# Correction factor effect on ABL equation

This (below) is a great article and so useful and informative… but my question would be how exactly does the correction factor described, effect the boundary layer equation and hence boundary layer thickness?

For example, say I have a boundary layer defined by u = u*/0.41 ( ln(z+z0)/zo )
OR u=uref ( (ln(z/zo)) / (ln(zref/zo)) ) and then I apply a correction factor = 0.583 say…
(to change from open terrain to city centre) how does this correction factor effect the boundary
layer equation and in turn the BL thickness?

Atmospheric boundary layer | Pedestrian Wind Comfort | SimScale

Hello, and thank you for using the Forum. Correction factor defined in the article are different factors used to account for variations in each wind engineering standards. These correction factors can be used in pedestrian wind comfort analysis, and they’re calculated for each standard. For example in NEN8100, this correction factor is calculated to scale down the wind data that is defined at 60 m to a wind data defined at 10 m.
Once the correction factor is calculated, this value is used to calculate the wind amplification factor, and along with other parameters the probability of the wind exceeding the threshold can be computed. You will see different correction factors for different terrain categories in each standard, because terrain roughness takes part in calculating the correction factors, see equation 14.
However, atmospheric boundary layer profiles presented here are the ones calculated by using equation 1 in the same page. In this equation, roughness value is used for different terrain categories. Since each wind engineering standard defines different values of the ground surface roughness , you will see different comparison graphs.
To summarize, to observe the difference in atmospheric boundary layer when switched from open terrain to city centre, you need to change the surface roughness value in boundary layer equation.
Hope this helps.

Hi both,

I think the correction factor you refer to @garcfd is the one we use to correct the meteorological wind speed. i.e. we have a reference speed, a meteorological wind speed, and then we have our wind speed result. The meteorological wind speeds (given at some weather stations) are going to be influenced by the terrain/context surrounding it, therefore we correct it. These correction factors in the tables can be calculated manually by using a blend height, a height that we consider free from terrain or surrounding influence.

Hope that helps,
Darren

1 Like

thanks both for your replies which are very useful - its beginning to make sense now!
Regards Giles.