# 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 ({False, True}, 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

kinematic_flux

Used 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:

$u_{*} = \sqrt{\left(\overline{u^{\prime}w^{\prime}}\right)^2 + \left(\overline{v^{\prime}w^{\prime}}\right)^2},$

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

$u_{*} = \sqrt{\left(\overline{u^{\prime}w^{\prime}}\right)^2}$