Variability and trends in the directional wave climate of the Southern Hemisphere

Abstract

The effect of interannual climate variability and change on the historic, directional wave climate of the Southern Hemisphere is presented. Owing to a lack of in situ wave observations, wave climate in the Southern Hemisphere is determined from satellite altimetry and global ocean wave models. Altimeter data span the period 1985 to present, with the exception of a 2‐year gap in 1989–1991. Interannual variability and trends in the significant wave height are determined from the satellite altimeter record (1991 to present), and the dominant modes of variability are identified using an empirical orthogonal function (EOF) analysis. Significant wave heights in the Southern Ocean are observed to show a strong positive correlation with the Southern Annular Mode (SAM), particularly during Austral autumn and winter months. Correlation between altimeter derived significant wave heights and the Southern Oscillation Index is observed in the Pacific basin, which is consistent with several previous studies. Variability and trends of the directional wave climate are determined using the ERA‐40 Waves Re‐analysis for the period 1980–2001. Significant wave height, mean wave period and mean wave direction data are used to describe the climate of the wave energy flux vector. An EOF analysis of the wave energy flux vector is carried out to determine the dominant modes of variability of the directional seasonal wave energy flux climate. The dominant mode of variability during autumn and winter months is strongly correlated to the SAM. There is an anti‐clockwise rotation of wave direction with the southward intensification of the Southern Ocean storm belt associated with the SAM. Clockwise rotation of flux vectors is observed in the Western Pacific Ocean during El‐Nino events. Directional variability of the wave energy flux in the Western Pacific Ocean has previously been shown to be of importance to sand transport along the south‐eastern Australian margin, and the New Zealand region. The directional variability of the wave energy flux of the Southern Ocean associated with the SAM is expected to be of importance to the wave‐driven currents responsible for the transport of sand along coastal margins in the Southern Hemisphere, in particular those on the Southern and Western coastal margins of the Australian continent. Copyright © 2009 Royal Meteorological Society

Periodicity and patterns of ocean wind and 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 oscillation lacks any significant features in the South Atlantic due to blocking of the east-moving extratropical storms by South America [Hemer et al, 2010]. The Indian Ocean shows opposing zonal patterns in the Westerlies with statistically significant correlation with the index.…”

“…High-quality wind and wave observations in excess of 20 years are available for climate research. These include voluntary observations along shipping routes [Gulev et al, 2003], point measurements at buoys [e.g., Bromirski et al, 2005;Menendez et al, 2008;Gemmrich et al, 2011], and spatial patterns from altimeters [e.g., Young, 1999;Woolf et al, 2002;Chen et al, 2002;Hemer et al, 2010;Young et al, 2011]. Some of these studies supplemented the measurements with detailed wave data from numerical models to provide space-time connections of the observed processes.…”

Satellite altimetry reveals spatial patterns of variations in the Baltic Sea wave climate

“…Even though wind direction is often considered a secondary parameter in climate studies, the impact of the rotation of wind patterns on wave fields is a generic issue (Hemer et al, 2010). This effect is comparatively strong in regional seas and large lakes with an elongated shape (Niu and Xia, 2016) where veering of the prevailing winds may lead to large changes in the fetch length.…”

“…The relevant observations span today > 20 years and thus provide a valuable source for understanding the course and possible reasons for regional climate changes. Satellite altimetry provides homogeneous and continuous (along a certain line) data about the sea state over large areas in the open ocean (Hemer et al, 2010;Izaguirre et al, 2011;Young et al, 2011). Several recent studies have addressed the options for its use in the Arctic Ocean (Liu et al, 2016;Stopa et al, 2016).…”