OCEAN AND CLIMATE - A QUANTITATIVE ANSWER, TOPEX POSEIDON

Since B. Franklin and F. Arago, the Oceans are known for their regulat or role in the climate evolution. Beyond this simple ascertainment, it is now necessary and possible to quantify more precisely the impact o f the Oceans in climate global changes. Accurate observations at a glo bal scale and over several decades, jointly used with dynamic models, are needed to solve this problem. One dedicated technique is radar alt imetry on-board satellites. Sea surface slopes and derived surface cur rents can thus be measured with a remarkable accuracy. The TOPEX/POSEI DON altimetry mission was optimized to fulfil this objective. this pro ject was jointly conducted by NASA and CNES with support of the associ ated scientific community involved in the design, the evaluation and t he analysis of the system. Two years after the launch (10 August 1992) , the results are even better than expected. Sea surface heights and v ariations are measured at a basin-scale, with an accuracy of 1-2 centi meters over 10 days. Such performances give access to the seasonal cha nges due to the thermal expansion between the two hemispheres, the int erannual variability and the detection and propagation of Kelvin and R ossby waves in the tropical regions. These observations can then be as similated in numerical models to describe and predict the ocean circul ation in four dimensions.