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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