fix: skip CF encoding for zarr arrays with native DateTime64 dtype (GH#11350)#11419
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fix: skip CF encoding for zarr arrays with native DateTime64 dtype (GH#11350)#11419C1-BA-B1-F3 wants to merge 1 commit into
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…H#11350) When writing to a zarr array with native DateTime64 dtype (zarr v3), skip CF datetime encoding. CF encoding converts datetime64 to int64 with units/calendar attributes, which corrupts data when written to a native DateTime64 zarr array — the int64 values get misinterpreted as raw epoch seconds instead of the encoded 'days since' values. Fixes pydata#11350
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Problem
When writing a dataset back to a zarr store with native dtype (zarr v3), the datetime values get corrupted. For example, and become and .
Root Cause
The function applies CF datetime encoding which converts to with and attributes. When these values (e.g., for "days since 2025-01-01") are written to a zarr array, the array interprets them as raw epoch seconds, resulting in corrupted data.
Fix
In , detect when an existing zarr array has a native dtype (via ). For these arrays, skip CF encoding and write the raw values directly, since zarr handles the datetime storage natively.
Changes
Testing
Fixes #11350