The K7RA Solar Update


We had seven days of no sunspots this week, but a sunspot was emerging on Thursday, June 5. Helioseismic holography revealed a high latitude sunspot on the opposite side of the Sun. Until recently, we had no idea what was happening on the far side of the Sun, the side directed away from Earth. For more information on helioseismology, check out this link.

The NOAA Space Weather Prediction Center sees a constant and quiet geomagnetic planetary A index of 5 through June 14. Geophysical Institute Prague predicts quiet conditions for June 6, quiet to unsettled June 7-8 and quiet again June 9-12. Sunspot numbers for May 29-June 4 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 68.1, 67.1, 66.9, 66.6, 67.1, 66.3 and 65.2 with a mean of 66.8. Estimated planetary A indices were 9, 11, 8, 8, 5, 4 and 4 with a mean of 7. Estimated mid-latitude A indices were 7, 7, 8, 6, 4, 3 and 2, with a mean of 5.3.

As promised last week, here is an update to the three-month moving averages of sunspot numbers:

Sep 05 39.3
Oct 05 28
Nov 05 36
Dec 05 40.6
Jan 06 32.4
Feb 06 18.1
Mar 06 27.7
Apr 06 38.5
May 06 39.7
Jun 06 28.9
Jul 06 23.3
Aug 06 23.5
Sep 06 21.2
Oct 06 24.1
Nov 06 23.1
Dec 06 27.3
Jan 07 22.7
Feb 07 18.5
Mar 07 11.2
Apr 07 12.2
May 07 15.8
Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07 5.4
Oct 07 3
Nov 07 6.9
Dec 07 8.1
Jan 08 8.5
Feb 08 8.4
Mar 08 8.4
Apr 08 8.9

I was able to calculate the value for April because we have all the data for March, April and May; the total of all daily sunspot numbers for those three months was 818. Dividing that value by 92 days gives us approximately 8.891 as the average. Note the average sunspot number has increased only slightly since last fall.

Jeff Lackey, K8CQ, of St Simons Island, Georgia, noted that in the table of zero-sunspot days presented last week, there was at least one error; they counted as 36 days the period from May 27-July 31, 1996. You can look at the whole Web site, not just the page we linked to last week. Jeff checked data in the table against an archive of sunspot data and found that the 66 days they reported as 36 days were actually over two periods, but neither was over 20 days. Jeff wrote, "Indeed, the run that ended on July 31 began on July8, making it a 14 day run. The beginning date of May 27 was for a run that ended on June 7. Between June 7 and July 8, the sunspot numbers were all non-zero."

Sorry about my mix-up in last week's Solar Report; readers saw in some versions of the bulletin a note about Labor Day. No, it is not celebrated in May. If you didn't see it, then you read a version edited by the very capable and wide awake staff at ARRL HQ.

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 in The ARRL Letter. 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.