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ARRL Propagation Bulletin ARLP006 (2003)

ARLP006 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7VVV
Seattle, WA  February 7, 2003
To all radio amateurs 

ARLP006 Propagation de K7VVV

Sunspot numbers dropped way down into the double-digits this week,
and compared with last week the average daily sunspot number was off
by nearly 51 points. Daily solar flux values declined last week and
then rose this week, so the average daily value for the week was
practically unchanged at less than two points higher. Solar flux is
expected to peak through next week around 170, with predicted daily
values for Friday through Sunday at 155, 160 and 165.

Geomagnetic conditions were quite active this week, with the average
daily planetary A index up over 8 points from last week. A solar
wind stream caused some high A and K index values, with the peak day
on Sunday when the planetary A index was 45 and K indices were as
high as 6, indicating a geomagnetic storm. Higher latitudes were
even more affected, and Alaska's College A index reach 58. This made
higher latitude HF communications more difficult. Moderate
geomagnetic conditions are predicted for the next few days, but
Monday could be unsettled.

January has passed, so let's look at the average daily solar flux
and sunspot numbers for the month to spot any trends.

Average daily sunspot numbers for August 2002 through January 2003
were 191.0, 206.4, 153.9, 159.8, 144.8 and 150.0. Average daily
solar flux for those same months was 183.9, 175.8, 167.0, 168.7,
157.2 and 144.0. This shows a downward trend. For the next 45 days
the predicted average daily solar flux is 140.3. For the same 45
days last year the actual daily solar flux averaged 188.8, so going
into the spring, MUFs (Maximum Usable Frequencies) should be lower
and general HF conditions a bit poorer. But during the same period
in 2001 the average daily solar flux was 147.3, only seven points
higher than the values predicted for the next month and a half. If
predicted values hold up (keeping in mind that forecasting out 45
days is chancy) conditions going into spring at least may not be
worse than 2001.

Pick a date a few weeks from now (in the middle of the 45 day period
mentioned above) and plug it into a popular propagation prediction
program. Then compare the 140.3 value for this year with 188.8 for
last year. This may give us some idea of how spring conditions might
be compared to last year. For instance, if I plot a path for March 1
from Texas to Brazil, 15 meters closes about four hours earlier in
2003 compared to 2002, and 10 meters closes about an hour and a half
earlier. I ran these numbers using W6ELprop, available free at

For more information about propagation and an explanation of the
numbers used in this bulletin, see the Propagation page on the ARRL
Web site at, and,
especially, the article "The Sun, the Earth, the Ionosphere," by
Carl Luetzelschwab, K9LA.

Sunspot numbers for January 30 through February 5 were 105, 96, 75,
61, 69, 77, and 89, with a mean of 81.7. 10.7 cm flux was 121.2,
120.4, 125.8, 126.7, 132.5, 134.8, and 140.1, with a mean of 128.8.
Estimated planetary A indices were 26, 18, 13, 45, 19, 24, and 12,
with a mean of 22.4.


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