Add age of air diagnostic functionality

cset-workflow/includes/aoa_diag.cylc

@@ -0,0 +1,19 @@
+{% if AOA_DIAG|default(False) %}
+{% for model in models %}
+{% for plev in AOA_PLEV %}
+[runtime]
+    [[aoa_diag_m{{model["number"]}}_plev{{plev}}]]
+    inherit = PROCESS
+    execution time limit = PT60M
+
+        [[[directives]]]
+        --mem=12000
+        --ntasks=12
+
+        [[[environment]]]
+        CSET_RECIPE_NAME = "ageofair.yaml"
+        CSET_ADDOPTS = "--AOA_PLEV={{plev}} --AOA_CYCLIC={{AOA_CYCLIC}} --MODEL_NAME='{{model["name"]}}'"
+        MODEL_NUMBER = {{model["number"]}}
+{% endfor %}
+{% endfor %}
+{% endif %}

cset-workflow/includes/plot_spatial_plevel_model_field.cylc

@@ -5,6 +5,8 @@
 [runtime]
     [[generic_plevel_spatial_plot_sequence_m{{model_number}}_{{sanitise_task_name(field)}}_lv{{sanitise_task_name(plevel)}}]]
     inherit = PROCESS
+        [[[directives]]]
+        --mem=4000
         [[[environment]]]
         CSET_RECIPE_NAME = "generic_plevel_spatial_plot_sequence.yaml"
         CSET_ADDOPTS = """

cset-workflow/meta/diagnostics/rose-meta.conf

@@ -464,3 +464,45 @@ help=Set to True if you want a one-to-one line; false if not.
 type=python_boolean
 compulsory=true
 sort-key=qq1h
+
+[template variables=AOA_DIAG]
+ns=Diagnostics/Other
+title=Run age of air diagnostic on specified pressure levels.
+description=Run the age of air diagnostic on model data.
+help=The age of air diagnostic provides a qualtitative view of how old air is within
+     the domain, by calculating a back trajectory at each grid point at each lead time
+     to determine when air entered through the lateral boundary. This is useful for
+     diagnosing how quickly air ventilates the domain, depending on its size and the
+     prevailing meteorology.
+     The diagnostic uses the u, v and w components of wind, along with geopotential height to
+     perform the back trajectory. Data is first regridded to 0.5 degrees.
+     Note: the code here does not consider sub-grid transport, and only uses the postprocessed
+     velocity fields and geopotential height. Its applicability is for large-scale flow O(1000 km),
+     and not small scale flow where mixing is likely to play a larger role.
+type=python_boolean
+compulsory=true
+trigger=template variables=AOA_PLEV: True;
+        template variables=AOA_CYCLIC: True;
+sort-key=aoa1
+
+[template variables=AOA_PLEV]
+ns=Diagnostics/Other
+title=AOA: Pressure Levels
+description=List of pressure levels to calculate the age of air diagnostic.
+help=The pressure levels must be specified in hPa, where the variables (U,V,W,Z)
+     exist on the pressure level.
+type=python_list
+compulsory=true
+sort-key=aoa2
+
+[template variables=AOA_CYCLIC]
+ns=Diagnostics/Other
+title=AOA: Use Cyclic Option
+description=If True, LAM is considered cyclic in the east/west direction.
+help=This option when True, will allow back trajectories to advect through the east/
+     west boundary and continue through the other side of the domain. This is useful
+     for large domains such as the cyclic tropical channel, where there is no east/
+     west boundary.
+type=python_boolean
+compulsory=true
+sort-key=aoa3

docs/source/reference/operators.rst

@@ -76,3 +76,9 @@ CSET.operators.convection
 
 .. automodule:: CSET.operators.convection
    :members:
+
+CSET.operators.ageofair
+-----------------------
+
+.. automodule:: CSET.operators.ageofair
+   :members:

src/CSET/operators/__init__.py

@@ -27,6 +27,7 @@
 import CSET.operators
 from CSET._common import parse_recipe
 from CSET.operators import (
+    ageofair,
     aggregate,
     collapse,
     constraints,
@@ -42,6 +43,7 @@
 
 # Exported operators & functions to use elsewhere.
 __all__ = [
+    "ageofair",
     "aggregate",
     "collapse",
     "constraints",