There was a big drop in solar activity over the past week, with the average daily sunspot numbers declining nearly 42 points to 77.6, and the average daily solar flux down 20 points to 114.7. Sunspot numbers for August 9-15 were 124, 105, 98, 76, 62, 46 and 32, with a mean of 77.6. The 10.7 cm flux was 131.2, 125.4, 119.7, 112.3, 108.1, 105.8 and 100.7, with a mean of 114.7. The estimated planetary A indices were 6, 4, 4, 7, 9, 7 and 6, with a mean of 6.1. The estimated mid-latitude A indices were 7, 4, 5, 7, 8, 7 and 7 with a mean of 6.4.

The solar flux has dropped below 100, where it is expected to remain through August 22. NOAA/USAF is predicting the solar flux to be on August 16 and 17 at 100, but it was actually 98.3 on August 16. The prediction for August 18 is 95, then 90 on August 19-22, then 100, 120 and 130 on August 23-25, and then rising to 135 on August 26-29. It is expected to drop below 100 again on September 12-15. This is almost exactly the forecast that was in The ARRL Letter on August 16, with the August 23-24 sunspot numbers dropping by five points on each day.

The predicted planetary A index is 10 on August 17, 14 on August 18, 12 on August 19-20, then 8 on August 21, 5 on August 22-23, 8 on August 24-25, 12 on August 26, followed by 5 on August 27-September 7, then 8 on September 8-10, and back down to 5 on September 11-14.

The weekly prediction of geomagnetic indicators from OK1HH says to watch for quiet-to-unsettled conditions on August 17-20, mostly quiet on August 21, quiet on August 22-24, quiet-to-active on August 25-26, mostly quiet on August 27-28, active-to-disturbed on August 29-30, and quiet again on August 31-September 1.

Many readers have commented that the short term view of the solar cycle has a recent peak around fall 2011, yet predictions still focus on spring 2013 for the peak of Solar Cycle 24. It is interesting to look back over the past two solar rotations, which is 55 days, and see an average compared with the same 55 days last year, June 23-August 16. The average daily sunspot numbers for those dates in 2009-2012 are 3.3, 26.5, 61.2 and 91.6. If we want to look at last fall’s peak, we can cherry pick the data, and chose the 55 day period of November 7-December 31, 2011. The average daily sunspot number then was 119.3, about 30 percent higher than current values.

This week, Russ Mickiewicz, N7QR, of Portland, Oregon (and later reader David Moore, and others) sent information on a new method for predicting solar flares by tracking decay rates in gamma radiation from radioactive elements.

Randy Crews, W7TJ, of Spokane, Washington, offered some opinions on future solar activity and propagation: “Reading K9LA’s excellent article in QST this past July, the graph on the cover pretty well confirms the good HF propagation bestowed on DXers for now, and if one ‘connects the dots,’ the HF propagation following the years after the peak (sometime in 2013) will be considerably different from what we all have experienced in the past 30 + years. Solar Cycles 21, 22 and 23 were good strong normal sunspot cycles. As we all can conclude from the numerous forecasts, Solar Cycle 24 will be a very low one. There will be much lower highs to drop from once the decline begins, and the low point of Solar Cycle 24 will occur much sooner, unlike the many years of previous cycles where solar activity declined from solar flux values of 200+. Carl is right: Enjoy and make the most of propagation now. Once the cycle turns, everyone will be surprised at the swiftness of the decline of high band propagation.”

Brendan Wahl, WA7HL, of Bisbee, Arizona, likes the N0HR Propfire program for the Firefox web browser. It displays the geophysical and solar data that WWV transmits at 18 minutes after each hour, and can also display sunspot number. You can get it for free here.

Ward Silver, N0AX, reports that DX Sherlock has a new URL: http://www.dxmaps.com/.

It turns out our Sun is not perfectly round. Check it out here.

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.