windspharm.tools should make clear that these functions are for use with NumPy arrays

[shoyer]

The docstrings currently do not indicate required types. They simple say that they take input in the form of a "data array".

[ajdawson]

These pre-date the existence of xarray so the DataArray confusion potential was not an issue. I guess the feeling was that you never need these unless you use the standard (numpy) interface so it isn't really an issue. I'm happy for the purpose of these to be made more explicit if it is a source of confusion.

[shoyer]

I didn't find the term "data array" specifically confusing -- just the lack of input/return value types (given that you support four different kinds of arrays in the package).