the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
How do extreme ENSO events affect Antarctic surface mass balance?
Abstract. Extreme El Niño-Southern Oscillation (ENSO) events have far-reaching impacts globally, yet their impacts on Antarctica are poorly understood. In particular, how extreme ENSO events influence Antarctica's mass balance remains uncertain, with few studies considering how extreme events could differ from moderate events. Here, we examine the impacts of past extreme El Niño and strong La Niña events over the period 1979–2018 on surface mass balance of Antarctica using a reanalysis-forced regional climate model. We find that Antarctic surface mass balance does not vary significantly during most of the simulated extreme events. Regional impacts differ between individual events and cannot be generalized across all extreme events. Enderby Land is an exception: significant increases in surface mass balance – approximately 32 % of the regional annual average – occur during all extreme El Niño events. Furthermore, during the 2015/16 extreme El Niño event, widespread and significant surface mass balance changes occurred across East and West Antarctic catchments. These changes are remarkable, extending outside the respective catchments' 5th and 95th probability distributions for September-November period. Our results suggest that future extreme ENSO events may continue to cause significant impacts in Antarctic surface mass balance. However, the magnitude and polarity of the potential impacts cannot be inferred from the limited information available on extremes contained in four decades of historical data. Further investigations using ice core data and large ensemble model simulations are needed to better understand the drivers of the spatial and temporal variability in this system.
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Status: open (until 25 Dec 2024)
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RC1: 'Comment on egusphere-2024-3425', Anonymous Referee #1, 27 Nov 2024
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General comment
This study uses a regional atmospheric model to investigate the impact of extreme ENSO events on the surface mass balance (SMB) of the Antarctic ice sheet. The detailed SMB change in many subregions and catchments is described quantitatively about the simulated results. While such information is of great value, the robustness of the conclusion is rather limited due to the smallness of the sample size (as the authors are well aware). More specifically, the conclusion drawn from the composite analysis of only three samples (for El Nino) is not highly convincing. Such a weakness of statistical power can be augmented by revealing the mechanism: why each ENSO event has a differing impact. Is the SMB difference between cases due to the difference in ENSO itself (and its teleconnection) or the effect of other internal variabilities near Antarctica? Neither the effect of other internal variabilities nor the difference of each ENSO event is analyzed in depth. I think the analysis needs to be strengthened to provide more robust insight into interpreting the results.
Specific comment
- Abstract, L.8-9: It is unclear how much of the observed anomaly is due to the ENSO during 2015/16. Other modes of variability can affect the SMB, and thus the result may not necessarily represent the ENSO response alone. Therefore, I am not sure if the statement of L.11-12 has its evidence within the manuscript.
- Conclusion, L.413-414: I did not understand that “SMB changes differ greatly between the ENSO events” on the one hand and “numerous catchments exhibit similar SMB responses when comparing the impacts of extreme and moderate ENSO events” on the other. How are they consistent? Does this indicate that the observed feature does not represent ENSO response? It is misleading to conclude that the SMB response (signal) to extreme and moderate ENSO events is similar if noise and noise are compared (or if the signals are embedded by noise due to the small sample size).
- Without the presented mechanism, it is unclear whether the differences between ENSO events are due to the diversity of ENSO itself or whether they are affected by other internal modes of variability. It would be helpful to present wave trains from the tropics to the Antarctic so that the link to each ENSO event becomes more visible. Then, whether the observed difference in the SMB anomaly arises from the difference in ENSO influences or the local variability may become clearer. There might be other ways to distinguish.
- In Fig. 3, the SLP anomaly appears different for each extreme ENSO. It would be helpful to show moisture fluxes and explain why the SMB anomaly in Enderby Land is the same for all three cases despite different SLP responses. It was only explained by noting that the location is in the center of the action.
- It is unclear what the benefit of using the regional model is. If the authors draw Figs 3 and 4 from the ERA5 dataset, are they very different? The authors should state the advantages of using the regional model. In particular, the resolutions of both models are not so much different (0.25 degrees vs. 27 km), and the SMB seems to be controlled primarily by moisture transport specified by the boundary conditions.
- Figures 3 (and 4): Please stress the meaning of statistical significance here. How should one interpret the statistical significance of a single event when each ENSO-induced SMB is so different (including signs in some places) from the others? Or note that the anomaly is significantly different from the baseline but it does not necessarily represent the ENSO response (alone).
Citation: https://doi.org/10.5194/egusphere-2024-3425-RC1
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