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ARRL Propagation Bulletin ARLP027 (2003)

ARLP027 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 27  ARLP027
From Tad Cook, K7RA
Seattle, WA  July 3, 2003
To all radio amateurs 

ARLP027 Propagation de K7RA

Average daily solar flux and sunspot numbers rose slightly last
week, by 24.6 for sunspots and 11.3 for solar flux.  Geomagnetic
indices were about the same, with average A index for the week just
two points higher.

The second quarter of 2003 ended on Monday, so now let us examine
quarterly averages of daily sunspot and solar flux numbers to try to
confirm a trend.

The average of the daily sunspot numbers during April 1 through June
30, 2003 was 107.3.  The average for the previous eight quarters was
164.8, 170.4, 198.1, 178.3, 165.3, 193.5, 152.7 and 120.3.

The average daily solar flux for the same period was 124.2, and
averages for the previous eight quarters were 166.7, 175.5, 219.1,
203.9, 156.4, 178.1, 164.2 and 134.3

The drop from 193.5 to 152.7, 120.3 and 107.3 for sunspot averages
and 178.1 to 164.2, 134.3 and 124.2 for solar flux shows a definite
and continuing decline of cycle 23.  The monthly sunspot averages
for May through June were 114.3, 89.6 and 118.4, and the solar flux
averages for the same period were 126.8, 116.6 and 129.4, so for the
short term May was down but June activity was back up.

Looking at the daily A index over the past week, Saturday was the
most active day, which was the first day of ARRL Field Day.  I
operated Class C mobile on 20 and 15-meter phone and CW while parked
in a cemetery west of my home in Seattle.  Sunday seemed more
difficult to me, with the only stations worked during the last hour
of Field Day being Class D stations operating from home.  On both
days our earth was awash in a fast solar wind that has continued,
making HF conditions dicey.  Saturday saw the return of a large
sunspot, which is now almost squarely aimed at earth.  This sunspot,
number 375, released several powerful solar flares in early June.

Another solar wind stream is flowing from a coronal hole, and it
should reach earth Thursday or Friday, July 3 or 4.  Predicted
planetary A index for the next few days is 20 to 25.  Solar flux
values are expected to continue to rise, perhaps peaking around 160
to 170 from July 7-9.  A hopeful prediction shows a low planetary A
index of 10-12 around July 9-10.  We were fooled before when a low A
index of 8 was predicted, with the forecast value revised upward due
to changing conditions just prior to the expected date, so don't
count on low A index predictions too much.  I have no idea when the
generally active geomagnetic conditions will cease.

60 meters opened for use today for amateurs in the United States.
I'm eager to hear reports from that band, which you can send to

Some possibly confusing prose in ARLP025 concerning the relationship
between A and K indices and geomagnetic conditions resulted in
further confusion in ARLP026.  Each index relates to a basic measure
of geomagnetic disturbance called nT.  The A index is a linear scale
referenced to nT, and the K index is a semi-logarithmic scale
referenced to nT.  Thanks to N0AX and K9LA for helping to straighten
all this out.

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  You can
write to the author of this bulletin at

Sunspot numbers for June 26 through July 2 were 122, 128, 151, 112,
159, 138, and 153, with a mean of 137.6. 10.7 cm flux was 118.9,
123.9, 123.9, 127.3, 128.2, 131.1, and 134.8, with a mean of 126.9.
Estimated planetary A indices were 19, 28, 32, 26, 20, 13, and 15,
with a mean of 21.9.


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