Guillaume Serazin - Imprint of low-frequency oceanic intrinsic variability on the global ocean

Event type: 
28 November 2018
2.00 - 3.00pm

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Guillaume Serazin
Climate Change Research Centre, UNSW, Sydney

Because the ocean is far from being calm and laminar, flow instabilities generate mesoscale eddies that interact with themselves and with the mean circulation, eventually yielding a complex turbulent behaviour. Not only these oceanic eddies tend to impact larger scales but they also affect longer timescales and may spontaneously generate a so-called oceanic intrinsic variability, up to decadal timescales. This oceanic intrinsic variability is part of the internal variability of the coupled climate system, yet it is barely taken into account in climate models because of their coarse ocean models. In this seminar, Guillaume presents to what extent the oceanic intrinsic variability has a significant imprint at the ocean surface and at depth over the global ocean. Two different approches, consisting in 50-member ensemble simulations and a long control run seasonally forced, are used to characterise the imprint of oceanic intrinsic variability on the spatio-temporal scales of sea level, the Atlantic meridional overturning circulation, and the ocean heat content. At midlatitudes, the imprint of oceanic intrinsic variability on those variables is important enough to yield a weak signal-to-noise ratio and complicate the interpretation of oceanic observations. The randomness of the intrinsic signal may also hamper the detection and attribution of regional fluctuations linked to the atmospheric forcing, such as changes in sea level and ocean heat content. Those results eventually provide evidence of the chaotic behaviour of the turbulent ocean, whose interaction with the atmosphere is still poorly-known.



Brief Biography: Guillaume is a Research Associate at the Climate Change Research Centre, UNSW, Australia. He received a Master of Science from Claude Bernard University, Lyon (France) and a Master of Engineering from École Centrale Lyon, Écully (France) in 2011. In 2012, he had a short work experience in the aeronautic industry before switching to research in geophysics. In early 2016, he completed a PhD in Physical Oceanography from Paul Sabatier University, Toulouse, while being based most of the time at the Laboratory of Glaciology and Geophysics of the Environment, Grenoble. From 2016 to 2018, he worked as a Post-doctoral Research Associate at the Laboratory of Studies in Geophysics and Spatial Oceanography. Guillaume studies oceanic turbulent flows with the support of high-resolution ocean models and observations. He mostly focuses on the impact of mesoscale oceanic eddies (O 100 km) on the climate system through their feedback with the atmosphere and their capacity to generate long-term fluctuation, sometimes called eddy-driven variability or intrinsic variability. At even smaller scales (O 1-10 km), he also studies submesoscale motions, characterised by fronts and filaments, and propagating internal waves, generated by the interaction of the barotropic tides with steep topographic features. To do so, he uses existing observations from in situ shipboard measurements of velocities, temperature and salinity, as well as from autonomous gliders and satellite altimeters. He eventually contributes to develop several numerical tools in Python for signal processing and analysing large geophysical datasets, within the community effort Pangeo.