THE RECENT INCREASE IN NORTH-ATLANTIC WAVE HEIGHTS

The nature and causes of the recent increase in North Atlantic wave he ights are explored by combining a numerical hindcast with a statistica l analysis. The numerical hindcast incorporates a IO-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 se a lever pressure (SLP) data is determined by means of a canonical corr elation analysis (CCA). Within the analysis domain, most of the varian ce in SWH and SLP is captured by two pairs of joint patterns. The lead ing pair consists of a SLP dipole resembling the North Atlantic Oscill ation (NAG) and a SWH dipole in spatial quadrature relation to it. Usi ng the CCA results, an extended statistical hindcast of monthly wave f ields is generated from sea level pressure data and used to quantitati vely estimate the systematic increase in wave heights since the 1960s. It is shown that an increasing trend in SWH at several northeast Atla ntic 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 degrees N has decreased during the same period.