ZCZC AP09
QST de W1AW
Propagation Forecast Bulletin 9 ARLP009
From Tad Cook, K7VVV
Seattle, WA February 27, 1998
To all radio amateurs
SB PROP ARL ARLP009
ARLP009 Propagation de K7VVV
Solar activity retreated again last week, with average sunspot numbers down twenty points and average solar flux down about five. Geomagnetic conditions were relatively quiet. Quiet conditions are expected to continue over the next few days, with the Friday through Sunday solar flux predicted to be 93, 92 and 90. Stable geomagnetic conditions should be good for the CQ Worldwide 160 Meter SSB Contest this weekend. Currently the most active solar region is number 8164, with 18 sunspots.
Over the next week look for solar flux to drift below 90, then rise above 90 after March 8, above 100 around March 12, and below 100 by March 18. Over the next month the days will be getting longer in the northern hemisphere, and we can look forward to typical Spring conditions with more daylight openings on the higher bands.
A chart on the web at http://www.dxlc.com/solar/cyclcomp.html compares the current solar cycle, now 21 months old, with the two previous cycles, dating back to June, 1976. This is part of the DX Listener's Club of Norway website mentioned in Propagation Bulletin ARLP006. The monthly smoothed sunspot number is obviously lagging for this cycle, and the month-by-month graphic comparison makes this very clear.
K7EEC wrote to ask that if flux numbers are high, does this mean that propagation is probably better? He also asked what the flux numbers measure. (Questions and comments are welcome via email to tad@ssc.com).
High solar flux is good for HF propagation, especially if A and K indices are low. During the peak of the sunspot cycle the solar flux is higher. Solar flux is a measurement of radio energy emitted by the Sun at 10.7 cm wavelength, which is 2800 MHz. This seems to correlate with ionization of the ionosphere. The denser the ionization, the higher the frequencies that it can reflect. More information can be found in Chapter 21 covering propagation in the 1998 ARRL Handbook, or The New Shortwave Propagation Handbook, by Jacobs, Rose and Cohen, published by CQ Magazine.
Sunspot Numbers for February 19 through 25 were 57, 29, 28, 38, 59, 78 and 69 with a mean of 51.1. 10.7 cm flux was 98, 95.7, 94.8, 95.5, 99.4, 98.6 and 94.7, with a mean of 96.7, and estimated planetary A indices were 7, 7, 4, 6, 11, 3, and 4, with a mean of 6.