Hello,

You may try to use formula of logarithmic wind profile (https://en.wikipedia.org/wiki/Log_wind_profile). In the simplest way: Uz=(U*/K)*[ln(Z/Zo)]

1) K=0.4, Z=10 m, Zo you find from table, depending on the earth surface type, Uz=your wind speed at height Z

2) There you derive value of U*

3) Put your U* back to the formula, now with Z=2 metres

Thank you for your answer!

When you thank for such a trivial thing it means you have to study a textbook very urgently

If the measurement is made at 10 m above a short grass surface (u10) you can use the equation of a logarithmic wind speed profile to obtain the velocity at 2m (u2)

u2 = u10 * 4 . 87 / ln ( 67 . 8 * 10 − 5 . 42 )  -->  u2 is approximately  = 0.75 * u10

more generally if your measurement is at height z (uz)

u2 = uz * 4 . 87 / ln ( 67 . 8 * z − 5 . 42 )

See FAO Irrigation and Drainage Paper No. 56

Crop Evapotranspiration

(guidelines for computing crop water requirements)

by ALLEN et al. 

logarithmic profile calculation recommended above with possible corrections due to stratifications can be found in introductory atmospheric science and BL textbooks such as "An introduction to Atmospheric Physics" by Fleagle and Businger. 

https://www.elsevier.com/books/an-introduction-to-atmospheric-physics/fleagle/978-0-12-260355-6

Hi:

The velocity profile is logarithmic where one variable, is the surface roughness could be different in different locations.   If you know the velocity at 10 meter and you know the roughness then you can calculate the speed at 2 meter.

Alternatively if you know the speed at 10 meter and say at 8 meter you can then solve for the roughness and find the wind speed at 2 meter.

See:  http://web.mit.edu/hurricanelab/ThesisWebsite.pdf

The approach depends on the surface because of the roughness mentioned above. Land surfaces have different issues than water surfaces. For water surfaces, the roughness changes as a function of the surface stress, which is in turn modified by stratification as pointed out by Gad. For water surfaces, code is available on line for the COARE model, or from my web pages for a collection of models (but not yet COARE). For land surfaces, you can use similar code to account for stratification, but can input a roughness length rather than letting the code solve for it.

http://coaps.fsu.edu/~bourassa/MFT_html/MFT_docs.php

https://coaps.fsu.edu/COARE/flux_algor/

Use Erwin Power law to convert wind speed at different vertical height

An introduction to boundary layer meteorology. Roland B. Stull. Reidel Publishing Co., Dordrecht. 1988

Apart from just calculating the log of wind profile in the surface layer and Harry ten Brink's senseless suggestion that you need an urgent review, you may need to also consider the stability of the atmosphere. People have applied M-O scaling theory in both unstable and stable atmospheres but have found difficulty in the latter. The self-similarity scaling relationship that is fundamental to surface layer theory breaks down in certain stability regimes with stability functions/parameters added to the basic theory to account for that. Despite these adjustments M-O still fails in the very stable limit.

Yes, if for design purpose or you are looking for some empirical correlations, please have a look at ASHRAE handbook Section 16.3, Eq(4) (if I remember it correctly). It gives a correlation of wind speed at different heights

Just got this question from a chat dedicated to UpgreenGrade Group in Iran. Here is a GH algorithm and a reference for similar situations to get Wind Profile. Hope it can be helpful after a while of this thread.

https://twitter.com/MahdiSoheyli/status/644195879746990080?s=20

Does anyone know how the 10-m threshold was established? Thanks!