Surface vs altitude data; terrain following
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This is a question about what data I'm seeing...
Here in California, the terrain varies from below sea level (Death Valley) to thousands of meters (Mt McKinley in the Sierra). I want to look up data (eg, dew point, wind, etc) on paths between two endpoints on the surface and along the path (thru the troposphere at various altitudes between the end points).
It appears that if I select "surface" altitude, the data follows the terrain, ie, I'll get the dew point at 2000m (or whatever) at a mountaintop and 0m at the seashore. The data is not from any one altitude, but follows the surface. Is this true?
It also appears that if I select a higher altitude, it will not terrain follow. It looks like I'll get the forecast data at that pressure level, regardless of the surface altitude underneath the weather picker... which is fine if the surface is lower than the current forecast altitude layer, but not so good if the surface is higher than the current forecast layer. In other words, say I set altitude to 1000m and the surface altitude underneath the path (or wherever I place the weather picker) varies from sea level at some spots to 2000m at other spots... I think I will see bogus "1000m" forecasts for the spots that are higher than 2000m.... right or wrong? if correct, would it make sense to present the data for the greater of (surface elevation, forecast elevation)?
Thanks,
Mike
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@k6ml
This post allows to understand how the model ‘see’ the atmosphere over a mountain: The pressure levels are seen ‘following the terrain’.
Your question does not concern wind, but you can easily imagine what you get if you set the altitude slider at 850hPa above a 3000m mountain. You will have a temperature approximatively similar to that at same pressure level above low terrain. While the temperature at surface on top of the mountain will be much lower and close to the reality.
What I do not understand is why you want to set the altitude slider at 1000m. If you hike just keep this slider at surface.
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I'm not hiking, I'm 'flying' thru the air along the path.
Actually, I'm transmitting millimeter radio waves from one mountaintop to another. (But an aviator planning a flight or a hiker wondering about the view from a mountaintop has a similar issue predicting clouds, crosswinds and other weather.) The attenuation of these waves varies strongly with absolute humidity (dew point, not relative humidity) as they
fly' thru the air. For a line of sight path between two mountains, the altitude above ground will vary with the underlying terrain and the earth's curvature.Your distance and planning weather picker tool is great for hikers... it follows the terrain, but not for people and radio (and visible light) waves flying thru the air... it reports surface forecast data along the path. I'd love a line of sight mode that follows the path between the two endpoints thru the air, reporting conditions along that line.
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The path tool reports the data at the surface, even for the IFR, VFR, etc non-hiker cases.
Also, it used to have a Meteogram option with more data variables, but still at the surface.
My dream path tool would have a mode that reports at least air temp, dew point (or dew point spread), clouds, precip & wind a regular points along the sloped/elevated line of sight path between two endpoints (perhaps with an option to elevate the end points above ground for legs of a flight path or those who build towers in the air).
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@k6ml said in Surface vs altitude data; terrain following:
between two endpoints on the surface and along the path
Sorry I did not realize it was in straight line in the air between 2 endpoints. It's clear now. The Route planner does not offer this option.
A workaround could be imagined, but it depends how many ‘paths’ or ‘endpoints’ you monitor. I guest they are fixed endpoints? -
If you only have a few paths, you can place favorites along those paths. They will be of course at surface agl. And for each favorite, calculate the altitude asl of the path above the favorite (a small geometry exercise :) but a little more tricky if you must take into account the earth curvature). Then on each favorite, the Sounding tool (better to use Sounding in plugins gallery) will give you the dew point, temperature, wind… at the calculated altitude i.e. on the line between your microwaves transmitter and receiver.
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@idefix37 That'a exactly what I do (favorites along the path). It's a bit tedious compared to a 'thru the air' Route planner option. Perhaps such an option could be added to route planner?
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@k6ml
Yes I can imagine particularly if you have many paths and favorites.
