ZCZC AP41
QST de W1AW
Propagation Forecast Bulletin 41 ARLP041
From Tad Cook, K7VVV
Seattle, WA October 9, 1998
To all radio amateurs
SB PROP ARL ARLP041
ARLP041 Propagation de K7VVV
Solar activity was down again last week, with the average sunspot number off by almost 54 points and the average solar flux down by nine points. Average solar flux for the previous 90 days was 129, and flux values were well below this number on every day. The active geomagnetic days were last Thursday, Friday and the following Wednesday, when the planetary A index was 20 or more.
For the next few days expect a slightly higher solar flux, with flux values on Friday, Saturday and Sunday predicted to be 135, 130 and 130. Solar flux should drop down below 125 until October 15, when it should begin to rise again, peaking around 140 from October 18 to 20, then dropping below 130 after October 23. Solar flux is expected to drop below 120 after October 26, then begin to rise around the end of the month. Expect unsettled conditions this Sunday, with a predicted planetary A index of 18, and again around October 15 and 24 due to coronal holes.
WA5IYX in Texas reported that possibly the highest MUFs so far in cycle 23 occurred on October 7. He said that this was largely a seasonal effect, and that commercial low band 2-way radio transmissions around 33 and 37 Mhz were coming in strong from the east coast.
This Fall is the season when we are starting to see 10 meter openings, and this Saturday there is a 10 meter sprint sponsored by Ten-Ten International where this band may show its stuff. It certainly helps to be at a lower latitude, as WA5IYX is. From the author's QTH in Seattle, a path projection to New York City run on a popular propagation program shows a slight chance of a 10 meter opening from 1800z to 2030z with a solar flux of 130. The MUF over that time varies from 21.8 to 22.8 Mhz. Run the same numbers from Los Angeles to Atlanta, and the opening stretches from 1400z to 0200z, and a period of excellent propagation from 1630z to 2200z, with MUF as high as 35.2 MHz. The southern path is about 500 miles shorter, but similar numbers are revealed when calculating a shorter northern path as well.
Sunspot Numbers for October 1 through 7 were 47, 51, 38, 21, 49, 68 and 98 with a mean of 53.1. 10.7 cm flux was 118.8, 112.7, 111.9, 114.8, 117.1, 117 and 124.2, with a mean of 116.6, and estimated planetary A indices were 21, 21, 14, 5, 7, 6 and 20, with a mean of 13.4.