I've just made some
changes to my monthly propagation charts.
I've added some more
data sources so that you can see the current solar and geomagnetic conditions as well
as the predicted HF coverage maps from the UK.
This means that you
can get an at a glance look at likely HF propagation conditions –
all on one page. The data include the current solar flux index, the
Kp index and also solar wind characteristics.
We have been
suffering from a number of recurring coronal holes recently (areas on
the sun where the magnetic field is weaker, letting plasma out to form the
high-speed solar wind).
If the magnetic
polarity of this solar wind is “south” (we say that its Bz is
pointing south) it is more likely to couple with the earth's magnetic
field and the hot plasma can flood in.
The net result is
the earth's magnetic field is distorted and we see this reflected in
the Kp index, which normally rises - a geomagnetic storm is in progress.
The initial effects
can be a short improvement in HF conditions, but these can be short
lived. We then see an overall drop in maximum useable frequencies,
the bands can get noisier and signals drop away, often with lots of
heavy fading (QSB). It can take 24-48 hours for the ionosphere to
recover, if it is not hit again.
The net effect is a
lowering of overall critical and maximum useable frequencies as the plasma hits and excessive
absorption, especially on polar paths.
We've seen a lot of
this recently with poor conditions on HF.
So for good HF
conditions look for settled geomagnetic conditions with a low K index
for a day or so, a low solar wind speed (less than 450 km/s) with a
Bz that is neutral or pointing north and a high solar flux index.
If you have a high
Kp index, a high solar wind speed and a Bz pointing south don't be
surprised if the bands aren't so good! This would not normally be seen in the monthly charts, which are an "average" for the month.
The charts are also
now being carried on the RSGB web site too at
http://rsgb.org/main/technical/propagation/hf-propagation/uk-short-path-monthly-forecast-maps/
which is why I have kept them long and thin to fit into the frame on
RSGB.org.
