ARRL

ARRL Propagation Bulletin ARLP032 (2003)

SB PROP @ ARL $ARLP032
ARLP032 Propagation de K7RA

ZCZC AP32
QST de W1AW  
Propagation Forecast Bulletin 32  ARLP032
From Tad Cook, K7RA
Seattle, WA  August 8, 2003
To all radio amateurs 

SB PROP ARL ARLP032
ARLP032 Propagation de K7RA

Average daily sunspot numbers and solar flux were up this week
compared to last. Geomagnetic indices remained about the same. The
quietest day was Tuesday, August 5, when the planetary A index was
9, the high latitude College A index was only 3, and the College K
index actually was 0 over two of the three-hour reporting periods
and one during four of the periods.

Tuesday was followed by the most active geomagnetic day, Wednesday,
August 6, when the planetary A index was 43 and the planetary K
index rose as high as 7. Normally the high latitude geomagnetic
indices are higher than the numbers at lower latitude. The planetary
A and K index are derived from observatories worldwide, and reflect
both high and mid latitude measurements. But on August 6, the high
latitude College A index (from the University of Alaska at
Fairbanks) was 37, actually lower than the planetary A index of 43
and about the same as the mid-latitude A index of 34.

A day with numbers closer to the norm for a stormy space weather day
on earth was Friday, August 1, when the mid-latitude A index was 28,
the planetary A index was 37 and the high latitude College A index
was 74. Because quiet geomagnetic conditions indicated by low
geomagnetic indices seem to correlate with better high frequency
propagation, one will often hear Alaskan radio amateurs complain
during extended periods of high geomagnetic activity that they just
can't work or hear anything. You can see the mid and high latitude
and planetary A and K indices for the past four weeks at
http://www.sec.noaa.gov/ftpdir/indices/DGD.txt .

Scott Cameron, KA1MUY lives in Maine and wrote to report increased
noise to the north during periods of high geomagnetic activity. He
notices a big difference if the A index is high, when he can point
his beam to the north and see a big jump in noise to over S9 on his
S-meter. He is fairly far north in Maine, at 43.89 degrees north
latitude, although not as far north as this author at 47.67 degrees.

Although folks on the east coast may think of Maine as the far
north, Seattle is actually about 260 miles closer to the North Pole
than Scott is in Pemaquid. The furthest north point in Maine is
47.4596 degrees north, which turns out to be about 14 miles south of
this author's location in Seattle, in terms of latitude. This brings
to mind some words from the late Jack Bock, K7ZR when writing in the
"Totem Tabloid," the newsletter of the Western Washington DX Club.
He often referred to locals as "Suffering Sevens," probably
expressing envy for our brethren in a lower latitude location such
as the 5th call area.

So what does the forecast show for the next few days? This weekend
is the Worked All Europe DX CW Contest, but the predicted planetary
A index for August 8 is 40 and 25 for August 9. This could be a
problem for amateurs in the author's area, because the path to
Europe is polar. The predicted solar flux for Friday through Monday,
August 8-11 is 130. The expected geomagnetic activity would be
caused when the earth moves into a solar wind from one of the sun's
coronal holes. The last good hope for the weekend is that the
interplanetary magnetic field is pointing north, and the earth seems
more affected when it turns south, as it did on Friday, August 1. A
good review of the interplanetary magnetic field is on the
Spaceweather web site at http://spaceweather.com/glossary/imf.html .

Don't miss the Perseids meteor shower, which peaks on August 12-13.
And be certain not to miss gazing up into the sky this month to
marvel at a brighter and closer Mars. On August 27 at 0915z, Mars
will be nearer to earth than at any time in the past 59,620 years.
The last time it was this close was around September 12 in 57,617
BC, when it was 34.62 million miles from earth. This time we'll have
to settle for Mars being 34.65 million miles away, nearly as close,
and in a light polluted environment that our distant Neanderthal
ancestors never dealt with.

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 http://www.arrl.org/tis/info/propagation.html .

Sunspot numbers for July 31 through August 6 were 65, 85, 95, 144,
138, 136, and 155, with a mean of 116.9. 10.7 cm flux was 102.1,
107.3, 111.4, 120, 122.5, 130.6, and 128.7, with a mean of 117.5.
Estimated planetary A indices were 32, 37, 21, 15, 14, 9, and 43,
with a mean of 24.4.
NNNN
/EX