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ARRL Propagation Bulletin ARLP039 (2003)

ARLP039 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 39  ARLP039
From Tad Cook, K7RA
Seattle, WA  September 26, 2003
To all radio amateurs 

ARLP039 Propagation de K7RA

At last, the sun is showing one large sunspot.  Sunspot 464 is
expanding rapidly, now part of an extended dark area about 13 earth
diameters wide.  A helioseismic holography image shows a large
sunspot currently on the side of the sun that faces away from the
earth, often referred to as ''the other side''.  Mentioning the name
of this method for sensing activity on the sun's far side always
generates email asking, ''what's that?'' so check for more info.  Of
course, any email is always welcome via

The emergence of this spot has raised the sunspot count and solar
flux higher than predicted a week ago, with solar flux about 20
points greater.  Solar flux for the past few days has edged above
130, and the prediction for September 26-29, Friday through Monday
is for flux values of 135, 130, 130 and 125.  Frantisek K. Janda,
OK1HH, of the Czech Propagation Interest Group reports that except
for October 13-17, the upcoming weeks will have quieter geomagnetic
conditions than have prevailed over the past five months.

This is the weekend of the CQ WW RTTY DX Contest, and currently the
interplanetary magnetic field points south.  This means that earth
is susceptible to blasts of energy from the sun.  Currently a solar
wind is flowing from a coronal hole on the sun, so predicted
planetary A index for Friday through Monday, September 26-29 is 15,
30, 20 and 15.  Saturday might be a bit rough for the contest, but
hope for change.  The sunspot count this week turned out to be
higher than we thought last week, another example of things

The season changed from summer to fall in the Northern Hemisphere on
Tuesday, and from winter to spring in the Southern Hemisphere.
Around the equinox is a great time for worldwide DX, because all
parts of the earth are bathed equally in the sun's energy.  When it
is summer in one hemisphere, the maximum usable frequency (MUF) is
lower during the day, so 10 through 15 meters are affected.  At that
same time, the other half of the earth has winter, and the
ionosphere over that region is exposed to a lot less radiation from
the sun.  At the equinox, winter or spring, the MUF is higher and
the whole world is affected the same.

For more information on propagation and an explanation of the
numbers used in this bulletin see the Propagation page on the ARRL
Web site,

Sunspot numbers for September 18 through 24 were 92, 71, 72, 64, 91,
133 and 121, with a mean of 92. 10.7 cm flux was 109.2, 111.1,
111.9, 119.9, 122.6, 124.9 and 133.5, with a mean of 119. Estimated
planetary A indices were 40, 32, 25, 21, 18, 17 and 33, with a mean
of 26.6.


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