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10 For certain observing types, such as those that are remotely sensed, the observation errors are correlated and these correlations are stateand time-dependent. In this work, we develop a method forâ€¦ (More)

The observation-error covariance matrix used in data assimilation contains contributions from instrument errors, representativity errors and errors introduced by the approximated observationâ€¦ (More)

- Serge Gratton, Amos S. Lawless, Nancy K. Nichols
- SIAM Journal on Optimization
- 2007

The Gaussâ€“Newton algorithm is an iterative method regularly used for solving nonlinear least squares problems. It is particularly well suited to the treatment of very large scale variational dataâ€¦ (More)

- Alexander J F Moodey, Amos S. Lawless, Roland W. E. Potthast, Peter Jan van Leeuwen
- 2013

We investigate the error dynamics for cycled data assimilation systems, such that the inverse problem of state determination is solved at tk, k = 1, 2, 3, . . ., with a first guess given by the stateâ€¦ (More)

Atmosphere only and ocean only variational data assimilation (DA) schemes are able to use window lengths that are optimal for the error growth rate, non-linearity and observation density of theâ€¦ (More)

- Ewan M. Pinnington, E. Casella, +5 authors Tristan Quaife
- 2016

Efforts to implement variational data assimilation routines with functional ecology models and land surface models have been limited, with sequential and Markov chain Monte Carlo data assimilationâ€¦ (More)

- Amos S. Lawless
- 2010

The analysis error variance of a 3D-FGAT assimilation is examined analytically using a simple scalar equation. It is shown that the analysis error variance may be greater than the error variances ofâ€¦ (More)

2 P.J. SMITH ET AL. be expected from coupled data assimilation. When compared to uncoupled initialisation, coupled assimilation is able to produce more balanced initial analysis fields, thus reducingâ€¦ (More)

- Amos S. Lawless
- 2013

Variational data assimilation is commonly used in environmental forecasting to estimate the current state of the system from a model forecast and observational data. The assimilation problem can beâ€¦ (More)

- Don Katz, Amos S. Lawless, Nancy K. Nichols, Michael J. P. Cullen, R. N. Bannister
- 2011

D. Katza, A. S. Lawless*a, N. K. Nicholsa, M. J. P. Cullenbâ€ and R. N. Bannistera aSchool of Mathematical and Physical Sciences, University of Reading, UK bMet Office, Exeter, UK *Correspondence to:â€¦ (More)