issues: 1706864252

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1706864252 I_kwDOAMm_X85lvK58 7838 Anomaly calculation with groupby leaves seasonal cycle 14111025 open 0     5 2023-05-12T03:34:07Z 2023-05-12T17:33:03Z   NONE      

What happened?

When calculating EOFS with sea surface temperature (SST) anomaly, We see the seasonal cycle still in the data. Tested with xarray v2023.03.0 and v202304.02, both have the same problem (seasonal cycle still in the data). So the anomaly calculated with groupby is not correct.

Attached is the results of using xarray v2023.04.02

What did you expect to happen?

The EOFs will not have seasonal cycle. Attached is the results from xarray v0.20.2

Minimal Complete Verifiable Example

```Python import xarray as xr import numpy as np import pandas as pd from eofs.xarray import Eof

url = 'http://kage.ldeo.columbia.edu:81/SOURCES/.LOCAL/.sst.mon.mean.nc/.sst/dods' ds = xr.open_dataset(url)

gb = ds.sst.groupby('time.month') ds_anom = (gb - gb.mean(dim='time')).compute() solver = Eof(ds_anom) pcs = solver.pcs(npcs=4,pcscaling=1) eofs = solver.eofsAsCorrelation(neofs=4)

eofs.plot(x='lon',y='lat',col='mode',col_wrap=4,add_colorbar=1) pcs.plot(x='time',col='mode',col_wrap=4); ```

MVCE confirmation

  • [ ] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
  • [X] Complete example — the example is self-contained, including all data and the text of any traceback.
  • [ ] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
  • [ ] New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS ------------------ commit: None python: 3.10.10 | packaged by conda-forge | (main, Mar 24 2023, 20:08:06) [GCC 11.3.0] python-bits: 64 OS: Linux OS-release: 4.13.16-100.fc25.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.12.2 libnetcdf: 4.8.1 xarray: 2023.4.2 pandas: 1.5.3 numpy: 1.23.5 scipy: 1.10.1 netCDF4: 1.6.0 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.6.2 nc_time_axis: None PseudoNetCDF: None iris: None bottleneck: None dask: 2023.4.0 distributed: 2023.4.0 matplotlib: 3.7.1 cartopy: 0.21.1 seaborn: None numbagg: None fsspec: 2023.4.0 cupy: None pint: None sparse: 0.14.0 flox: None numpy_groupies: None setuptools: 66.0.0 pip: 23.0.1 conda: None pytest: None mypy: None IPython: 8.12.0 sphinx: None 
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     13221727 issue

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