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ARRL Propagation Bulletin ARLP015 (1999)

ARLP015 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7VVV
Seattle, WA  April 9, 1999
To all radio amateurs 

ARLP015 Propagation de K7VVV

Solar activity perked up a little bit this week, with average solar
flux rising almost 15 points to 118.9 and average sunspot numbers up
over 40 points to 89.6.  The reporting week (which runs from
Thursday through Wednesday) began with unsettled geomagnetic
conditions, and a planetary A index of 14.  One year ago the average
sunspot numbers were 89.4, about what they were this week, and
average solar flux was 121.8, 10 points higher than this week.

K6UJ wrote to ask about A and K indices and what they mean.  This is
a frequently asked question.  The K index is updated every three
hours, and you can hear the latest number on WWV at 18 minutes after
the hour, or hear it any time by telephone at 303-497-3235.  The K
index is a measure of geomagnetic instability, and the higher the
number, the greater is the absorption of radio signals, especially
over polar paths.  A one point change in K is a big change.  Every
day there is a new A index, and it is based on the K index for the
previous 24 hours.  A one point change in the K index results in a
large change in the A index.

If the K index is 0 for all eight reporting periods in a day, then
the A index is 0.  If the K is 1, the A is 3, if it is 2, the A is
7, if K is 3, the A is 15, if K is 4, the A is 27, if K is 5, the A
is 48, if K is 6, the A is 80, if K is 7, the A is 180, if K is 8,
the A is 240, and if the K is 9 for 24 hours then the A is 400.  Of
course, it is rare for the K index to be the same value for all
eight 3-hour periods in a day, and so the A comes out to be
something between the numbers given above.  For instance, on April 1
when the planetary A index was 14, this was the result of K readings
of 5, 5, 2, 2, 2, 2, 1 and 1.

Among other mail this week was a humorous letter from N6TP showing a
correlation between the solar flux and his employer's stock price.
He showed this to his fellow telephone company employees on April 1.

Several letters also arrived remarking on the disappointing sunspot
and solar flux numbers, which many feel should be higher given that
we are one year away from the predicted peak of cycle 23.  W2LO
noted that he has been watching the numbers since cycle 19 in the
1950s, and he feels something is wrong.  W8GF sent similar
sentiments, and wondered if this cycle peaked last December.  KH6BZF
was asked for comments, and noted that after a cycle peak there are
many solar flares, and this has not happened yet.  He also said he
feels that this cycle has not hit the high solar phase yet.

For this weekend, look for a solar flux of 140, 139 and 135 for
Friday through Sunday, with a planetary A index of 10, 10 and 8 for
those same days.  Beyond the weekend look for the solar flux to drop
below 130 after April 15, below 120 a few days later, bottoming out
below 115 from April 23-25.  It should rise above 120 after April
29, and to 130 by May 4.  Look for active geomagnetic conditions
around April 25, continuing with unsettled conditions through May 1.

Sunspot Numbers for April 1 through 7 were 59, 50, 77, 90, 111, 119
and 121 with a mean of 89.6.  10.7 cm flux was 103, 99.5, 102.7,
115.9, 132.6, 137.4 and 141.4, with a mean of 118.9, and estimated
planetary A indices were 14, 10, 8, 13, 11, 9 and 9, with a mean of

The path projection for this week is from Southern California:

To Western Europe, 80 meters 0230-0600z, 40 meters 0130-0700z, 30
meters 0000-0830z, 20 meters 1300-0130z and 0630-0730z, 17 meters
1400-2300z, 15 meters 1530-2200z, and possibly 12 meters 1830-2100z.

To Eastern Europe, 80 meters around 0300z, 40 meters 0200-0400z, 30
meters 0130- 0630z, 20 meters 1300-1600z, 17 meters 1500-2000z, 15
meters 1700-1900z.

To Southern Africa, 80 meters 0200-0430z, 40 meters 0130-0500z, 30
meters 0030-0530z, 20 meters 2230-0700z, 17 meters 2000-0200z, 15
meters 1500-0130z, 12 meters 1430-0030z, 10 meters 1800-2230z.

To the Caribbean, 80 meters 0130-1100z, 40 meters 0000-1200z, 30
meters 2230-1300z, 20 meters 1200-0600z, 17 meters 1300-0500z, 15
meters 1330-0330z, 12 meters 1500-0100z, 10 meters 1700-2200z.

To South America, 80 meters 0130-1030z, 40 meters 0100-1100z, 30
meters 0000-1200z, 20 meters 2200-1400z, 17 meters 1300-0730z, 15
meters 1330-0630z, 12 meters 1430-0530z, 10 meters 1530-0300z.

To Hawaii, 80 meters 0400-1430z, 40 meters 0300-1530z, 30 meters
open all hours, strongest 0500-1300z, weakest 2000-2230z, 20 meters
1500-0900z, 17 meters 1630- 0700z, 15 meters 1730-0500z, 12 meters
1900-0100z, 10 meters possibly 1900-0030z.

To South Pacific, 80 meters 0500-1400z, 40 meters 0430-1500z, 30
meters 0330-1600z, 20 meters open all hours, strongest 0500-1000z,
weakest 2030-2300z, 17 meters 1700-0800z, 15 meters 1730-0700z, 12
meters 1800-0600z, 10 meters 1800-0230z.

To Australia, 80 meters 0730-1330z, 40 meters 0700-1430z, 30 meters
0600-1530z, 20 meters 0400-1700z, 17 meters 0230-0900z, 15 meters
2000-0830z, 12 meters 2100-0700z, 10 meters 2130-0500z.

To Japan, 80 meters 0900-1400z, 40 meters 0800-1430z, 30 meters
0630-1600z, 20 meters 1900- 2030z and 0230-0930z, 17 meters
1930-0830z, 15 meters 2000-0700z, 12 meters 2100- 0400z, 10 meters

To Central Asia, 40 meters around 1330z, 30 meters 1230-1430z, 20
meters 1300-1700z and 0000-0300z, 17 meters 1430-1900z, 15 meters
0100-0530z and 1630-1800z, 12 meters and 10 meters around 0200z.


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