ARLP020 Propagation de K7RA:
May 16, 2003

Propagation Forecast Bulletin 20 ARLP020
From Tad Cook, K7RA
Seattle, WA May 16, 2003
To all radio amateurs

ARLP020 Propagation de K7RA

Disturbed conditions triggered by a continuous solar wind stream appear to go on and on, week after week, seemingly without end. Nice quiet conditions would result from a daily A index of 10 or lower. Average daily conditions near that level haven't been reported since the week of February 20-26 when the daily average A index was 11.1, or January 9-15 when it was 9.1.

Conventional wisdom says that disturbed conditions occur more often when the solar cycle has passed the peak and is headed down, and recent experience seems to bear this out. Recent forecasts for daily solar flux and planetary A index don't predict a daily A index below 10 until May 31.

A plot from Jim Secan and Northwest Research Associates shows the decline of the solar cycle over the past year at The latest projection has solar flux rising over the next few days to 110 on Saturday, May 17, 120 on Sunday and 125 on Monday. The daily planetary A index projection shows an unsettled 15 thought the weekend, rising to 20 on Monday.

The solar flux and sunspot numbers were lower this week than last, but the A index was higher. The average daily sunspot number dropped around 100 points from 146 to 46.4, and daily solar flux was down over 40 points to 95.5. Average daily A index rose from 20.7 to 29.3.

Last week we mentioned Scott Craig, WA4TTK and his solar plotting utility freeware available at Scott says he usually gets 100-150 visits per day to his web page, but last Friday when the bulletin came out he got 270, and Saturday it was 393.

The announcement this week about the new 60-meter band brings speculation about propagation characteristics. Initially this will probably be used just for domestic communications, since no other country has adopted these frequencies for the amateur service. A quick look with a propagation prediction program shows the band opening and closing at hours somewhere between the 75 and 40-meter bands.

With W6ELprop looking from Seattle to Atlanta, assuming that the band is legal one month from now and the sunspot number is around 100, 60-meters seems to open a half hour earlier than 75- meters and close a half hour later. Signal strengths during the peak hours, which for the above parameters are from 0500-1000z, are between the levels for 40 and 75-meters as well. A similar projection for mid-September from California to Ohio shows similar characteristics, although with more hours of darkness the openings are longer.

Mark Roberts, KD5SMF sent an email this week asking for a source for the numbers used in the W6ELprop software, a free windows-based program that can be downloaded at I wrote to him and said that it is probably better to take an average of several days sunspot numbers and use that instead of the latest daily solar flux. You can get both values at, and several daily K indices from

The latest mid-latitude K index is on WWV at 18 minutes after each hour, or you can get the WWV message on the telephone at 303-497-3235. The text of that hourly message is available on the web at

For more information on propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at You can write to the author of this bulletin at

Sunspot numbers for May 8 through 14 were 33, 23, 22, 47, 66, 59, and 75, with a mean of 46.4. 10.7 cm flux was 100.9, 97.1, 92.7, 91.5, 93.9, 96.1, and 96.3 with a mean of 95.5. Estimated planetary A indices were 30, 29, 43, 31, 18, 27, and 27, with a mean of 29.3.