`AtmosSimulation` Constructor Refactor

[nefrathenrici]

This issue continues the refactoring to improve the user interface for setting up and running simulations. The ultimate goal is to move towards a more composable interface:

using ClimaAtmos
# Define the model, domain, and initial conditions as objects
model = AtmosModel(; moisture = Microphysics1Moment)
domain = SphereDomain(; h_elem = 30)
initial_condition = DryBaroclinicWave()
sim = AtmosSimulation(; model, domain, initial_condition)
solve_atmos!(sim)

The only way to construct an AtmosSimulation is via the monolithic get_simulation function, which requires an AtmosConfig. A new constructor which doesn't require AtmosConfig will be introduced. Responsibilities of get_simulation currently include comms_context setup, model and space creation, diagnostics initialization, and state/cache allocation.

Core Changes

1. New AtmosSimulation Constructor

   A new, composable AtmosSimulation constructor will be introduced. It will serve as the primary user-facing entry point and will have a signature similar to:

   AtmosSimulation(; model, domain, initial_condition, surface_setup, comms_context, params, dt, start_date, many_more_kwargs...)

   This constructor will be responsible for the final steps of setting up the simulation, including:

   • Initializing diagnostics
   • Allocating the state and the cache
   • Creating the integrator object

2. AbstractDomain structs

   To replace the use of parsed_args in get_spaces, new AbstractDomains will be added. These structs will store all spatial information currently contained in parsed_args (e.g., x_min, x_elem, z_stretch, nh_poly, dz_bottom). The initial hierarchy matches parsed_args["config"] and will include:

   • SphereDomain
   • ColumnDomain
   • BoxDomain
   • PlaneDomain

Refactoring of parsed_args-Dependent Functions

A significant part of this work involves refactoring the many "type getter" functions that currently depend on the parsed_args. These functions will have new methods that accept types/vals rather than parsed_args. The key functions include:

• get_spaces: Will be refactored to dispatch on the new AbstractDomain types.
• get_callbacks: Needs to be adapted to receive configuration (like output frequency) via explicit arguments or structs instead of parsed_args.
• get_diagnostics: Similar to callbacks, its behavior will need to be configured directly. I expect this and the callbacks will be the biggest obstacle in the refactor, since it will be cumbersome to pass vectors of diagnostics/callbacks so we will need some convenience functions to simplify this aspect of simulation configuration.
• get_surface_setup: Turned into keyword argument: AtmosSimulation(; surface_setup = ...)
• get_tracers: Can be determined from the AtmosModel info for now since the only tracers available prescribed aerosols when applicable.
• get_steady_state_velocity: Will use val or types for topography info.
• get_state_restart: Will be simplified to take just a file path and comms_ctx.
• ode_configuration: This will likely take many keyword arguments since it takes many parsed_args at the moment.

[Sbozzolo]

For what is worth, Simon, Charlie and I were trying to use directly ClimaCore's spaces in ClimaAtmos (instead of adding a new struct). The convenience constructors in ClimaCore were a step in this direction. If you need access to quantities like x_min, x_elem, you could tackle that on the ClimaCore side (as we did with z_min, z_max, for example).