friction_velocity#
- metpy.calc.friction_velocity(u, w, v=None, perturbation=False, axis=- 1)#
Compute the friction velocity from the time series of velocity components.
Compute the friction velocity from the time series of the x, z, and optionally y, velocity components.
- Parameters
u (array-like) – The wind component along the x-axis
w (array-like) – The wind component along the z-axis
v (array-like, optional) – The wind component along the y-axis.
perturbation (bool, optional) – True if the u, w, and v components of wind speed supplied to the function are perturbation velocities. If False, perturbation velocities will be calculated by removing the mean value from each component.
axis (int) – The index of the time axis. Default is -1
- Returns
array-like – The corresponding friction velocity
See also
kinematic_fluxUsed to compute the x-component and y-component vertical kinematic momentum flux(es) used in the computation of the friction velocity.
Notes
The Friction Velocity is computed as:
\[u_{*} = \sqrt[4]{\left(\overline{u^{\prime}w^{\prime}}\right)^2 + \left(\overline{v^{\prime}w^{\prime}}\right)^2},\]where :math: overline{u^{prime}w^{prime}} and :math: overline{v^{prime}w^{prime}} are the x-component and y-components of the vertical kinematic momentum flux, respectively. If the optional v component of velocity is not supplied to the function, the computation of the friction velocity is reduced to
\[u_{*} = \sqrt[4]{\left(\overline{u^{\prime}w^{\prime}}\right)^2}\]For more information on the subject, please see [Garratt1994].