Register Account

Login Help

ARRL Propagation Bulletin ARLP033 (2004)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 13, 2004
To all radio amateurs 

ARLP033 Propagation de K7RA

Big sunspot 649 rotated back into view this week, and sunspot and
solar flux numbers are up.  The average daily sunspot number for
this week (August 5-11) rose over 35 points (from the previous week)
to 77.9, and average daily solar flux was up over 18 points to
106.5.  There were no large geomagnetic events, only some periods of
unsettled to active conditions.

Sunspot 649 is currently in the center of the visible solar disk,
pointed straight toward earth.  It is a possible source of solar
flares over the next few days.  Solar flux is expected to rise over
the weekend, peaking below 170 from August 15-17.  The Prague
Geophysical Institute predicts unsettled geomagnetic conditions for
August 13, unsettled to active conditions for August 14, and quiet
to unsettled conditions for August 15-16.

A solar cycle prediction released from NOAA SESC this week still
shows the current cycle bottoming out around the end of 2006 and the
start of 2007.  It shows the lowest sunspot numbers from December
2006 to January 2007, and the lowest solar flux values from
September 2006 through April 2007.

For the start of the next cycle, the prediction goes out as far as
December 2007 with a predicted smoothed sunspot number of 21, which
is around the same value predicted for January-February 2005.  So
with the cycle declining, their guess is that sunspot activity
shouldn't return to the level of early 2005 until the end of 2007.

This suggests that activity won't return to our current levels until
some time in 2008, although it is important to remember that
activity in the rising part of the cycle increases more rapidly than
it declines on the down side of the cycle.

Thomas Giella, KN4LF, wrote to announce a new email listserver for
propagation discussions hosted by  You
can sign up on the web at,, or
subscribe by sending an email with the word "subscribe" in the
message body or subject line to,

Reader David Moore sent the following URL,, which links to
an article about research into the injection of solar wind plasma
into the earth's magnetic field.

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service propagation page at,

Sunspot numbers for August 5 through 11 were 36, 52, 71, 77, 101, 93
and 115 with a mean of 77.9.  10.7 cm flux was 88.9, 91, 94.6,
104.8, 113.9, 121.4 and 130.8, with a mean of 106.5.  Estimated
planetary A indices were 7, 7, 20, 5, 13, 14 and 13, with a mean of
11.3.  Estimated mid-latitude A indices were 5, 3, 11, 2, 12, 12 and
10, with a mean of 7.9.


Instragram     Facebook     Twitter     YouTube     LinkedIn