QST de W1AW
Propagation Forecast Bulletin 36 ARLP036
From Tad Cook, K7VVV
Seattle, WA September 3, 1999
To all radio amateurs
SB PROP ARL ARLP036
ARLP036 Propagation de K7VVV
Sunspots and solar flux were both up this week, with sunspot number averages rising over 100 points. Average solar flux was up nearly 34 points, and flux values reached a new high for cycle 23 on Saturday, at 248.4. The last time flux values were this high was on the downside of cycle 22 on February 26, 1992 when it was 253.
Geomagnetic indices were fairly active, with September 1 the most active day. Planetary A index was 22, and the K indices were 4 or 5 over most periods. In higher latitudes, the College index (from Alaska) had an A index of 37 on that day, with K indices as high as 6.
Solar flux has been falling since the weekend, and over the next few days (Friday through Sunday) the values are predicted at 150, 140 and 130. Planetary A index is forecast at 10 for all three days, so conditions should be stable for this weekend's All Asia DX Phone Contest.
Beyond the weekend look for solar flux to bottom out around 125 on September 8 or 9, then rise above 140 after the middle of the month, peaking around 220 on September 23 or 24. September 12-16 should have unsettled geomagnetic conditions, with A indices around 15.
August showed a continued upward trend in solar flux. Average flux values for April through August were 117.2, 148.4, 169.8, 165.6 and 170.7.
KF7E sent the URL http://space.rice.edu/ISTP/justdials.htm, along with some comments about the ionosphere's D layer. Jim mentioned that in the summer the D layer is thicker and more absorptive, and the LUF (Lowest Usable Frequency) increases. Since the MUF (Maximum Usable Frequency) is lower, this puts a ''squeeze'' on propagation, where there are fewer usable HF bands. But he also mentioned a tradeoff. While the MUFs are lower, 20 meter propagation extends long into summer evenings due to slower ion recombination, but closes sooner in the winter because of less ionization from sunlight and faster recombination.
Sunspot numbers for August 26 through September 1 were 176, 194, 225, 229, 212, 190 and 137 with a mean of 194.7. 10.7 cm flux was 222.2, 223.1, 248.4, 218.2, 198.1, 182.7 and 162.8, with a mean of 207.9, and estimated planetary A indices were 13, 13, 14, 10, 20, 18 and 22, with a mean of 15.7.
Here are some path projections for the All Asia DX Phone Contest this weekend.