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October 19th 03, 11:48 PM

On Sat, 18 Oct 2003 23:45:40 GMT,
(Tomas) wrote:

Propagation has been degraded for the last few days as a result of an
active to stormy geomagnetic field. This increased geomagnetic activity is
due to a coronal hole that is located at the right place on the sun's
coronoa such that the plasma spewing out of it is reaching our Earth's
Magnetosphere, rather than missing us. And, the Interplanetary Magnetic
Field component of this elevated solar wind has been mostly negative in its
orientation in relationship with the Earth's magnetic field lines. This
makes our geomagnetic field weaker, and more easily disturbed. When the
geomagnetic field becomes weak and disturbed, it has an influence on the
chemistry of the ionosphere such that the ions begin to recombine with
atoms and particles, much like the recombination that takes place during
the nighttime darkness. So, the maximum usable frequencies are lowered.
But, at the same time, the D layer might remain ionized enough to continue
to absorb the lower frequencies. This combined to "close" the window on
higher HF frequencies.

While solar activity has been low (very few flares, and none of them large,
as well as a lower number of sunspots and a moderate 10.7-cm solar flux
reading), the coronal hole activity has become active again after a few
weeks of quiet. The beginning of October was pretty nice. Moderate solar
activity with higher flux readings, but very low coronal hole activity and
lower solar wind speeds with mostly a positive component of the IMF. But,
we're going to continue to see periods of increased geomagnetic storms for
the remainder of the Fall season, and somewhat beyond.

73 de Tomas, NW7US (AAR0JA/AAM0EWA)

Thanks for the details. Geomagnetic storm alone would have sufficed,
but now I know what one is;-)

mike

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