Store cp and rho for computing OHC anomalies

We don't want to rely on retrieving them from namelists at
runtime because the `self.namelist` object may not exist.

The mesh filename also needs to be stored since it isn't
necessarily available from the streams object at runtime.

Author: xylar

mpas_analysis/ocean/climatology_map_ohc_anomaly.py

@@ -182,6 +182,12 @@ class RemapMpasOHCClimatology(RemapMpasClimatologySubtask):
 
     min_depth, max_depth : float
         The minimum and maximum depths for integration
+
+    cp : float
+        Specific heat of seawater [J/(kg*degC)]
+
+    rho : float
+        Reference density of seawater [kg/m3]
     """
 
     def __init__(self, mpas_climatology_task, ref_year_climatology_task,
@@ -239,6 +245,8 @@ def __init__(self, mpas_climatology_task, ref_year_climatology_task,
         self.run_after(ref_year_climatology_task)
         self.min_depth = min_depth
         self.max_depth = max_depth
+        self.cp = None
+        self.rho = None
 
     def setup_and_check(self):
         """
@@ -255,6 +263,9 @@ def setup_and_check(self):
         self.ref_year_climatology_task.add_variables(self.variableList,
                                                      self.seasons)
 
+        self.cp = self.namelist.getfloat('config_specific_heat_sea_water')
+        self.rho = self.namelist.getfloat('config_density0')
+
     def customize_masked_climatology(self, climatology, season):
         """
         Compute the ocean heat content (OHC) anomaly from the temperature
@@ -298,10 +309,10 @@ def _compute_ohc(self, climatology):
         ds_mesh = xr.open_dataset(self.meshFilename)
         ds_mesh = ds_mesh.isel(Time=0)
 
-        # specific heat [J/(kg*degC)]
-        cp = self.namelist.getfloat('config_specific_heat_sea_water')
-        # [kg/m3]
-        rho = self.namelist.getfloat('config_density0')
+        cp = self.cp
+        assert cp is not None, "Specific heat 'cp' has not been set"
+        rho = self.rho
+        assert rho is not None, "Reference density 'rho' has not been set"
 
         units_scale_factor = 1e-9
 

mpas_analysis/ocean/time_series_ohc_anomaly.py

@@ -31,6 +31,17 @@
 class TimeSeriesOHCAnomaly(AnalysisTask):
     """
     Performs analysis of ocean heat content (OHC) from time-series output.
+
+    Attributes
+    ----------
+    cp : float
+        Specific heat of seawater [J/(kg*degC)]
+
+    rho : float
+        Reference density of seawater [kg/m3]
+
+    meshFilename : str
+        The path to the MPAS mesh file
     """
     # Authors
     # -------
@@ -132,17 +143,37 @@ def __init__(self, config, mpasTimeSeriesTask, controlConfig=None):
             plotTask.run_after(anomalyTask)
             self.add_subtask(plotTask)
 
+        self.cp = None
+        self.rho = None
+        self.meshFilename = None
+
+    def setup_and_check(self):
+        """
+        Store the specific heat and reference density of seawater for use
+        in OHC calculations.
+        """
+        super().setup_and_check()
+
+        self.cp = self.namelist.getfloat('config_specific_heat_sea_water')
+        self.rho = self.namelist.getfloat('config_density0')
+        self.meshFilename = self.get_mesh_filename()
+
     def _compute_ohc(self, ds):
         """
         Compute the OHC time series.
         """
         # for convenience, rename the variables to simpler, shorter names
         ds = ds.rename(self.variableDict)
 
-        # specific heat [J/(kg*degC)]
-        cp = self.namelist.getfloat('config_specific_heat_sea_water')
-        # [kg/m3]
-        rho = self.namelist.getfloat('config_density0')
+        # these need to be set at setup time, not at runtime because piclking
+        # means the namelists and streams objects they come from aren't
+        # available at runtime
+        cp = self.cp
+        assert cp is not None, "Specific heat 'cp' has not been set"
+        rho = self.rho
+        assert rho is not None, "Reference density 'rho' has not been set"
+        meshFile = self.meshFilename
+        assert meshFile is not None, "Mesh filename has not been set"
 
         unitsScalefactor = 1e-22
 
@@ -152,8 +183,6 @@ def _compute_ohc(self, ds):
         ds.ohc.attrs['units'] = '$10^{22}$ J'
         ds.ohc.attrs['description'] = 'Ocean heat content in each region'
 
-        meshFile = self.get_mesh_filename()
-
         # Define/read in general variables
         with xr.open_dataset(meshFile) as dsMesh:
             # reference depth [m]