ZCZC AP11
QST de W1AW
Propagation Forecast Bulletin 11 ARLP011
From Tad Cook, K7RA
Seattle, WA March 12, 2004
To all radio amateurs
SB PROP ARL ARLP011
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 month.
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 http://www.arrl.org/tis/info/propagation.html.
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 13.3.