QST de W1AW
Propagation Forecast Bulletin 54 ARLP054
From Tad Cook, K7VVV
Seattle, WA December 27, 2002
To all radio amateurs
SB PROP ARL ARLP054
ARLP054 Propagation de K7VVV
Geomagnetic activity was up quite a bit this week, but solar flux and sunspot numbers were down. The average daily planetary A index, an indicator of geomagnetic activity, was over double last week's average. Average daily sunspot numbers were down by over 20% and average daily solar flux was down by over 10%, a drop of 41.7 and 19.6 points respectively. The most active days were Thursday, December 19 when the planetary A index was 21 and Monday, December 23 when it was 26. The mid-latitude numbers were more moderate, but Alaska's College A index was 39 and 40 on those two days.
Sunspot numbers dropped dramatically in the past few days. On Christmas Day the sunspot number was only 77, the lowest value in nearly a year and a half, when the sunspot numbers were 59 and 64 at the end of July, 2001. The day after Christmas the sunspot number dropped even lower, to 62.
Brian, W2BRI writes about poor conditions on 80 meters recently. He checks a D-region absorption map (perhaps the one at http://www.sel.noaa.gov/rt_plots/dregion.html) when he notices poor conditions, and it always seems to correlate with an elevated X-ray level. He notices lots of fading and high angle attenuation with close-in stations inaudible but stations further away heard okay.
Over the next few days we should see continued geomagnetic activity. A coronal hole is spewing a solar wind stream that is expected to yield a Friday through Sunday planetary A index of 20, 25 and 20. Solar flux over those same days should drop to around 125, 120 and 115.
Next week's bulletin will have some end of year numbers. It won't be final until next week, but the average daily sunspot number for the calendar year so far is 178.3. This contrasts with 170.3 for 2001, 173 for 2000 and 136.3 for 1999, which is surprising, since the peak of the cycle was expected to be a couple of years ago.
Sunspot numbers for December 19 through 25 were 225, 203, 199, 168, 160, 119, and 77, with a mean of 164.4. 10.7 cm flux was 192.9, 196.6, 183.9, 172, 158.9, 147.3, and 131.9, with a mean of 169.1. Estimated planetary A indices were 21, 16, 18, 12, 26, 18, and 14, with a mean of 17.9.