کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
507128 865096 2012 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Variational chemical data assimilation with approximate adjoints
موضوعات مرتبط
مهندسی و علوم پایه مهندسی کامپیوتر نرم افزارهای علوم کامپیوتر
پیش نمایش صفحه اول مقاله
Variational chemical data assimilation with approximate adjoints
چکیده انگلیسی

Data assimilation obtains improved estimates of the state of a physical system by combining imperfect model results with sparse and noisy observations of reality. In the four-dimensional variational (4D-Var) framework, data assimilation is formulated as an optimization problem, which is solved using gradient-based optimization methods. The 4D-Var gradient is obtained by forcing the adjoint model with observation increments. The construction of the adjoint model requires considerable development effort. Moreover, the computation time associated with the adjoint model is significant (typically, a multiple of the time needed to run the forward model). In this paper we investigate the use of approximate gradients in variational data assimilation. The approximate gradients need to be sufficiently accurate to ensure that the numerical optimization algorithm makes progress toward the maximum likelihood solution. The approximate gradients are obtained through simplified adjoint models; this decreases the adjoint development effort, and reduces the CPU time and the storage requirements associated with the computation of the 4D-Var gradient. The resulting approach, named quasi-4D-Var (Q4D-Var), is illustrated on a global chemical data assimilation problem using satellite observations and the GEOS-Chem chemical transport model.


► The paper examines approximate gradients in 4D-Var data assimilation.
► Approximate gradients are obtained through different simplified adjoint models.
► The approach decreases the adjoint development effort.
► The approach reduces the CPU time and storage requirements for 4D-Var assimilation.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Computers & Geosciences - Volume 40, March 2012, Pages 10–18
نویسندگان
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