Meteotsunamis in the northern Baltic Sea and their relation to synoptic patterns

Low-tidal coastal regions, such as the Baltic Sea, are known to be particularly vulnerable to exceptional high-frequency sea level oscillations such as meteotsunamis. Possibilities of studying sub-hourly sea level variations have recently improved, owing to advancement in temporal resolution of tide gauge observations. In this work, we study high-frequency (period <6 h) sea level oscillations – strongest of which we consider to be meteotsunamis – on the coast of Finland, in the northern Baltic Sea, using quality-checked 1-min observations collected between 2004 and 2015 at 13 tide gauge stations. The intensity of the oscillations varies substantially between stations due to local coastal morphologies. The most intense oscillations predominantly occur in late summer and autumn, although the seasonality may differ between sub-regions. Measured atmospheric data and reanalysis products related to the strongest events reveal two distinct types of atmospheric processes and governing synoptic patterns that are mostly associated with warmer and colder period of year. Consequently, meteotsunamis are classified as summer-type or winter-type events. Most of the summer-type events are caused by surface atmospheric pressure jumps associated with mesoscale convective systems, which are advancing northward over the sea and are embedded into a mid-troposphere jet overtopping an inflow of warm low-troposphere air. At the surface, weak air pressure gradients due to a high-pressure area to the east and a low-pressure area to the west of the Baltic are usually found during summer-type events. The winter-type events, on the contrary, are mostly related to cold fronts and strong northerly-northwesterly-westerly winds at the surface layer. Contrary to summer-type events, surface atmospheric pressure jumps are not necessarily detected during the strongest winter-type events. Deep lows and extratropical cyclones are commonly centered to the north of the Baltic Sea and, at the mid-troposphere level, there is a pronounced westerly jet stream. A hypothesis about the generation mechanism of intense high-frequency sea level oscillations is given: Proudman resonance appears to be the main driver of summer-type events, whereas the main driver of winter-type events is less clear.

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Funding Information: This work was supported financially by VYR (National Nuclear Waste Management Fund) through SAFIR2018 (The Finnish Research Programme on Nuclear Power Plant Safety 2015–2018). Comments raised by the two anonymous reviewers greatly improved the manuscript. Travel of H. P. was supported by the Doctoral Programme in Atmospheric Sciences of the University of Helsinki. The work of J. Š. was supported by ERC-StG-853045 SHExtreme and by HRZZ IP-2019-04-5875 StVar-Adri. We thank Jan-Victor Björkqvist and Milla Johansson for helpful comments and Hanna Boman for help with the sea level data. We thank Krešimir Ruić (Faculty of Science, University of Split, Croatia) and Clare Lewis (University of Reading and Plymouth Marine Laboratory, UK) for sharing information on the unpublished Adriatic and the northern Europe meteotsunami events, respectively. The study has utilized research infrastructure facilities provided by FINMARI (Finnish Marine Research Infrastructure network). Funding Information: This work was supported financially by VYR (National Nuclear Waste Management Fund) through SAFIR2018 (The Finnish Research Programme on Nuclear Power Plant Safety 2015–2018). Comments raised by the two anonymous reviewers greatly improved the manuscript. Travel of H. P. was supported by the Doctoral Programme in Atmospheric Sciences of the University of Helsinki . The work of J. Š. was supported by ERC-StG-853045 SHExtreme and by HRZZ IP-2019-04-5875 StVar-Adri. We thank Jan-Victor Björkqvist and Milla Johansson for helpful comments and Hanna Boman for help with the sea level data. We thank Krešimir Ruić (Faculty of Science, University of Split, Croatia) and Clare Lewis (University of Reading and Plymouth Marine Laboratory, UK) for sharing information on the unpublished Adriatic and the northern Europe meteotsunami events, respectively. The study has utilized research infrastructure facilities provided by FINMARI (Finnish Marine Research Infrastructure network). Publisher Copyright: © 2022 The Authors

Keywords

Baltic sea, High-frequency sea level oscillations, Meteotsunami, Sea level extremes, Sea level variations

DOI

10.1016/j.wace.2022.100527

Citation

Pellikka, H, Šepić, J, Lehtonen, I & Vilibić, I 2022, ' Meteotsunamis in the northern Baltic Sea and their relation to synoptic patterns ', Weather and Climate Extremes, vol. 38, 100527 . https://doi.org/10.1016/j.wace.2022.100527

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https://urn.fi/URN:NBN:fi:aalto-202211306674

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[article-cris] Insinööritieteiden korkeakoulu / ENG

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Meteotsunamis in the northern Baltic Sea and their relation to synoptic patterns

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