The K7RA Solar Update


Solar activity rose moderately this week, with the average daily sunspot numbers up nearly 3 points to 120.9, and the average daily solar flux rising more than 28 points to 166.8. There was quite a bit of geomagnetic activity -- the most happening on July 9 -- when the mid-latitude A index reached 29, the planetary A index was 30 and Alaska’s college A index was 60. Sunspot numbers for July 5-11 were 122, 131, 127, 113, 137, 122 and 94, with a mean of 120.9. The 10.7 cm flux was 164.6, 157.7, 158.4, 177.7, 173.8, 173.4 and 161.7, with a mean of 166.8. The estimated planetary A indices were 14, 16, 8, 13 30, 13 and 10, with a mean of 14.9. The estimated mid-latitude A indices were 13, 14, 8, 15, 29, 15 and 10, with a mean of 14.9.

Sunspot group 1520 was directly facing Earth on July 12 at 1653 UTC when it spewed out an X.14 class solar flare. We’ve seen flares off to one side or another that had limited effect, but this one was aimed straight at us. There was an immediate sudden ionospheric disturbance (SID) event, and the resulting CME should reach Earth sometime around 1020 UTC Saturday, July 14. This could be bad news for operators in the IARU HF World Championship and other operating events this weekend. The accuracy of the 1020 UTC impact estimate is +/- 7 hours.

The latest prediction shows planetary A index at 8, 18 and 15 on July 13-15, then 5 on July 16-26, then 20 on July 27-29, 10 on July 30-31, 15 on August 1-2, 10 on August 3-4, 8 on August 5, and then 5 on August 6-22. The predicted solar flux is 165 on July 13-15, then 160, 145, 130, and 120 on July 16-19, 105 on July 20-21, then 115, 120, 130, 140, 145 and 150 on July 22-27, and 165 on July 28-August 2, 160 on August 3-4, then 165, 155, and 150 on August 5-7, and 145 on August 8-10. If you check here and compare the July 11 and July 12 predictions, you can see a big difference between the forecast in this bulletin (July 12) and the one presented in this week’s ARRL Letter, based on the July 11 projection.

Over the past week, four new sunspot groups appeared. On July 7, group 1520 was new and on July 8, older group 1517 (visible since July 1) disappeared. On July 9, group 1513 (visible since June 26) was gone and 1521 was new. On July 10, group 1515 (visible since June 27) disappeared, and on July 11 group 1518 (around since July 4) was gone. On June 12, two new groups -- 1522 and 1523 -- appeared.

Petr Kolman, OK1MGW, again provides us with the Czech Propagation Interest Group geomagnetic activity forecast. Expect unsettled to active conditions on July 13-15, mostly quiet July 16-18, and then quiet-to-unsettled July 19-21.

You can follow progress of any geomagnetic disturbance this weekend by checking here and here. Note the last site is available in Dutch, French and German by selecting your language of choice in the drop-down on upper right.

I’ve received even more e-mail about the old BC-458 SSB conversion, including some corrections to the correction in the last edition of the Solar Update. I won’t cover the subject any longer in this bulletin, but the original March 1956 QST article by Anthony Vitale, W2EWL, is a treat to look at (you must be an ARRL member and logged in to the ARRL website to view this article).

Walt Knodle, W7VS, of Bend, Oregon sent along an article titled “MRI of the Sun's Interior Motions Challenges Existing Explanations for Sunspots.” You can read articles about the most recent solar flare here and here.

Jon Jones, N0JK, sent a message about the big recent 6 meter opening and notes it was June 29, not June 30: “In Kansas, we were at the edge of it. N0LL worked MM0AMW at 1219 UTC followed by LA7HJA at 1545 UTC. I logged JW7QIA at 1642 UTC. I was running 100 W and a 2-element Yagi portable for the contact. He was using a stack of two 5-element Yagis. I heard him for about five minutes. The VE4SPT/b EO26 was 599 at the same time.”

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.