polaris.ocean.vertical.elevation.apply_vertical_reduction

polaris.ocean.vertical.elevation.apply_vertical_reduction(da, reduction, z_mid=None, z_interface=None, min_level_cell=None, max_level_cell=None)

Reduce a field with a vertical dimension to a horizontal map

Slicing at the sea surface, the seafloor, a layer index or an elevation are cases of one operation: each picks one layer of each column, or the two layers an elevation falls between, for any DataArray. Only the last of them reads the vertical geometry.

Parameters:

• da (xarray.DataArray) – The field to reduce, with an nVertLevels dimension

• reduction (VerticalReduction) – How to reduce it, from parse_vertical_reduction()

• z_mid (xarray.DataArray, optional) – The elevation of layer midpoints, needed only to interpolate to an elevation

• z_interface (xarray.DataArray, optional) – The elevation of layer interfaces, as for z_mid

• min_level_cell (xarray.DataArray) – The zero-based index of the topmost valid layer of each column

• max_level_cell (xarray.DataArray) – The zero-based index of the bottommost valid layer of each column

Returns:

da_map (xarray.DataArray) – The reduced field, without an nVertLevels dimension, masked where the reduction falls outside the column, and with the attributes of da, since a slice of a field has the field’s units and name

Raises:

ValueError – If the reduction is a range, or if what it needs was not passed