Manage turbulence time-stepping

INTERFACE:

    subroutine do_turbulence(nlev,dt,depth,u_taus,u_taub,z0s,z0b,h,      &
                             NN,SS,xP)

DESCRIPTION:

This routine is the central point of the turbulence scheme. It determines the order, in which turbulence variables are updated, and calls other member functions updating the TKE, the length-scale, the dissipation rate, the ASM etc. Note, that the list of arguments in do_turbulence() corresponds exactly to those mean flow and grid-related variables required to update the turbulent quantities. These variables have to be passed from a 3-D model, if the turbulence module of GOTM is used for the computation of the turbulent fluxes. Do not forget to call init_turbulence() from the 3-D model before the first call to do_turbulence().

The variable turb_method determines the essential structure of the calls in do_turbulence(). At the moment, the following model types are available:

• turb_method = 0 corresponds to the "convective adjustment" algorithm, see section 3.2.16. Since this model is not a real one-point turbulence closure, it is not called from do_turbulence but directly from the main GOTM loop.
• turb_method = 1 corresponds to a purely algebraic description of the turbulent diffusivities.
• turb_method = 2 corresponds to models computing the diffusivities from the TKE and the turbulent length scale according to (44). TKE and length scale are computed from dynamic PDEs or algebraic relations, an empirical (i.e. not derived from a second-order model) stability function is used, see section 4.7.12.
• turb_method = 3 corresponds to a second-order model for the turbulent fluxes.

The second-order models fall into different categories, depending on the value of second_method. These models, discussed in detail in section 4.4, are listed in the following.

• second_method = 1 corresponds to algebraic quasi-equilibrium models with scaling in the spirit of Galperin et al. (1988), see section 4.7.40.
• second_method = 2 corresponds to algebraic models assuming $P_b=\epsilon_b$, and hence using (72). Furthermore, full equilibrium $P+G=\epsilon$ and $P_b=\epsilon_b$ is assumed for the computation of ${\cal N}$ and ${\cal N}_b$ in (65), see section 4.7.39
• second_method = 3 corresponds to algebraic models assuming full equilibrium $P+G=\epsilon$ and $P_b=\epsilon_b$ for the computation of ${\cal N}$ and ${\cal N}_b$ in (65). Now, however, also an equation for (half) the buoyancy variance $k_b$ is solved, leading to the appearance of the counter-gradient term in (74), see section 4.7.38. This model is not yet fully tested and therefore not available.

Depending on the values of kb_method and epsb_method, different algebraic or differential equations for $k_b$ and $\epsilon_b$ are solved for second_method = 3,4.

USES:

    IMPLICIT NONE
 
    interface
       subroutine production(nlev,NN,SS,xP)
         integer,  intent(in)                :: nlev
         REALTYPE, intent(in)                :: NN(0:nlev)
         REALTYPE, intent(in)                :: SS(0:nlev)
         REALTYPE, intent(in), optional      :: xP(0:nlev)
       end subroutine production
    end interface

INPUT PARAMETERS:

 
    number of vertical layers
    integer,  intent(in)                :: nlev
 
    time step (s)
    REALTYPE, intent(in)                :: dt
 
    distance between surface
    and bottom(m)
    REALTYPE, intent(in)                :: depth
 
    surface and bottom
    friction velocity (m/s)
    REALTYPE, intent(in)                :: u_taus,u_taub
 
    surface and bottom
    roughness length (m)
    REALTYPE, intent(in)                :: z0s,z0b
 
    layer thickness (m)
    REALTYPE, intent(in)                :: h(0:nlev)
 
    boyancy frequency squared (1/s^2)
    REALTYPE, intent(in)                :: NN(0:nlev)
 
    shear-frequency squared (1/s^2)
    REALTYPE, intent(in)                :: SS(0:nlev)
 
    TKE production due to seagrass
    friction (m^2/s^3)
    REALTYPE, intent(in), optional      :: xP(0:nlev)

REVISION HISTORY:

    Original author(s): Karsten Bolding, Hans Burchard,
                        Lars Umlauf