repeated-dates

The repeated-dates source is used to repeat a single source multiple times, so that its data are present on multiple dates. A simple example of this is when you have a source that contains a constant field, such as orography or bathymetry, that you want to have repeated on all the dates of the dataset.

The general format of the repeated-dates source is:

repeated-dates:
    mode: mode
    # ... parameters related to the mode ...
    source:
      # ... a source definition ...

where source is any of the operations or sources described in the previous sections. The mode parameter can be one of the following:

constant

repeated-dates:
  mode: constant
  source:
    xarray-zarr:
      url: dem.zarr
      variable: dem

The constant mode accepts an optional date: key:

If date: is set to a specific datetime, the inner source is invoked for that single date and the resulting fields are broadcast over all of the recipe’s dates. The value is validated at recipe-parse time so an invalid string fails fast. Example:
```
repeat-dates:
  mode: constant
  date: 2020-01-01 00:00:00
  source:
    mars:
      class: od
      param: z
      type: an
      levtype: sfc
```
If date: is null (or omitted), the inner source is invoked with an empty date list — which is the supported way to plug in a fixed, fully-specified MARS request whose date/time are already baked into the source block. This is the typical pattern for dateless forcings such as a single orography field retrieved with its own hard-coded MARS coordinates.
```
repeat-dates:
  mode: constant
  date: null
  source:
    mars:
      class: od
      expver: "0001"
      stream: oper
      type: an
      levtype: sfc
      param: z
      date: 20200101
      time: 0
```

climatology

repeated-dates:
  mode: climatology
  year: 2019
  day: 15
  source:
    grib:
      path: some/path/to/data.grib
      param: [ some_param ]

closest

repeated-dates:
  mode: closest
  frequency: 24h
  maximum: 30d
  skip_all_nans: true
  source:
    grib:
      path: path/to/data.grib
      param: [ some_param ]