the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Oct 2025
Topographic Effects of Svalbard on Warm and Moist Air Intrusions into the Central Arctic
Abstract. Warm air intrusions (WAIs) along the North Atlantic pathway are key drivers of warm extremes in the central Arctic. The Svalbard archipelago acts as a major topographic barrier in the middle of this gateway, but its role in modulating WAIs and their impacts has not been studied in detail. We combine (i) high-resolution regional ICON simulations with and without Svalbard’s topography, (ii) Lagrangian back-trajectories, and (iii) observations from the MOSAiC expedition to analyze a strong WAI event in mid-April 2020, and extend the analysis with (iv) climatological composites from an ICON simulation for 2000–2022. Based on the April 2020 case study, we show that Svalbard’s influence can extend ~500 km downstream over sea ice and was observed near 84° N during MOSAiC. The response depends on the static stability of the impinging flow: stable conditions favor flow-around with barrier and gap winds and a broad lee wake, leading to downstream reductions in wind speed (by >5 m s-1), near-surface temperature (>3 K), and column-integrated water vapor (>1 kg m-2). Under less stable flow-over conditions, föhn signatures yield lower-tropospheric warming (>1 K) and drying, reduced low-level cloud cover (>20 %), and decreased (increased) downwelling longwave (shortwave) radiation (>20 W m-2). Springtime composites reveal that these signals recur during southerly advection events, can extend several hundred kilometers into the central Arctic, and vary in character with poleward wind speed, moisture transport, and static stability linked to the synoptic situation. Together, the results demonstrate that Svalbard’s topography systematically modulates the dynamical and thermodynamic imprint of WAIs, with effects detectable far downstream in both model experiments and MOSAiC observations.
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Status: open (until 31 Dec 2025)
- RC1: 'Comment on egusphere-2025-4535', Anonymous Referee #1, 03 Dec 2025 reply
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RC2: 'Comment on egusphere-2025-4535', Benjamin Kirbus, 08 Dec 2025
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Review: “Topographic Effects of Svalbard on Warm and Moist Air Intrusions into the Central Arctic”, J. Landwehrs et al., DOI: 10.5194/egusphere-2025-4535
The manuscript by Landwehrs et al. investigates the impact of Svalbard’s up to ~1700 m high topography on warm, moist air masses intruding into the inner Arctic. The authors begin with a detailed case study of an intense mid-April 2020 Warm Air Intrusion (WAI). They combine ICON simulations (basically a “control” vs. “flat Svalbard” sensitivity study) with shipborne observations collected aboard research vessel Polarstern during the MOSAiC expedition. To further investigate the case, a Lagrangian trajectory analysis is conducted and used to complement the Eulerian model evaluations. Finally, the findings of the case study are generalized, using an ICON model climatology extending over ~20 years in time. Through the wealth of methods applied in a meaningful way, the impact of Svalbard’s mountain ranges on downstream winds, air temperatures, and the surface energy budget in the central Arctic are clearly unraveled.
Overall, this study is conducted with a sound methodological approach, written well, and offers clear and insightful figures. As I am not aware of any such comprehensive investigation of Svalbard’s topographic impact on WAIs existing yet, I think the article will be a very good contribution to the research field.
Below are some minor specific comments I have. All things considered, I recommend accepting the manuscript with minor revisions.
Specific Comments:
- Lines 6-9: Here and throughout the manuscript, you mostly limit your analysis to the effects in the lee of Svalbard (such as the decrease of wind speeds, near surface temperatures etc.). But as you showed in your figures and shortly hinted towards, the effects to the west and east of Svalbard (such as an actual increase in wind speeds) seem just as important and interesting to me. Maybe one or two additional sentences could be added throughout the article to highlight the effects outside the lee more.
- Line 35: There is a comma or semicolon missing before “Elvidge et al.”.
- Lines 41+44: I prefer the term “cloud dissipation” over “cloud clearance”.
- Line 70: please introduce the abbreviation “RV” in “RV Polarstern”.
- Line 82: Why did you limit your climatological analyses to spring? There might be some differences in Svalbard’s topographic influence on WAIs between the seasons. Vertical stability and flow regimes most probably differ, so it might have been interesting to see a seasonal analysis. Furthermore, I would be interested to know if the topographic impact is evolving over time, given that the Arctic climate system is rapidly changing. But these points are more food for thought than a criticism of the article.
- Caption of Figure 3: I would again mention the duration of trajectories (which has a great impact on the data shown) and thus start the caption as “Maximum topography and subsidence for 36-hour backward trajectories…”.
- Caption of Figure 4: here and elsewhere, you mention a Gaussian filter. Can you describe how this was chosen/defined? Additionally, I would specify in the caption that subplots (g,h) relate to ICON_ctrl.
- Lines 172f: I would formulate this a bit more carefully: “The closer match between ICON_ctrl and MOSAiC observations supports the idea that Svalbard’s …”.
- Captions of Figs. 7 & 9: I would adjust the last sentence to “Black squares (circles) indicate air parcel positions 6 (12) hours back in time …”.
- Lines 224f: An interesting point. Does Svalbard mostly cause a diversion/delay of the WAI, or also a change in introduced moist static energy into Arctic? Cloud formation / precipitation / diabatic processes around come to mind. Can it be quantified how much the meridional energy flux is reduced by Svalbard's topography? Again, these are just some ideas / general questions I had.
- Line 264: It could be argued that putting this section (“3.1.4 Topographic effects on moisture and clouds”) before discussing the SEB in 3.1.3, as the difference in cloud structures drives the observed changes. But I think leaving it as-is would also be fine.
- Lines 288f: I don’t find the abbreviated “25-50%ile”, “100%ile” particularly well readable. I would prefer something like “25th-50th percentile”, “100th percentile”.
- Line 289: Please correct the unit of IVT to “kg m-1 s-1”. Please check for correct unit throughout manuscript.
- Line 311f: You write: “potentially due to the release of more latent heat”. Can’t you check in ICON whether this is true or not?
- Lines 330ff: You focus on separating cases with high vs. low stability. Are there any other parameters that determine Svalbard's topographic influence?
- Line 367: You could specify: “Within this wake, Svalbard’s topographic effects in the control vs. flat experiment …”.
- Line 378: You only used the abbreviation “MAM” once. I would leave out defining it, and then here write it out: “March-April-May”.
- Lines 390ff: I agree that these could be very interesting follow-up studies. Using a coupled model for those could be of great benefit.
Citation: https://doi.org/10.5194/egusphere-2025-4535-RC2
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Review of “Topographic effects of Svalbard on warm and moist air intrusions into the central Arctic” by Landwehrs et al.
This manuscript presents a detailed model based case study of the impact of Svalbard’s topography on a warm air intrusion event in the Arctic, that impacted the MOSAiC expedition in April 2020 and demonstrates the impact that Svalbard’s topography has on downstream atmospheric conditions. The case study analysis is thorough and contrasts strong versus weak stability flow over Svalbard. A longer time period climatological analysis is also presented confirming that results seen in the case study occur regularly. The manuscript is well written and the figures clearly display the relevant results. As such I recommend accepting this manuscript with very minor revisions, described below.
Minor comments
Line 130: It would be useful to state the number of trajectories initialized at each pressure level and the total over all pressure levels.
Figure 3: In the figure caption or text please explain why not all times and heights have plotted values in this figure. Is it because only trajectories that have passed over Svalbard are shown so times and heights without plotted data indicate trajectories that did not pass over Svalbard?
Line 196: Fig 2a should be Fig 2b since this sentence is referring to wind speed not temperature.