Spatial dependence of extreme seas in the North East Atlantic from satellite altimeter measurements

The extremal spatial dependence of significant wave height in the North East Atlantic is explored using Joint Altimetry Satellite Oceanography Network satellite altimeter observations for the period 2002–2018, and a spatial conditional extremes model motivated by the work of Heffernan and Tawn. The analysis involves (a) registering individual satellite passes onto a template transect, (b) marginal extreme value analysis at a set of locations on the template transect and transformation from physical to standard Laplace scale, (c) estimation of the spatial conditional extremes model for a set of locations on a template transect, and (d) comparison of extreme spatial dependence for different template transects. Inferences for two transects considered are qualitatively similar; however, for the “normal ascending” transect running approximately south-west to north-east lying between Iceland and the United Kingdom, extremal spatial dependence is found to decay more quickly than for the second “opposite descending” transect running approximately north-west to south-east to the west of Ireland