Publication Detail

Observing System Simulation Experiments (OSSEs) with Ensemble Kalman Filters in Nantucket Sound, Massachusetts

Pengfei Xue, Changsheng Chen, Robert C Beardsley, Richard Limeburner
16 pp.
MITSG 11-05
$5.50 DOM / $7.50 INT

Observing system simulation experiments (OSSEs) were performed for Nantucket
Sound, Massachusetts, as a pilot study for the design of optimal monitoring networks
in the coastal ocean. Experiments were carried out using the ensemble Kalman filter
(EnKF) for data assimilation with ensemble transform Kalman filter (EnTKF) and
proper orthogonal decomposition (POD) for selecting the optimal monitoring sites. The
singular evolutive interpolated Kalman filter (SEIK) was compared with EnKF for the
data assimilation efficiency. Running the unstructured grid Finite‐Volume Community
Ocean Model (FVCOM) with perturbed initial fields of currents, water temperature, and
salinity show that in this shallow coastal system, the velocity and surface elevation are
able to restore themselves back to the true state over an inertial time scale after perturbation
without data assimilation, while the water temperature and salinity are not. This
suggests that in this vertically well mixed region with strong tidal influence, monitoring
should be targeted at water properties rather than velocities. By placing measurement
sites at an entrance or exit or a location with the maximum signal variance (EnTKF) or
at extrema of the dominant EOF spatial modes (POD), we evaluated the capability of
EnTKF and POD in designing the optimal monitoring site for the forecast model system in
this region. The results suggest that understanding the multiscale dynamical nature of
the system is essential in designing an optimal monitoring network since “optimal” sites
suggested by an assimilation method may only represent a local‐scale feature that has
little influence on a region‐wide system. Comparing EnKF and SEIK simulations shows
that SEIK can significantly improve the data assimilation efficiency by reducing the
ensemble number and increasing the convergence rate.

Journal, book, proceeding reprints

Parent Project

Project No.: 2010-R/RC-116
Title: Development and Validation of the Water Quality Model System for Massachusetts Coastal Waters

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