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The K7RA Solar Update


With calmer solar activity, geomagnetic conditions were stable this week. The average daily sunspot numbers were down 7.6 points to 17.7, and the average daily solar flux dropped two points to 71. The average planetary A index declined 6.4 points to 7.9, and mid-latitude A index dropped 2.7 points to 6.4. Sunspot numbers for June 3-9 were 17, 18, 25, 12, 12, 12 and 28, with a mean of 17.7. The 10.7 cm flux was 74.6, 71.9, 70.3, 68, 68.5, 71.9 and 71.5, with a mean of 71. The estimated planetary A indices were 13, 16, 6, 7, 6, 3 and 4, with a mean of 7.9. The estimated mid-latitude A indices were 13, 11, 6, 5, 4, 3 and 3, with a mean of 6.4.

Four new sunspot groups emerged this week. Group 1077 made a brief appearance on June 5, and 1078 on June 8-10. The area of 1078 grew rapidly, from 80 millionths of a solar hemisphere to 180 on June 9, and 200 on June 10. On June 9, sunspot group 1079 appeared at 10 millionths of a solar hemisphere, and on June 10, sunspot group 1080 emerged, also at 10 millionths of a solar hemisphere. Old sunspot group 1072, last seen on May 28, might return over June 11-13. All current sunspot groups are in the far southwest of the solar disc, and should disappear soon as they move across the horizon.

Just 10 more days until the summer solstice on June 21 at 1128, after which the days become shorter. ARRL Field Day is on the sixth and seventh day of summer, June 26 and 27.

The latest NOAA/USAF forecast has planetary A index at 5 on June 11-15, 10 on June 16-17, back for 5 on June 18-24, 12 on June 25 and 15 on June 26-27 (Field Day). Two weeks from now is a bit far off for an accurate forecast, but an A index of 15 would mean somewhat unsettled conditions. Solar flux predictions are 72 on June 11-12, 70 on June 13-17, 72 on June 18, 75 on June 19-26 and 72 on June 27 through July 1. Geophysical Institute Prague predicts quiet conditions on June 11-14, unsettled June 15, unsettled to active June 16 and unsettled June 17. Of course, we want sunspot numbers and solar flux high, and A index low for good HF propagation.

Vic Morris, AH6WX, lives in the northwest area of the island of Hawaii, in Waikoloa. He has noticed the low solar flux values of late. He wonders, “Does anyone have an explanation for the marked decrease in solar flux since February? At one point we peaked at 94, seemingly indicating the long overdue increase expected for Solar Cycle 24? But the June 6 reading of 68 is, I believe, the lowest value of 2010 to date.”

Yes Vic, the values are lower, and they don’t seem to track very well with sunspot numbers. Normally, when sunspot numbers increase, so does solar flux, a measurement of 2.8 GHz energy received from the Sun.  But a glance here shows the generally declining flux.

Vic is correct about higher solar flux earlier this year. It was 90 or above on January 11-14, and again February 7-13 and March 12-13. It was below 70 on May 13 and May 16-20, and again June 6-7. It was exactly 68.0 for the noon reading on June 6, and that was the lowest solar flux recorded this year, although the morning reading that day (morning and afternoon readings don’t count for the official flux value, which is taken at local noon) was just 67.7.

I don’t know why this is happening, although there is some seasonal variation. Due to the variation in distance from the Sun, the observed flux values are lower at this time of the year. On June 6 when solar flux was only 68, the adjusted value (to compensate for the variation in distance) was 70. Of course, we care about the actual measured value, since that is what affects the ionosphere, but the adjusted value is a more accurate reading of actual activity from the Sun.

If we look back at the readings earlier this year, we see the opposite effect from adjusted values. On January 12-13, the observed solar flux was 93.3 and 90.5, but the adjusted values were 90.2 and 87.5. Not sure why adjusted values would ever be lower, but I’ll check on that.

Vic continues: “I can see the effects of the low solar flux on over-the-pole 20 meter propagation to Europe here in the evening. There were quite a few good openings to Europe earlier in the spring when flux values were well into the 80s. These have mostly disappeared the past 2-3 weeks. Note I do not have a beam or tower at this point, just a vertical antenna. I’ve managed about 150 DXCC countries here over about 6 years by doing a lot of listening.”

Brian Webb, KD6NRP, sent an impressive list of countries worked in the past few years via PSK31, a very powerful digital mode that works well with weak signals. He runs under 100 W and uses low antennas (12 feet high, although he didn’t say what kind) from his 50×50 foot back yard.

Pat Rose, W5OZI, in Junction, Texas (EM00cl), reports that on June 3 at 2238, he worked JE1BMJ on 6 meters, a distance of 10,315 km. Both signal reports were 579, but very soon it was over.

The day prior, Rich Molinski, WB2KWF, in Smithfield, Virginia, observed some great 2 meter propagation. He is in FM16 and worked EM25 (Eastern Oklahoma) on 2 meters at 2230. He also worked K0FX (Colorado) and W0FY (Missouri). He said also that 6 meters was great on June 4.

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




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