Variability of the Winter Wind Waves and Swell in the North Atlantic and North Pacific as Revealed by the Voluntary Observing Ship Data

Abstract

This paper analyses secular changes and interannual variability in the wind wave, swell, and significant wave height (SWH) characteristics over the North Atlantic and North Pacific on the basis of wind wave climatology derived from the visual wave observations of voluntary observing ship (VOS) officers. These data are available from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) collection of surface meteorological observations for 1958-2002, but require much more complicated preprocessing than standard meteorological variables such as sea level pressure, temperature, and wind. Visual VOS data allow for separate analysis of changes in wind sea and swell, as well as in significant wave height, which has been derived from wind sea and swell estimates. In both North Atlantic and North Pacific midlatitudes winter significant wave height shows a secular increase from 10 to 40 cm decade Ϫ1 during the last 45 yr. However, in the North Atlantic the patterns of trend changes for wind sea and swell are quite different from each other, showing opposite signs of changes in the northeast Atlantic. Trend patterns of wind sea, swell, and SWH in the North Pacific are more consistent with each other. Qualitatively the same conclusions hold for the analysis of interannual variability whose leading modes demonstrate noticeable differences for wind sea and swell. Statistical analysis shows that variability in wind sea is closely associated with the local wind speed, while swell changes can be driven by the variations in the cyclone counts, implying the importance of forcing frequency for the resulting changes in significant wave height. This mechanism of differences in variability patterns of wind sea and swell is likely more realistic than the northeastward propagation of swells from the regions from which the wind sea signal originates.

Periodicity and patterns of ocean wind and wave climate

“…The resemblance to the wind results implies this mode has dominant cyclic features related to the wind waves with only subtle effects from the basin-wide swells. Sterl and Caires [2005] suggested the wave pattern of the AO is strongly associated with the winds and Gulev and Grigorieva [2006] and Semedo et al [2011] both confirm this hypothesis from independent data sets. The frequency domain analysis is able to extract more detailed features of the wave field.…”

“…Mode 3 best represents the structure of the AO with high energy in the North Atlantic. This mode resembles the first EOF of Wang and Swail [2001] from their 40 year wave data set generated by R1, Semedo et al [2011] from ERA-40, and Gulev and Grigorieva [2006] from ship observations. The EOF analysis in the frequency domain captures strong repeating patterns associated with the wave climate.…”

“…Recent studies have applied climate indices to explain the inter-annual wave variability in the North Atlantic [Bacon and Carter, 1991;Swail and Cox, 2000;Woolf et al, 2002;Gulev and Grigorieva, 2006], North Pacific [Graham and Diaz, 2001;Tsai et al, 2012;Bromirski et al, 2013], Southern Ocean [Hemer et al, 2008[Hemer et al, , 2010Bosserelle et al, 2011], Northern Hemisphere [Shimura et al, 2013], and globally Sterl and Caires, 2005;Young, 1999;Izaguirre et al, 2011;Fan et al, 2012;Stopa et al, 2013a]. The EOF approach in the time domain allows comparison with findings from previous studies and provides a basis to relate the frequency domain results.…”

“…The wave climate in the North Atlantic has been investigated more than any other region with numerous studies describing its variability in terms of the AO [Bauer, 2001;Swail and Cox, 2000;Cox and Swail, 2001;Wang and Swail, 2001;Woolf et al, 2002;Gulev and Grigorieva, 2006;Izaguirre et al, 2011;Fan et al, 2012]. The North Atlantic is largely seasonal with energetic waves in the boreal winter and calm conditions in the summer, while the South Atlantic has less variation throughout the year.…”

ICOADS Release 2.5: extensions and enhancements to the surface marine meteorological archive

“…We highlight just a few as a representative set. The visual estimated wave data have been processed and summarised for the global ocean (Gulev and Grigorieva, 2006). Similarly, a widely used climate research cloud data product, the Extended Edited Synoptic Cloud Reports from Ships and Land Stations Over the Globe (EECRA) (Hahn et al, 1995(Hahn et al, , 1999, has been created.…”