ARRL

ARRL Propagation Bulletin ARLP029 (2002)

SB PROP @ ARL $ARLP029
ARLP029 Propagation de K7VVV

ZCZC AP29
QST de W1AW  
Propagation Forecast Bulletin 29  ARLP029
From Tad Cook, K7VVV
Seattle, WA  July 12, 2002
To all radio amateurs 

SB PROP ARL ARLP029
ARLP029 Propagation de K7VVV

Conditions are still a bit in the doldrums, with solar flux and
sunspot numbers fairly flat. This week average daily sunspot numbers
were up over 24 points and average daily solar flux was down nearly
12 points, when compared to the previous week. Of course this seems
low compared to the great conditions last fall, but the numbers are
slightly higher than they were for the same week last year.

In the July 13 Propagation Forecast Bulletin last year covering July
5-11, 2001, average sunspot numbers were only 98.1 and average solar
flux was 124.6. One thing that skewed the numbers a bit this time
was on the last day of last week's reporting period the solar flux
jumped unusually high, and the next day, which was the first day of
the current reporting period (July 5), it was now the sunspot number
that was high.

The current outlook is for a slowly rising solar flux of 135 for
July 12-13, 140 for July 14-15, and 145 for July 16-17. There isn't
any forecast for higher numbers above this narrow range for the near
future. The prediction for the planetary A index for Friday through
Monday is 8, 15, 10 and 8. There is a new large sunspot coming
around the sun's northeast limb, and another large spot on the sun's
far side, as detected by helioseismic holography imaging. It has
been a while since this imaging scheme was mentioned in this
bulletin, and you can read more about it at
http://spaceweather.com/glossary/farside.html.

A good source for an explanation of shortwave propagation and some
of the numbers used in this bulletin (by K9LA) is at
http://www.arrl.org/tis/info/k9la-prop.html. This is part of the
ARRL Technical Service propagation page at
http://www.arrl.org/tis/info/propagation.html.

This week our earth has reached its aphelion, the farthest distance
from the sun in its annual orbit. Earth's orbit has an eccentricity
of 1.7 percent, and this week we are nearly 95 million miles from
our closest star. When we are at the closest point, or perihelion,
we are almost 92 million miles from the sun. There was an article on
http://www.cnn.com saying that the aphelion will be this Saturday,
but according to the U.S. Naval Observatory at
http://aa.usno.navy.mil/data/docs/EarthSeasons.html it was on July
6. The perihelion for 2002 was January 2, and in 2003 and 2004 it
will be January 4.

In this bulletin we report the observed solar flux from the Dominion
Radio Astrophysical Observatory in Penticton, British Columbia,
about 160 miles east of Vancouver. They have a nice web site at
http://www.drao.nrc.ca.

Energy is measured at 2.8 GHz with a parabolic dish pointed at the
sky. Of course this value would vary somewhat with the distance from
the observation point to the sun. So to account for this difference
and give a measurement that might be more indicative of the level of
energy from the sun at that frequency, there is an adjusted value of
solar flux. On July 6 at the aphelion the observed solar flux at
2000z was 133.5, but the adjusted flux value was 138. At the
perihelion the observed 2000z flux was 231.1, but the adjusted value
was adjusted down to 223.5. April 2 or 3 must be about half way in
between, and the observed and adjusted values on those days are
quite close. You can see a very large table of the solar flux values
measured thrice daily at
http://www.drao.nrc.ca/icarus/www/current.txt.

Sunspot numbers for July 4 through 10 were 175, 149, 123, 121, 125,
129 and 118, with a mean of 134.3. 10.7 cm flux was 146.3, 138.8,
133.5, 136.9, 130.9, 136.3, and 128.8, with a mean of 135.9.
Estimated planetary A indices were 7, 13, 23, 11, 10, 16, and 11,
with a mean of 13.
NNNN
/EX