Observing Sea States

Abstract

Sea state information is needed for many applications, ranging from safety at sea and on the coast, for which real time data are essential, to planning and design needs for infrastructure that require long time series. The definition of the wave climate and its possible evolution requires high resolution data, and knowledge on possible drift in the observing system. Sea state is also an important climate variable that enters in air-sea fluxes parameterizations. Finally, sea state patterns can reveal the intensity of storms and associated climate patterns at large scales, and the intensity of currents at small scales. A synthesis of user requirements leads to requests for spatial resolution at kilometer scales, and estimations of trends of a few centimeters per decade. Such requirements cannot be met by observations alone in the foreseeable future, and numerical wave models can be combined with in situ and remote sensing data to achieve the required resolution. As today's models are far from perfect, observations are critical in providing forcing data, namely winds, currents and ice, and validation data, in particular for frequency and direction information, and extreme wave heights. In situ and satellite observations are particularly critical for the correction and calibration of significant wave heights to ensure the stability of model time series. A number of developments are underway for extending the capabilities of satellites and in situ observing systems. These include the generalization of directional measurements, an easier exchange of moored buoy data, the measurement of waves on drifting buoys, the evolution of satellite altimeter technology, and the measurement of directional wave spectra from satellite radar instruments. For each of these observing systems, the stability of the data is a very important issue. The combination of the different data sources, including numerical models, can help better fulfill the needs of users.

Megagravel deposits on the west coast of Ireland show the impacts of severe storms

“…Improvements in ocean data gathering have greatly improved our understanding of storm‐wave behaviour (Ardhuin and Orfila, ; Ardhuin et al ., ), as well as providing better estimates of extreme wave heights (e.g. Takbash et al ., ; Young and Ribal, ).…”

Observing Requirements for Long-Term Climate Records at the Ocean Surface

“…This scope presently excludes the consideration of records derived from satellite data only as these have a maximum record length of about 40 years and are the subject of other papers in this issue (e.g., Ardhuin et al, 2019;Bourassa et al, 2019;O'Carroll et al, 2019). We note that many of the themes contained in this paper are relevant to both in situ and satellite data.…”

“…Substantial effort has been put into the construction of stable and accurate SST records (Merchant et al, 2012(Merchant et al, , 2014. Other variables where satellites will play an important part in the construction of long-term CDR are for clouds and radiation (e.g., Loeb et al, 2012), winds (e.g., Verhoef et al, 2017), and waves (e.g., Young et al, 2011;Ardhuin et al, 2019). However, to date only SST has extended the satellite record back in time using in situ observations.…”

Sea state bias in altimetry measurements within the theory of similarity for wind-driven seas

“…Gommenginger, Srokosz, Challenor et al, 2003a;Quilfen, Chapron and Serre, 2004;Mackay, Retzler, Challenor et al, 2008). However, U 10 being estimated with parametric models contributes an additional error up to 20% (Ardhuin, Stopa, Chapron et al, 2019).…”