Diagnose tracer budgets

[zhihua-zheng]

Here are some example codes that calculate buoyancy budget terms in Oceananigans. Starting from here, we can implement tracer budget diagnostics in the future.

using Oceananigans.TurbulenceClosures: ∇_dot_qᶜ
using Oceananigans.Models.NonhydrostaticModels: tracer_tendency
using Oceananigans.Utils: SumOfArrays

grid = model.grid
advection = model.advection
u, v, w = velocities = model.velocities
b = model.tracers.b
total_velocities = (u = SumOfArrays{2}(u, model.background_fields.velocities.u),
                    v = SumOfArrays{2}(v, model.background_fields.velocities.v),
                    w = SumOfArrays{2}(w, model.background_fields.velocities.w))
ADVb = -KernelFunctionOperation{Center, Center, Center}(div_Uc, grid, advection, total_velocities, b)
ADVB = -KernelFunctionOperation{Center, Center, Center}(div_Uc, grid, advection, velocities, model.background_fields.tracers.b)
DIFb = -KernelFunctionOperation{Center, Center, Center}(∇_dot_qᶜ, grid, model.closure, model.diffusivity_fields, Val(1), b,
                                                        model.clock, fields(model), model.buoyancy)
∂ₜb = KernelFunctionOperation{Center, Center, Center}(tracer_tendency, grid, Val(1), Val(:b), advection, model.closure,
                                                      b.boundary_conditions.immersed, model.buoyancy, model.biogeochemistry,
                                                      model.background_fields, velocities, model.tracers, model.auxiliary_fields,
                                                      model.diffusivity_fields, model.forcing.b, model.clock)

[tomchor]

Thanks, @zhihua-zheng, that's great!