Derived Variables¶

Derived variables are computed quantities added to the dataset before any stat function runs. They transform raw input variables (e.g. u/v wind components) into derived quantities (e.g. wind speed) that can then be passed to any stat via data_vars.

Each derived function is registered under a short name and returns a single xr.DataArray.

Usage in config¶

Full form¶

calls:
  - func: mean
    data_vars: [wspd, hs]
    derived_vars:
      - name: wspd       # variable name added to the dataset
        func: wspd       # registered derived function
        uwnd: u10        # override default input variable name
        vwnd: v10

Shorthand¶

When the output variable name, the function name, and all input defaults are the same, a bare string can be used:

derived_vars:
  - wspd          # equivalent to {name: wspd, func: wspd}

Stacking multiple derived variables¶

calls:
  - func: quantile
    data_vars: [uorb_bed, uorb_5m]
    derived_vars:
      - name: uorb_bed
        func: uorb
        z: 0.0
      - name: uorb_5m
        func: uorb
        z: 5.0
    q: [0.50, 0.90, 0.99]

Note

Derived variables listed in derived_vars are automatically included when computing the stat, even if they are not explicitly listed in data_vars.

Available functions¶

Function	Page	Description
`wspd`	Wind	Wind speed from u/v components
`wdir`	Wind	Wind coming-from direction
`cspd`	Ocean Current	Sea water speed from current components
`cdir`	Ocean Current	Sea water going-to direction
`tp`	Wave Parameters	Peak wave period from peak frequency
`douglas_sea`	Wave Parameters	Douglas sea scale (0–9)
`douglas_swell`	Wave Parameters	Douglas swell scale (0–9)
`crossing_seas`	Wave Parameters	Boolean crossing-seas flag
`uorb`	Wave Orbital Velocity	Significant horizontal wave orbital velocity
`clear_sky`	Sky Conditions	Boolean clear-sky mask from cloud fraction
`covered_sky`	Sky Conditions	Boolean overcast mask from cloud fraction