The global distribution of the seasonal sea level cycle calculated from coastal tide gauge data

Data from 1043 tide gauges around the world have been used to map the global distribution of the seasonal cycle of mean sea level at the coast. Large-scale features, such as the autumn-spring phase dependence of the annual cycle in each hemisphere, can be seen to be superimposed upon a complexity of regional spatial variability. This variability stems from local meteorological, oceanographic and hydrological (river runoff) forcings. Significant differences in the seasonal cycle are observed at the opposite sides of even small land areas. At ocean islands the annual cycle usually has an amplitude ≤ 75 mm, while that of the semiannual component is below 20 mm. It is evident that coastal recorders cannot be used to infer the seasonal cycle of sea level over most of the deep ocean and that the future will require joint analyses of tide gauge and satellite altimeter data.