The K7RA Solar Update
Solar activity was down again this week -- this is the third week in a row with sunspot numbers lower than the week prior. On January 20, we reported an average daily sunspot number of 116.9 for January 12-18, 98.7 the next week, followed by 62 the week of January 26-February 1, and now 40.4 during the latest period. Sunspot numbers for February 2-8 were 85, 39, 43, 37, 27, 24 and 28, with a mean of 40.4. The 10.7 cm flux was 118, 111.1, 107, 102.7, 112, 107.2 and 97.2, with a mean of 107.9. The estimated planetary A indices were 4, 6, 6, 6, 4, 12 and 10, with a mean of 6.9. The estimated mid-latitude A indices were 3, 4, 7, 6, 5, 10 and 9, with a mean of 6.3. On Tuesday, February 7, the daily sunspot number was 24, the lowest since mid-August 2011, when it was 0 and 13 on August 14-15.
The solar flux forecast -- which roughly tracks sunspot numbers; we don’t have access to any short term sunspot number forecast -- has also been lowered steadily over recent weeks. The latest forecast from NOAA/USAF has solar flux at 100 on February 9-11, 105 on February 12, and 110 on February 13-24. The predicted planetary A index is 8 on February 9-10, 5 on February 11, 8 on February 12-13, 5 on February 14-22, 8 on February 23, and back to 5 from February 24 through the end of the month.
Looking at the lower frame on the Solar Data Plotting Utility from WA4TTK, it appears that we are down from a peak of activity late last year. You can see the same trend here (toward the middle of the page) on the graph showing sunspot and flux values over the past year.
In mid-January, the solar flux forecast for February 17-21 was 165, which was important because the ARRL International DX CW Contest is on February 18-19. More sunspots and higher solar flux would mean higher usable frequencies, increasing the chance that 10 and 15 meters would give good results. But by January 24, the prediction was down to flux values of 155 on February 11-13, 150 on February 14-19, and 145 on February 20-23.
Then on February 4, the forecast went down again, with predicted flux at 125, 130 and 155 on February 11-13, 150 on February 14-19, and 145 on February 20-23. The next day, the forecast said 125 on February 11, 130 on February 12-13, with the rest of the forecast unchanged from a day earlier. Two days later on February 7, it was another downward revision, with flux of 100, 105, 110 and 115 on February 11-14, and 110 on February 15-24. Then a day later on February 8, it changed again, with solar flux at 100 on February 9-11, 105 on February 12, and 110 on February 13-24. The latest forecast (February 9) is revised upward, with solar flux of 105 and 115 on February 10-11,120 on February 12-13, 125 on February 14, 130 on February 15-16, 120 on February 17 and 110 on February 18-24.
The predicted planetary A index is 8 on February 10, 5 on February 11, 8 on February 12-13, 5 on February 14-22, 8 on February 23, and 5 on February 24-March 1.
Jon Jones, N0JK, of Wichita, Kansas, reports a couple of 6 meter spots. On February 8, he heard XE2O/b (EL05) for more than two hours, from 2330 to after 0130 UTC on 50.068 MHz on E-skip. He also had E-skip to Texas and Arizona. Stations in the Dallas/Fort Worth worked FK8CP (New Caledonia, in the South Pacific) on 6 meters around 0200 on February 9 via a trans-equatorial e-skip link. Last week, Jon reported hearing the C6AFP beacon (Bahamas) on 50.04 MHz on January 30 around 1700.
Russ Mickiewicz, N7QR, of Portland, Oregon, sent a link to an article in IEEE Spectrum about risks to power grids from solar storms.
Randy Crews, W7TJ, of Spokane, Washington, has an observation about recent solar conditions: “This bottom is the longest I can remember since I was licensed in 1964. Usually we have about 12 months of very low activity and the solar flux punches up over 100 in about 12-15 months from the cycle bottom. This time, it took two-and-a-half years, from the August 2008 low until February 14, 2011. This time last year the solar flux had not yet crossed 100. February 14 was the real breakout, as chartists would say. Past solar cycles have bottomed with a sunspot number of about 10-12. The sunspot number at the bottom of the past cycle was approximately 1.5! It’s been a long, long dry spell for the higher bands.”
Randy also notes: “Of all the winter months, February conditions are unique. February is a combination for winter and spring propagation, with increases in daylight of three minutes per day (at 49 degrees north latitude) and still having very low D-layer absorption. Daylight is approximately 10 hours in duration, and the grayline paths are almost a carbon copy of those in October. Propagation will change almost daily as spring approaches. It is an excellent time of the year to DX or contest.”
Don’t miss the excellent and thought-provoking article about propagation in the March 2012 issue of QST by Eric Nichols, KL7AJ entitled “Three Wrong Assumptions About the Ionosphere.” Eric reminds us that the ionosphere is not spherical or smooth, and he explains how propagation through it is not reciprocal, or the same coming back as it is going out.
And finally, the headline on the AP wire article read “Plane Crash Held Caused by Sun Spots. Ghost Wave Blamed for Disaster.” But the date was December 1938, the peak of sunspot cycle 17. Read it here. If you look at the 20th century solar data here, you can spot the peak of Solar Cycle 17, two before the big one -- Solar Cycle 19 -- in the late 1950s.
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.