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To aviators, the definition of turbulence by measuring the results is widely known: example. But if we were to generate a turbulence forecast as a meteorologist, there need to be some kind of physical parameters that constitute the different levels of turbulence.

Maybe something like "wind vertical velocity" or "vorticity" etc. ...

What are these parameters and what different levels are defined?

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Image source

Turbulence is merely the measure of Reynolds number of a fluid at rest or motion ( (turbulence occurs when fluid is in motion) let's say you light up a cigarette and when the smoke is at the tip of cigarette you see it flows upwards uniformly and this is because the fluid is in laminar flow and as it expands into its vicinity it becomes turbulent. so what is the physics here? basically, reynolds number defines if a fluid is laminar or turbulent. Reynolds number is defined as the ratio of inertial to viscous forces experienced on a body. when divided it gives a number without any units. If the Reynolds number is less than 2100 then the flow is laminar and greater than 4000 it's turbulent and if it's between 2100 and 4000 its transitional flow (which is rare and instantaneous)

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    $\begingroup$ Thanks, and which number would you map to the different levels of "moderate" and "severe" ? $\endgroup$ – Ulu83 Jul 27 '17 at 9:18
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    $\begingroup$ The numbers you mention are for pipe flows, and it would be good to quote your sources (both for the image and the numbers/text) $\endgroup$ – ROIMaison Jul 27 '17 at 9:21
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    $\begingroup$ OK, welcome to Aviation SE, and thanks for the input :) I've included your source in the answer. That being said, this question mainly focuses on weather related turbulence, of course this is the same phenomenon as in the pipe flow, but it might not be the answer the OP is looking for. $\endgroup$ – ROIMaison Jul 27 '17 at 9:29
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    $\begingroup$ oh alright, I'll try to stick to the details of the subject next time. thank you :) $\endgroup$ – Harsha Arya Jul 27 '17 at 9:31
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    $\begingroup$ It may also be worthwhile to point out that the Reynolds number requires a flow speed and a characteristic size for its computation, so the Reynolds associated with a large aircraft may be in the 1e7~1e8 range, while that same aircraft will have a much lower Reynolds on its boundary layer or near the wingtips. $\endgroup$ – AEhere supports Monica Jul 27 '17 at 12:41

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