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Research takes steps to improve the ocean wave climate record 

Work by the Climate Change Initiative’s Sea State project team has produced a new long-term global record of ocean waves that is helping to understand the evolution of marine climate and its impacts. 

The sea state climate, or simply 'wave climate' is a statistical description of the oceans long-term surface wave pattern. Sea state is one of several Essential Climate Variables required by the UNFCCC to support the understanding of the climate system, while also having a range of ocean and coastal engineering applications.

Wave hindcasting

The researchers, from the Institut de Physique du Globe de Paris and Brest University and including Fabrice Ardhuin, the Sea State_cci project science lead, employed a technique often referred to as hindcasting in a recently published paper, titled Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016).

As surface waves are generated by wind, the authors used wind data from the Climate Forecast System Reanalysis (CFSR) – a dataset recomputed by accounting for the interactions of the various components of the Earth system– to drive a model of the ocean’s long-term wave field from the late 1970s through to 2016 and compare it to the observations.

Benefits of altimeter data

Importantly, the team adjusted the output in line with wave height observations from satellite altimeters, generated by the Sea State_cci and its precursor project, GlobWave. These altimeter observations data were calibrated across several different satellite missions, and so provided a source of independent consistency over the time series.

The authors performed the analysis using monthly averages of the wave heights, which makes the output more suitable for use in climate studies. Moreover, they found that applying the altimeter-based adjustments significantly reduced errors in the wave field. They noted also that the upper wave heightsthroughout the hindcast were more stable, so the adjusted datasets appears to be more suitable for investigating extreme wave events.

Going to earlier times with seismometers

The paper also demonstrated the capability of using seismic data that record “microseisms”, a background seimic noise generated by ocean waves, and for which data exist going back to the 1890s or in regions when no other data exists for validating the satellite data. Hence using global seismic arrays, it is possible to validate sea state variability in the southern hemisphere and for years before 1993.  

Sea State_cci project

Part of the ESA Climate Change Initiative, the Sea State project represents a sustained effort to deliver global, high-quality sea-state information observations for climate. 

This project aims to build on the first multi-mission inter-calibrated satellite wave dataset produced as part of the ESA GlobWave project, by improving its accuracy and long-term stability to make it better suited to the requirements by the climate science and modelling communities.

Project page --> cci.esa.int/seastate

Paper reference --> Justin E. StopaFabrice ArdhuinEleonore Stutzmannand Thomas Lecocq(2019). Sea State Trends and Variability: Consistency Between Models, Altimeters, Buoys, and Seismic Data (1979–2016)https://doi.org/10.1029/2018JC014607