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ARRL Propagation Bulletin ARLP037 (2002)

ARLP037 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7VVV
Seattle, WA  September 6, 2002
To all radio amateurs 

ARLP037 Propagation de K7VVV

Average daily sunspot numbers for the week were higher this week
than last, and average solar flux was slightly lower.  Geomagnetic
indices were unsettled for most of the week, and then on Wednesday
there was a surprising jump in geomagnetic activity.  This began on
Tuesday evening in North America after the interplanetary magnetic
field near earth unexpectedly turned south.

The earth's magnetic field forms a bubble around the planet that
helps protect against effects from the solar wind.  Where the
interplanetary magnetic field meets earth's magnetic field is called
the magnetopause.  Earth's magnetic field points north at this
point.  If the interplanetary magnetic field points south at the
magnetopause, it partially cancels the earth's magnetic field at
this point of contact and lets in the solar wind.  This is what
happened on Wednesday, and the results were impressive auroral
displays and a planetary K index of six.

Over the next few days solar flux is expected to rise, with values
over 200 by Sunday, then peaking around 230 by the end of next week.
Don't forget that the autumnal equinox is soon.  This year it will
be on September 23 at 0448 UTC.  High frequency propagation is
improving as we move from summer to fall.

There is an interesting and informative space physics text on the
net, which has lots of information on the sun, the magnetosphere,
solar wind, and many other topics.  You can find it at  N4RYX wrote to ask
about some basic propagation information, and as we've mentioned in
the past, check and

In the past we've mentioned the WM7D solar resource page at  You'll find links
there to some interesting historical charts of sunspot cycles.  Now
W3DF writes to remind us of his historical solar activity charts at  Note that it links
to a cycle 19-23 comparison at,
and many other interesting views of solar data.

Sunspot numbers for August 29 through September 4 were 146, 150,
153, 187, 227, 266 and 215, with a mean of 192. 10.7 cm flux was
169.3, 170, 180.3, 180.5, 173.8, 171.4, and 171.3, with a mean of
173.8. Estimated planetary A indices were 10, 10, 13, 13, 14, 10,
and 42, with a mean of 16.


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