5.11 Wind Stress

5.11.1 Command Status

Optional.

5.11.2 Description

Wind stress may be applied as a surface forcing term when wind boundary conditions such as CYC_HOLLAND, W10 or W10_GRID are specified. The Wind Stress Model command selects the wind stress parameterisation. Supported wind stress model implementations are summarised in Table 5.18, with links to the relevant implementation sections below. Commands are listed in Table 5.19. Associated drag coefficients depend on the selected model and may be defined as a wind speed dependent transfer coefficient or a constant bulk coefficient. Default parameter values are applied where optional inputs are not specified.

Wind stress model science is provided in Appendix B.9.

Table 5.18: Wind Stress Implementations

Model Implementation	Description
Wu	Wu wind stress parameterisation.
Constant	Constant bulk wind stress coefficient.
Kondo	Kondo wind stress parameterisation.

Table 5.19: Wind Stress Commands

Command	Description
Wind Stress Model	Optional – Selects the wind stress parameterisation. Options are 1 (Wu), 2 (Constant) or 3 (Kondo). Default: 1 (Wu).
Wind Stress Parameters	Conditional – Inputs are dependent on the Wind Stress Model command. Can be used to update the default coefficients for the Wu and Kondo Wind Stress Models.
Bulk Momentum Transfer Coefficient	Optional – Specifies the constant bulk momentum transfer coefficient

5.11.3 Wu

The Wu wind stress model is the default. Wind stress is scaled using a wind speed dependent transfer coefficient defined by the Wind Stress Parameters command (Equation (B.109)). This parameterisation applies a piecewise-linear approximation of the transfer coefficient as a function of wind speed. Typical coefficient values are provided if no user values are specified.

! Wu Wind Stress Model
Wind Stress Model == 1 ! {1 Wu} | 2 Constant | 3 Kondo
Wind Stress Parameters == 0.0,0.0008,50.0,0.00405 ! {0.0} Wa (m/s) , {0.0008} Ca (-), {50.0} Wb (m/s), {0.00405} Cb (-)

5.11.4 Constant

The Constant wind stress model uses a spatially constant bulk momentum transfer coefficient to compute wind stress. The coefficient is specified using the Bulk Momentum Transfer Coefficient command.

! Constant Wind Stress Model
Wind Stress Model == 2 ! {1 Wu} | 2 Constant | 3 Kondo
Bulk Momentum Transfer Coefficient == 0.0013 ! {0.0013} CDN (-)

5.11.5 Kondo

The Kondo wind stress model calculates the bulk momentum transfer coefficient internally using an empirical formulation based on wind speed (Equation (B.111)). A user specified scale factor may optionally be applied using the Wind Stress Parameters command to adjust the magnitude of the calculated coefficient.

! Kondo Wind Stress Model
Wind Stress Model == 3 ! {1 Wu} | 2 Constant | 3 Kondo
Wind Stress Parameters == 1.0 ! {1.0} Scale factor (-)