mass ejection enhanced E-skip.

Charley Shaffer, K7NW asked about the book Rebels on the Air by Jesse Walker, and if that was really me as a teenager, as described in the opening to a chapter. Yes, that was me at age 15. I was WA7CSK back then, and a volunteer at the little listener-supported FM broadcast station described in the book.

Next week I will be out of town and I’ve asked Tomas Hood, NW7US, to write the bulletin. He is propagation editor for CQ Magazine, and has a Web site devoted to HF propagation. If you are on Facebook, check out his very useful propagation page by searching for “Space Weather and Radio Resources at”

All times listed are UTC, unless otherwise noted.

Amateur solar observer Tad Cook, K7RA, of 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 each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.




Instragram     Facebook     Twitter     YouTube     LinkedIn