Meteotsunami

A meteotsunami is born from the interaction of the atmosphere and the sea. Usually a thunder or a gust front moves over the area, and effects a small change in air pressure. When the front moves over the sea with a speed that is equal to the velocity of the tsunami wave in the sea, the front will intensify the wave it created continuously.

Meteotsunami acts like a tsunami wave. A tsunami wave moving in deep water is imperceptible, but as the wave arrives to the shore its energy packs into a smaller water volume and the wave height grows significantly. The wavelength can be up to kilometers long, which is much bigger than with normal wind induced waves.

Meteotsunamis are not as powerful as tsunamis caused by earthquakes, and notable oscillations in water level are usually restricted in individual bays or straits. The phenomenon is detected in places where the shape of the coast and the sea floor intensify the wave. In Finland the wave heights have been around a meter at most, and they have not caused any significant damage. Unexpected currents and changes in water level can still cause dangerous situations for boaters.

The phenomenon is quite common e.g. at the Mediterranean, where it is known as a rissaga. In Finland noticeably large meteotsunamis are rare, but small changes in water level caused by the same phenomenon are more common than thought before.

On the 8th August 2010 a strong thunder storm moved over the Gulf of Finland from south to north and effected a meteotsunami. The time is UTC-time. Source: Pellikka et al. 2014.

Observations about rapid sea level changes in Finland that may be meteotsunamis, can be reported to the Oceanographic Services, meripalvelut@fmi.fi or by telephone 029 539 6436.