One of the most surprising discoveries made by altimeters is the amplitude of seasonal signals. The mean variation in sea level is in fact more than 10 centimetres between cold and warm ocean seasons, and even more in enclosed or semi-enclosed seas. This seasonal cycle is roughly two months out of step with the calendar seasons, due to the inertia of the oceans in propagating heat or cold to deeper waters.
One of the major questions today in the ocean/atmosphere and climate fields concerns the production of reliable seasonal climate predictions. Even if it will probably be impossible to predict the weather on a given day more than (at the utmost) two weeks in advance, the ocean’s influence on the atmosphere should enable the trends of the approaching seasons to be forecasted. This is already providing interesting results in tropical areas. Temperate areas are more difficult, but several projects are underway, which are aiming to predict what the weather will be like next summer – drier or wetter, hotter or colder than the average.