NW7US Propagation Update: 20-XI-2003

A severe geomagnetic storm is in progress at this time.  As I
write this bulletin, the planetary K index (Kp) is at 7.  The
Aurora Index is at 10 (maximum).  The Bz (horizontal component of
the Interplanetary Magnetic Field) is strongly negative (oriented
southward), at -55.1 nanoTeslas.  This stormy geomagnetic activity
is causing strong ionospheric recombination, decreasing the
maximum usable frequencies on all radio link paths.  HF propagation
at all latitudes is poor.

This geomagnetic storm is a result of the arrival and passage of a
coronal hole mass ejection from 18-XI-2003.  The solar wind speed
increased from 430 km per second to 750 km per second, with a very
strongly negative horizontal IMF component.  Whenever the Bz is 
negative (whenever the horizontal IMF component is oriented 
southward), the IMF combines with the magnetosphere in such a way
as to create geomagnetic disturbances and ionospheric storms.
Aurora is also a typical result of such interaction.

This geomagnetic storm is expected to continue through the end of
20-XI-2003.  Additional CME arrivals may continue to keep the 
geomagnetic activity high.

At 0747Z, 20-XI-2003, a flare peaked at M9.6, further causing 
degradation of the HF propagation, on the sunlit area of the Earth.
Continued C, M, and possible X flares are possible today and for
the next week.  The major sunspot groups from the end of October
and the beginning of November have and are returning into view,
increasing solar activity.

Today's HF propagation outlook is poor.  While the 10.7-cm flux 
is climbing, the continued geomagnetic storm will significantly
degrade higher frequency propagation.  The moderate to major flare
activity expected will also degrade mid-HF frequencies.  Nighttime
propagation on low to mid HF frequencies will also suffer, as the
E-layer will be significantly recombined, decreasing its MUF.

VHF propagation via Aurora, Aurora-E, and Trans-equitorial 
propagation (TEP) will be fair to good.  I welcome reports, if
any, of your success on VHF during this period.

More information as events warrent will be posted in follow-up
bulletins.  Live information is on-going at
http://prop.hfradio.org/ and a discussion is at
http://hfradio.org/forums/



73 de Tomas, NW7US (AAR0JA/AAM0EWA)
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