Wednesday, November 21, 2007

Propagation Forecast Bulletin

Propagation Forecast Bulletin 48 ARLP048
From Tad Cook, K7RA
Seattle, WA November 21, 2007
To all radio amateurs

ARLP048 Propagation de K7RA

This is an off-schedule bulletin before Thanksgiving. Because ARRL headquarters is closed on Friday, the day this bulletin is normally released, and this bulletin was written before the end of our reporting week (which is Thursday through Wednesday), the sunspot, solar flux and geophysical numbers normally at the end of this bulletin will appear in a new propagation bulletin on Monday, November 26. Friday, November 30 will find us back on the regular schedule.

Another sunspot appeared in the past week, but just for two days, November 16-17. The sunspot number was 13 on both days. Neil Klagge, W0YSE of Layton, Utah wondered why the last Propagation Forecast Bulletin ARLP047 said there was only one sunspot on November 6 when the sunspot number for that day was 11. That is because of the arcane method used to derive sunspot numbers. A sunspot number of 11 means just one sunspot. The number is derived by counting 10 points for each sunspot group, and adding one point for each spot. So 11 is also the minimum non-zero sunspot number.

It is either 0, or 11, or something higher, with nothing from 1-10. So in reality, this week when we said there was one sunspot for November 16-17, because the sunspot number was 13, that can onlymean that there was one group of sunspots, but three spots were observed, although they were tiny.

We had some geomagnetic activity this week from a coronal wind stream. On November 20 the planetary K index rose to 6 for one period, and the planetary A index for the day was 28. Alaska's College A index was 48. The predicted planetary A index for November 21-27 is 20, 15, 10, 8, 15, 10 and 5. Note that this weekend, November 24-25, is the CQ Worldwide DX CW Contest. Sunspot and solar flux numbers should remain about the same, with an occasional spot appearing, and solar flux hanging around 70 or slightly lower.

Jon Jones, N0JK noted some trans-equatorial 6-meter e-skip propagation from Florida to Brazil on the evening of November 18. From 2358z November 18 through 0002z November 19, KE4WBO worked PY2XB. K4CVL, also in Florida, worked P43A in Aruba on 6 meters at the same time, 0001z. All reported good signals.

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For more information concerning radio propagation, see the ARRL Technical Information Service at, For a detailed explanation of the numbers used in this bulletin see, An archive of past propagation bulletins is at Monthly propagation charts between four USA regions and twelve overseas locations are at, .
(Source: ARLP048 via Dave Raycroft/ODXA & Larry Van Horn)