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ARRL Propagation Bulletin ARLP011 (2004)

ARLP011 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 11  ARLP011
From Tad Cook, K7RA
Seattle, WA  March 12, 2004
To all radio amateurs 

ARLP011 Propagation de K7RA

As expected, conditions weren't bad last weekend for the ARRL
International DX Phone Contest.  Solar flux and sunspot numbers
didn't rise, but geomagnetic indices stayed stable.  Average daily
sunspot numbers dropped from the week before (February 26 to March
3) by nearly 24 points, and average daily solar flux was about the
same, down by slightly more than two points.

On March 9, the earth passed into a solar wind, and geomagnetic
indices rose.  For March 9-11 the planetary A index was 21, 40 and
26, the mid-latitude Fredericksburg A index was 11, 36 and 17, and
the high latitude (Alaskan) College A index was 42, 47 and 61.

This meant that at mid latitudes HF bands were probably usable on
March 9 and 11 (but not on the 10th) but in Alaska, the bands
probably sounded dead.  This was no doubt the case for KB7MBI and
AL7FS over the past few days.  Alan Dujenski, KB7MBI near Seattle
and Jim Larsen, AL7FS in Anchorage have been comparing QRP logs and
are frustrated by the lousy propagation of late in Alaska.  Alan
wrote to ask about Alaskan propagation, and commented that his
friend Jim often hears nothing on HF frequencies.

This propagation, or lack of it, is normal for Alaska, at least when
geomagnetic conditions are active or stormy.  Those magnetic lines
of force converge toward the poles, and all that energy gets
concentrated, yielding polar cap absorption.  The convergence and
concentration was intense enough this week that aurora was visible
down into northern parts of the "lower 48" states.

Over the next few days geomagnetic conditions should settle down.
The predicted planetary A index for March 12-15 is 20, 15, 10 and 8.
Solar flux should drop down to around 100 by the beginning of the
week (Monday, March 15).  We are moving toward spring propagation
conditions, with the vernal equinox about a week from now.

Currently a large sunspot, number 570 is moving into the center of
the visible solar disk, directly facing the earth.  It is a possible
source of flares.  A holographic image of the sun's far side shows a
modest sunspot group, which may visit us before the end of the

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

Sunspot numbers for March 4 through 10 were 53, 55, 61, 53, 55, 40
and 56 with a mean of 53.3.  10.7 cm flux was 97.5, 106.7, 104.5,
106.1, 107.8, 108.7 and 112.6, with a mean of 106.3.  Estimated
planetary A indices were 7, 8, 5, 6, 6, 21 and 40, with a mean of


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