Pierre-Yves Le Traon

The 2012 Fridtjof Nansen Medal is awarded to Pierre-Yves Le Traon for his excellent contributions to and leadership in establishing satellite altimetry as a quantitative observational technique for research on mesoscale ocean variability, ocean circulation and sea level.

Pierre-Yves Le Traon from the very beginning of his career has been involved in oceanography from space. Early developments of the first high precision satellite altimetry mission Topex/Poseidon lead to finding a major role in promoting oceanographic applications of this technique. At CLS, a subsidiary of the CNES, the French Space Agency, he was strongly involved in subsequent altimeter missions, in the end leading to a data set of more than 18 years of continuous multi-satellite and equal high-quality coverage of the world’s ocean. Le Traon’s work led to spectacular improvements of the accuracy of altimetry-based sea surface heights measurements (from several decimetres to 1-2 cm) allowing extremely important results in ocean dynamics using space data. His early work on the Geosat data started his careful interpretation of altimeter data (Le Traon et al., 1990). His foresight of using TOPEX data for improving the ERS-1 data (Le Traon et al., 1995), plus a series of papers in 1995-1999, laid the foundation for creating the multi-mission data set that was described in Ducet et al. (2000). As a team leader and scientifically inspiring he initiated important studies, for example, Ducet and Le Traon (2001) on kinetic energy and Reynolds stress, Brachet et al. (2004) on eddy propagation, and Pascual et al. (2006) on the impact of combined data from 4 altimeters. His major scientific contributions thus cover several areas of ocean dynamics, ranging from meso scale ocean circulation using multi mission altimetry data, its importance in the global ocean circulation, for the Mediterranean sea level he showed the major role of NAO (North Atlantic Oscillation)-driven atmospheric forcing on the Mediterranean circulation and sea level variability. In addition to providing new and important insights into the spatial structure of mesoscale variability, his work provided a benchmark against which all numerical ocean general circulation models have been and continue to be compared to assess model performance. Le Traon’s contribution to developing and establishing operational oceanography in France and in Europe is remarkable. He contributed much to the concept of data assimilation (through GODAE), that is the basis for oceanic prediction using ocean circulation models, and space and in situ data. The emergence of the MERCATOR group in France and the “MYOCEAN” GMES (Global Monitoring for Environment and Security) project in Europe was only possible by involvements of scientists like Le Traon. His keen interest in sustained operational oceanography got him involved in the development of the Argo project. In several studies he demonstrated the use of altimetry data to validate the Argo temperature and salinity data and on the determination of the steric contribution to sea level change, moving his interest to climate studies. LeTraon’s contribution has firmly established altimetry as an oceanographic tool. LeTraon is honoured with the Nansen Medal 2012 for his impressive contributions to many aspects of observational oceanography both from space and in situ data.