Sea surges around the Gulf of Lions and atmospheric conditions

This paper analyses sea surge variations measured at four tide-gauge stations (Port-Vendres, Sète, Grau-de-la-Dent and Marseille) almost evenly located around the Gulf of Lions (NorthWestern corner of Mediterranean Sea) and their relationships with local-scale winds and regional-scale atmospheric patterns (i.e. weather regimes). On the whole 20th century, more than 80% of sea surge > 20 cm occurs in winter and the analyses focus on October to March semester. There is a strong in-phase relationship between the four tide-gauge stations at hourly and daily time scales on the period 1986–1995. The highest sea surges in the Gulf of Lions are associated with a strong negative phase of the North Atlantic oscillation. Around 70% of sea surge > 40 cm at all stations occur during “Greenland Above” and “Blocking” weather regimes, when extratropical storms travelled on a southern track and are associated with onshore southerly winds that drag water toward the coast of the Gulf of Lions. Port-Vendres and mostly Marseille tide-gauge stations are also sensitive to northerly winds due to the local orientation of the coast. The frequency of southerly winds significantly increases since 1950, while the frequency of northerly winds decreases consistent with the increase of sea surges in the Gulf of Lions.