Introduction to Ensemble Data Assimilation

Steven J. Fletcher

Cooperative Institute for Research in the Atmosphere,

Colorado State University

Plan of talk

• Kalman Filter• EnKF• Inflation and Localization• ETKF• LETKF• MLEF• En4DVAR• 4DEnVAR

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Localized Ensemble Transform Kalman FilterLETKF

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Maximum Likelihood Ensemble Filter (MLEF)

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Hybrid 3D VAR

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Hybrid 4D Var or En4DVAR

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NDEnVAR

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4DEnVAR – Four Dimensional Ensemble VARThe approach presented here is similar to that of Ensemble 4D VAR (En4DVAR) but was

designed to AVOID the TLM and adjoints. 4DEnVAR extends to four dimensions for all the En4DVAR equations, but now applying them to the sequence of states in trajectories rather than at the single time at the beginning of the window. This implies that we can use an implicit localized ensemble covariance

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