engleski

High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic preconditioning

During the last decade many national tide gauge networks have been upgraded to measure sea level with a higher sampling rate (1-min). Concurrently, through a number of tsunami warning systems and data sharing services, these data became freely available to scientific community, allowing for regional and ocean studies of high-frequency component of sea level oscillations. Presented study focuses on an analysis of 1-min sea level time series collected at 32 Mediterranean tide gauge stations with 4 or more years of data available between 2008 and 2014. The data is available at the I OC website (http://www.ioc-sealevelmonitoring.org). Sea level time series were de-spiked, de-tided, linearly interpolated, high-pass filtered and analysed. Several important points were revealed: (i) high-frequency sea level oscillations are often widespread and can affect areas from the eastern Spanish to the western Greek coast ; (ii) during the Mediterranean-wide events, oscillations typically first occur in the Western Mediterranean, and then their occurrence propagates within the next few days to the Eastern Mediterranean (Greece) ; (iii) oscillations occur throughout the year but are, depending on area, strongest from April to August ; and (iv) high-frequency sea level oscillations are often associated with higher-than-average mean sea level conditions, adding to a possible danger of flooding ; also, they are occasionally related to dangerous meteotsunami events. Synoptic conditions observed during the 48 strongest events were analysed in more detail. These events typically occur during: (i) presence of low mean sea level pressure with a centre northwest from the affected area ; (ii) inflow of warm African air in the lower troposphere ; (iii) strong south-western winds and the jet at mid-tropospheric levels embedded in (iv) instable atmospheric levels. Analysis of sea level data combined with statistics of appearance of favourable synoptic pattern has a potential to further contribute to the flooding hazard assessment.

sea level; high-frequency; Mediterranean

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