implicit_diffusion can be turned on without a turbconv model and with vert_diff = false

[Sbozzolo]

And if you do so, you'll get the error

ERROR: LoadError: type NamedTuple has no field ᶜK_u
Stacktrace:
  [1] getproperty
    @ ./Base.jl:37 [inlined]
  [2] macro expansion
    @ ~/repos/ClimaAtmos.jl/src/prognostic_equations/implicit/implicit_solver.jl:400 [inlined]
  [3] Wfact!(A::ClimaAtmos.ImplicitEquationJacobian{…}, Y::FieldVector{…}, p::ClimaAtmos.AtmosCache{…}, dtγ::Float64, t::Float32)
    @ ClimaAtmos ~/.julia/packages/NVTX/pfSOQ/src/macro.jl:194
  [4] step_u!(int::ClimaTimeSteppers.DistributedODEIntegrator{…}, cache::ClimaTimeSteppers.RosenbrockCache{…})
    @ ClimaTimeSteppers ~/.julia/packages/ClimaTimeSteppers/Na6yl/src/solvers/rosenbrock.jl:134
  [5] macro expansion
    @ ~/.julia/packages/ClimaTimeSteppers/Na6yl/src/integrators.jl:265 [inlined]
  [6] step_u!(integrator::ClimaTimeSteppers.DistributedODEIntegrator{…})
    @ ClimaTimeSteppers ~/.julia/packages/NVTX/pfSOQ/src/macro.jl:194
  [7] __step!(integrator::ClimaTimeSteppers.DistributedODEIntegrator{…})
    @ ClimaTimeSteppers ~/.julia/packages/ClimaTimeSteppers/Na6yl/src/integrators.jl:237

instead of an informative error telling you that it doesn't make sense

[szy21]

Just to clarify, we should be able to turn on implicit diffusion without a turbconv model. What doesn't make sense is to have implicit_diffusion with both vert_diff: false and turbconv: nothing.

[Sbozzolo]

Just to clarify, we should be able to turn on implicit diffusion without a turbconv model. What doesn't make sense is to have implicit_diffusion with both vert_diff: false and turbconv: nothing.

Thank you, I updated the title