Dr Ryan Holmes

Dr Ryan Holmes

Physical oceanographer

About me

I am a physical oceanographer interested in ocean physics, climate and modelling. My research focuses on how processes acting on small-scales, such as turbulent mixing and mesoscale eddies, influence the large-scale ocean circulation and its variability. I use theoretical techniques combined with a range of idealized and realistic ocean models and analysis of oceanographic data to better understand interactions across scales in the ocean in order to represent them properly in low-resolution models.

I obtained my PhD in 2016 from Stanford University. Between 2016 and 2021 I held several postdoctoral positions at the University of New South Wales in the Climate Change Research Center and the School of Mathematics and Statistics. In 2021 I joined the School of Geosciences at the University of Sydney as an Australian Research Council (ARC) Discovery Early Career Researcher Award (DECRA) Fellow. In 2023 I joined the Bureau of Meteorology as a Climate Scientist working in research.

Research Interests

My research interests include:

  • Equatorial dynamics, turbulent mixing and tropical instability waves: I am interested in equatorial dynamics and in particular how processes on short timescales (months to seconds), such as tropical instability waves (TIWs), internal gravity waves and small-scale turbulence, influence the large-scale tropical circulation and its modes of variability such as the El-Nino Southern Oscillation (ENSO). My PhD work focused on TIWs and their role in driving mixing in the equatorial Pacific (e.g. their modulation of shear-driven turbulence, Holmes and Thomas 2015 J. Phys. Oceanogr.). More recently I have shown that the chaotic nature of TIWs influences ENSO predictability (Holmes et al. 2019 Climate Dynamics). I have also been collaborating with scientists at the National Centre for Atmospheric Research (NCAR, USA) to study variability of turbulent mixing at the Equator from observations and a hierarchy of high-resolution models. My recently funded ARC DECRA project Mixing and air-sea coupling in the Pacific: Toward better El Nino forecasts aims to further develop out understanding of air-sea interactions at the mesoscale in the tropical Pacific and feed that understanding into improvements in low-resolution models that are used to provide El Nino forecasts.

  • Ocean heat transport in temperature space: The ocean is warmed by air-sea heat fluxes at low-latitudes and warm temperatures and cooled in the mid- and high-latitudes at colder temperatures. To maintain a steady state the ocean must therefore move heat not only from low to high latitudes (meridional heat transport), but also from warm to cold temperatures (diathermal heat transport). By developing a suite of novel heat transport diagnostics within the MOM5-based Australian community global ocean model ACCESS-OM2, I study how the ocean’s diathermal and meridional heat transport depends on parameterized diffusive mixing processes (Holmes et al. 2018 J. Phys. Oceanogr., 2019 Geophysical Research Letters). This diagnostic framework allows the role of mixing processes to be isolated and quantified, including the `artificial’ numerical mixing arising from the numerical discretization of tracer transport Holmes et al. 2021 J. Adv. Mod. Earth Sys..

Heat Transport Schematic

Figure 1: A schematic illustrating heat flows above, below and across the 15C and 20C isotherms from a MOM5 global ocean model simulation. Much of the heat that is transported northward in the Atlantic is ultimately sourced from heat uptake and turbulent mixing in the tropical Pacific (see Holmes et al. 2019 Geophysical Research Letters for more information).

  • Abyssal ocean circulation and mixing: I am interested in diapycnal mixing and how it influences abyssal ocean circulation and the conversion of Antarctic Bottom Water into lighter water. As mixing in the abyssal ocean is seafloor-intensified the topography of the seafloor has a strong influence on abyssal circulation pathways (de Lavergne et al. 2017 Nature and Holmes et al. 2018 J. Phys. Oceanogr.). My more recent work focuses on using theoretical techniques and idealized process modelling to understand how tracers are transported in the abyssal ocean in order to inform future field tracer release experiments (Holmes et al. 2019 J. Phys. Oceanogr.).

  • Antarctic coastal circulation and ice shelf melting: I am involved in a series of projects aimed at understanding the mechanisms that drive warm Circumpolar Deep Water onto the Antarctic continental shelf and into contact with vulnerable ice shelves, with worrying implications for global sea level rise. One such mechanism highlighted by our work involves the transport of heat onto the continental shelf by bottom Ekman transport associated with coastally trapped barotropic waves Spence, Holmes et al. 2017 Nature Climate Change.

Antarctic Kelvin Wave

Figure 2: The pathway of a barotropic Kelvin wave propagating around the Antarctic peninsula. On the west side of the peninsula (blue box) the Kelvin wave drives circulation changes that can bring warm circumpolar deep water onto the continental shelf and into contact with the vulnerable ice shelves (see Spence et al. 2017 Nature Climate Change for more information)

This website contains my CV, a list of publications, conference talks and a short summary of some of the projects that I am currently involved in. If you wish to know more or have any other questions, please contact me at r.holmes@sydney.edu.au