ZCZC AP08
QST de W1AW
Propagation Forecast Bulletin 8 ARLP008
From Tad Cook, K7RA
Seattle, WA February 20, 2004
To all radio amateurs
SB PROP ARL ARLP008
ARLP008 Propagation de K7RA
Average daily sunspot numbers were down a little this week, as compared to those of a week earlier, as were the daily solar flux numbers. Average daily planetary A index was slightly higher. Geomagnetic indices settled down February 16-19 to yield some nice HF conditions. There weren't many sunspots, so the MUF wasn't as high as it was, say, several years ago, but the quiet conditions are a welcome respite from the stormy geomagnetic conditions of late.
The quiet conditions should continue though this weekend-- good news for those participating in the ARRL International DX Contest (CW). Predicted planetary A index for Friday through Monday, February 20-23, is 10, 10, 12 and 12. Solar flux is expected to stay below 100 until around Leap Year Day, February 29.
Carl Luetzelschwab, K9LA, has an interesting article in the March issue of Worldradio about low-band propagation during the solar minimum. He tested the theory that 160 meters is better during the low part of the solar cycle, and he proposes that what helps the lower frequencies is not really an absence of sunspots, but quieter geomagnetic conditions. Because solar activity is lower during the years around the solar minimum, there is less chance of flares or coronal holes upsetting the geomagnetic field.
A disturbed geomagnetic field can severely affect signals passing through high latitudes. He found that stations situated where they can propagate signals to their destination without passing through the high-latitude auroral zone may have a great advantage during periods of greater solar activity. For instance, K9LA's path to Europe is a polar path, so he is affected by polar absorption when the K index is high.
He compared notes with Tom Rauch, W8JI, in Georgia, whose paths to most major ham populations stays outside the auroral zone. W8JI can work much more 160 meter DX during the cycle peak than K9LA can.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site.
Sunspot numbers for February 12 through 18 were 65, 71, 64, 75, 81, 22 and 23, with a mean of 57.3. The 10.7 cm flux was 112.2, 107.8, 103.7, 102.1, 98.7, 101.9 and 97.7, with a mean of 103.4. Estimated planetary A indices were 28, 21, 18, 18, 7, 5 and 8, with a mean of 15.