Fix control run support for El Nino 3.4 Index

[xylar]

We need to drop the nOceanRegions dimension from the control dataset just as we do for the main dataset.

Checklist

• Testing comment in the PR documents testing used to verify the changes

[xylar]

Testing

I performed a main vs. control analysis run using E3SM-Project/zppy#772 and this branch. With this fix, the indexNino34 analysis runs successfully whereas without it, I got errors:

analysis task indexNino34 failed during run 
Traceback (most recent call last):
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/mpas_analysis/shared/analysis_task.py", line 323, in run
    self.run_task()
    ~~~~~~~~~~~~~^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/mpas_analysis/ocean/index_nino34.py", line 274, in run_task
    nino34Ref = self._compute_nino34_index(regionSSTRef, calendar)
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/mpas_analysis/ocean/index_nino34.py", line 371, in _compute_nino34_index
    return self._running_mean(anomaly, wgts)
           ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/mpas_analysis/ocean/index_nino34.py", line 502, in _running_mean
    runningMean[k] = sum(wgts * inputData[k - sp:k + sp + 1].values)
    ~~~~~~~~~~~^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/dataarray.py", line 905, in __setitem__
    self.variable[key] = value
    ~~~~~~~~~~~~~^^^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/variable.py", line 903, in __setitem__
    indexing.set_with_indexer(indexable, index_tuple, value)
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/indexing.py", line 1169, in set_with_indexer
    indexable[indexer] = value
    ~~~~~~~~~^^^^^^^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/indexing.py", line 1715, in __setitem__
    self._safe_setitem(array, key, value)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/indexing.py", line 1698, in _safe_setitem
    raise exc
  File "/lcrc/soft/climate/e3sm-unified/e3smu_1_12_0/chrysalis/conda/envs/e3sm_unified_1.12.0_compute/lib/python3.13/site-packages/xarray/core/indexing.py", line 1689, in _safe_setitem
    array[key] = value
    ~~~~~^^^^^
ValueError: could not broadcast input array from shape (5,) into shape (1,)

The results with errors are in:

/lcrc/group/e3sm/ac.xylar/zppy/mpas_analysis_model_vs_model/v3.LR.historical_0091/post/analysis/mpas_analysis/ts_1850-2014_climo_1985-2014

The successful ones are in:

/lcrc/group/e3sm/ac.xylar/zppy/mpas_analysis_model_vs_model/v3.LR.historical_0091_el_nino_fix/post/analysis/mpas_analysis/ts_1850-2014_climo_1985-2014

[xylar]

Further testing

I successfully ran the test suite. The output is here:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/xasaydavis/analysis_testing/chrysalis/fix-el-nino-main-vs-control/