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ARRL Propagation Bulletin ARLP041 (2003)

ARLP041 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 41  ARLP041
From Tad Cook, K7RA
Seattle, WA  October 10, 2003
To all radio amateurs 

ARLP041 Propagation de K7RA

In last week's bulletin we looked at the weekly averages for daily
solar flux and sunspot numbers and reported that both had risen,
from 92 to 125 for sunspots and 119 to 133.6 for solar flux.  This
week it has dropped lower than it was two weeks ago.  Average daily
sunspot number was 86.7 and average daily solar flux was 115.8.  But
this week represents the second week in a row that geomagnetic
indices have dropped, indicating a quiet and stable earth
environment for HF radio propagation.

Currently we are within a solar wind stream, but a north-pointing
interplanetary magnetic field keeps geomagnetic activity to a
minimum.  Current projections from the U.S. Air Force show stable
geomagnetic conditions over the next few days, with planetary A
index around 10 from October 10-12.  Following this weekend on
Monday, it shows planetary A index rising to 30 for October 13-14.
The forecast from Frantisek Janda, OK1HH, shows quiet geomagnetic
conditions on October 10, quiet to unsettled conditions on October
11-12, unsettled to active on October 13, and unsettled again on
October 14 and 15.  Predicted solar flux from the Air Force is 105
for October 10-11, 100 for October 12, and 95 for October 13-14.
Following this is a rise in solar flux, passing 110 around October
16, 120 on October 18, 130 on October 21, and 135 on October 25-26.
These are rough estimates based upon the last solar rotation.

There is a 10-meter sprint contest starting today, October 10.  You
can find details at  As we move
toward winter, 10 meters will be less useful.  If you use a
propagation prediction program, such as W6ELprop, compare projected
ten-meter conditions this weekend with projected ten-meter
connections for September 23.  You can see that 10 meters is already
closing a little earlier than at the equinox.  To test the seasonal
propagation variation further, try running the same tests for the
weekend of the ARRL 10 Meter contest, which is December 13-14.  You
can download the W6ELprop software free from

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  Write to
the author at

Sunspot numbers for October 2 through 8 were 75, 104, 89, 101, 93,
76 and 69, with a mean of 86.7. 10.7 cm flux was 124.8, 120.1, 119,
109.6, 112.1, 111.9 and 113.3, with a mean of 115.8. Estimated
planetary A indices were 9, 16, 9, 9, 10, 13 and 9, with a mean of


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