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Validation of the SatGEM Velocity Dataset using Argo Data


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Roach, C 2009 , 'Validation of the SatGEM Velocity Dataset using Argo Data', Honours thesis, University of Tasmania.

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Available under University of Tasmania Standard License.


The 4D SatGEM velocity model of the Southern Ocean has been derived from
satellite altimetry and a Gravest Empirical Mode (GEM) model of temperature and
salinity. The validity of the SatGEM model is assessed in this study by numerical
forward modelling of Argo float trajectories through the 4D velocity fields.
Univariate statistical analysis of simulated and actual path lengths, together
with analysis of the misfit between simulated and actual surfacing positions, suggests
that the SatGEM model provides an adequate representation of the gross features of
the Southern Ocean. However, on a local scale there is significant variability in misfit
due to a combination of statistical fluctuations, the limited SatGEM model resolution
and complex local velocity fields.
A high proportion of large relative misfit cycles are apparent for short Argo
path lengths suggesting that the Argo float trajectories in these areas may be strongly
influenced by complex small-scale flow features that cannot be adequately resolved in
the SatGEM model. Argo float cycles with path lengths in excess of 50km and small
relative misfits are effectively randomly distributed. However statistically significant
clusters of large relative misfit cycles are apparent particularly in areas of known
small-scale eddy current development such as east of the Kerguelen Plateau and also
in the Brazil-Falklands Convergence where GEM models based on satellite altimetry
are known to be inaccurate. The angular misfit for medium and small relative misfit
Argo cycles is normally distributed suggesting that variability in this case arises due
to statistical processes. The uniform distribution of angular misfit for large relative
misfit cycles is suggestive of more random chaotic processes likely related to flow
bifurcations in zones with complex velocity structure. In these cases the relative misfit
is highly sensitive to the initial descent position of the float in the velocity model.
Validation of the SatGEM model using Argo float data suggests that velocity
models derived from satellite altimetry and GEM derived temperature and salinity
fields can provide adequate representations of ocean dynamics for large-scale
investigations but the small-scale applications of these models are limited primarily
by their spatial resolution and hence their inability to accurately model complex local
flow features.

Item Type: Thesis - Honours
Authors/Creators:Roach, C
Keywords: Argo Flout, gravest, empirical model, partical tracking
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