ARRL

ARRL Propagation Bulletin ARLP005 (2003)

SB PROP @ ARL $ARLP005
ARLP005 Propagation de K7VVV

ZCZC AP05
QST de W1AW  
Propagation Forecast Bulletin 5  ARLP005
From Tad Cook, K7VVV
Seattle, WA  January 31, 2003
To all radio amateurs 

SB PROP ARL ARLP005
ARLP005 Propagation de K7VVV

Again this week the solar numbers were lower, with average daily
solar flux down over 9 points and average daily sunspot numbers down
over 25. Solar flux has probably reached a minimum for the short
term at about 125, and should slowly rise over the next ten days.
There aren't any large clusters of sunspots visible, but a
holographic image of the sun's far side shows a complex of spots
which will eventually rotate into view.

Over the past week the quietest geomagnetic day was January 27 when
K and A indices at all latitudes were quiet low. Other than the
27th, conditions have generally been unsettled to active, indicating
higher absorption on higher latitude paths. The latest prediction is
for unsettled to active conditions on Friday, with a planetary A
index around 20, then a drop back to quieter conditions on Saturday,
followed by active geomagnetic conditions on Sunday and Monday.

With lower solar flux and sunspot numbers, 10-meters will probably
not be back as strong this year as daylight lengthens into spring.
A year ago the average daily solar flux for the week was over 122
points higher than it was this week (you can see the data in old
bulletins at http://www.arrl.org/w1aw/prop/ ).

If you do a projection with a popular propagation path prediction
program from California to Japan on 10-meters using numbers from a
year ago, it shows a probable opening from 2200-0230z. But plug in
this week's numbers, and the opening shortens by half, from
2230-0030z. As the sunspot numbers and solar flux (they're loosely
related) decline, the MUF or Maximum Usable Frequency declines, and
the great openings on the higher bands become scarce.

Dan Maguire, AC6LA wrote this week to talk about some new software
he wrote that combines antenna modeling with propagation
predictions. Called MultiNEC 2.0, you can read all about it at
http://www.qsl.net/ac6la/multiprop.html . A summary of his other
software is at http://www.qsl.net/ac6la/ .

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, http://www.arrl.org/tis/info/propagation.html and,
especially, the article "The Sun, the Earth, the Ionosphere," by
Carl Luetzelschwab, K9LA.

Sunspot numbers for January 23 through 29 were 123, 129, 103, 133,
134, 133, and 173, with a mean of 132.6. 10.7 cm flux was 135.9,
129.8, 128.9, 125, 121.3, 125.6, and 124.4, with a mean of 127.3.
Estimated planetary A indices were 19, 15, 28, 17, 8, 12, and 14,
with a mean of 16.1.
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/EX