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ARRL Propagation Bulletin ARLP053 (2003)

ARLP053 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 53  ARLP053
From Tad Cook, K7RA
Seattle, WA  December 24, 2003
To all radio amateurs 

ARLP053 Propagation de K7RA

Because of the holiday this week, the propagation bulletin won't be
transmitted from W1AW on Friday, December 26. This is an interim
bulletin for Wednesday. Look for another one Monday morning,
December 29, which will contain the seven days of Thursday through
Wednesday sunspot, solar flux and planetary A index numbers normally
sent on Friday.

Solar flux and sunspot numbers have been rising after a short-term
minimum around December 9-12. Last Friday's bulletin reported
sunspot numbers for December 11-17 of 35, 36, 40, 48, 42, 71 and 92,
and the rising trend continued, with values of 114, 113, 104, 105,
152 and 142 for December 18-23. From a low flux value on December
11, daily solar flux through December 23 was 86, 87, 88, 92, 101,
106, 118, 123, 123, 130, 133, 138 and 142.

December 21 and 22 had the only geomagnetic disturbance of this
week. This was from a solar wind originating in a coronal hole that
earth passed through beginning December 21. The solar wind did not
cause big aurora displays. At this time of the year, geomagnetic
disturbances are less common than they are in fall or spring. This
is due at least in part to a seasonal variation in the earthly
magnetosphere as it relates to the sun's field. See an explanation
including the geometry of this seasonal variation in a NASA article
from three months ago at,

Solar flux is expected to peak over the next couple of days.
Predicted solar flux for today through December 28 is 145, 150, 150,
145 and 140. More sunspots and higher solar flux combined with a
quiet geomagnetic field are a great combination for HF propagation,
and we shouldn't be disappointed over the next week. The predicted
planetary A index is around 10 for every day until January 1, when
recurring activity is expected to disturb conditions until January

Now that the nights are long, 160, 80, 60 and 40 meters should
provide good propagation between sunset and sunrise. Compared to 11
weeks ago, for example, openings should come a bit earlier and the
low bands should close much later for paths throughout the northern

Bob Reed, W2CE wrote to say that these propagation bulletins, NW7US
Solar E-alerts and DX bulletins are posted automatically on the Ham
Radio DX List, an email listserver. Subscribe 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


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