QST de W1AW
Propagation Forecast Bulletin 46 ARLP046
From Tad Cook, K7RA
Seattle, WA November 14, 2003
To all radio amateurs
SB PROP ARL ARLP046
ARLP046 Propagation de K7RA
With big sunspots rotating from view, sunspot numbers and solar flux values plummeted. The daily sunspot number was 330 on October 29, and a little over a week later it was 12 and 11. The average daily sunspot number for two weeks ago was 201.4, followed by 171 the next week and 32.6 last week. Similarly, average daily solar flux for the same three weeks was 249, 195.7 and 94.8.
Some readers have written, wondering if this solar cycle would have three peaks. But the graphs of solar activity that we see showing the peaks several years after the event are based on smoothed sunspot numbers graphed with a moving average. For instance, if you go back 90 days and average the sunspot numbers from the previous 90 days with the numbers from the subsequent 90 days, you have a 180 day average centered on that date. The next day do the same average calculation, but with the oldest day dropping off and a new day averaged in, 90 days in the future. When graphing this moving average, a smoothed representation of the sunspot cycle emerges in which it is much easier to see where the peak was, but only well after the date, when enough data has emerged to get a smoothed number.
So if we assume the recent huge sunspots will gradually fade away as they rotate back facing earth over the next couple of solar rotations, the recent jump in the numbers will show up as a wiggle on the graph. The size of that wiggle is dependent on how smooth a running average one chooses to observe.
A little over a week ago on November 6, sunspot 495 was still visible, and it disappeared by November 7, leaving a spotless disk. The sunspot number that day was 11. In the following days some tiny sunspots emerged, 498, 499 and 500. Sunspot 498 was disappearing from view by November 13. Now on November 14 sunspot 484 is re-emerging from its trip around the other side of the sun. It was very active when last visible, but is now smaller. Sunspots 486 and 488 should follow it, and we should see a rise in solar activity. Based on the previous solar rotation solar flux and sunspot numbers should peak again around November 23-25.
This weekend is the ARRL November Phone Sweepstakes. Right now, the interplanetary magnetic field points south, leaving earth vulnerable to flares and solar wind. A solar wind stream is currently affecting earth, and this weekend should have unsettled to active geomagnetic conditions with a slowly rising solar flux. The predicted planetary A index for Friday through Monday is 30, 30, 25 and 25. Solar flux values for those same days are expected to be 105, 110, 115 and 120.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at http://www.arrl.org/tis/info/propagation.html.
Sunspot numbers for November 6 through 12 were 12, 11, 29, 47, 47, 43 and 39, with a mean of 32.6. 10.7 cm flux was 97.8, 91, 92.7, 93, 94.6, 95.6 and 98.7, with a mean of 94.8. Estimated planetary A indices were 14, 8, 10, 25, 30, 51 and 26, with a mean of 23.4.