Atmospheric Drivers of Oceanic North Swells in the Eastern Caribbean

Timothy W Hawkins,Theodore Allen,Isabelle Gouirand,Ali Belmadani

doi:10.3390/jmse10020183

Abstract

Large wintertime ocean swells in the Caribbean, known as north swells, generate high surf and expose communities, ecosystems, and infrastructure to hazardous conditions. Empirical orthogonal functions and cluster analyses using ERA5 reanalysis swell data are performed to characterize north swells in the eastern Caribbean and to establish a ranked list of historical events. ERA5 atmospheric and swell data are used to create basin-scale sea-level pressure, surface wind and swell composites for north swell events of different magnitudes. Additionally, storm events are identified in the mid-latitude North Atlantic Ocean. North swells are predominantly generated by storms that intensify off the North American east coast. However, there is a subset of moderately sized swells associated with a westward-located high-pressure system in the North Atlantic. While lower sea-level pressure and stronger surface winds are important for generating larger swells, the location of the low-pressure center and storm track as well the zonal speed of the storm are critical in the development of large eastern Caribbean north swells. The largest such events are associated with storms located comparatively further southeast, with a more zonal trajectory, and slower zonal speed. Large storms located further northwest, with a more southwest to northeast trajectory, and faster zonal speeds are associated with weaker north swells or in many cases, no significant north swell in the eastern Caribbean.

Highlights

Wind-generated surface ocean waves are an illustration of the atmospheric forcing on the ocean, where steady surface winds drive wave growth and subsequent swell propagation across the ocean (e.g., [1])
The North Atlantic wave climate has the largest seasonal variation among ocean sub-basins, which results from a combination of highly variable seasonal wind forcing and Atlantic basin geometry that prevents the penetration of yearround Southern Ocean swells [2,3,4]
While the atmospheric processes that drive ocean waves are mostly restricted to specific latitudinal bands within the North Atlantic sub-basin, waves can propagate over long distances and in various directions in the form of energetic, long-period swell (e.g., [5])

Summary

Introduction

Wind-generated surface ocean waves are an illustration of the atmospheric forcing on the ocean, where steady surface winds drive wave growth and subsequent swell propagation across the ocean (e.g., [1]). The largest (smallest) wave heights and periods are observed in winter (summer) due to increased (decreased) average westerly wind intensity [2]. Climatological wind intensity is modulated by the meridional pressure gradient between the subtropical anticyclone and the subpolar low, the pressure gradient itself being driven by the temperature gradient between the tropics and high latitudes, which peaks in boreal winter. While the atmospheric processes that drive ocean waves are mostly restricted to specific latitudinal bands within the North Atlantic sub-basin (e.g., mid-latitude storm tracks, easterly trade winds, and tropical cyclones), waves can propagate over long distances and in various directions in the form of energetic, long-period swell (e.g., [5]). Boreal wintertime mid-latitude storm activity to the east of the North American continent

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