ARRL

ARRL Propagation Bulletin ARLP051 (2002)

SB PROP @ ARL $ARLP051
ARLP051 Propagation de K7VVV

ZCZC AP51
QST de W1AW  
Propagation Forecast Bulletin 51  ARLP051
From Tad Cook, K7VVV
Seattle, WA  December 6, 2002
To all radio amateurs 

SB PROP ARL ARLP051
ARLP051 Propagation de K7VVV

Average sunspot numbers were up a bit this week, and average daily
solar flux barely changed. Geomagnetic indices were quieter.

Now that December is here, let's review average daily solar flux and
sunspot numbers for November, and compare them with previous months.
Here are monthly averages for solar flux and sunspot numbers for
this year. From January through November, 2002 the average daily
sunspot number for each month was 189, 194.5, 154.3, 144.4, 146,
183.5, 191, 206.4, 153.9 and 159.8. Average daily solar flux for the
same months was 227.3, 205, 179.2, 141.4, 148.7, 174.4, 183.9,
175.8, 167 and 168.7.

This weekend is the ARRL 160-Meter Contest. It would be good to have
low geomagnetic activity for this contest. Right now the predicted
planetary A index for Friday through Monday is 12, 15, 20 and 15.
This indicates unsettled to active conditions on Saturday and Sunday
due to coronal hole effects. There is a chance of moderate solar
flare activity over the next few days. Solar activity is likely to
be low. Predicted solar flux for the next few days is 160-175.

Chester, KD5TFK wrote in to ask, "How much longer can we expect
great propagation on 10-meters?" He assumes we are on the downside
of the current solar cycle.

One way to look at this is to compare likely conditions for the
10-meter contest coming up the weekend of December 14-15. Last year
the average daily solar flux around the time of the contest was
about 228. This year it is likely to be about 175. If we check the
weekly Preliminary Report and Forecast of Solar Geophysical Data
from the NOAA SEC web site at
http://www.sec.noaa.gov/weekly/index.html, they run an occasional
prediction for smoothed sunspot and solar flux numbers. The last
prediction was at the end of the November 5 issue. The smoothed flux
value they are predicting for December 2003 is about 41 points lower
than for December 2002, so let us use a value of 134 for December of
next year. Next try plugging these dates and values into W6ELprop
(see the site, http://www.qsl.net/w6elprop/ ).

If I do a 10-meter prediction for last December from Seattle to
Japan using a flux value of 228, I show a good predicted opening
from 2230-0130z with a relative dB level of 21. Run the same test
with a solar flux of 175, and the period shortens to 2230-0030z. Do
it again with 134 for the solar flux, and it shows a possibility of
an opening around 2300z.

Try it again on 10-meters from Dallas to Brazil. Last year has a
strong opening from 1300-0030z, this year 1330-2330z, and next year
1400-2200z. The solar activity will gradually decrease, and
10-meters will be affected.

Sunspot numbers for November 28 through December 4 were 124, 107,
150, 97, 155, 135, and 144, with a mean of 130.3. 10.7 cm flux was
139.7, 141.3, 146.2, 149.6, 146.1, 145.9, and 148.7, with a mean of
145.4. Estimated planetary A indices were 15, 14, 16, 16, 11, 11,
and 12, with a mean of 13.6.
NNNN
/EX