QST de W1AW
Propagation Forecast Bulletin 4 ARLP004
From Tad Cook, K7VVV
Seattle, WA January 28, 2000
To all radio amateurs
SB PROP ARL ARLP004
ARLP004 Propagation de K7VVV
The predicted geomagnetic storm for last weekend turned up a day late and with some lower numbers. Instead of peaking with a planetary A index of 35 on Saturday, the big number was 25 on Sunday. Conditions settled back toward normal on Tuesday and Wednesday, and solar flux as well as sunspot numbers declined as well.
Average solar flux for the reporting week, which runs Thursday through Wednesday, was down over 50 points to 148.6 compared to the previous week. Average sunspot numbers were down over 90 points to 135.6.
For this weekend expect more active geomagnetic conditions, beginning today. Predicted planetary A index for Friday through Sunday is 25, 25 and 18, and the expected solar flux for those days is 130, 130 and 125. Solar flux is expected to continue low through the first of February, then rise above 130 by February 3, above 160 by February 6, above 190 by February 9, and peak near 205 around February 11 or 12.
Following this, solar flux is expected to bottom out again for the short term around 135 from February 23-28. For most of February, expect quiet geomagnetic conditions, except for unsettled conditions around February 1, 7, and 25-27, and active conditions around February 23-24.
K0SR, who lives in the Minneapolis area sent an email this week with some observations on propagation from the 45th parallel. He notices that when the K index goes above 3, he hears next to nothing on HF, except domestic stations to the south working DX. He has also noticed on pictures from space of aurora that there is frequently a finger pointing down over his QTH. The author of this bulletin has also noticed the north-south discrepancy in HF propagation. Seattle is over 2-1/2 degrees north of Minneapolis in terms of latitude, and K7ZR has frequently referred to local hams in a DX bulletin column as ''Suffering Sevens.''
K0SR writes: ''When conditions are unsettled, the bands actually go in the tank during the greyline. It is a good indication that something bad is happening when signals disappear at sunrise/sunset, and then come back a little bit an hour later. This happens much more often than greyline enhancement does, and is apparent on all bands.
If you look at the sunrise/sunset times over a given path, we sometimes see a peak in propagation at the ''maximum dark'' time, for example the midpoint between our sunset and European dawn. This is frequently the best opening of the night. It isn't unusual to have our best low band opening at 0300z, and hear nothing at European dawn''.
Sunspot numbers for January 20 through 26 were 119, 144, 126, 135, 133, 141 and 151 with a mean of 135.6. 10.7 cm flux was 170.7, 159.3, 150.6, 140.5, 140.7, 137.4 and 140.7, with a mean of 148.6, and estimated planetary A indices were 12, 3, 19, 25, 17, 7 and 7, with a mean of 12.9.
Here are some path projections comparing Minneapolis, Minnesota to Houston, Texas for this weekend when the geomagnetic field should have a negative effect on propagation from northern latitudes.