| 10 Apr 2026
Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength
Abstract. An intermediate-complexity moist general circulation model is used to investigate the forcing of localized storm tracks by land–sea contrast, horizontal gradients in ocean heat uptake, planetary albedo, and topography. The additivity of the response to these building blocks is investigated. Building on previous work focusing on stationary waves, the storm track patterns and strength are not simply the linear additive sum of the response to each surface inhomogeneity. As observed on Earth, the SH storm tracks are stronger than those in the NH, and also stronger over ocean basins than over continents. In this model, the most important building block for this asymmetry is land-sea contrast, however, there is substantial non-additivity both in the regional structure and also the hemispheric asymmetry. An energy budget perspective offers some insight on the causes of the non-additivity, and highlights how the net impact of each building block on outgoing longwave radiation is dependent on the existence of the other two. Relatively small changes in oceanic heat transport from the Southern Ocean to the North Atlantic have a pronounced impact on the individual terms making up the energy budget, however there is substantial cancellation between these terms leading to a small impact on the NH vs. SH asymmetry in storm track strength. The detailed structure of albedo has a weak impact on the NH vs. SH asymmetry due to substantial cancellation between the changes in individual terms making up the energy budget, even though the albedo profile has a large impact on the overall transient eddy activity in each hemisphere.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Weather and Climate Dynamics.
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Review of “Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength”
This paper uses the MiMA GCM to investigate how three surface inhomogeneities, land-sea contrast, topography, and ocean heat transport, individually and jointly shape the zonal localization and hemispheric asymmetry of midlatitude storm tracks. The authors quantify both isolated and full nonlinear responses to each building block, and use a moist static energy budget to attribute the stronger SH storm tracks to specific terms in the energy balance. The main conclusions are that (i) all three building blocks contribute to storm track localization with substantial non-additivity, (ii) land-sea contrast is the most important factor for the NH/SH asymmetry, and (iii) observationally poorly constrained ocean heat transport can have significant effects on the non-additivity of the different surface inhomogeneities.
The experimental framework is well-designed and represents clear progress over earlier idealized studies by combining realistic geography with the flexibility to isolate individual forcings, and by comparing the NH and SH. The conclusion that storm track strength is very sensitive to uncertainties in ocean heat transport is an important result and should inspire future research. This study contains a wealth of results, for which there is simply not enough space for discussion. I believe the authors did a great job at summarizing the detailed analysis and condensing out the most important take-home messages. Nevertheless, I feel two aspects deserve more attention in the discussion of the results: (i) the role of moisture, and (ii) the interpretation of the weakening effect of land-sea contrast on the storm tracks.
General comments
The role of moisture: Moisture has significant effects on the organization of storm tracks through latent heat release (e.g., Schemm, 2023; Auestad et al., 2025), and its effects on blocking anticyclones are well documented (e.g., Steinfeld et al., 2020). Hence, I assume that the presence of moisture will also have a role in partitioning MSE fluxes into transient eddy and stationary eddy contributions, which will likely be modulated by the separate building blocks as well. While this is beyond the scope of the current analysis, the progress in our understanding of the role of moisture for storm track structure since Brayshaw’s studies, in my opinion, would motivate a short discussion in the outlook section of this paper.
The weakening effect of land-sea contrast: The result that land-sea contrast weakens storm track strength was a bit unintuitive to me at first. I believe that in this study, this can be mostly understood as a localization of the storm tracks, and with that the introduction of stationary waves, and so I agree with the reasoning of the study. However, from a weather perspective, land-sea contrast in the North Pacific and North Atlantic storm tracks has been shown to invigorate cyclone development (Brayshaw et al. 2009). First, such air-sea interaction can again impact the organization of the storm tracks (e.g., Wenta et al., 2024). Second, the scope of WCD also aims at connecting weather and climate dynamics, and here there would be an opportunity to achieve this by adding some more context to the presented results, that would also strengthen the relevance of the work for other communities.
Specific comments
L198: In section 3, the T45 run (Fig. 1d) also struggles with the tilt of the NA storm track when compared to T85 (1b) and ERA5 (1a). The tilt is a key zonal asymmetry in the NH with large relevance for the downstream climate, so I suggest adding this aspect to the discussion of the model differences here.
L232: You mention a damping effect of TOPO on the SH TKE, particularly for Fig. 6f. But there is also a pronounced equatorward shift of the TKE. Visually the weakening tendency seems more prominent in the SH. First, is there a good reason you do not mention the meridional shift effect? And second, why is there an opposing sign in this shift between the hemispheres (poleward shift in the NH, but an equatorward shift in the SH)?
L432-433: In afar could the strengthening of stationary eddies and the weakening of transient eddies through the introduction of surface inhomogeneities simply be understood as a localization of the storm tracks in longitude?
Technical comments
Figure 3 caption: ?? equation
L159: Check citation format Oort and VONDER
References
Auestad, H., Shibu, A., Ceppi, P., & Woollings, T. (2025). The latent heating feedback on the mid‐latitude circulation. Geophysical Research Letters, 52(18), e2025GL116437.
Brayshaw, D. J., Hoskins, B., & Blackburn, M. (2009). The basic ingredients of the North Atlantic storm track. Part I: Land–sea contras
Schemm, S. (2023). Toward eliminating the decades‐old “too zonal and too equatorward” storm‐track bias in climate models. Journal of Advances in Modeling Earth Systems, 15(2), e2022MS003482.
Steinfeld, D., Boettcher, M., Forbes, R., & Pfahl, S. (2020). The sensitivity of atmospheric blocking to upstream latent heating–numerical experiments. Weather and Climate Dynamics, 1(2), 405-426.
Wenta, M., Grams, C. M., Papritz, L., & Federer, M. (2024). Linking Gulf Stream air–sea interactions to the exceptional blocking episode in February 2019: a Lagrangian perspective. Weather and Climate Dynamics, 5(1), 181-209.