Setting up a Coupled Simulation

For more information about the bucket model, please see the bucket model tutorial.

This tutorial verbally describes how to set up a simulation for a coupled simulation. More detail for coupled runs can be found in the ClimaCoupler.jl documentation.

Background

Recall that in order to drive the system in standalone mode, the user must provide prescribed functions of time for the water volume flux in precipitation, for the net downward shortwave and longwave radiative energy fluxes, for the atmospheric temperature T_a, wind speed u_a (m/s), specific humidity q_a, and air density ρ_a (kg/m^3) at a reference height h_a (m). The values of these quantities at any given time are stored in p.drivers.

Turbulent surface fluxes are computed by the bucket model at each step of the simulation, using the land surface properties as well as the prescribed atmospheric properties, according to Monin-Obukhov theory. These fluxes, as well as the net radiation, are stored in the cache of the bucket model: p.bucket.turbulent_fluxes.lhf, p.bucket.turbulent_fluxes.shf, p.bucket.turbulent_fluxes.vapor_flux, p.bucket.R_n, where they are accessible when boundary conditions are required in the ODE functions (right hand side) of the prognostic equations. Similarily, the precipitation rates are provided from prescribed conditions and stored in p.drivers.P_liq, p.drivers.P_snow.

Coupled simulations

In a coupled simulation, this changes in two key ways. First, the coupler now computes the turbulent surface fluxes and the net radiative flux for the bucket, but it still does so by calling the functions (turbulent_fluxes!, net_radiation!) defined in ClimaLand. This means that the coupler avoids needing to have any internal knowledge about how these fluxes are computed. In order for this to work, though, the fields in p.drivers need to be updated. The second key change then is that the coupler updates these fields directly with the atmopsheric state provided to it by the atmosphere model. As in standalone runs, the cache is updated with the correct fluxes.

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