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 Previous: Surfin': Take a Mac Break |  Next: ARRL Passport Featured at 2007 ARRL National Convention |
Average daily sunspot numbers rose very little this week, less than 6 points to 7.3. There were no major geomagnetic upsets, only slightly unsettled conditions on the first day of August. We saw eight straight days of no sunspots, then a spot or two over four days, then no spots on the first two days of August. A week from now, August 10, we may see the beginning of several days with a few sunspots every day. Expect unsettled geomagnetic conditions centered on August 7 and again on August 10. Geophysical Institute Prague predicts quiet conditions August 3-5, quiet to unsettled August 6, unsettled to active August 7, and back to quiet August 8-9.
Sunspot numbers for July 26 through August 1 were 0, 0, 13, 14, 13, 11 and 0 with a mean of 7.3. The 10.7 cm flux was 68.4, 68.7, 69.9, 69, 68.9, 68 and 68.8, with a mean of 68.8. Estimated planetary A indices were 9, 8, 4, 14, 10, 6 and 17 with a mean of 9.7. Estimated mid-latitude A indices were 6, 6, 3, 11, 10, 4 and 15, with a mean of 7.9.
There were 6 and 2 meter reports this week. On Sunday, July 29, Dick Bingham, W7WKR, who lives in the very remote mountain village of Stehekin, Washington (reached by boat), reports that he began hearing 6 meter beacons around 1800 UTC, and until 2300 UTC he worked 22 grids, including HR9BFS in EK66 (Honduras) as well as Washington, California, Idaho, Montana, Colorado, Texas and Utah. Dick is blocked by a high ridge running northwest to southeast, with takeoff elevations in excess of 25 degrees, so he doesn't hear the northeastern United States and Canada.
Victor Woodling, WB4SLM, reported interesting E-skip on 2 meters, and from EM82 he worked EM14, EM15 and EM25, all around 2100z on Sunday. He lives in Centerville, Georgia, and during a 30 meter QSO with his father, W9JNH in Texas, he heard long delayed echoes on his CW signal around 2133-2135 UTC.
Four days earlier on June 25, Roger Lapthorn, G3XBM, reported his best 6 meter DX ever when he worked Paul Clement, K1TOL, in Maine on CW. Roger was running just a few watts into a vertical mounted on the side of his house. Roger says the distance was more than 5000 kilometers.
With July over, we can spin some numbers and look for trends.
Monthly averages of daily sunspot numbers for April 2006 through July 2007 were 55.2, 39.6, 24.4, 22.6, 22.8, 25.2, 14.7, 31.5, 22.2, 28.2, 17.3, 9.8, 6.9, 19.8, 20.7 and 15.6. Monthly averages of daily solar flux for the same period were 88.9, 80.9, 76.5, 75.8, 79, 77.8, 74.3, 86.3, 84.4, 83.5, 77.7, 72.2, 72.4, 74.4, 73.7 and 71.6.
Looking at three-month smoothed sunspot numbers, we can now add the July numbers to May and June, showing the three-month average centered on June. These numbers are based on data from the past 21 months -- November 2005-July 2007:
• 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
These numbers are calculated like this: April 1-June 30 is 91 days. Add all the daily sunspot numbers over those three months, then divide by 91. The result is approximately 15.8, centered on May, the middle month. Likewise, May 1-July 31 has 92 days, and the sum of daily sunspot numbers over that period divided by 92 is 18.7.
If the average of daily sunspot numbers for the 31 days of August turns out to be more than 20 (meaning the sum of all the sunspot numbers for the month exceeds 620), we should see the three-month average centered on July rise above the June average. We will see that result in ARLP037, on September 7.
This three-month moving average of sunspot numbers is turning out to be a nice indicator of cycle trends, with the average smoothly declining from December through March and increasing since. We'll know some day, perhaps in a year or two, if the low number in March is a good indicator of cycle minimum or not. Users of Scott Craig's Solar Data Plotting Utility may have noticed that this cycle minimum so far doesn't look as long as the previous minimum around 1995-1997. But if we are at the minimum or just passed it, then we are only looking at probably half of its eventual length on the graph. I hope the upturn comes soon, and is dramatic.
For more information concerning radio propagation, see the ARRL Technical Information Service. A detailed explanation of the numbers used in this bulletin can be found here. An archive of past propagation bulletins can be found here. Monthly propagation charts between four USA regions and 12 overseas locations are available at http://www.arrl.org/qst/propcharts/.
Amateur solar observer Tad Cook, K7RA, 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. Readers may contact the author via e-mail.
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