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Will the “meteotsunamis” become more numerous?

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How will the meteotsunamis – a relatively unknown phenomenon – in the decades to come? Little studied so far, this question is the subject of a dedicated scientific campaign on European coasts. The preliminary results support the hypothesis of a significant increase in risk, in particular in the Mediterranean area.

When we talk about the phenomenon of tsunami, we usually think of ocean waves triggered as a result of an underwater volcanic eruption or earthquake. However, there is also a lesser known category, the meteotsunamis, whose triggers are this time of atmospheric origin. Outside of lakes, it is most of the time sudden pressure disturbances linked to gravity waves.

Any coast separated from the seabed by a relatively wide continental shelf is exposed to the risk of meteotsunami – or meteorological tsunami. However, although the phenomenon is usually less powerful and more localized than classic tsunamis, it is nevertheless able to cause significant damage in vulnerable regions. To better anticipate and protect against such events, a precise understanding of their operation is therefore necessary.

SHExtreme project: understanding and anticipating meteotsunamis

From this perspective, the issue of climate change inevitably arises. The meteotsunamis will they be more and more frequent as the planet warms? And what about their intensity? It is, among other things, to answer these questions that the project SHExtreme was born. By studying the physical processes at work and how they are expected to evolve in the future, the researchers hope to provide sufficient illumination to allow efficient adaptation of exposed coastal areas. Started in September 2020, the project is expected to continue until August 2025.

Atmospheric gravity wave uncovered by the condensation of water vapor. This is what gave birth to this amazing roll-shaped cloud. Credits: NASA.

“We know how the atmosphere and the ocean interact … but we want to know what precisely helps these atmospheric processes to develop, what kind of larger scale conditions allow these finer processes”, detailed Jadranka Šepić, meteorologist at the University of Split (Croatia) and director of SHExtreme. An important point to note and that even if the conditions conducive to meteotsunamis do not change, the mere rise in sea level is enough to accentuate the vulnerability of the coastal environment.

“The first thing is thatthey will occur from a higher sea level, so they will be more dangerous ”, confirms the researcher. “But the second thing we need to check is what will happen to these gravity waves. Will they happen more or less often? If they occur less often, the two effects may cancel each other out. But if we have more, then there is a problem: you have a meteotsunami which is more likely to occur and which will start from a higher sea level ”.

The Mediterranean, a particularly exposed region

The preliminary results available to date show an increase in certain sectors of the Mediterranean. A particularly vulnerable region because it consists of an extensive coastline and inhabited by a large population. It is mainly in summer, where the risk is naturally present, that the increase is predicted. In question, the rise of hot and dry air from the Sahara, 1,500 to 2,000 meters above azure waters. The particular superposition of air masses that results almost always leading to the occurrence of gravity waves.

However, in areas such as the Balearic Islands, the occurrence of these Saharan ascents should increase. The frequency of meteotsunamis who accompany them would therefore do the same. These results nevertheless remain to be confirmed and specified in the years to come. “We hope to be able to show which parts of European coasts are most in danger, now and also in the future”, Jadranka Šepić advances. What is certain is that, one way or another, the project SHExtreme will be rich in lessons.



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