Wave Climate of the Southern Ocean

Abstract

<p>Although the Southern Ocean is often viewed as a very remote area, it plays a critical role in global climate. Waves generated in intense Southern Ocean storms propagate across the Indian, Pacific and Atlantic Oceans and define the wave climate for many areas of these oceans. In addition, the wind and wave climate of the Southern Ocean plays an important role in determining the rate of decay of Antarctic glaciers which are an important element in global sea level change. Despite this important role, little is known about the wind and wave climate of this vast region. This paper will bring together a series of unique datasets to provide a comprehensive view of this wind and wave climate. These datasets include: the long duration model reanalysis dataset ERA-I, a 33-year calibrated and validated altimeter dataset and buoy data from four deployments. These buoys have been located at: Macquarie Island (540S), Campbell Island (520S), a site west of South America (550S) and the Southern Ocean Flux Buoy south of Tasmania (460S). Data from these buoy deployments spans a total of approximately 7 years and provides directional spectra in unique long fetch environments. In addition to providing valuable data for model validation, engineering design and Naval Architecture, these combined datasets provide new insights into air-sea interaction under extremely long fetch conditions. The paper will also use the satellite datasets to investigate changes in wave conditions in recent decades and the role that climate variability plays in such changes. This analysis will examine: long-term trends, annual variability and multi-year oscillations.</p>

Identifying oceanographic conditions conducive to coastal impacts on temperate open coastal beaches and the importance of empirical impact data

“…Despite some seasonality, both Port Fairy and Inverloch have an energetic wave climate throughout much of the year (Figure 3). This is consistent with conditions across the Southern Ocean which has a largely spatially homogeneous wave climate and shows minimal seasonal variability compared to similar latitudes in the Northern Hemisphere (Young et al 2020). As found in Port Fairy and Inverloch, the Southern Ocean experiences only a 25% difference in summer-winter H s , which is owed to the almost continuous fetch for wind-wave generation in this region (Young et al 2020).…”

“…The southern coast of Australia is considered to have one of the most globally energetic wave climates (Hemer and Gri n 2010;Hughes and Heap 2010) generated from the almost continuous fetch around the Southern Ocean and strong westerly winds (Young et al 2020). Deep-water wave conditions are spatially variable, particularly along the Victorian coastline in the southeast of Australia (Figure 1) where wave blocking from Tasmania and other islands in Bass Strait, as well as the shallow and wide continental shelf acting to reduce wave energy and limit fetch along the central part of the Victorian coast (McSweeney 2020).…”

“…In fact, wave direction was considered a more signi cant factor in generating coastal impacts along Australian's east coast during the 2016 East Coast Low compared to the wave height, which was not considered to be exceptionally high for this region (Mortlock et al 2017). Although a more westerly wave approach in Port Fairy and Inverloch would seemingly reduce exposure due to the local shoreline orientation, waves tracking from this direction are likely to have more energy due to the unique wind-wave climate that traverses the Southern Ocean (Young et al 2020). Degree of exposure is also in uenced by blocking (Young et al 2020) within Bass Strait, where Tasmania and other offshore Islands have been shown to reduce wave propagation from the South (McSweeney 2020).…”

“…Although a more westerly wave approach in Port Fairy and Inverloch would seemingly reduce exposure due to the local shoreline orientation, waves tracking from this direction are likely to have more energy due to the unique wind-wave climate that traverses the Southern Ocean (Young et al 2020). Degree of exposure is also in uenced by blocking (Young et al 2020) within Bass Strait, where Tasmania and other offshore Islands have been shown to reduce wave propagation from the South (McSweeney 2020). These effects are evident in the results, owing to the fact that directionality has a lesser in uence on event occurrence in Port Fairy with only 57% of events occurring under a more westerly wave climate, compared to 80% in Inverloch.…”

New Directional Wave Satellite Observations: Towards Improved Wave Forecasts and Climate Description in Southern Ocean

“…As contemporary satellite products cannot fully optimize wind sea, the latter remains a notable source of model errors, resulting in an overestimation of significant wave height (positive bias). This is exacerbated in the Southern Ocean (Zieger et al., 2015)—a region covering an uninterrupted band of water around Antarctica south of the main landmasses of Africa, Australia, and South America—that is dominated by strong westerly winds, which blows all‐the‐year‐round with almost unlimited fetches and speed in excess of 13 m/s during summer months and 18 m/s during winter months (Young et al., 2020). These intense winds generate some of the fiercest waves on the planet with high percentiles of wave height exceeding 5 m during summer and 7 m during winter (e.g., Babanin et al., 2019; Barbariol et al., 2019; Letraon et al., 2019; Vichi et al., 2019; Young et al., 2020).…”