Mean Sea Level as seen by other techniques

Tides gauges

The longest sea level time series are provided by tide gauges. Some of them (not many) measured the sea level for more than a century. However, they support the effects of the movements of continents, and are very unevenly distributed around the globe: necessarily close to shore, but many more, and the oldest in Europe and the United States.

In situ temperature/salinity observations

: Maps of thermosteric Sea level trends computed from Argo and XBT data. (Credits S. Guinehut, CLS) .

Global monthly maps of thermosteric (resp. steric) sea level for the 0-700 m layer are constructed from in situ data (Argo profiling floats, XBTs) from the individual Temperature T (resp. Temperature/Salinity T/S).

Models

Sea level trend between 1993 and 2001, computed from Mercator Océan (1/4°) global sea surface height without assimilation (in order not to have the influence of altimetric data, which are among the assimilated data). This map is similar to the one obtained from Topex/Poseidon over the same period, with variations that look alike (e.g. rise of the level over the West Tropical Pacific, drop over the East. (Credits A. Lombard, Legos, G. Garric, Mercator Ocean).

Ocean models describe the ocean in three dimensions (horizontally and vertically) as well as its evolution over time (temporal dimension or fourth dimension). A model is a mathematical description of physical phenomena. For the ocean, as for the atmosphere, the mathematical model describes the movement of fluids (water, air) on the surface of the Earth, as well as transporting of heat (temperature) and matter (salts) associated with the fluid movements. This results in equations which describe the current, the temperature and the salinity at any place in the modelled zone and as a function of time.