The K7RA Solar Update


We're still looking at a quiet sun, but currently a solar wind is disturbing the Earth's magnetic field. Six meter operators -- after enjoying a fine season of sporadic E propagation this summer -- may see some added excitement from auroral propagation. Check here for updated indicators.

The planetary A index was 33 on Thursday, September 4, the highest daily number in over a year. I don't know when it was last that high, but the closest recent numbers were 32 on April 23, and 31 on March 27. Planetary A index for September 5-10 is predicted to be 20, 15, 8, 5, 5 and 5. It is expected to rise to 20 on September 14. Sunspot numbers for August 28-September 3 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 66.1, 66.8, 67.1, 66.7, 65.8, 66 and 66.2 with a mean of 66.4. Estimated planetary A indices were 2, 3, 3, 3, 4, 3 and 7 with a mean of 3.6. Estimated mid-latitude A indices were 2, 2, 2, 2, 2, 2 and 7 with a mean of 2.7.

There has been some news about the current solar minimum regarding continuous days without spots. August was the first calendar month with no sunspots since 1913. Of course, there have been periods longer than 30 days, but generally over a two calendar-month period in which there were some sunspots in each month. As of Thursday, September 4, there have been 46 continuous days with no spots. That is the seventh longest period of no spots, looking back over 150 years to the mid-19th century. If there are no sunspots through this Sunday, at 49 days this will be the fourth longest spot-free period.

But not everyone is reporting zero sunspots for August. If you go here, check out the archives on the upper right side, changing the date to August 21 and August 22. Both those days show a sunspot number of 11 (look at the left side of the page), indicating a single spot which had a magnetic signature indicating a new Solar Cycle 24 origin. This is the same number that Zurich shows, but not NOAA, which didn't assign it a number because it was so short lived.

Both May and June 1913 were spotless, part of a continuous spotless run of 92 days from April 8 to July 8. Solar Cycle 19 was the biggest solar cycle on record; it is interesting to note that it was preceded by long periods without spots. There was a 26 day spotless run from February 15 to March 4, 1953, followed by 27 days from January 12 through February 7, 1954, with another 30 days beginning on June 3, 1954 and running through July 2.

In case you've forgotten what a spotted Sun looks like, take a peek at seven years ago, on September 1, 2001.

In a little over two weeks, the autumnal equinox (September 22) arrives -- the start of the fall season and a sweet spot for HF propagation. Without sunspots, HF is still useful for long distance communication. Plugging in zero for sunspots with one of the popular propagation programs shows 20 meters to be the best overall. Figuring a path from Texas to Brazil, W6ELprop shows 20 meters at the equinox begins opening around 1800 UTC, with signals steadily rising, then closing around 0200 UTC. Seventeen meters looks productive with rising signal strength throughout the day, starting at 1600 UTC with signals rising until the band closes around 0000 UTC. Both 40 and 30 meters also look productive, with 40 opening around 2300 UTC, and rising signals, especially after 0000 UTC. It stays strong all night, dying out after local sunrise; 30 meters looks good over that path from 2300-0700 UTC.

Evan Rolek, K9SQG, of Beavercreek, Ohio, notes that although signal levels are overall much lower because of lack of sunspots, there are still big variations. For instance, two months ago he worked an S9 station from India on 40 meters with a wire loop at 12 feet.

Bud Frohardt, W9DY, is mobile in Elgin, Illinois. After being on the air recently, he thought perhaps sunspots had returned. On August 26, he was operating CW mobile on 20 meters and says he was able to work many more stations than in recent months. In just 37 minutes, he worked all continents. He says European stations were all over the band with excellent signals until he turned off the radio at 2215 UTC.

Ken Tata, K1KT, of Warwick, Rhode Island, reported tropospheric propagation on Thursday night, September 4. He likes the VHF propagation maps here and notes it showed a band of propagation extending all up and down the Eastern seaboard.

Russ Ward, W4NI, of Nashville, Tennessee, sent in a tip on an interesting article he read about geomagnetic events. Titled "Elusive Onset of Geomagnetic Substorms," it appeared in the August 15, 2008 issue of Science, volume 321, pages 920-921.

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 in The ARRL Letter. 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.