ARRL

ARRL Propagation Bulletin ARLP012 (2001)

SB PROP @ ARL $ARLP012
ARLP012 Propagation de K7VVV

ZCZC AP12
QST de W1AW  
Propagation Forecast Bulletin 12  ARLP012
From Tad Cook, K7VVV
Seattle, WA  March 23, 2001
To all radio amateurs 

SB PROP ARL ARLP012
ARLP012 Propagation de K7VVV

Last week's bulletin mentioned the possibility of solar flares from
sunspot group 9373. This week we've seen a resulting major
geomagnetic storm, which began on Monday. The disturbance reached a
peak on Tuesday, with a planetary A index of 66 and planetary K
indices of 5, 6 and 7. The high latitude college A index was 105,
and the K index reached 8 at that station, which is in Fairbanks,
Alaska.

The energy released produced dramatic auroral displays. Check out
the images at http://spaceweather.com/aurora/gallery_20mar01.html .
My favorite is the one taken at Banff, Alberta shown at
http://www.bowfort.com/~webcam/archive/aurora5/Mar21_00:21-1_large.jpg .
It's my favorite not because of the dramatic display in the sky, but
the way the light plays on the ground.

Prior to the storm, 10 meter fans were enjoying good conditions.
With the equinox this week, springtime HF conditions should be at a
peak, when the southern and northern hemispheres each get an equal
amount of solar radiation. N7QHC in Seattle reported hearing both
sides of a QSO between a New Zealand and California station on 10
meters, with the distant station booming in. This was with a very
crude no-gain antenna on the Seattle end of the circuit.

Average solar flux this week was 144.2 which is slightly lower than
it was during this week in 1999, when it was 147.5. Last year at
this time it was 207.8. Sunspot number variations were also similar.
This week the average sunspot number was 101.7, the same week last
year it was 183.3 and this week in 1999 it was 117.4. So we are
currently still enjoying the peak of cycle 23, but conditions are
more like they were at this time two years ago.

But what do the lower solar flux numbers mean, for example, for the
10 meter Seattle to New Zealand path mentioned above? Not a lot, it
turns out, although the higher activity means that the same path was
probably open longer at this time last year. When running a 10 meter
path projection over that path using W6EL's MiniProp program, for
the average solar flux this week it shows an estimate of signal
levels based upon 100 watts and a dipole at each end.

For this year, it shows the band opening around 2030z with signals
about 13 dB above noise, then rising slightly to around 14 dB above
noise around 0130z. After that, the probability of an opening fades,
and becomes unlikely after 0330z. For last year, the program shows
the opening beginning around 1900z at 13 dB above the noise, dipping
to 9 dB from 2200 to 2300z, then rising to 15 dB around 0300z, 17 dB
above noise at 0400z, and 20 dB at 0530z.

This weekend is the CQ Worldwide WPX Phone contest. Solar flux rose
sharply to 183 on Thursday, and the latest projection shows solar
flux around 180 for the next week. There may be unsettled
geomagnetic conditions this weekend. Current projections show the
planetary A index for Friday through Monday at 15, 10, 12 and 12.
Disturbances over the weekend would probably be due to a coronal
mass ejection that left the sun's western limb on Tuesday, but was
not aimed directly at earth.

Sunspot numbers for March 15 through 21 were 126, 86, 90, 91, 85, 98
and 136 with a mean of 101.7. 10.7 cm flux was 136.1, 139.9, 134.2,
139.8, 147, 153.3 and 159.4, with a mean of 144.2, and estimated
planetary A indices were 3, 2, 4, 7, 22, 66 and 19 with a mean of
17.6.
NNNN
/EX