Ensemble Kalman Filter: Current Status and Potential
In this chapter we give an introduction to different types of Ensemble Kalman filter, describe the Local Ensemble Transform Kalman Filter (LETKF) as a representative prototype of these methods, and several examples of how advanced properties and applications that have been developed and explored for 4D-Var (four-dimensional variational assimilation) can be adapted to the LETKF without requiring an adjoint model. Although the Ensemble Kalman filter is less mature than 4D-Var (Kalnay 2003), its simplicity and its competitive performance with respect to 4D-Var suggest that it may become the method of choice.
KeywordsKalman Filter Data Assimilation Ensemble Member Outer Loop Ensemble Forecast
I want to thank the members of the Chaos-Weather group at the University of Maryland, and in particular to Profs. Shu-Chih Yang, Brian Hunt, Kayo Ide, Eric Kostelich, Ed Ott, Istvan Szunyogh, and Jim Yorke. My deepest gratitude is to my former students at the University of Maryland, Drs. Matteo Corazza, Chris Danforth, Hong Li, Junjie Liu, Takemasa Miyoshi, Malaquías Peña, Shu-Chih Yang, Ji-Sun Kang, Matt Hoffman, and present students Steve Penny, Steve Greybush, Tamara Singleton, Javier Amezcua and others, whose creative research allowed us to learn together. Interactions with the thriving Ensemble Kalman Filter community members, especially Ross Hoffman, Jeff Whitaker, Craig Bishop, Kayo Ide, Joaquim Ballabrera, Jidong Gao, Zoltan Toth, Milija Zupanski, Tom Hamill, Herschel Mitchell, Peter Houtekamer, Chris Snyder, Fuqing Zhang and others, as well as with Michael Ghil, Arlindo da Silva, Jim Carton, Dick Dee, and Wayman Baker, have been a source of inspiration. Richard Ménard, Ross Hoffman, Kayo Ide, Lars Nerger and William Lahoz made important suggestions that improved the review and my own understanding of the subject.
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