As promised in the April 19th edition of The ARRL Letter, this week’s bulletin features a report on recent solar activity and solar cycle progression from Carl Luetzelschwab, K9LA.

Both the solar flux and sunspot numbers reached a short term low on April 8-11, but they are now rising again. For the past week -- April 12-18 -- the average daily sunspot numbers more than doubled, compared to the previous seven days, rising more than 39 points to 71.7. The average daily solar flux increased from 95.9 to 105.1. On April 19, the day following this period, the daily sunspot number rose dramatically from 96 to 122, as did solar flux values, from 121.5 to 137.8.

Sunspot numbers for April 12-18 were 50, 50, 65, 77, 86, 78 and 96, with a mean of 71.7. The 10.7 cm flux was 95.3, 97.7, 98.1, 101.7, 107.9, 113.8 and 121.5, with a mean of 105.1. The estimated planetary A indices were 13, 19, 9, 5, 5, 8 and 8, with a mean of 9.6. The estimated mid-latitude A indices were 11, 13, 7, 5, 5, 8 and 7, with a mean of 8. Since April 10, there have been 11 new sunspot groups: One each on April 10-13, two on April 14, one on April 16, two on April 17 and one each on April 18-19.

The predicted solar flux for April 20-25 is 135, followed by 130 on April 26-27, 105 on April 28, 100 on April 29-30, 95 on May 1-9, then rising to 100 on May 10-12, 105 on May 13-18, and 110 on May 19-22. The predicted planetary A index is 8, 5, 5, 7, 12, and 12 on April 20-25, 5 on April 26-29, 8 on April 30, 5 on May 1-7, 8, 12, 15 and 10 on May 8-11, and 5 on May 12-20.

Alaska Dispatch ran an article with video on the solar flare that Carl mentions in his report below.

Toni Umlandt, DD3EO, mentioned another resource in response to our mention in last week’s Solar Update of a public remotely controlled SDR radio receiver in Walla Walla, Washington that anyone can use via the Internet. This lists 36 SDR receivers, and I think all of them can be used simultaneously by multiple users.

K9LA’s Report

Monday, April 16, we saw moderate solar activity, which was due to an M1.7 X-ray flare around 1745 UTC. But since then, solar activity has continued at low levels. There is an extremely small chance of X-class flares (1 percent) and a slightly greater chance of M-class flares (around 20 percent at most).

With solar activity continuing at low levels, the ascent of Solar Cycle 24 has slowed dramatically in the past couple months. For example, after a monthly mean 10.7 cm solar flux peak in November 2011 of 153, the next three months saw ever-decreasing monthly means (141, 133 and 107 for December, January and February, respectively). March (last month) recovered a bit, with a monthly mean 10.7 cm solar flux of 115, but April so far appears to be headed for another low 10.7 cm solar flux monthly mean (through April 17 the monthly mean is hovering around 100).

These low monthly means have taken a toll on the smoothed 10.7 cm solar flux. Since early 2009, the smoothed 10.7 cm solar flux rose nicely. But the recent low monthly means have resulted in the smoothed value pretty much leveling off in the past two months at around 118. Does this mean we’ve reached Solar Cycle 24’s peak? Not necessarily -- other solar cycles have had similar slow-downs, but then the solar activity picked up again to continue the increase of the smoothed value. The monthly means during the next several months will be interesting to observe, and may tell us how high Solar Cycle 24 will ultimately go.

Regardless of what happens, now is the time to get on the higher bands and take advantage of F2 region propagation. If Solar Cycle 24 performs to the nominal prediction from the Marshall Space Flight Center, we’re pretty much there. If it performs more to the nominal prediction of the International Space Environment Service, then we still have better propagation in the next year or so.

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.