QST de W1AW
Propagation Forecast Bulletin 31 ARLP031
>From Tad Cook, K7RA
Seattle, WA August 1, 2003
To all radio amateurs
SB PROP ARL ARLP031
ARLP031 Propagation de K7RA
Strong geomagnetic activity continues. The estimated Planetary A
Index is a number derived from observations at geomagnetic
observatories around the world. The higher the A index, the higher
the geomagnetic activity, and generally this is worse for HF
We like to see low geomagnetic activity with lots of sunspots for
great HF propagation. Unfortunately, after the peak of a solar cycle
we can experience long periods of active geomagnetic conditions.
This week the average daily planetary A index jumped to 21.9 from
16.1 the previous week.
Sunspots and solar flux were down quite a bit from the previous
week. Average daily sunspot numbers dropped from 195.3 to 74.6, and
average daily solar flux went from 147.7 to 106.2.
Daily solar flux values are expected to stay around 105-115 from
August 1-8, and then rise to around 140 from August 12-18. The
planetary A index for Friday through Monday, August 1-4 is expected
to be 25, 20, 15 and 10. August 4-6 is expected to be a quiet
geomagnetic period, worth a try for reasonable HF propagation.
Now that July has passed, we can look at some monthly averages for
solar flux and sunspot numbers.
Due to some high values around the middle of the month, July
actually had higher average daily sunspot numbers than any month
since January. The monthly average sunspot numbers, January through
July, were 150, 87.9, 119.7, 114.3, 89.6, 118.4 and 132.8.
July's average daily solar flux was just a little lower than the
June values. Average daily solar flux values for January through
July were 144, 124.5, 133.5, 126.8, 116.6, 129.4 and 127.7.
The fall equinox is a little over seven weeks away. HF conditions
should improve as the days grow shorter and we move from summer to
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 www.arrl.org/tis/info/propagation.html.
Sunspot numbers for July 24 through 30 were 134, 94, 52, 60, 56, 63,
and 63, with a mean of 74.6. 10.7 cm flux was 125.2, 111.6, 102.6,
101.7, 103.4, 99.9, and 98.7, with a mean of 106.2. Estimated
planetary A indices were 10, 11, 26, 24, 17, 36, and 29, with a mean
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