Dense CTD survey versus glider fleet sampling: comparing data assimilation performance in a regional ocean model west of Sardinia
<p>The REP14-MED sea trial carried out off the west coast of Sardinia in June 2014 provided a rich set of observations from both ship-based conductivity–temperature–depth (CTD) probes and a fleet of underwater gliders. We present the results of several simulations assimilating data either...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Ocean Science |
| Online Access: | https://www.ocean-sci.net/14/1069/2018/os-14-1069-2018.pdf |
| Summary: | <p>The REP14-MED sea trial carried out off the west coast of
Sardinia in June 2014 provided a rich set of observations from both
ship-based conductivity–temperature–depth (CTD) probes and a fleet of underwater gliders. We present the results of
several simulations assimilating data either from CTDs or from different
subsets of glider data, including up to eight vehicles, in addition to
satellite sea level anomalies, surface temperature and Argo profiles. The
Western Mediterranean OPerational forcasting system
(WMOP) regional ocean model is used with a local multi-model ensemble optimal
interpolation scheme to recursively ingest both lower-resolution large-scale
and dense local observations over the whole sea trial duration. Results show
the capacity of the system to ingest both types of data, leading to
improvements in the representation of all assimilated variables. These
improvements persist during the 3-day periods separating two analyses. At
the same time, the system presents some limitations in properly representing
the smaller-scale structures, which are smoothed out by the model error
covariances provided by the ensemble. An evaluation of the forecasts using
independent measurements from shipborne CTDs and a towed ScanFish deployed at
the end of the sea trial shows that the simulations assimilating initial CTD
data reduce the error by 39 % on average with respect to the simulation
without data assimilation. In the glider-data-assimilative experiments, the
forecast error is reduced as the number of vehicles increases. The simulation
assimilating CTDs outperforms the simulations assimilating data from one to
four gliders. A fleet of eight gliders provides similar performance to the
10 km spaced CTD initialization survey in these experiments, with an overall
40 % model error reduction capacity with respect to the simulation without
data assimilation when comparing against independent campaign observations.</p> |
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| ISSN: | 1812-0784 1812-0792 |