[HCDX] NW7US Propagation Update: 22-XI-2003

[Tomas NW7US <nw7us@xxxxxxxxxxx>]

Howdy,

The high geomagnetic activity that occurred during the passage
of the coronal hole mass ejection (CME) from 18-XI-2003 has
decreased, and remained at low levels for the last few reporting
periods.  At the same time, the 10.7-cm flux is greater than 170.
Solar wind speed at the time of this writing is just over 550 km
per second, with a slightly negative interplanetary magnetic
field horizontal component orientation (the Bz is -2.8 nT).  This
has led to fair HF signal propagation, with normal propagation
conditions over low-latitude paths, fair propagation over mid-
latitude paths, and fair to poor propagation over high-latitude
paths.

The coronal mass ejection observed in association with the M9-
class flare of 20-XI-2003 is likely to glance the Earth's
magnetosphere during the later half of 22-XI-2003 UTC.  This CME
should combine with an anticipated high coronal hole solar wind
stream to produce further minor storm activity.  The expected
elevated solar wind speed is a result of a coronal hole that is
now in a position where it is spewing plasma directly into the
Earth's direction.  The combination of the higher solar wind
speed and the glancing of the arriving CME will lead to active
to minor storm levels from late 22-XI-2003 UTC and into
23-XI-2003 UTC.  There is a slight chance of the geomagnetic
field to reach major storm levels at some latitudes during this
weekend.

The 10.7-cm flux levels are expected to continue to rise slightly
to a maximum of about 200 over the next day or so.  The >10MeV
proton flux levels have been remaining moderate.  According to
the POSE observations at the time of writing this bulletin,
however, there is a very little polar cap proton presence.  When
very energetic protons (>10 MeV) produced by processes at the sun
and interplanetary space arrive at Earth and enter the atmosphere
over the polar regions, ionization is greatly enhanced at
altitudes below 100 km.  Ionization at these low altitudes is
particularly effective in absorbing HF radio signals and can
render HF communications impossible throughout the polar regions.
Since we are not seeing significant wide-spread proton activity
right now over the poles, E-layer ionization is mostly normal at
these high latitudes.

The big sunspot groups from late October and early November, now
numbered 501, 507, and 508, are quite a bit smaller this time
around.  However, they do have enough magnetic complexity to
produce M-class flares.  There is a sixty percent chance of an
M-class flare, and a fifteen percent chance of an X-class flare.
Most of the flares expected will be in the C-class range.  This
will mostly impact the lower frequencies on the sunlit side of
the Earth.

HF propagation conditions will continue to be fair to normal for
most of today (22-XI-2003 UTC), but will slightly degrade late
in the day and into Sunday.  Late Sunday, conditions may improve
slightly, and then by Monday should again be mostly normal over
all latitudes except for some degradation over the poles.

VHF propagation is expected to be quiet with very slight chance
of any Auroral.  However, there might be a slight chance of some
F-layer openings, and of transequatorial propagation during the
afternoon and evening hours local time.  There have been some
reports of Sporadic-E, but openings are expected to be rare.

More information as events warrant 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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