ARRL

ARRL Propagation Bulletin ARLP015 (2003)

SB PROP @ ARL $ARLP015
ARLP015 Propagation de K7RA

ZCZC AP15
QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 11, 2003
To all radio amateurs 

SB PROP ARL ARLP015
ARLP015 Propagation de K7RA

Sunspots and solar flux values dropped this week after a rise the
week prior. Average daily sunspot numbers were down nearly 72
points, while average daily solar flux values were down nearly 21
points. Solar flux is expected to decline, dropping below 100 by
Sunday, April 13. It should reach a minimum around 85 from April
16-17.

A solar flux value of 85 is about equivalent to a nominal sunspot
number of 28.7. Solar flux at 70 or below is generally what you see
when the sunspot count is 0. For instance, for over a month from
September 13 to October 20, 1996 the sunspot number was 0 every day.
Solar flux during this period ranged from 66.4 to 70. On Monday of
this week helioseismic holography revealed a large sunspot group
forming on the sun's far side.

This was another week with active geomagnetic conditions, although
the planetary A index never went above 26. April 8 brought a brief
G1 level geomagnetic storm caused by solar wind. On April 10 earth
is entering another solar wind stream. The predicted planetary A
index value for Friday is 20, followed by 15 for every day through
April 19.

Pat, W5OZI in Texas wrote last week to say he'd been hearing his own
backscatter echoes from the south on 6-meters. He was working ZP6CW
in Paraguay with the ZP6 beaming west. On April 4 Pat wrote,
"Yesterday, was the same, highlighted by a QSO with 5W1SA in Western
Samoa at 2202z followed an hour later with a quick QSO with ZL3TY."

Spaceweather.com is showing a neat drawing of twenty days of a
sunspot group's progression across the solar disk, from March 12
through March 31. See it at
http://spaceweather.com/swpod2003/10apr03/blom.jpg.

This web site is produced by Dr. Tony Williams, who has a new
service out called Space Weather Phone. This service provides verbal
alerts of space weather events, and you can set alert levels and
times of day when it will call you concerning geomagnetic storms and
aurora warnings.  You can learn about it at
http://www.spaceweatherphone.com.

Here are some web sites we haven't mentioned in awhile. Check
http://www.sec.noaa.gov/solar_images/index.html for an archive of
solar images. For daily space weather, check
http://www.sec.noaa.gov/SWN/ and http://spaceweather.com. For daily
space weather alerts, check
http://www.sec.noaa.gov/alerts/solar_indices.html.

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 http://www.arrl.org/tis/info/propagation.html.

Sunspot numbers for April 3 through 9 were 154, 148, 94, 75, 77, 52,
and 88, with a mean of 98.3. 10.7 cm flux was 155.7, 165.5, 137.4,
125.9, 115.6, 112.3, and 109.4, with a mean of 131.7. Estimated
planetary A indices were 14, 26, 23, 9, 6, 20, and 25, with a mean
of 17.6.
NNNN
/EX