| 23 Feb 2026
A Multi-Method Antarctic Atmospheric Blocking Dataset (1979–2024)
Abstract. Atmospheric blocking is a key driver of persistent circulation anomalies and associated extreme events in the Southern Hemisphere, yet its characteristics around Antarctica remain poorly understood due to methodological diversity and the absence of a consolidated, long-term dataset. This study presents a new multi-method Antarctic atmospheric blocking dataset covering the period 1979–2024, derived from ERA5 reanalysis and constructed using multiple blocking detection approaches applied consistently across the Southern Hemisphere (25° S–90° S). The dataset integrates diagnostics based on 500 hPa geopotential height and vertically integrated potential vorticity within a unified framework for spatial filtering, event definition, and temporal tracking. It provides instantaneous blocking masks, spatiotemporally tracked event catalogues, time series, and aggregated climatologies that are directly comparable across methods. The results reveal only weak large-scale similarities in Antarctic blocking across detection approaches, mainly related to high latitude occurrence and seasonal modulation. In contrast, pronounced method dependent diversity is evident in blocking frequency, spatial extent, the number of detected blocking events, and persistence. Geopotential height-based methods identify a broader spectrum of anticyclonic flow regimes, including events extending into the Antarctic interior, whereas potential vorticity-based methods isolate fewer, more spatially confined events that emphasize dynamically coherent upper-level disturbances near the polar vortex. Event-based diagnostics further reveal systematic trade-offs between event frequency and duration, illustrating how different methodological choices preferentially capture either shorter-lived circulation anomalies or more persistent blocking structures. These contrasts arise from the diverse dynamical expressions of blocking at high southern latitudes, indicating that no single diagnostic fully captures Antarctic blocking behavior. Key uncertainties relate to threshold sensitivity, spatial filtering, and diagnostic formulation, which should be considered when interpreting blocking statistics and inter-method differences. By providing a consistent and openly accessible resource, this dataset allows direct intercomparison of blocking definitions, supports evaluation of climate models over Antarctica, and provides a foundation for future studies of blocking-related circulation variability and extreme events.
General comments:
The paper is well structured and readable, and addresses a region that is not commonly discussed in atmospheric blocking papers. While I have some clarifying questions about the methodology below, I think that the overall work is quite robust and a useful contribution to the literature.
Specific comments:
Line 93: How does ERA5 improve representation of the Southern Hemisphere, relative to ERA-Interim, in a manner that is relevant to the topic at hand? Better representation of wind, temperature, moisture transport?
Line 127: If you had hourly data, why not use the full hourly resolution rather than 6hr resolution? Was it resource constraints or something else, like trying to maintain consistency with past papers?
Line 128: What is the vertical resolution? 50hPA, something else?
Sections 2.3.2 and 2.3.3: Initially I struggled to understand the difference between the two methods just based on the text/Table 1. It took looking at the Figure 1 schematic for me to finally understand it . They both sounds like they’re anomaly-based from the descriptions, but one is called “Absolute threshold” and the other is called “standard deviation-based anomaly”. Would suggest revising the text of these two sections to more clearly outline the calculation steps, as Figure 1 does a very nice job of explaining it visually.
Section 2.3.4: The data has 6hr resolution, but the thresholds are established on a daily basis? (my assumption based on line 246) Does that mean that the full day has a single threshold rather than one per time step? If so, why that single daily threshold and not per time step?
Figure 4: Would like to see the polygons in 4b) shown in all items, not just b), so that it is clear which areas are being summarized in Table 2.
Line 429 and Section 4.1/4.2 in general: Would we expect to see much blocking over Antarctica at all for the Z500 gradient method given the constraints of the latitudinal range? Trying to compare the frequencies of the Z500 gradient method and the other methods in the higher latitudes is rather misleading given the different latitudinal extents. Discussion should account for this fact.
Figure 5: as with Figure 4, would like to see the polygons shown so that it’s clear which areas are being summarized in the table
Table 2: Perhaps would be more appropriate as a figure? It’s very hard to easily digest this information in its current format. Suggest something like grouped boxplots.
Figure 9: Would it be possible to provide a background color of a relevant field, such as 500hPA geopotential height, to provide some context to what exactly is being captured by the various methods? It would be interesting to see how “accurate” or “inaccurate” the various methods are or what they are specifically capturing (i.e., a ridge vs a rex block vs an omega block). Perhaps not feasible if it obscures the contours, but maybe worth trying?
Section 4.5: I found this discussion to be rather unsatisfying with respect to the events being shown in Figure 9. It discusses the results in broad strokes rather than referring to what happened during the specific selected events. For example, in 9d, what is going on with those contours off the eastern coast of South America? Did they merge with their respective counterparts in 9e, or was that the detection of a local anomaly rather than a persistent blocking feature?