A method for assimilating Lagrangian data into a shallow-water-equation ocean model

Salman, H., Kuznetsov, L., Jones, C. K. R. T. and Ide, K. (2006) A method for assimilating Lagrangian data into a shallow-water-equation ocean model. Monthly Weather Review, 134 (4). pp. 1081-1101. ISSN 0027-0644

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Abstract

Lagrangian measurements provide a significant portion of the data collected in the ocean. Difficulties arise in their assimilation, however, since Lagrangian data are described in a moving frame of reference that does not correspond to the fixed grid locations used to forecast the prognostic flow variables. A new method is presented for assimilating Lagrangian data into models of the ocean that removes the need for any commonly used approximations. This is accomplished by augmenting the state vector of the prognostic variables with the Lagrangian drifter coordinates at assimilation. It is shown that this method is best formulated using the ensemble Kalman filter, resulting in an algorithm that is essentially transparent for assimilating Lagrangian data. The method is tested using a set of twin experiments on the shallow-water system of equations for an unsteady double-gyre flow configuration. Numerical simulations show that this method is capable of correcting the flow even if the assimilation time interval is of the order of the Lagrangian autocorrelation time scale (TL) of the flow. These results clearly demonstrate the benefits of this method over other techniques that require assimilation times of 20%–50% of TL, a direct consequence of the approximations introduced in assimilating their Lagrangian data. Detailed parametric studies show that this method is particularly effective if the classical ideas of localization developed for the ensemble Kalman filter are extended to the Lagrangian formulation used here. The method that has been developed, therefore, provides an approach that allows one to fully realize the potential of Lagrangian data for assimilation in more realistic ocean models.

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Mathematics (former - to 2024)
UEA Research Groups:	Faculty of Science > Research Groups > Quantum Fluids Faculty of Science > Research Groups > Centre for Photonics and Quantum Science
Depositing User:	Vishal Gautam
Date Deposited:	18 Mar 2011 14:22
Last Modified:	23 Jul 2024 13:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/20799
DOI:	10.1175/MWR3104.1

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