The Recent Increase in North Atlantic Wave Heights

Abstract

The nature and causes of the recent increase in North Atlantic wave heights are explored by combining a numerical hindcast with a statistical analysis. The numerical hindcast incorporates a 10-yr history (1980?89) of North Atlantic, twice daily wind analyses to generate a monthly averaged significant wave height (SWH) history. The hindcast compares favorably with published monthly averaged SWH observations. The link between model-generated wintertime monthly SWH and monthly averaged sea level pressure (SLP) data is determined by means of a canonical correlation analysis (CCA). Within the analysis domain, most of the variance in SWH and SLP is captured by two pairs of joint patterns. The leading pair consists of a SLP dipole resembling the North Atlantic Oscillation (NAO) and a SWH dipole in spatial quadrature relation to it. Using the CCA results, an extended statistical hindcast of monthly wave fields is generated from sea level pressure data and used to quantitatively estimate the systematic increase in wave heights since the 1960s. It is shown that an increasing trend in SWH at several northeast Atlantic locations since 1960 or so is related to the systematic deepening of the Icelandic low and intensification of the Azores high over the last three decades. The analysis suggests that wave height south of 40°N has decreased during the same period.