Some aspects of the seasonal sea level variations around Spain

Abstract

Tide gauge stations are used to investigate the seasonal variability of sea level around Spain, which exhibits a well‐defined annual cycle and a small but distinguishable semiannual cycle in all stations. The contribution of different sources to observed sea level has been analyzed. The effect of wind and atmospheric pressure has been explored, analyzing sea level residuals computed with a barotropic ocean model forced by the meteorological fields. Sea level corrected for meteorological forcing contains only an annual signal, indicating that the semiannual cycle in the observed sea levels is mainly forced by these meteorological agents. Additional data sets (sea surface temperature satellite images and climatologies) are used to show that the annual cycle is related to the seasonal steric anomaly, which accounts for ∼60% of the cycle amplitude. The lack of agreement between the annual phases of sea level and steric anomaly cycles for the stations located in the continental margin of the Atlantic Ocean suggests the existence of other effects in the observed sea levels related to seasonal changes in ocean circulation. On the contrary, open‐ocean stations of the Canary Islands have sea level annual cycles phase locked with the steric anomaly cycles, although amplitudes differ significantly from one station to the other. This fact is interpreted as the local response to large‐scale seasonal fluctuations of the Canary Current. Sea level cycle in stations within the semienclosed Mediterranean Sea suggests the existence of a hydrological cycle that must include a seasonal barotropic signal through the Strait of Gibraltar.