A Sun with no sunspots! The quiet Sun returned -- through Thursday, April 22, there have been eight days straight with no sunspots. A new spot began to emerge on Wednesday, but it quickly faded. For the next 10 days NOAA/USAF predict solar flux at 78, 78, 80, 80, 80, 78, 76, 80, 80 and 80. Solar flux values above 80 aren’t predicted until May 20-23, with a value of 85, but that is too far into the future to predict accurately. They also predict the return of sunspot group 1061 on April 23-25; that sunspot group was previously visible on April 5-10.

Sunspot numbers for April 15-21 were 0, 0, 0, 0, 0, 0 and 0, with a mean of 0. The 10.7 cm flux was 74.5, 74.8, 73.9, 74.7, 75.4, 75.6 and 76.1, with a mean of 75. The estimated planetary A indices were 8, 4, 2, 2, 5, 5 and 6, with a mean of 4.6. The estimated mid-latitude A indices were 5, 2, 1, 1, 3, 4 and 4, with a mean of 2.9. Planetary A index for April 23-May 2 is predicted to be 8, 6, 5, 5, 5, 8, 8, 5, 5 and 5. Geophysical Institute Prague predicts quiet to unsettled conditions for April 23, then quiet April 24-26, quiet to unsettled April 27 and back to quiet for April 28-29.

Carl Luetzelschwab, K9LA, has a new propagation column about Solar Cycle 24 in the current issue of WorldRadio Online. Carl’s columns are always worthwhile, and a new issue of WorldRadio appears on the 20th day of each month.

We’ve seen some reports of 10 meter activity over the past couple of weeks. Julio Medina, NP3CW, of Puerto Rico, reports that on April 9 he saw an opening to the Pacific on 10 meters: “H44MS at 2122 SSB, KH6CE Henry, ZL4IV Rick at 2159, HR1RJF, KC5JAR from Texas and LU5FCI at 2255.”  Around the start of the month, he had 6 meter openings to South America.

Pat Dyer, WA5IYX, sent in a report generated by DX Sherlock, which automatically collects propagation data from a network of WSPR stations; WSPR stands for Weak Signal Propagation Reporter. Pat said that on April 12, 10 meters opened up to the Pacific, which is normal after a geomagnetic storm. You can go here to generate your own propagation snapshots, including maps.

Peter Sils, KD0AA, of Nixa, Missouri, wrote that there was “a wonderful 10 meter opening on Wednesday, April 14 at 8:30 PM CDT. I was alerted by Mark, K0ABC, via Nixa ARC e-mail that there was a Tahiti station on. I proceeded to work FO8RZ, ZL1BYZ and VK7ZE on a NB6ZEP antenna up 30 feet with 100 W. What a wonderful opening it was!”

Bill Alsup, N6XMW, of San Francisco, wrote “I read years ago that there was a correlation between how closely the planets aligned and the sunspot cycle, the idea being that the more intense the gravitational pull on the Sun, the more sunspots would appear. Evidently, they more or less align every 11 years. I have never seen any other reference to that concept.”

That was by J.H. Nelson, a forecaster at RCA who wrote about it in the 1950s. The reason you never heard of it since the 1970s (although astrologers like it) is that it didn't work and it proved to be no better than chance at predicting anything. What Nelson worked out was a system in which certain planetary alignments were thought to put some sort of tidal influence on the Sun, and that there were more solar flares at those times, causing HF radio disruption. He kept records for many years and worked out a system that when these alignments occurred, there was a three day period in which these events were likely to occur. So if the alignment is on Wednesday, the disruption could occur Tuesday through Thursday.

In the early 1980s, the Skeptical Inquirer published an article where they went over his records and counted the number of occurrences per year. Then they randomly distributed the same number of dates over each calendar year, using the three day rule. The correlation was no worse than Nelson's predictions. So it had zero prediction value, because you could just as easily toss dice. A stopped clock is correct twice per day. Check out this article that mentions Nelson’s work. It also talks about false correlations. I also dug up an interesting thread on Nelson here.

Several people wrote in to comment about volcano ash and propagation, and this is from Tom Segalstad, LA4LN, of Oslo, Norway: “Some countries have allowed radio amateurs to use the 70 MHz (4 meter) band. A number of contacts are being made every day on this band between radio amateurs in some European countries via meteor scatter using the K1JT digital modes JT6M and FSK441.

“On 14 April this year, the Icelandic volcano Eyjafjallajökull started an explosive eruption that produced a high column of volcanic ash. With westerly winds, the ash cloud was blown toward Europe in the stratosphere. In the NRAU (Nordic Radio Amateur Union) Nordic Activity Contest on 70 MHz on Thursday 15 April, we experienced fairly poor propagation on 70 MHz meteor scatter (MS). Being a geologist (with a degree in volcanology), I wondered if the poor MS propagation could be due to volcanic ash attenuation. The very fine ash grains would not be expected to be large enough to cause reflections of radio signals at 4 meters, being a fairly large VHF wavelength.

“During the days after the start of the volcanic eruption -- with continued ash eruption from the volcano -- airplanes were grounded at airports all over Western Europe for several days and passengers were not allowed to travel. Continued experiments between LA4LN and G4DEZ (and others) on 70 MHz found that the signals (bursts and pings) via meteor scatter were weaker, less frequent and shorter than experienced during normal conditions, and what would be expected from meteor data from the Virgo satellite. A complete MS QSO with JT6M on 70 MHz, which usually would take some 15 minutes between G4DEZ and LA4LN (distance about 1000 km) now took about three times longer. We see no other explanation to this attenuation than the presence of the thick, fresh volcanic ash clouds between Iceland and Western Europe.

“After some days with reduced ash eruption from the volcano, the air traffic started again, and the MS propagation on 4 meters seemed to go back to normal. The 6 meter MS reflections did not seem to be affected to the same degree as the MS attenuation experienced on the 4 meter band. But this may also be because radio amateurs generally have better antennas and more transmitting power on 6 meters than on 4 meters. It would be interesting to hear if other radio amateurs had experiences with peculiar radio propagation associated with volcanic eruptions”.

Thanks, Tom!

All times listed are UTC.

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.