EAMxx: allow perturbation of restart files (not just ic)

[mahf708]

in

E3SM/components/eamxx/src/control/atmosphere_driver.cpp

Line 1380 in 01d73b8

// Compute IC perturbations of GLL fields (if requested)

we are able to perturb select fields in the IC so to create multiple trajectories. Unfortunately, this only happens if we are starting the model from scratch

E3SM/components/eamxx/src/control/atmosphere_driver.cpp

Lines 872 to 877 in 01d73b8

	// Initialize fields
	if (m_run_type==RunType::Restart) {
	restart_model ();
	} else {
	set_initial_conditions ();
	}

proposal: allow users to request a perturbation even in restart files, potentially with an additional runtime guard to ensure the user actually means they actually want this (in a way, a compounded perturbation since it will happen at every restart).

rationale: really helpful to navigate tricky waters/winds/instabilities

impl: add these to components/eamxx/cime_config/namelist_defaults_eamxx.xml as well so that hey are exposed as runtimes and add corresponding docs under components/eamxx/docs/user

caveat: the current impl of this perturbation is under the "initial_conditions" heading of runtime configuration,

E3SM/components/eamxx/cime_config/namelist_defaults_eamxx.xml

Lines 730 to 736 in 01d73b8

	<!-- Information about perturbed fields-->
	<perturbed_fields type="array(string)" doc="IC fields (with level dimension) to apply a random perturbation to based on the parameters below."/>
	<perturbed_fields type="array(string)" COMPSET=".*DP-EAMxx">T_mid</perturbed_fields>
	<generate_perturbation_random_seed type="logical" doc="Whether or not to generate a random seed for perturbation.">false</generate_perturbation_random_seed>
	<perturbation_random_seed type="integer" doc="Random seed used for perturbation. Will be overridded by generate_perturbation_random_seed=true.">0</perturbation_random_seed>
	<perturbation_limit type="real" doc="Defines a range [1-x, 1+x] which perturbation will be taken from.">0.001</perturbation_limit>
	<perturbation_minimum_pressure type="real" doc="Minimum pressure (relative to a reference level pressure profile) for which perturbation will be applied.">900.0</perturbation_minimum_pressure>

and so one would need to think about hijacking this section so that it applies to restart capabilities or a whole new set of duplicated params are used elsewhere in the namelist_defaults_eamxx.xml file.