One of the
challenge of tropoducting qso is to get good
forecasts data to display
a map of what can be the situation in an area or on
a particular path,
at a given time.
With all qso's made and maps around, we see that on
ZS-FR path the real world doesn't match exactly the
forecast
maps
all time... Hummm, why? Just to mention some reasons
:
-First,
we use meteorological models of what should be the
troposphere at a
given future time, in a given area. Models are
models, with their part
of uncertainty, with a level of confidence, and
there are different
models.
-Second, on the path, at a given time, the
troposphere is a 3D medium,
longitude, latitude and ....height!
-Third, the color scale to display the maps are not
the same
with the different sources.
-Fourth, the altitudes taken in account for drawing
a map play a big
role in the way they show forecasts
-Fith, the location of the stations, altitude,
inland path, make
difference.
-.....
To
make things very short, best tropo occurs when there
is increase of T°
in altitude and decrease of humidity, more
than the standard
way
they should (which would give normal tropo
conditions). These anomalies
make the N refractive index to change more than
standard at some
altitudes. We can have several layers of good tropo.
As these
anomalies can happen at different altitudes, giving
what i call High
Tropo, or Low tropo, that we experienced on ZS-FR
paths...we
sometimes see, very nice forecast maps but no qso,
and also the
opposite!
So i try to show more about the situation. Not
perfect, but
just an approach.
I
made maps of troposphere from ZS2 and ZS5 to
FR, showing the
Relative Humidity and the T° fonction of the
altitude, in hPa.
1000 hPa is about 200m, 950 hPa is 500m altitude,
900 hPa is 1000m and
850 hPa is 1500m. Not perfectly true, but quite
closed.
My main maps so far show only difference of N
between 1000m and sea
level, coded in color, could be acceptable for
inland < 250m
altitude.
If
for the same time, you look at the vertical
troposphere map for a path,
you can see the predicted zones and altitudes with
T° increase and
decrease in Humidity. X is approximative longitude
on the path, Y is
altitude.
The color code (humididy) is not perfect but i tried
to match
the main map colors. White curves are T°, green are
altitude. So
you can see that some areas are low, some others
high tropo... So that
is probably why sometimes, we don't have qso, even
if main area maps
show
potential... Again, this is experimental, but can be
extra indicator...
Grid Analysis and Display System (GrADS) is used to
build images.
Vertical maps will open in new window so you can
compare, between 2 windows of your
browser, between standard area maps and vertical
troposphere view, for
the ZS-FR
paths.
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