Abstract
Abstract. We analyse changes in meteotsunami occurrence over the past century (1922–2014) in the Gulf of Finland, Baltic Sea. A major challenge for studying these short-lived and local events is the limited temporal and spatial resolution of digital sea level and meteorological data. To overcome this challenge, we examine archived paper recordings from two tide gauges, Hanko for 1922–1989 and Hamina for 1928–1989, from the summer months of May–October. We visually inspect the recordings to detect rapid sea level variations, which are then digitised and compared to air pressure observations from nearby stations. The data set is complemented with events detected from digital sea level data 1990–2014 by an automated algorithm. In total, we identify 121 potential meteotsunami events. Over 70 % of the events could be confirmed to have a rapid change in air pressure occurring shortly before or simultaneously with the sea level oscillations. The occurrence of meteotsunamis is strongly connected with lightning over the region: the number of cloud-to-ground (CG) flashes over the Gulf of Finland were on average over 10 times higher during the days when a meteotsunami was recorded compared to days with no meteotsunamis in May–October. On a monthly level, statistically significant differences between meteotsunami months and other months were found in the number of CG flashes, convective available potential energy (CAPE), and temperature. Meteotsunami occurrence over the past century shows a statistically significant increasing trend in Hamina, but not in Hanko.
Highlights
On 29 July 2010, in Pellinki, in the Porvoo archipelago, Gulf of Finland (Fig. 1), a summer resident witnessed an exceptional event:I have spent all my summers in Pellinki, for the 50th time, and from 1989 in this place
For Hanko, data from the 1980s is largely missing (Fig. 5) and there are only three possible events found in the tide gauge charts, of which one is detected in the 15 min data
Over 70 % of the events were confirmed to coincide with a sudden change in air pressure
Summary
On 29 July 2010, in Pellinki, in the Porvoo archipelago, Gulf of Finland (Fig. 1), a summer resident witnessed an exceptional event:. I have spent all my summers in Pellinki, for the 50th time, and from 1989 in this place. During that time I have seen the water rise, fall and flow in various ways, but what I saw on 29 July was something totally new. When I stepped out of the door on that beautiful and calm morning I heard an exceptional sound, like a foaming torrent. . My impression is that during that time (40 min) the water rose and fell about 40 cm 3–4 times. The waves rose very rapidly, in 2–3 min (Eyewitness report, translated from Finnish)
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