The average daily sunspot numbers increased about 60 percent during the past week (May 31-June 6), when compared to the previous seven days (May 24-30). The increase was 48.5 points, from 81.9 to 130.4. The average daily solar flux was also up: 18.6 points from 111.6 to 130.2. Sunspot numbers for May 31-June 6 were 76, 151, 113, 133, 155, 154 and 131, with a mean of 130.4. The 10.7 cm flux was 117.3, 128.6, 129.1, 129.4, 128.2, 138.7 and 140, with a mean of 130.2. The estimated planetary A indices were 10, 6, 9, 19, 16, 17 and 17, with a mean of 13.4. The estimated mid-latitude A indices were 7, 6, 8, 16, 14, 15, and 17, with a mean of 11.9.

The increase in activity began June 1. On May 29, the daily sunspot number was 73, with four sunspot groups visible: 1486, 1488, 1490 and 1492. On May 30, the size of groups 1486, 1488 and 1492 diminished, but 1490 grew, and the sunspot number was 78. On May 31, sunspot groups 1486 and 1488 disappeared, and new groups 1493, 1494 and 1495 appeared, but the daily sunspot number was still about the same, 76. On June 1, three new groups appeared -- 1496, 1497 and 1498 -- and the daily sunspot number jumped to 151. The next day, the sunspot number was 113.

On June 3, sunspot group 1499 appeared and the sunspot number was 133. On June 4, three more sunspot groups arose, 1500, 1501 and 1502, and two groups disappeared, 1490 and 1492. The sunspot number jumped again, this time to 155, the high for the week and the highest since May 14 when it was 156.

On June 5, group 1492 emerged again (briefly), and 1495 and 1501 faded, and new sunspot group 1503 appeared. The sunspot number was 154, about the same as June 4. On June 6, groups 1492 and 1500 disappeared, and the sunspot number dropped to 131. On Thursday, June 7, the daily sunspot number dropped to 98, and sunspot groups 1502 and 1503 were gone. Solar flux also made a big drop, from 140 on June 6 to 128.2 on June 7.

Actually, the noon solar flux on June 6 at the observatory (in Penticton, British Columbia) was 151.9, but because NOAA reported it as 140. From past experience, we know that the higher number was an outlier, a value indicating that the 2.8 GHz receiver at the Penticton observatory must have been overwhelmed with radiation, perhaps from solar wind, that made accurate measurement of solar flux difficult. This is similar to front-end overload in a receiver, when a strong nearby signal swamps the input.

If you click here, you can examine the raw numbers from Penticton. There are three readings per day, at 1700, 2000 and 2300. The local noon (2000) reading is the official solar flux value for the day. Judging from the readings just before (138.7, 133.6 and 132.7) and just after (134.5, 131.4 and 128.2) the June 6 noon reading, an estimated value of 140 seems generous. Compare these readings to the solar flux numbers in the NOAA table of values and you can see how the Penticton flux values resolved at one digit past the decimal point are presented as whole numbers.

There are some nice photos of the observatory at Penticton in a 2011 presentation by astrophysicist Kenneth Tapping here.

Geomagnetic activity peaked on June 3, when the planetary A index was 19 and the high-latitude college A index was 33. The activity continues, with the planetary A index on June 4-6 at 16, 17 and 17, and the predicted planetary A index for June 8-11 at 8, 5, 10 and 10, followed by 5 on June 12-17. Geomagnetic activity is expected to increase again, with a predicted planetary A index on June 18-20 at 15, 12 and 8. For June 21-25, a planetary A index of 5 is expected, followed by another peak at 15 on July 1 and again on July 15. The predicted solar flux is 130 on June 8-10, 135 on June 11, 130 on June 12, and 125 on June 13-15, 115 on June 16-18, and 110 on June 19-26.

The recent geomagnetic activity was caused by a coronal hole, an opening in our Sun’s magnetic field allowing solar wind to spew forth.

Petr Kolman, OK1MGW, of the Czech Propagation Interested Group, says there is a “high probability of changes in solar wind which may cause changes in magnetosphere and ionosphere, expected on June 17-18.” He also says to watch for quiet to active conditions June 8-9, quiet to unsettled June 10, quiet June 11-12, quiet to active June 13, mostly quiet June 14, quiet to unsettled June 15-16, quiet to active June 17, mostly quiet June 18, active conditions on June 19, quiet to unsettled June 20-21, mostly quiet June 22-23, and quiet to unsettled again on June 24-27.

Just after last week’s Solar Update was posted, this came in from Mark Bell, K3MSB of Airville, Pennsylvania: “Just a quick note on 6 meter happenings from FM19. I’ve only been on 6 meters since about 2005, but this year I’ve seen openings into the Caribbean, South America and Europe in late May, which is a few weeks earlier than typical. On May 26 at 2231, I worked FG8AR, followed shortly thereafter by J69MV. May 31 at 0049 yielded HK7AAG, who was up and down with deep fading. At 1555 on the same day, I worked Costas, SV1DH, in KM18; he was putting out a decent signal into the East Coast.”

And last, baby boomers -- those of us born in the United States between 1946 and 1964 -- of a certain age may recall the scary early-1960s, when we lived with fear of The Bomb, and the Cold War raged in the news. There was great fear of Russia and the Eastern Block, and we would see occasional references in the news to the Soviet newspaper Pravda and what seemed to us like wild propaganda. At the same time, we saw public service announcements on television about Radio Free Europe, transmitting a USA version of truth (Pravda, by the way, literally translates from Russian as “true” or “truth”) to those behind the Iron Curtain, who we were told were hungry for an alternative to state-controlled media. Well, Pravda is still publishing, and it turns out Radio Free Europe is still broadcasting. Check out this wild story from RFE quoting a Russian scientist who posits that increased solar activity correlates with periods of heightened social unrest.

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.