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 digitized 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 small jump 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 flashes over the Gulf of Finland were on average over ten 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.
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.
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