ARRL

ARRL Propagation Bulletin ARLP038 (1999)

SB PROP @ ARL $ARLP038
ARLP038 Propagation de K7VVV

ZCZC AP38
QST de W1AW  
Propagation Forecast Bulletin 38  ARLP038
From Tad Cook, K7VVV
Seattle, WA  September 17, 1999
To all radio amateurs 

SB PROP ARL ARLP038
ARLP038 Propagation de K7VVV

Solar flux and sunspot numbers were up this week.  Average solar
flux rose about ten points and average sunspot numbers were up
almost 33 points when compared to the week previous.  Next week is
important because Thursday is the autumnal equinox, which is
generally a good time for HF propagation.  Solar flux is expected to
rise over the week, peaking around 220 on Thursday, when the hours
of darkness are equal in the southern and northern hemispheres.
After September 26 flux values should drop below 200, down to 140 by
the end of the month, and fall to a minimum around 105 on October 5.

For this weekend, look for the Friday through Sunday solar flux to
be 160, 165 and 170, and planetary A index to drop from 25 to 20 to
12.  The A index has been high this week, which has not been good
for HF conditions.  The worst day was Monday, when the A index
registered a very stormy 38.  The K index was consistently 4 and 5
throughout the day.  Wednesday and Thursday were also bad, with an A
index of 32 and planetary K index as high as 7.  On Thursday the
College A index in Alaska was 63.  Alaskan HF operators were
probably able to hear very little, although VHF fans outside of the
higher latitudes likely had fun.

All of these disruptions were caused by a series of solar flares and
coronal holes, throwing proton energy that disrupts the ionosphere
and bends the earth's magnetic field.  Geomagnetic conditions are
not expected to really settle down until after October 1, when the A
index should stay below 10.  Sunspot region 8674 is rotating into
view, and could produce more flares and coronal holes.

Sunspot numbers for September 9 through 15 were 113, 107, 145, 126,
183, 158 and 155 with a mean of 141.  10.7 cm flux was 106.5, 122,
122.5, 140.8, 154.6, 156.4 and 154.9, with a mean of 136.8, and
estimated planetary A indices were 8, 15, 10, 26, 38, 23 and 32,
with a mean of 21.7.

Here is a path projection for this weekend from the geographical
center of the contiguous 48 United States, somewhere in Kansas.

To Europe, 80 meters 0000-0730z (peaking 0300-0430z), 40 meters
2230-0830z (best 0130-0530z), 30 meters 2130-1000z (peaking
0100-0530z), 20 meters all hours, best 0100-0530z, 17 meters
1400-2330z, 15 meters 1300-2230z, 12 meters 1530- 2100z (best
1900-2000z), 10 meters 1600-2100z, strongest toward the end of the
day.

To Southern Africa, 80 meters 0000-0430z, 40 meters and 30 meters
2300-0500z, 20 meters 2130-0600z, 17 meters 2000-0300z, 15 meters
1700-0200z, 12 meters 1600-0100z, 10 meters 1430-0000z.

To South America, 80 meters 0030-1000z, 40 meters 2330-1030z, 30
meters 2300-1100z, 20 meters 2200-1200z, 17 meters 1200- 1430z and
1900-0430z, 15 meters 1230-0400z (strongest toward the end of the
period), 12 meters 1300-0230z, 10 meters 1400-0130z.

To the Caribbean, 80 meters 0000-1030z, 40 meters 2200-1230z, 30
meters open all hours, strongest 0100-0930z, weakest 1600- 1830z, 20
meters 1200-0430z, 17 meters 1300-0230z, 15 meters 1330-0100z, 12
meters 1600-2230z, 10 meters 1730-2030z.

To Australia, 80 meters 0900-1300z, 40 meters 0830-1400z, 30 meters
0800-1430z, 20 meters 0700-1530z, 17 meters 1330-1700z and
0500-0630z, 15 meters 1400-1700z and 0430-0530z, 12 meters around
0400z, 10 meters 0200-0300z.

To Japan, 80 meters 0830-1300z, 40 meters 0730-1330z, 30 meters
0700-1430z, 20 meters 1330-1630z and 0500-0600z, 17 meters
0200-0530z and 1430-1700z, 15 meters 2000-0430z, 12 meters
2030-0300z and 10 meters 2100-0200z.

To Hawaii, 80 meters 0400-1330z, 40 meters 0300-1430z, 30 meters
0200-1530z, 20 meters all hours, best 0500-1200z, weakest
1900-2200z, 17 meters 1530-0630z, 15 meters 1600-0530z, 12 meters
1630-0400z, 10 meters 1700-0300z.
NNNN
/EX