[ RadSafe ] wind at 10 meters or nearer the ground?

[Mora Cañadas Juan Carlos]

You can use some models that are well known:

A simple model, widely used in Europe (developed by Clarke, R. H. : NRPB) and useful for the atmospheric layer nearest to the ground (less than 1000 m), says that  wind velocity can be calculated at any height knowing the wind velocity at 10 m, and a factor (n) that is a function of ground roughness.

u(z)=u(10)*(z/10)^n

Where z is your new height.

n ranges from 0.07 (for sea) to 0.39 (for cities or woodland).

Hotspot uses the model  for a height of 2 m, but the equation is in the same form:

u(H)=u(2)*(H/2)^p

Here H is your new height.
and
p ranges from 0.07 to 0.60, depending on stability class and terrain roughness.

This models comes from J Irwin. "A theoretical variation of the wind profile power-law exponent as a function of surface roughness and stability", Atmospheric environment.  (1979).

You can also find another general models, but they usually only changes the exponent using empirical data.

Hope this can help you.

Juan Carlos.

__________________________________________________________________
Juan Carlos Mora Cañadas
Unidad de Protección Radiológica del Público y del Medio Ambiente
CIEMAT - Edificio 3, Planta 0, Despacho 18.
Avda. Complutense, 22
28040 Madrid
Tlf.           91.346.66.83
Fax.         91.346.61.21
__________________________________________________________________ 



-----Mensaje original-----
De: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] En nombre de Michael McNaughton
Enviado el: martes, 03 de junio de 2008 17:33
Para: radsafe at radlab.nl
Asunto: [ RadSafe ] wind at 10 meters or nearer the ground?

Air dispersion models typically use wind data at a height of 10 m. 
This is reasonable for a typical stack; but what if the release and the receptor are both nearer the ground where the wind velocity is less than at 10 m? Recall that according to the standard air-dispersion models, the wind velocity is in the denominator, so the concentration is inversely proportional to the wind velocity. 
Therefore, using the wind velocity at a height of 10 m significantly underestimates the concentration.

Have any of you dealt with this problem.

Thanks, mike

Mike McNaughton
Los Alamos National Lab.
email: mcnaught at LANL.gov or mcnaughton at LANL.gov
phone: 505-667-6130; page: 505-664-7733 


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