Sunspots made a strong return this week -- and so did geomagnetic activity. The average daily solar flux increased 4.2 points to 79.6; on Wednesday, May 5, the daily sunspot number reached 77, the highest in nearly four years. The sunspot number hasn’t been as high since May 28, 2006, when it was 78. Sunspot numbers for April 29-May 5 were 0, 12, 13, 47, 61, 70 and 77, with a mean of 40. The 10.7 cm flux was 76.2, 78.6, 77.8, 79.5, 80.3, 81.7 and 83.2, with a mean of 79.6. The estimated planetary A indices were 6, 4, 4, 39, 27, 10 and 8, with a mean of 14. The estimated mid-latitude A indices were 4, 2, 1, 18, 19, 7 and 6 with a mean of 8.1.

Last Friday -- April 30 -- sunspot group 1064 appeared and then faded after the third day. On Sunday, groups 1065, 1066 and 1067 appeared, and the next day 1063 made a reappearance, along with new group 1068. Group 1069 arose on May 4 and 1065 disappeared. 1070 appeared on May 5. Group 1069 grew quickly and the sunspot number rose from 61 to 70 and then 77 on Wednesday, but dropped to 45 on May 6 when groups 1066 and 1077 disappeared.

The solar flux rose steadily from 76.2 on April 29, to 83.2 on May 5 but dropped more than four points to 79.1 on May 6. NOAA and USAF predict solar flux to decline over the next few days, with the May 7-10 flux values at 78, 76, 75 and 75. This probably indicates another short, quiet period with little or no sunspot appearances.

A look at the STEREO mission image on Friday morning shows no bright spots (indicators of magnetic activity and sometimes sunspots) coming up. STEREO achieved 89 percent coverage on May 6, and is expected to reach 90 percent on June 18, 2010. We should expect 95 percent coverage by October 12.

Along with increased sunspots come rising geomagnetic activity. The peak days were Sunday and Monday when the planetary A index was 39 and 27, and the K index went as high as 6 over several three hour periods.

NOAA and USAF predict planetary A index for May 7-13 at 9, 12, 12, 8, 8, 5 and 5. Geophysical Institute Prague predicts quiet conditions for May 7, unsettled May 8, quiet to unsettled May 9-10, unsettled May 11 and quiet May 12-13.

Now that April has ended, we can look at sunspot averages for the past month and the past three month period.

The average daily sunspot number for April was only 11.2, down from 21.3, 31 and 25.2 for January through March. The three month moving average centered on March was 22.3, close to the averages of 22.4 and 25.7 centered on January and February.

Look on page 10 of the NOAA Space Weather Operations Preliminary Report and Forecast for May 4. It shows the current sunspot cycle peaking at a smoothed value of 90 in February, all the way through July 2013. Also note how the monthly sunspot numbers this year as reflected in the graph decline from the projected values.

Tomas David Hood, NW7US, who edits the Propagation column in CQ Magazine, has a propagation resource. He also has a Facebook page that features frequent reports and comments on solar activity and propagation. On Facebook do a search for “Space Weather and Radio Resources at HFRadio.org.”

Bob Kile, W7RH, had a comment regarding this week’s increasing sunspot activity: “Shucks Tad, I really enjoyed the last minimum of 2007-2010. The activity level on 160 meters was superb and conditions were fantastic even out west!” Bob has been quite happy with the low solar activity and quiet geomagnetic conditions over the past few years, as his main interest is 160 meters. He lives in Las Vegas, but operates a 160 meter HF remote base station in a remote quarter of Northern Arizona. Bob has planted acres of antennas, and controls the station remotely. It sits on a 20 acre piece of land that he purchased at a popular online auction site. Check here for pictures and info.

Bill Echols, NI5F, of Jackson, Mississippi had a comment on the 70 MHz propagation in Europe (where it is an amateur band) and aircraft traffic, contrails and volcanic ash. Bill writes: “It very well may be that jet contrails provide the normal mechanism for enhanced 70 MHz paths, rather than the jet itself. Many years ago, it was noted in England that the US stealth aircraft could be detected after the fact by scanning for the moisture in jet contrails between 55 and 70 MHz, and comparing that ‘signature’ against the normal metallic returns. Obviously, if there had been stealth aircraft during the observation window, the number of contrail returns would be higher than the metallic returns. The jets on our stealth aircraft were modified in classified ways to minimize, and in most cases, eliminate this method of detection. I actually remember seeing something about this in amateur literature once; if I remember correctly, it was in an RSGB periodical somewhere in the early 1990s.”

Robert Steenburgh, KA8JBY, of Houston, Texas says that the annual Space Weather Workshop at the Space Weather Prediction Center concluded a week ago, and soon material presented there will be available. There is also a link to past conferences where you can find slides and other material presented from 1999-2009. Until his recent retirement, Robert worked as the US Air Force Liaison to the Space Weather Prediction Center in Boulder. Now he is in Houston working for NASA’s Space Radiation Analysis Group.

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 at k7ra@arrl.net.