Sounding Plugin - for paraglider pilots
Hi, amazing plugin ;)
One question (sorry if a dummy one):
How do you determine where the green line starts on the ground?
I see that "The green line shows the temperature of an ascending parcel" but why on the ground it has this particular temperature?
Is there some meteorological constant or formula based on which we know that a bubble would need this-or-that higher temperature than surrounding to start rising?
Correct me if I'm wrong, but to my mind, this starting point is crucial in understanding how strong and how high thermals will be, so I'm wondering (as a gliding pilot) how exactly to interpret this and how to actually know when during the day my lovely bubbles will start to rise.
It should be the temperature at 2m forecasted by the model used for the sounding
@matikru The green line starts at air temperature + some constant (4 or 5C if I remember correctly).
Check a typical example:
You can see that the value of the constant usually doesn't matter that much for the days we are interested in. You have to remember that we look at a model which is an imperfect prediction plus the nature of the soil varies greatly inside a single cell of the model (cells are 9x9km for ECMWF).
In practice it works reasonably well. The air close to the ground doesn't usually get warmer as it would start rising.
If the cloud cover is thick it might be harder for the air temperature to become that warm.
If the temperature (red) and green line (parcel) slowly converge instead of being parallel, that could also be due to the poor resolution of the model (there are not that many points along the altitude axis).
Hope this helps.
@vicb thanks for this clarification.
But, since as you noted "The air close to the ground doesn't usually get warmer as it would start rising" do I understand correctly that the green line should actually start (at the ground level) quite at the same temperature level that the red line starts?
So actually this 4-5 C constant is introduced just for better usability of the diagram, as this green and the red line would just overlap usually?
Btw - I get it now that considering model errors etc. it doesn't make such a difference, I just want to understand the logic behind.
I'm thinking, isn't it that sometimes it will be quite misleading? In this example, it doesn't look like convection at all, no chance for cumulus, since dry adiabat is steeper than air temperature change.
But, looking at the green line starting 4-5 C higher than the red line there's this impression that there will be convection, even a cumulus is depicted at 800.
Or am I missing something totally? :)
Mostly what I mean is that the rising air don't get as warm as the ground.
I think that rising air typically needs a few more degree than the surrounding air to rise.
@matikru yes you still need to interpret what you see. In your screenshot the air is stable (converging lines that I mentioned in a previous message) + there seems to be stratus where the blue line is close to the red line below 1000m
Cirrus at this altitude? You probably mean Stratus ?
EduardoSG last edited by
I tend to agree with @matikru that the green dry adiabat seems too optimistic.
Not only in stable days, but also in well mixed days.
Although the core might start at the ground a few degrees hotter than the surrounding air; by the time it reaches the top of the CBL, there is no difference in temperature for the thermal as a whole, and it is humidity that keeps "pushing" upwards.
Now we are on the off season in the southern hemisphere, but will compare to reality in the flying season.
Of course I am aware we are talking forecasts, and there is always uncertainty and error, but I think the green line adds to that error on the optimistic side.
"@matikru The green line starts at air temperature + some constant (4 or 5C if I remember correctly)."
It looks like you add 3 degrees: https://github.com/vicb/windy-plugin-sounding/blob/ce22dc08d0d436fee4024ab54dc1642bf6762369/src/containers/containers.js#L28
A 2 degrees shift seems to match fairly well with the thermal top overlay, within a few 100 feet.
dodohjk | Premium last edited by dodohjk
The scale in the bottom right is an approximate scale that uses the standard height levels used in aviation like
950hPa / 2 000ft / 600m
850hPa / 5 000ft / 1500m
700hPa / 10 000ft / 3000m
300 hPa / 30 000 ft / 9000m
These are approximately equal and used for easy conversion between different unit. However they are not exact.
In fact heights of pressure levels changes with different weather conditions. eg cooler temps have pressure levels closer to the ground as the air is denser.
More info can be found here https://en.wikipedia.org/wiki/International_Standard_Atmosphere
Anyway the scale on the left is the model calculated height taking account of the meteo conditions (i think at least).
I am pretty sure that the scale on the windy map on the right is the correct values at the "model pressure height" which is an approximate height in m or feet.
..... at lower levels
point "B" marks the temp. at 600 hPa (13800 ft, FL140)
but the diagram shows 12000 ft (1800ft off).