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ARRL Propagation Bulletin ARLP052 (2003)

ARLP052 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 52  ARLP052
From Tad Cook, K7RA
Seattle, WA  December 19, 2003
To all radio amateurs 

ARLP052 Propagation de K7RA

What could be better than a rising sunspot count and declining
geomagnetic activity?  If it were a couple of years ago, we could
enjoy more sunspots.  But for this part of the solar cycle, HF
conditions are good, having improved over the past few days.

During this week in 1999, average daily sunspot number was around
132, in 2000 it was 186 and it was 200 in 2001.  Average planetary A
index for all those weeks was less than 10.  This week's sunspot
numbers have risen (42, 71, 92 and 114 for December 15-18).  At the
same time over the same four days, planetary A index has dropped
(25, 11, 10, 8) as well as the mid-latitude A index (18, 9, 4, 2).
Often we don't get this combination.  When the sun cooperates and
shows expanding sunspots, raising the MUF, we often get space
weather that disturbs the earth's geomagnetic field and the
ionosphere, raising absorption of HF signals and causing havoc with
propagation.  Now with the modest rise in sunspots we have declining
geomagnetic indices, a welcome combination.

Over the next few days conditions are likely to change.  By Sunday,
December 21, earth should meet a solar wind generated by a coronal
hole.  Predicted planetary A index for this weekend is between 15
and 20, but it should quiet down in the following days.  Solar flux
for this weekend is predicted around 135, and flux values should
rise to a peak around 140 by December 22-23.  Solar flux may drop
below 100 by the New Year.

If geomagnetic indices go low after the weekend and sunspots
increase, we should see improved HF conditions, although for the
northern hemisphere Monday will have the least sunlight of any day
of the year.  This means slightly lower average MUF values than were
seen a few weeks earlier, if all other factors were equal.  A
forecast from the Prague Geophysical Institute shows December 24-25
as the quietest geomagnetic days over the next week.

Andy Cohan, AB0YT is a student in Physics and Astronomy at the
University of Iowa and president of the UI Radio Club, W0IO.  His
friend is doing a research project in which she needs geomagnetic K
index data for the past five years.  I pointed him toward which has data
going back to 1868.  Plots of planetary K index values going back
several years are at

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

Sunspot numbers for December 11 through 17 were 35, 36, 40, 48, 42,
71 and 92 with a mean of 52. 10.7 cm flux was 86.1, 87.2, 87.8,
92.4, 100.8, 106.3 and 117.5, with a mean of 96.9. Estimated
planetary A indices were 40, 23, 28, 24, 25, 11 and 10, with a mean
of 23.


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