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| Titel |
The impact of initial spread calibration on the RELO ensemble and its application to Lagrangian dynamics |
| VerfasserIn |
M. Wei, G. Jacobs, C. Rowley, C. N. Barron, P. Hogan, P. Spence, O. M. Smedstad, P. Martín, P. Muscarella, E. Coelho |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 20, no. 5 ; Nr. 20, no. 5 (2013-09-11), S.621-641 |
| Datensatznummer |
250086045
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| Publikation (Nr.) |
 copernicus.org/npg-20-621-2013.pdf |
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| Zusammenfassung |
A number of real-time ocean model forecasts were carried out successfully at
Naval Research Laboratory (NRL) to provide modeling support and numerical guidance to the CARTHE GLAD
at-sea experiment during summer 2012. Two RELO ensembles and three single
models using NCOM and HYCOM with different resolutions were carried out. A
calibrated ensemble system with enhanced spread and reliability was developed
to better support this experiment. The calibrated ensemble is found to
outperform the un-calibrated ensemble in forecasting accuracy, skill, and
reliability for all the variables and observation spaces evaluated. The
metrics used in this paper include RMS error, anomaly correlation, PECA,
Brier score, spread reliability, and Talagrand rank histogram. It is also
found that even the un-calibrated ensemble outperforms the single forecast
from the model with the same resolution.
The advantages of the ensembles are further extended to the Lagrangian
framework. In contrast to a single model forecast, the RELO ensemble provides
not only the most likely Lagrangian trajectory for a particle in the ocean,
but also an uncertainty estimate that directly reflects the complicated ocean
dynamics, which is valuable for decision makers. The examples show that the
calibrated ensemble with more reliability can capture trajectories in
different, even opposite, directions, which would be missed by the
un-calibrated ensemble. The ensembles are applied to compute the repelling
and attracting Lagrangian coherent structures (LCSs), and the uncertainties
of the LCSs, which are hard to obtain from a single model forecast, are
estimated. It is found that the spatial scales of the LCSs depend on the
model resolution. The model with the highest resolution produces the finest,
small-scale, LCS structures, while the model with lowest resolution generates
only large-scale LCSs. The repelling and attracting LCSs are found to
intersect at many locations and create complex mesoscale eddies. The fluid
particles and drifters in the middle of these tangles are subject to
attraction and repulsion simultaneously from these two kinds of LCSs. As a
result, the movements of particles near the Deepwater Horizon (DWH) location
are severely limited. This is also confirmed by the Lagrangian trajectories
predicted by the ensembles. |
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