ARLP039 Propagation de K7VVV:
September 20, 2002

Propagation Forecast Bulletin 39 ARLP039
From Tad Cook, K7VVV
Seattle, WA September 20, 2002
To all radio amateurs

ARLP039 Propagation de K7VVV

Average sunspot numbers were up a bit this week compared to last, and solar flux on average was about the same. Solar flux peaked in the short term on September 10 at 220.5 and has been mostly declining since. Solar flux on Tuesday through Thursday of this week was 194, 176.8 and 165.3, and for Friday though Sunday is predicted at 165, 160 and 155. Sunday's value may continue for a few more days and should be the minimum for the near term. Assuming returning activity from the current solar rotation, solar flux is expected to peak again around October 6-11.

The big news this week though is the autumnal equinox, set for early this Monday UTC. 10-meters is seasonally best around this time, and K7SS reports a great opening during the recent Worked All Europe contest between the West Coast and Europe on 10-meters on Friday and Saturday mornings. He is also hearing Africa via longpath on 15-meters at night, and 20-meters is staying open quite late toward the west.

Gary, N8MJZ asks why the equinox is good for DX. Around the equinox the southern and northern hemispheres get approximately an equal amount of sunlight. This means that there aren't any short days anywhere on the planet with the accompanying early winter band closings, and with more equal solar radiation around the earth MUFs are generally higher.

Go to for an article about a new space weather forecasting initiative funded by the National Science Foundation. This article also references the ''Windows to the Universe'' site at, which has a number of interesting features, including views of electron densities in the ionosphere and details on ionospheric sounding.

Sunspot numbers for September 12 through 18 were 258, 246, 256, 168, 190, 228 and 225, with a mean of 224.4. 10.7 cm flux was 212.4, 206.1, 206.9, 187.8, 182.6, 194, and 176.8, with a mean of 195.2. Estimated planetary A indices were 17, 16, 11, 8, 8, 13, and 14, with a mean of 12.4.