The World Ocean Wave Fields Discerned From ERA-Interim Spectra

A wave field is a spatial expanse of the ocean surface in which waves of a single meteorological event are generated and propagate until their energy dissipates and disperses to the point where they are not detectable any further. Since water as a transport medium allows the superposition of waves of different sizes traveling in different directions, the typical sea surface is composed of several coexisting and overlapping fields. Historically, the methods for describing waves were based on bulk parameters (e.g., H-s, T-z), but the modern methods based on the wave spectrum, provide us with all the information necessary to distinguish individual wave fields out of the composed set. Weather prediction centers archive nowadays point spectra time series with global coverage and spanning long periods of time. The statistical characterization of such data shows that long-term spectral patterns are few and well defined at each location, and they can be associated with a specific meteorological forcing (e.g., distant swells, trade-winds, local jets). The objective of this work is to consolidate the local point information as to obtain spatially coherent wave fields, discerning them from each other to determine their characteristics. Individual wave fields can be regarded as a new source of information, useful for a wide range of applications such as data assimilation, sediment transport, biomass productivity, among others. For climate-related purposes time and space variability can be analyzed, identifying trends, anomalies, and tele-connections. These climate aspects are explored here through an illustrative example focused on the southern trade-winds' field. Plain Language Summary Wind-generated waves on the ocean surface continue to exist long after the wind intensity decreases, changes direction, or ceases altogether. This means that the surface of the water has a longer memory of the effect of the wind than the atmosphere itself. Furthermore, our current methods for wave description record all the small and large waves traveling in different directions by means of the basic variable, which is the wave spectrum. Climate prediction centers produce and store wave spectra with global coverage, spanning time periods of decades. In this way, detailed atmospheric information can be obtained from wave data, with the advantage that the signal of waves is more stable, regular, and easier to analyze than the signal of the wind itself. In this study, a new methodology is presented to extract wave fields from series of spectra. This information provides a better insight in various fields of application, such as climate variability, weather model predictions, among others.