Satgen 200   A New HF Propagation Mode    by GM4IHJ           23rd Jan 93
The BID on this msg is SGEN200 . USE THAT BID IF YOU RETRANSMIT THIS MSG

Everybody knows that HF Propagation of Radio Waves allows us to
communicate to distant places around the world, beyond line of sight,
using the refractive properties of the Earth's Ionosphere.
The Ionosphere has 3 major zones. The D layer at about 60 km altitude. The
E layer at about 100km and the F layer around 300 km. These definitions
are very loose and they vary greatly in the course of a 24 hour day, with
levels of ionisation being very low at night, thereby considerably
reducing the value of the highest radio frequency which can be propagated.
Typically at this part of the 11 year solar activity cycle, more than 2
years after cycle maximum, the highest oblique incidence propagated
frequencies over temperate latitudes , average roughly 27 to 31 MHz by
day, and, about 7 MHz by night.
It has come as a considerable surprise therefore, to find that signals
from satellite RS12 on 29.408 MHz have been propagating for up to 6000 kms
over the night time Arctic in the winter Nov/Dec 92 season. When the
ground above 67N latitude has not been seeing the Sun, at  all, at any
time of day or night.
On 18 different days in the period 10 Nov to 19 Dec 92, propagation from
RS12 was observed going right across the Arctic into UK from places as far
away as Dutch Harbour in the Aleutian Islands and Kamkatchka in the
Russian Far East.  These places are up to 6500 kms from UK. 
These events are not confined to UK. In UK they have occured between
roughly 1000 ut and 1500 ut . In the Pacific NorthWest of USA, they have
been observe roughly 8 hours later. A separation commensurate with their
120 W Longitude. On some days , 3 successive orbits , roughly 105 minutes
apart , have featured this unusual polar propagation.
NM7M has been observing events from the Pacific NW of USA. He has been in
touch with some of his former professional colleagues, and reports that
papers in, or coming in, Radio Science and the Journal of Geophysical
Research, discuss the topic of " Drifting F region Electron Density
Structures" in/above the Polar Cap, in respect of both the Arctic and
Antarctic regions. The suggestion is that the F region Electron Density
Structures may drift from the dayside oval into the polar cap, when
certain conditions apply in the Interplanetary Magnetic Field.
It remains to be seen how often these phenomena repeat over North Polar
regions. Perhaps they will continue ( may be at lower frequencies ) in the
forth coming Northern winters right through Solar cycle minimum. Certainly
GM4IHJ's log records events of this nature in both winter 91/92 and winter
92/93. Equally important and more timely now that events in the Northern
Polar cap appear to have temporarily ceased, is the Southern Hemisphere
Winter this coming June / July / August 93. Can VK and ZL radio amateurs
look for RS10 and RS12 beacons this coming Southern winter, when these
satellites are going to or from the other side of the South Pole towards
or away from VK and ZL. The time to listen is around local magnetic noon
(LMN)  LMN -2 to + 4 hours or so . Local magnetic noon occurs in the
Southern Hemisphere when a straight line from the Sun comes through your
station and then goes on to cross over the SOUTH MAGNETIC POLE ( not the
rotation pole). Any ZL VK station wanting more info pse packet GM4IHJ
quoting your postal address . 73 de GM4IHJ @ GB7SAN