The formation and fate of internal waves in the South China Sea

Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they affect a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for man-made structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, making it challenging to observe them and to include them in numerical climate models, which are sensitive to their effects6,7. For over a decade, studies8-11 have targeted the South China Sea, where the oceans' most powerful known internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their mechanism of generation, variability and energy budget, however, owing to the lack of in situ data from the Luzon Strait, where extreme flow conditions make measurements difficult. Here we use new observations and numerical models to (1) show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena, (2) reveal the existence of >200-metre-high breaking internal waves in the region of generation that give rise to turbulence levels >10,000 times that in the open ocean, (3) determine that the Kuroshio western boundary current noticeably refracts the internal wave field emanating from the Luzon Strait, and (4) demonstrate a factor-of-two agreement between modelled and observed energy fluxes, which allows us to produce an observationally supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions

An international perspective on graduate education in physical oceanography

During the inaugural Physical Oceanography Dissertation Symposium in June 2002 we found that the graduate school experience varied markedly amongst the 20 international participants. The diversity of backgrounds led to lively discussion about the differences between physical oceanography programs. Here we review the length, content, and quality of education for graduate programs in Australia, France, Germany, the UK, and the USA. We also comment on the financial, social, and scientific status of graduate students in these countries. Graduate programs in physical oceanography face the challenge of introducing students to the wide range of tools and techniques which define the field, ranging from observational work and remote sensing, through dynamical theory and laboratory experiments, to numerical modelling. While individual character largely determines the success of the PhD experience, a graduate education in physical oceanography should include the following factors to best serve students in their future career: solid mentorship, regular department level progress checks, course work, summer schools, field work, practise in communication skills, scientific and social integration, international exchange, and stable and sufficient funding. We propose a model four year physical oceanography graduate degree structure, distilled from the best aspects of international physical oceanography programs