QST de W1AW
Propagation Forecast Bulletin 16 ARLP016
>From Tad Cook, K7VVV
Seattle, WA April 19, 2002
To all radio amateurs
SB PROP ARL ARLP016
ARLP016 Propagation de K7VVV
Average daily sunspot number was up slightly and the average solar
flux was down a couple of points this week, but the big news was the
high geomagnetic activity. On Wednesday the planetary A index was
41, and K indices over several reporting periods were 6, which is
very high. The high latitude College A index was 73 and the College
K index reached 7.
On April 15 at 0400z a full halo coronal mass ejection blasted away
from the sun. At 1100z on April 17 energy from that coronal mass
ejection struck earth's magnetosphere, triggering a geomagnetic
storm. Several hours earlier another coronal mass ejection left the
sun, and effects from it may be felt on Friday or Saturday.
On Thursday the prediction from the U.S. Air Force was for a
planetary A index of 40 on Friday, 50 on Saturday, and 20 on Sunday.
It also shows solar flux bottoming-out for the short term around 170
on Sunday or Monday, then rising above 200 after April 29.
With a predicted geomagnetic storm this weekend expect particularly
bad propagation over polar paths, conditions worsening for higher
latitudes, and some transequatorial propagation, but only because
that may be the only HF propagation available. Sometimes it is
assumed that transequatorial propagation (signals crossing the
equator) is enhanced during geomagnetic storms, but actually these
signals at times are the only audible ones.
There was more 6-meter news, this time from W4NTI. From East Central
Alabama (EM73) he worked Chile and Argentina last Friday evening
from 0019 to 0052z. This was with only a three-element Yagi at 30
Last week's bulletin presented a problem for users of WA4TTK's solar
data plotting utility. This program grabs the data in the paragraph
below and adds it to a database for charting. Unfortunately if you
look at the second sentence in the first paragraph of last week's
bulletin, it contains a string of words identical to one found at
the end of every bulletin. I can't spell it out here, or I would
cause the same problem all over again. You can get the plotting
utility to ignore that error if you take out that line. Or you can
use the ftp function in the program to download the data from ARRL.
Sunspot numbers for April 11 through 17 were 235, 263, 257, 236,
243, 172 and 137 with a mean of 220.4. 10.7 cm flux was 197.4,
211.9, 226, 210.3, 203.3, 195.7 and 193.5, with a mean of 205.4, and
estimated planetary A indices were 13, 13, 14, 13, 7, 10 and 41 with
a mean of 15.9.
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