bigleaf (version 0.7.0)

wind.profile: Wind Speed at Given Heights in the Surface Layer

Description

Wind speed at a given height above the canopy estimated from single-level measurements of wind speed.

Usage

wind.profile(data, heights, Tair = "Tair", pressure = "pressure",
  ustar = "ustar", H = "H", wind = "wind", zr, zh, d = NULL,
  frac_d = 0.7, z0m = NULL, frac_z0m = NULL, estimate_z0m = TRUE,
  stab_correction = TRUE, stab_formulation = c("Dyer_1970",
  "Businger_1971"), constants = bigleaf.constants())

Arguments

data

Data.frame or matrix containing all required variables

heights

Vector with heights for which wind speed is to be calculated.

Tair

Air temperature (deg C)

pressure

Atmospheric pressure (kPa)

ustar

Friction velocity (m s-1)

H

Sensible heat flux (W m-2)

wind

Wind speed at height zr (m s-1); only used if stab_correction = TRUE

zr

Instrument (reference) height (m)

zh

Canopy height (m)

d

Zero-plane displacement height (-)

frac_d

Fraction of displacement height on canopy height (-); only used if d is not available

z0m

Roughness length (m), optional; only used if stab_correction = FALSE (default=0.1)

frac_z0m

Fraction of roughness length on canopy height (-), optional; only used if stab_correction = FALSE (default=0.1), only used if z0m is not available

estimate_z0m

Should z0m be estimated from the logarithmic wind profile? If TRUE (the default), arguments z0m and frac_z0m are ignored. See roughness.parameters for details.

stab_correction

Should stability correction be applied? Defaults to TRUE

stab_formulation

Stability correction function used (If stab_correction = TRUE). Either "Dyer_1970" or "Businger_1971".

constants

k - von-Karman constant (-) Kelvin - conversion degree Celsius to Kelvin cp - specific heat of air for constant pressure (J K-1 kg-1) g - gravitational acceleration (m s-2)

Value

A data.frame with rows representing time and columns representing heights as specified in heights.

Details

The underlying assumption is the existence of a logarithmic wind profile above the height d + z0m (the height at which wind speed mathematically reaches zero according to the Monin-Obhukov similarity theory). In this case, the wind speed at a given height z is given by:

$$u(z) = (ustar/k) * (ln((z - d) / z0m) - \psi{m}$$

The roughness parameters zero-plane displacement height (d) and roughness length (z0m) can be approximated from roughness.parameters. \(\psi{m}\) is omitted if stab_correction = FALSE (not recommended). If estimate_z0m = TRUE, z0m is first estimated from the wind profile equation and then used in the equation above for the calculation of u(z) (see e.g. Newman & Klein 2014).

References

Monteith, J.L., Unsworth, M.H., 2008: Principles of Environmental Physics. 3rd edition. Academic Press, London.

Newman, J.F., Klein, P.M., 2014: The impacts of atmospheric stability on the accuracy of wind speed extrapolation methods. Resources 3, 81-105.

See Also

roughness.parameters

Examples

# NOT RUN {
df <- data.frame(Tair=25,pressure=100,wind=c(3,4,5),ustar=c(0.5,0.6,0.65),H=c(200,230,250)) 
wind.profile(df,heights=seq(18,40,2),zr=40,zh=25,d=16)

# }