QST de W1AW
Propagation Forecast Bulletin 20 ARLP020
>From Tad Cook, K7RA
Seattle, WA May 16, 2003
To all radio amateurs
SB PROP ARL ARLP020
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
www.nwra-az.com/spawx/ssne-year.html. 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
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
Last week we mentioned Scott Craig, WA4TTK and his solar plotting
utility freeware available at
www.craigcentral.com/mystuff.asp. 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
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 www.qsl.net/w6elprop/. 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
sec.noaa.gov/ftpdir/latest/DSD.txt, and several daily K
indices from sec.noaa.gov/ftpdir/latest/DGD.txt.
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 sec.noaa.gov/ftpdir/latest/wwv.txt.
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 www.arrl.org/tis/info/propagation.html. You can
write to the author of this bulletin at email@example.com.
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.
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