The K7RA Solar Update


This week, we saw three days -- August 21-23 -- with no sunspots, and the average daily sunspot numbers for the week -- August 19-25 -- declined over 28 points to 8, compared to the previous week. The average daily solar flux was down more than 8 points to 75.3. The last period of three days or more without sunspots ended on May 20, 2010, about 100 days ago. Sunspot numbers for August 19-25 were 11, 11, 0, 0, 0, 11 and 23, with a mean of 8. The 10.7 cm flux was 77.9, 77.1, 75.5, 74.6, 74.9, 73.6 and 73.5, with a mean of 75.3. The estimated planetary A indices were 5, 4, 3, 4, 7, 18 and 20, with a mean of 8.7. The estimated mid-latitude A indices were 3, 1, 3, 0, 5, 13 and 15, with a mean of 5.7.

Sunspot group 1100 disappeared on August 21, only to return August 25. In this case, the sunspot group didn’t transit the non-Earth-facing side of the Sun, but it just faded from view, returning just as it is about to rotate off of the Sun’s western limb. Sunspot group 1101 appeared on August 24, and on August 25, it had grown to three times its initial size. The daily sunspot numbers for August 24-26 were 11, 23 and 23.

Remember: The sunspot number is not the same as the number of sunspots. The smallest non-0 sunspot number is 11; it gets 10 points for being a sunspot group and one point for containing one sunspot. The sunspot number of 23 on August 25-26 represents two sunspot groups at 10 points each -- one containing one sunspot (1 point) and the other containing two sunspots (2 points). On August 25, it appears that a new smaller sunspot may be emerging between the eastern horizon and sunspot group 1101.

A stiff solar wind from a coronal hole increased geomagnetic activity, and the planetary A index for August 21-26 was 3, 4, 7, 18, 20 and 11. The latest projection shows this decreasing, with the planetary A index on August 27-28 at 10 and 8, followed by a quiet reading of 5 until September 19. Solar flux for the same period is expected to be 75 for August 27-September 3, then 85 on September 4-5. We’ll see the  fall equinox in a few weeks -- this is a good time for HF propagation. The autumnal equinox will be at 0309 UTC on September 23, 2010.

David Moore of Morro Bay, California sent in another article about the weak Sun and solar conveyor belt, this time from the National Science Foundation.

Jeff Hartley, N8II, of Shepherdstown, West Virginia, sent this in on August 23: “Lots of great over and near-the-pole propagation was a daily occurrence on 17 and 20 meters since Thursday, August 19. The RDA Russian contest was a blast with many new Russian vanity calls in many areas of Asia worked here. It’s interesting to note that around 0100 local (2100 UTC) in European Russia, there was a nice opening from UA1 to UA6 into here on 20 meters, whereas only UA6 was workable in the 2-3 hours before that. I love the calls like RG8U, RG6G, R7AA and R9DX. Around 0140, I actually had a very nice run of Russian Asians from zone 17-18 at around 80-100 per hour for about 25-30 minutes. UA0YAY in Zone 23 was loud on CW. Signals from the big guns were S9+. Seventeen meters has been open daily to Southeast Asia around 1300-1430. Over the past few days I have heard YB4IR, and worked VR2XMT, 9M6NRO, 9V1DE, UA0SV and some JAs, most with good signals. Fifteen meters was pretty punk until today, when a few Europeans were finally heard around 1500.”

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.