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B21

CumulusX default thermal strength @ 2000 feet

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Peter - can you confirm how the lift profile changes with height using the *default* CumulusX settings at 1pm on a summer day at 40 degrees North (i.e. Mifflin)?

I read your notes on it in the CumulusX documentation but couldn't work out the actual values. 'Default' doesn't have an inversion layer and the weak layer near the ground is quite short, but when soaring at 2500 feet MSL (1700 feet AGL) I'm able to reach quite a few thermals (at the default 5 thermals per 100 square kilometers) but I'm finding it difficult to find lift. The 'default' thermal strengths are quite strong in the settings so I don't really understand it.

There's a possibility the default has the thermal strengths much weaker at 2000 feet MSL (1200 AGL) than they would be for real - if so I need to work out how to change the settings so the lift strength is good from 1500 feet upwards.

Thanks,

Ian

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Hi Ian,

actually, there should not be excessive weakening in that altitude. Yet, the default settings have an inversion layer with a 25 % probability and a 25% (max) ending between 300-600 m below the ceiling and being 150-300 m thick.

This means, depending on your situation (on random base) the minimal thermal strength may be found in an altitude of at least 6500 ft - 600m - 300m/2 = 4000 ft MSL, when the ceiling is 6500ft.

Additionally, there is a ground layer of 300 m, so that the full thermal strength is ground altitude + 1000ft.

Probably your problem is wind. It is certainly wise to turn off the spirals and switch to the CumulusX! clouds, because the spirals will cheat you. They are always vertical, regardless of the wind. If you are using a spiral to find the lift, when there is wind, it will be useful only when you are close to the cloud base.

To check, you can screw down the leaning factor to zero, then leaning is no longer there and the spirals are correct.

Overall, with the many included effects, it is hardly possible even for me, to make an easy prediction which the thermal will be exactly at in a certain condition. Since the last version, the debug window remains effective also in slew mode, so you can analyse the lift situation yourself. I have made quick test with fair weather and could not find unexpected behaviour (Summer, 13:00 LT)

best regards,

Peter

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thanks for this Peter - helpful to know.

Ian

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