Coupled simulations with Oceananigans

[mukund-gupta]

Hello! I was wondering if there is a smart way to implement coupling with an active atmosphere model. Currently, I have been running in a loop, as follows (pseudo code):

while(model.clock.time < stop_time)
    # Running Ocean model
    simulation.stop_iteration += 1
    run!(simulation)

    # Running atmosphere model
    run_atm!(sim_atm)

    # Updating boundary conditions
    update_BCs!(BCs)
end

I attempted to use simulation callbacks to achieve this without a loop, as follows:

function coupling_callback(sim,sim_atm,BCs)
    # Running atmosphere model
    run_atm!(sim_atm)

    # Updating boundary conditions
    update_BCs!(BCs)
end

simulation.callbacks[:atm_callback] = Callback(coupling_callback(sim,sim_atm,BCs), IterationInterval(1))
run!(simulation)
[coupling_example.txt](https://github.com/CliMA/Oceananigans.jl/files/9285356/coupling_example.txt)

but I get an error.

Below is simplified example illustrating that error:

## Initializing grid and architecture
Nx = 10
Ny = 10
Nz = 10
Δz = 2.5
Δy = 1000.0
Δx = 1000.0
grid = RectilinearGrid(CPU(), size = (Nx, Ny, Nz),x = (0, Δx*Nx), y = (0, Δy*Ny), z = (-Δz*Nz,0), halo=(3,3,3), topology=(Periodic, Bounded, Bounded))
architecture = "CPU"

## Setting up model
model = NonhydrostaticModel(
    grid=grid,
    tracers = (:T, :S),
)

# Setting up iterations
Δt = 60
stop_time = Δt*3
simulation = Simulation(model, Δt=Δt, stop_time=stop_time)

# Testing callback
test_var = 1
function test_callback(sim, test_var)
    my_var += 1
    println("test" * string(test_var))
    return test_var
end
simulation.callbacks[:my_callback] = Callback(test_callback(simulation, test_var), IterationInterval(1))

# Running
run!(simulation)

and the error message is copied below:

LoadError: MethodError: objects of type Int64 are not callable
Maybe you forgot to use an operator such as *, ^, %, / etc.

Any advice on this would be helpful, thanks!

[glwagner]

This functionality will probably eventually be achieved through the ClimaCoupler: https://github.com/CliMA/ClimaCoupler.jl

But it's not operational yet, I don't think.

Rather than run! you should probably use time_step!(sim) which just takes one time-step. A possible design is in this (now closed) PR which shows how to couple two Oceananigans simulations:

#1916

[mukund-gupta]

That sounds good - thanks for the tips!