Hobart
Seminar Abstract
Friday 7 August 2009, **2.00pm** (Tas time)
CSIRO Auditorium, Hobart
Andrew Meijers
Post Doc Fellow
CSIRO Marine and Atmospheric Research
Hobart
Combining hydrography and altimetry to observe the variability and dynamics of the ACC
I present a gravest empirical mode (GEM) projection of temperature and salinity fields in the Southern Ocean that, combined with satellite altimetry, produces time evolving temperature, salinity and velocity (satGEM) fields, and use these to observe the mean and synoptically varying properties of the Southern Ocean from 1992-2006.
Although these fields accurately estimate a pointwise mean southward eddy heat transport of -37.7 KWm2 in the SAF, the global mean northward eddy heat and freshwater transports of -0.08±0.01 PW and 0.025±0.01 Sv are small due to the satGEM's inability to resolve eddy tilt. An explicit eddy tracking method produces similar transports, and as the two methods work at different length scales we combine them for a minimum bound on the eddy transport across the SAF of 0.14±0.03 PW of heat southward and 0.04±0.03 Sv of freshwater northward.
There is a warming (1.219±0.089 Wm2) and weak freshening (5.85±0.16 mmy-1m2) of the ACC induced by adiabatic water mass movement between 1992-2006. The diabatic contribution due to heat and freshwater fluxes drives a cooling (-0.628±0.129 Wm2) and freshening (30.27±0.70 mmy-1m-2), with a net trend of 0.591±0.093 Wm-2 and 36.12±0.68 mmy-1m-2. Although there is no trend in zonal ACC mass transport at any longitude, nor a change in eddy kinetic energy, eddy number or eddy meridional property transport, there is substantial variability driven by the Southern Annular Mode (SAM) and the El Nino Southern Oscillation (ENSO). The SAM influences the Southern Ocean at frequencies of less than three months, while ENSO operates on interannual timescales. The ENSO driven trend in the Pacific dominates the total adiabatic heat and freshwater content change during strong El Nino and La Nina years (1997-2002), while outside this period the SAM is a greater contributor, but with a lag of 4-5 years.
An increased SAM leads to a roughly circumpolar 5% increase in the zonal volume transport of the ACC. Additionally, there is a clear lag of 1.6-3.2 years between an increase in the SAM and an increase in the EKE and number of eddies across the whole ACC. The response of eddy heat and freshwater transport is less clear, but at a similar lag there is an increase of 0.01-0.1 PW of southward heat transport and 0.01-0.1 Sv of northward freshwater transport across the SAF. The weak transport response to wind stress change and lagged eddy transport indicates that the ACC is in an eddy saturated state.
Seminar recording
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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart
For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research
0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania
(03) 6226 2971
Last updated
14/08/09
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