The K7RA Solar Update


Weakened sunspots faded this week, and we were buffeted with more geomagnetic instability, but without the dramatic geomagnetic storms of the previous week. The average daily sunspot numbers fell more than 20 points to 12.1, and the average solar flux dropped nearly three points to 75.1. Sunspot numbers for April 8-14 were 23, 11, 11, 0, 14, 14 and 12, with a mean of 12.1. The 10.7 cm flux was 75.7, 76, 75, 74.6, 74.5, 74.9 and 75.1, with a mean of 75.1. The estimated planetary A indices were 11, 6, 3, 8, 22, 3 and 9, with a mean of 8.9. The estimated mid-latitude A indices were 9, 4, 3, 8, 18, 2 and 8, with a mean of 7.4.

April 11 saw no sunspots, with group 1061 appearing April 5-10, and sunspot group 1062 showing April 12-14. By Thursday, group 1062 was gone and we may see still more days without sunspots. The predicted solar flux for April 16-24 is 75, 77, 78, 79, 80, 82, 84, 80 and 80. The predicted planetary A index for those same days is 5, 7, 12, 8, 7, 8, 5, 5 and 5. Geophysical Institute Prague predicts quiet conditions for April 16, quiet to unsettled April 17, active conditions April 18, quiet to unsettled April 19, quiet April 20-21 and quiet to unsettled April 22.

The new ARRL Web site is up, and the links to propagation information appearing at the end of each weekly bulletin have changed. See the links toward the end of this bulletin.

Carl Luetzelschwab, K9LA, had comments about Jim Secan’s observations in the last propagation bulletin: “Your statement about your discussion with Jim Secan in your last bulletin is really two issues. Once you sort those out and understand them, you’ll see that I totally agree with Jim. I can’t speak for anyone else, though.

“Issue 1 -- Due to the daily variation of the ionosphere, our model of it was developed based on the correlation between the smoothed sunspot number and monthly median ionospheric parameters. This gives us a statistical model of the ionosphere over a month’s time frame. Unfortunately, it’s not a real-time model. Because of the high correlation between the smoothed sunspot number and the smoothed solar flux, either index can be used to properly use our prediction software. This is what I’ve always preached -- that you should use a smoothed solar index (not that it matters, but I prefer smoothed sunspot number for historical reasons) and understand that the results are statistical in nature over a month’s time frame. This is how the developers of our predictions intended them to be used.

“Issue 2 -- Jim is trying to derive a solar index that represents what the ionosphere is doing real-time by forcing the model of the ionosphere to agree with a bunch of ionosondes. His results indicate that the average of solar flux over the last seven days works best to give the least error.

“So the difference in the two issues is the time frame being used. Issue one is a long-term effort (over one month) to correlate a solar index to data from one ionosonde, and issue two is a short-term effort (daily, hourly) to correlate a solar index to data from many widely separated ionosondes that don’t agree very well with each other at the same time of day.”

Steve Wamback, KK2W, of Angola, New York, wrote: “I just wanted to report very strange 10 meter propagation conditions on Sunday Evening at 10:18 EDT (Monday 0218 UTC), two hours past my local sunset. I just happened to tune through the 10 meter band by chance as I occasionally do. I heard James, KH6CB, in a QSO. Tuning further to 28.4 MHz, I heard VK4TJF (also James) just finishing a QSO, so I threw in my call sign with my 100 W and G5RV. He heard me and we exchanged 5×6 reports and a short QSO. Signals on the band persisted for about a half hour then dissipated. I find night time 10 meter openings to be extremely rare (I once worked a PJ4 after dark once during a December contest. Meteor scatter?).” That is odd propagation. Perhaps multi-hop sporadic-E? The path is more than 9000 miles. Steve has the longest listing I’ve ever seen.

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.