ENSO-Antarctica

Analysis Scripts used for the publication:

Huguenin, M. F., Holmes, R. M., Spence, P., & England, M. H. (2024). Subsurface warming of the West Antarctic continental shelf linked to El Niño-Southern Oscillation. Geophysical Research Letters, 51, e2023GL104518. https://doi.org/10.1029/2023GL104518

Packages and Functions

I use the following main python3 (Van Rossum and Drake, 2009) packages which are publicly available online:

cartopy for creating maps (MetOffice, 2010)
numpy for numerical operations (Oliphant, 2007)
xarray for loading in and working with .nc data files (Hoyer and Hamman, 2017)

Analysis Scripts

To create the perturbation experiment input files (i.e., the climatological atmospheric forcing with added ENSO-associated anomalies on top), we use the following script: Fig1_time_series_spatial_patterns_highlighting_ENSO_teleconnection.ipynb. It calculates the mean spatial anomalies for each of the ACCESS-OM2 input files during the four strongest El Niño and La Niña events since 1958, scales them with the idealised time series associated with ENSO and adds them to the RYF forcing files.

List of Main Manuscript Figures

Fig. 1: Experimental design of the new spin-up. Fig1_time_series_spatial_patterns_highlighting_ENSO_teleconnection.ipynb

Fig. 2: Response of the West Antarctic continental shelf during the peak of El Niño and La Niña events at months 12 and 24 of the simulations. Fig2_response_of_West_Antarctic_shelf_to_peak_EN_and_LN_event.ipynb

Fig. 3: Time series of West Antarctic subsurface shelf temperature and heat budget terms during El Niño and La Niña simulations. Fig3_time_series_of_West_Antarctic_subsurface_heat_budget_and_Ekman_anomalies.ipynb

Fig. 4: Summary schematic of anomalous physical processes on the West Antarctic continental shelf during El Niño and La Niña events. Fig4_schematic_of_physical_changes_in_West_Antarctica_during_ENSO.pptx

List of Supporting Information Figures

Fig. S1 & Fig. S2: Spatial maps of sea level pressure and surface wind anomalies during the peak of the four strongest El Niño and La Niña events since 1958. ASL_spatial_patterns_and_winds_during_ENSO.ipynb

Fig. S3 & Fig. S4: Spatial maps of the atmospheric forcing fields used for the El Niño simulation in the model. all_forcing_fields_ENFull_LNFull_spatial_maps.ipynb

Fig. S5: Composites of the Southern Annular Mode index during strong El Niño and La Niña events. Same script as for Fig. 1

Fig. S6: Spatial maps of mean sea surface temperature anomalies during the peak of four strong El Niño and four strong La Niña events since 1958. Same script as for Fig. 1

Fig. S7: Model temperatures and velocities in the Amundsen Sea. Calculating_undercurrent_strength.ipynb

Fig. S8: The second-order subsurface Eulerian heat budget anomalies on the West Antarctic continental (100 m - 1000 m, 150°W to 60°W) during the El Niño and La Niña simulations. Same script as for Fig. 3

Fig. S9: Time series of Niño 3.4 and sea ice volume anomalies. Same script as for Fig. 3

Fig. S10: Time series of the accumulated anomalous heat content on the West Antarctic continental shelf during the El Niño and La Niña simulation. Same script as for Fig. 3

Fig. S11 & Fig. S12: Spatial maps of atmospheric anomalies during periods when the Interdecadal Pacific Oscillation (IPO) is in a positive (negative) phase. IPO_index_and_regression_maps_JRA55_ERA5.ipynb

Fig. S13: Model temperature evaluation with Marine Mammals Exploring the Oceans Pole to Pole project (MEOP, Treasure et al., 2017). seal_data_comparison_from_adele.ipynb and Model_evaluation_with_JRA55_and_SOSE.ipynb

Fig. S14: As in Fig. S13 but for salinities. seal_data_salinity_comparison_from_adele.ipynb

Fig. S15: Model evaluation with mooring data from the Pine Island (Webber et al., 2017). evaluating_oles_pine_island_mooring_data.ipynb

Fig. S16: Sea level anomalies during the El Niño and La Niña simulations. sea_level_anomalies_ENSO.ipynb

A Note on the Model Input for the Perturbation Experiments

The full forcing for the El Niño and La Niña simulations is constructed by adding for each input field the ENSO spatial patterns multiplied by the composite time series to the climatological repeat year forcing. That means, for example for the surface air temperature field during El Niño, we multiply the tas_10m spatial map (x,y) in ENSOAnt_data/FigS5_All_Spatial_Maps_anoms_EN.nc with composite time series (t), the fifth column in ENSOAnt_data/Fig1d_Time_Series_Composite_EN.nc, and add the resulting field (t, x, y) to the repeat year forcing (t, x, y).

Full 5 TB Model Output Data on the NCI Supercomputer Gadi

| Description of simulation | From where I run the simulation | Input files                      | Output stored on              |
| ------------------------- | ------------------------------- | -------------------------------- | ----------------------------- |
| Control run               | * + 01deg_jra55_ryf_Control/    | /g/data/ua8/JRA55-do/RYF/v1-3/   | ** + 01deg_jra55_ryf_Control/ |
| El Niño simulation        | * + 01deg_jra55_ryf_ENFull/     | /g/data/ua8/JRA55-do/RYF/v1-3/   | ** + 01deg_jra55_ryf_ENFull/  |
| "    "    "    "          |                                 | *** + forcing_mean_anoms_ENFull/ |                               |
| La Niña simulation        | * + 01deg_jra55_ryf_LNFull/     | /g/data/ua8/JRA55-do/RYF/v1-3/   | ** + 01deg_jra55_ryf_LNFull/  |
| "    "    "    "          |                                 | *** + forcing_mean_anoms_LNFull/ |                               |
| Location of repeat year climatological forcing: /g/data/ua8/JRA55-do/RYF/v1-3/                                                 |

* /home/561/mv7494/ ** /g/data/e14/mv7494/access-om2/archive/ *** /g/data/e14/mv7494/ENSOAnt_input/

To Do:

clean up scripts
upon acceptance, check final order of SI figures and update the list including the link to scripts
upon acceptance, check all data and update metadata in the ENSOAnt_data folder
rename scripts so they are easier to understand
when final, push to zenodo and create doi

licongren/ENSO-Antarctica_scripts