Swell and Wind-Sea Distributions over the Mid-Latitude and Tropical North Atlantic for the Period 2002–2008

We present an analysis of wind-sea and swell fields for mid-latitude and tropical Atlantic for the period 2002–2008 using a combination of satellite data (altimeter significant wave height and scatterometer surface winds) and model results (spectrum peak wave period and propagation direction). Results show a dominance of swell over wind-sea regimes throughout the year. A small but clear decrease in swell energy and an associated increase in wind-sea potential growth were observed in the NE trade winds zone. A seasonal summertime increase in wind-sea energy in the Amazon River mouth and adjacent shelf region and in African coast was apparent in the results, probably associated to a strengthening of the alongshore trade winds in these regions. Albeit with a significantly smaller energy contribution of wind-seas as compared to swell energy, we could say that a kind of mixed seas is more evident in the trade winds region, with the remaining area being highly dominated by swell energy. An analysis of wave-age shows the absence of young-seas. Only ~2% of all data points was classified as wind-sea, a classification confirmed by a fit to a theoretical relation between wind speed, peak period, and significant wave height for fully developed wind-seas. 1. Introduction Information on wave conditions is critical for human activities at sea. Among other activities, shipping, fishing, offshore industry, naval operations, coastal management and protection, can be adversely affected by wave conditions [1]. Government officials need timely wave information and forecasting results for decision-making. These information are necessary in the preparedness for and mitigation of ocean disasters, as well as sea-going rescue activities. Wave information may also be important in the calculations of ocean-atmosphere exchange of heat and momentum. It is now well established that the drag coefficient , needed for calculating the wind stress and momentum fluxes, is dependent on wave height or wave age [2]. At very high winds and waves, may be smaller than conventionally calculated due to formation of foam layers caused by steep wave breaking water that is sheared by the strong winds [3–5]. These results indicate that wave information should be taken into account in atmospheric modeling, particularly for cases of very strong weather systems. Perhaps the most used lowest order classification of wave regimes is that one which separates the wave field into either, wind-sea or swell. The first regime is associated to a growing or equilibrium wave spectrum where peak period waves have