Computational Geosciences

, Volume 20, Issue 5, pp 1133–1153

Quantifying initial and wind forcing uncertainties in the Gulf of Mexico

  • Guotu Li
  • Mohamed Iskandarani
  • Matthieu Le Hénaff
  • Justin Winokur
  • Olivier P. Le Maître
  • Omar M. Knio
Original Paper

DOI: 10.1007/s10596-016-9581-4

Cite this article as:
Li, G., Iskandarani, M., Hénaff, M.L. et al. Comput Geosci (2016) 20: 1133. doi:10.1007/s10596-016-9581-4
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Abstract

This study aims at analyzing the combined impact of uncertainties in initial conditions and wind forcing fields in ocean general circulation models (OGCM) using polynomial chaos (PC) expansions. Empirical orthogonal functions (EOF) are used to formulate both spatial perturbations to initial conditions and space-time wind forcing perturbations, namely in the form of a superposition of modal components with uniformly distributed random amplitudes. The forward deterministic HYbrid Coordinate Ocean Model (HYCOM) is used to propagate input uncertainties in the Gulf of Mexico (GoM) in spring 2010, during the Deepwater Horizon oil spill, and to generate the ensemble of model realizations based on which PC surrogate models are constructed for both localized and field quantities of interest (QoIs), focusing specifically on sea surface height (SSH) and mixed layer depth (MLD). These PC surrogate models are constructed using basis pursuit denoising methodology, and their performance is assessed through various statistical measures. A global sensitivity analysis is then performed to quantify the impact of individual modes as well as their interactions. It shows that the local SSH at the edge of the GoM main current—the Loop Current—is mostly sensitive to perturbations of the initial conditions affecting the current front, whereas the local MLD in the area of the Deepwater Horizon oil spill is more sensitive to wind forcing perturbations. At the basin scale, the SSH in the deep GoM is mostly sensitive to initial condition perturbations, while over the shelf it is sensitive to wind forcing perturbations. On the other hand, the basin MLD is almost exclusively sensitive to wind perturbations. For both quantities, the two sources of uncertainty have limited interactions. Finally, the computations indicate that whereas local quantities can exhibit complex behavior that necessitates a large number of realizations, the modal analysis of field sensitivities can be suitably achieved with a moderate size ensemble.

Keywords

Polynomial chaos expansion Empirical orthogonal function Sensitivity analysis Basis pursuit denoising 

Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  • Guotu Li
    • 1
  • Mohamed Iskandarani
    • 2
  • Matthieu Le Hénaff
    • 3
    • 4
  • Justin Winokur
    • 1
  • Olivier P. Le Maître
    • 5
  • Omar M. Knio
    • 1
  1. 1.Department of Mechanical Engineering and Material ScienceDuke UniversityDurhamUSA
  2. 2.Rosenstiel School of Marine and Atmospheric ScienceUniversity of MiamiMiamiUSA
  3. 3.Cooperative Institute for Marine and Atmospheric StudiesUniversity of MiamiMiamiUSA
  4. 4.NOAA Atlantic Oceanographic and Meteorological LaboratoryMiamiUSA
  5. 5.LIMSI-CNRSOrsayFrance

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