Dynamics of a marine heatwave: what happens below the surface?

Extreme temperatures in the ocean are getting more frequent and intense, impacting marine ecosystems and industries. However the subsurface signature of these marine heatwaves is still largely unknown, in particular in shallow coastal areas where most of the ecological damages occur.

In addition to sustained observations, the Australian Integrated Marine Observing System (IMOS) now aims at sampling the coastal ocean during marine heatwaves with real-time deployments of ocean gliders. Gliders are automated underwater vehicles which measure the water properties between the ocean floor and the surface for a few weeks. Two of such deployments were successfully finalised, sampling the eastern shelf of Tasmania during the latest marine heatwave event in the Tasman Sea in summer / spring 2019.

The project aims at understanding the extent and characteristics of marine heatwaves using glider measurements and complementary satellite and moored observations. Key questions include the temporal evolution, from the onset to the decline of the extreme event, and the influence of the local oceanography such as currents and wind-driven processes on the persistence and variability of these anomalous temperatures. The student will use programming language to analyse this unique dataset and compute the heat budget equations.

Basic knowledge of oceanography and experience in Matlab or Python are required. The project will be based at UNSW Sydney, co-supervised by Amandine Schaeffer (UNSW), Jessica Benthuysen (AIMS) and Neil Holbrook (UTAS).

Contact: a.schaeffer@unsw.edu.au

Understanding how precipitation extremes scale in future climates

While global climate models (GCMs) remain our best tool for investigating the Earth’s system response to anthropogenic forcings, their spatial resolution (generally hundreds of km) is much coarser than the scales of the key processes leading to precipitation extremes (e.g. intense convective rainfall events). Therefore, parametrizations are necessary and the simulation of precipitation is not explicitly resolved in models. Spatial resolution is finer in regional climate models (RCMs) (generally tens of km), which is expected to improve the simulation of precipitation extremes that are very sensitive to spatial contrasts and topography. However, even at the scales of regional models parametrizations are still required.

Global and regional models have advantages and disadvantages for studying precipitation extremes, but how their output scales with respect to the other is rarely compared. In particular, it is unclear how the future changes in precipitation extremes from large ensembles of regional climate models compare to those from global models. This project will assess how precipitation projections for Australia from global and regional models scale using the latest start-of-the-art GCMs and RCMs.

Requirements: Some prior programming and data visualisation experience (e.g. Python, NCL, MATLAB, R, etc.).

This project is supervised by A/Prof Lisa Alexander and Dr Margot Bador (UNSW Sydney). Please contact l.alexander@unsw.edu.au for more information.

 

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PhD Project: Wake interference by swimming crocodiles

Crocodiles, including the saltwater crocodile (Crocodylus porosus) have the remarkable ability to swim underwater at high speed while barely making a ripple at the surface. It has been hypothesized that crocodiles are able to do this because the bony ridges on the crocodile’s back (called scutes or osteoderms) produce destructively interfering wake patterns at the water surface, like noise-cancelling headphones. Understanding and replicating this phenomena could have important implications for submarine and ship hull design.

In this project, we will evaluate this hypothesis using a combination of theory, numerical modelling, and laboratory experiments using 3D-printed crocodile models in a wave flume. Experience with Python programming is essential. This project will be co-supervised by Dr Geoff Vasil (U. Sydney), Dr Chris Lustri (Macquarie) and Dr Shane Keating (UNSW).

Click here for key dates and to submit your application online.

Asymmetry of the ocean’s thermohaline circulation

The ocean is highly turbulent. Pathways of free-floating buoys are chaotic and circulation patterns are dominated by mesoscale eddies – the ocean’s equivalent to atmospheric storms. The ocean is at the same time organised.

Substances injected into the ocean follow broad and distinct routes near the sea surface from the Pacific to the Atlantic Ocean. As a result the North Pacific and North Atlantic Ocean’s are in marked contrast. The Pacific is cold and fresh and the Atlantic is warm and salty. Known as the thermohaline circulation, this helps maintain Europe’s relatively mild climate.

This project will explore the link between the asymmetry in northern hemisphere climates, the thermohaline circulation and the atmospheric forcing which sets the eventual temperature and salinity of sea-water. The project will pivot on the hypothesis that, by accident of geography and the position of southern hemisphere winds, warm saline water preferentially flows into the Atlantic. Moreover these effects will dictate the stability of the thermohaline circulation and European climate over coming centuries.

This project is supervised by Dr Jan Zika (UNSW Sydney). Please contact j.zika@unsw.edu.au for more information.

Submit your application by Oct 26 2018 for commencement in Term 1, 2019.

Linking the seasonal cycle of ocean water masses to transient climate change

In boreal winter the North Atlantic and Pacific Oceans become cold, dense and turbulent. Oxygen, carbon and other substances are drawn out of the atmosphere and ventilated into the deep ocean. In boreal summer, as the surface layers in the north warm, cooling and ventilation begins in the southern hemisphere in earnest.

The process of seasonal ventilation dictates the ocean’s role in climate – both present and future. Only in the last decade has a systematic understanding of seasonal ventilation become possible due to the presence of thousands of autonomous buoys (ARGO) and satellites measuring upper ocean temperature and salinity. Likewise never has the need to quantify it been more pressing.

This project will combine the latest observations to generate a quantitative picture of the formation, ventilation and destruction of cold dense water masses in both hemispheres. A key novelty of this project will be the use the water-mass transformation framework. Using this framework variability in water mass properties is attributed to surface heating and cooling, evaporation and precipitation, mixing and energetic drivers such as wind forcing.

This project is supervised by Dr Jan Zika (UNSW Sydney). Please contact j.zika@unsw.edu.au for more information.

Submit your application by Oct 26 2018 for commencement in Term 1, 2019.