Climate Change Research Centre

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1 Lagrangian particles to study the ocean circulation All trajectories of buoys in the Global Drifter Program Erik van Sebille With input from Matthew England, Judith Helgers, Claire Paris, Bernadette Sloyan, Ashwanth Srinivasan and Jan Zika Climate Change Research Centre

2 Numerical floats: Lagrangian analysis in an ocean model Output from ocean model runs is typically 1s of TeraBytes Hard to analyse these outputs My interest in ocean models is to analyse connectivity How and on what time scale does water flow from one location to another Important for ocean mixing and propagation of tracers Can bring physical and marine oceanography together In its most simple form, Lagrangian analysis is the integration of the velocity field x(t) =x() + Z t u( )d The CMS uses a 4th order Runge-Kutta method for the integration Lagrangian floats in an evolving 2D stream function Using the Connectivity Modeling System (CMS), available from Google Code

3 Investigating ocean connectivity Potential oil spill from Tar Sands Meltwater from Greenland Arctic mid-depth Circulation Mediterranean Outflow mixing Radionuclides from Fukushima disaster Atlantic surface pathways Deep jets in South Atlantic Agulhas leakage Indian-Atlantic inter-ocean exchange Deep Water Formation around Antarctica Tasman leakage Pacific-Indian inter-ocean exchange

4 The Currents around Australia Indonesian Throughflow (ITF) Pacific equatorial currents Leeuwin Current East Australia Current (EAC) Tasman front Tasman leakage Tasman Sea eddies Antarctic Circumpolar Current (ACC)

5 Defining Tasman leakage Indian Ocean Pacific Ocean Forward integration Backward integration Release line

6 Studying Tasman leakage The method used A movie of all the Tasman leakage particles Using the 3D velocities in the Japanese OFES model Global domain, forced by NCEP winds Horizontal resolution of.1, 54 vertical layers Data available for 26 years as three-day averages Release floats every 3 days south of Tasmania Only release when local current is westward Integrate floats both forward and backward in time Movie available at Van Sebille et al., 212, Geophys Res Lett

7 Tracing particles backwards and forwards 1N Transport through grid cell [Sv] Tasman leakage in OFES data Latitude [degrees] 1S 2S 3S S.2 1E 11E 12E 13E 14E 15E 16E 17E 18E Longitude [degrees] Van Sebille et al., 212, Geophys Res Lett

8 Variability of Tasman leakage Time series of Tasman leakage in OFES data Tasman leakage across 146.4E [Sv] (c) 14-year Tasman leakage: 4.2 ± 4.3 Sv Tasman leakage across 146.4E [Sv] Seasonal cycle of Tasman leakage J F M A M J J A S O N D Month Tasman leakage vs Southern Ocean winds 49S Time [AD] 49.5S 7 The ramp-up effect: It takes 1% of the particles more than three years to travel from 35S in the EAC to 146E south of Tasmania. Latitude of zero wind stress curl [degrees] 5S 5.5S 51S 51.5S 52S 52.5S Tasman leakage across 146.4E [Sv] Van Sebille et al., 212, Geophys Res Lett 53S Time [AD]

9 The tracer fluxes associated with Tasman leakage Analysis of Tasman leakage in TS-space (a) (b) (c).7.8 Tasman leakage across 146.4E [Sv/psu/degC] Transport [Sv] Transport [Sv] Temperature [degc] Temperature [degc] Salinity [psu] Salinity [psu] Van Sebille et al., 212, Geophys Res Lett

10 What is the role of eddies in Tasman leakage? 32S Example trajectories Five example trajectories 34S 36S Latitude [degrees] 38S 4S 42S 44S 46S 135E 14E 145E 15E 155E Longitude [degrees] Van Sebille et al., 212, Geophys Res Lett

11 Particles in your model? The Connectivity Modeling System (CMS) is off-line and extremely fast, and can cope with many different kinds of data I ve run CMS in HYCOM, OFES, ECCO2, UVic, SOSE, CCSM4, NEMO, Periant and AVISO altimetry But CMS s not limited to ocean models. We re now even considering modeling the advection of rubble on glaciers The only thing needed is 3D (or 2D) velocity fields on sufficient hight temporal resolution Sufficient here is in relation to the Eddy Kinetic Energy. Below 5 days temporal resolution for fine-res ocean models Possibly up to monthly temporal resolution for ocean climate models For more information, visit code.google.com/p/connectivity-modeling-system/ or