The K7RA Solar Update


Solar activity took a serious nosedive this week, with the average daily sunspot numbers dropping to a value less than half the previous week’s average -- down nearly 43 points to 32.6. The solar flux values were also off, down nearly 12 points to 95.9. The low point for sunspot numbers was April 9-10, when the daily sunspot number was 24 for both days. But subsequently we witnessed a rise, hitting 28 and 50 on April 11-12. Sunspot numbers for April 5-11 were 50, 39, 38, 25, 24, 24 and 28, with a mean of 32.6. The 10.7 cm flux was 100.9, 97.4, 98.5, 93.3, 94.5, 93.3 and 93.4, with a mean of 95.9. The estimated planetary A indices were 13, 4, 10, 5, 4, 8 and 5, with a mean of 7. The estimated mid-latitude A indices were 11, 3, 6, 3, 2, 6, and 5, with a mean of 5.1.

The current prediction shows solar flux at 95 on April 13-19, then suddenly jumping to 105 on April 20-21, 110 on April 22-25, back to 105 on April 26-28, 100 on April 29-30, and 95 on May 1-9. The predicted planetary A index is an unsettled 18 on April 13, 12 on April 14, 10 and 8 on April 15-16, 5 on April 17-23, 10 and 8 on April 24-25, 5 on April 26-29, 8 on April 30, and 5 on May 1-7. This is an improvement from yesterday’s forecast, which had solar flux at 90 for the next few days. You can keep up with the daily revisions here.

If you looked here or here recently, you may have noticed missing geomagnetic mid-latitude K indices from Fredericksburg, Virginia on April 7-9. They had a computer issue, and that data is lost forever. So the mid-latitude A index shown in this bulletin for those days is the author’s very rough -- and unscientific -- wild guess.

Click here for an interesting article on helioseismology and the next solar cycle. Here is an interesting article from the Naval Research Laboratory about coronal cells. See a similar article on the same subject here.

Check out an Internet-connected Software Defined Radio in Walla Walla, Washington. I’ve just been listening to 40 meter CW, and with a mouse click,  you can also select 20 meters. This can support multiple simultaneous users tuning independently. Thanks to Joshua Gibbs, KD7PAJ, of Shoreline, Washington for the information.

I received this report on April 5 from a member of WA9YSD, The Kite Flier’s Radio Club: “Today around 1730 UTC, I was listening to some week stateside CW signals on 40 meters. I heard this strange fading signal and noticed the noise floor was fading, as well. So I switched to 17 meters and observed more fading signals on the background noise. I then went to and saw that the CME ejection was late or missed us. I guess it was just late because I was amazed on hearing it hit us.”

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 and 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.