Generalized inversion of a global numerical weather prediction model     

A. F. Bennett  B. S. Chua  L. M. Leslie 《Meteorology and Atmospheric Physics》1996,60(1-3):165-178

Summary We construct the generalized inverse of a global numerical weather prediction (NWP) model, in order to prepare initial conditions for the model at time t=0 hrs. The inverse finds a weighted, least-squares best-fit to the dynamics for –24<t<0, to the previous initial condition att=–24, and to data att=–24,t=–18,t=–12 andt=0. That is, the inverse is a weak-constraint, four-dimensional variational assimilation scheme. The best-fit is found by solving the nonlinear Euler-Lagrange (EL) equations which determine the local extrema of a penalty functional. The latter is quadratic in the dynamical, initial and data residuals. The EL equations are solved using iterated representer expansions. The technique yields optimal conditioning of the very large minimization problem, which has 10⁹ hydrodynamical and thermodynamical variables defined on a 4-dimensional, space-time grid.In addition to introducing the inverse NWP model, we demonstrate it on a medium-sized problem, namely, a study of the impact of reprocessed cloud track wind observations (RCTWO) from the 1990 Tropical Cyclone Motion Experiment (TCM-90). The impact is assessed in terms of the improvement of forecasts in the South China Sea att=+48 hours. The calculation shows that the computations are manageable, the iteration scheme converges, and that the RCTWO have a beneficial impact.  相似文献   

Large motion analysis of compliant structures using euler parameters     

C. Y. Liam  N. J. Shankar  K. S. Chua 《Ocean Engineering》1989,16(5-6)

The large motions that a compliant offshore structure experiences were analysed using Euler parameters. Firstly, the equations of motion of a rigid body undergoing large translations and rotations were obtained using the Lagrangian formulation. Secondly, the hydrodynamic forces acting on the structure were calculated using the modified Morison's equation. A tension-leg platform (TLP) subjected to an oblique incident wave was then analysed using the above formulation. This was followed by an analysis of an articulated tower for comparison with the results of other researchers. An example showing the tower undergoing subharmonic oscillations was also included.  相似文献   

Euler–Lagrange equations for the spectral element shallow water system     

J.C. Levin  D.B. Haidvogel  B. Chua  A.F. Bennett  M. Iskandarani   《Ocean Modelling》2006,12(3-4):348-377

We present the derivation of the discrete Euler–Lagrange equations for an inverse spectral element ocean model based on the shallow water equations. We show that the discrete Euler–Lagrange equations can be obtained from the continuous Euler–Lagrange equations by using a correct combination of the weak and the strong forms of derivatives in the Galerkin integrals, and by changing the order with which elemental assembly and mass averaging are applied in the forward and in the adjoint systems. Our derivation can be extended to obtain an adjoint for any Galerkin finite element and spectral element system.We begin the derivations using a linear wave equation in one dimension. We then apply our technique to a two-dimensional shallow water ocean model and test it on a classic double-gyre problem. The spectral element forward and adjoint ocean models can be used in a variety of inverse applications, ranging from traditional data assimilation and parameter estimation, to the less traditional model sensitivity and stability analyses, and ensemble prediction. Here the Euler–Lagrange equations are solved by an indirect representer algorithm.  相似文献   

Weak and strong constraint data assimilation in the inverse Regional Ocean Modeling System (ROMS): Development and application for a baroclinic coastal upwelling system   总被引：4，自引：2，他引：4  

Emanuele Di Lorenzo  Andrew M. Moore  Hernan G. Arango  Bruce D. Cornuelle  Arthur J. Miller  Brian Powell  Boon S. Chua  Andrew F. Bennett 《Ocean Modelling》2007,16(3-4):160-187

We describe the development and preliminary application of the inverse Regional Ocean Modeling System (ROMS), a four dimensional variational (4DVAR) data assimilation system for high-resolution basin-wide and coastal oceanic flows. Inverse ROMS makes use of the recently developed perturbation tangent linear (TL), representer tangent linear (RP) and adjoint (AD) models to implement an indirect representer-based generalized inverse modeling system. This modeling framework is modular. The TL, RP and AD models are used as stand-alone sub-models within the Inverse Ocean Modeling (IOM) system described in [Chua, B.S., Bennett, A.F., 2001. An inverse ocean modeling system. Ocean Modell. 3, 137–165.]. The system allows the assimilation of a wide range of observation types and uses an iterative algorithm to solve nonlinear assimilation problems. The assimilation is performed either under the perfect model assumption (strong constraint) or by also allowing for errors in the model dynamics (weak constraints). For the weak constraint case the TL and RP models are modified to include additional forcing terms on the right hand side of the model equations. These terms are needed to account for errors in the model dynamics.Inverse ROMS is tested in a realistic 3D baroclinic upwelling system with complex bottom topography, characterized by strong mesoscale eddy variability. We assimilate synthetic data for upper ocean (0–450 m) temperatures and currents over a period of 10 days using both a high resolution and a spatially and temporally aliased sampling array. During the assimilation period the flow field undergoes substantial changes from the initial state. This allows the inverse solution to extract the dynamically active information from the synthetic observations and improve the trajectory of the model state beyond the assimilation window. Both the strong and weak constraint assimilation experiments show forecast skill greater than persistence and climatology during the 10–20 days after the last observation is assimilated.Further investigation in the functional form of the model error covariance and in the use of the representer tangent linear model may lead to improvement in the forecast skill.  相似文献   

The Mourne Mountains     

R. Lloyd Praeger 《Proceedings of the Geologists' Association. Geologists' Association》1895,14(4):148-152

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Variations of thermospheric winds in northern scandinavia between 1980 and 1986: A study of geomagnetic activity effects during the last solar cycle     

David Rees  N. D. Lloyd  T. J. Fuller-Rowell  Ake Steen 《Surveys in Geophysics》1987,9(2):197-214

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Relationship between paleotemperatures of metamorphic dolomites and ESR determined Mn(II) partitioning ratios     

Roger V Lloyd  David N Lumsden  Jay M Gregg 《Geochimica et cosmochimica acta》1985,49(12):2565-2568

An Electron Spin Resonance (ESR) study of the distribution of Mn(II) between Mg sites and Ca sites in 28 contact metamorphic dolomite samples suggests that the distribution is temperature sensitive. The data can be modelled by alternative interpretations. In the first a polynomial equation approximates the trend of the data suggesting an exponential relation with Mn(II) ratios decreasing to a stable value of 10 with increasing temperature (to near 900°C). The second suggests two groups of dolomites. One group, close to the intrusion (< 100 m), has a low partitioning ratio (10 to 30), possibly increasing linearly with increasing distance from the intrusive contact. The second group (100 to 400 m) increases in scatter and distribution ratio (20 to 215) with increasing distance. Whatever the detailed relationship, we conclude that Mn partitioning is related to the thermal halo of the intrusion and that lower ratios result from higher temperatures. Mn(II) partitioning ratios may yield absolute paleotemperature data when calibrated against other techniques.  相似文献   

Late Cenozoic stable isotope stratigraphy and paleoceanography of DSDP sites from the east equatorial and central north Pacific Ocean     

Lloyd D. Keigwin 《Earth and Planetary Science Letters》1979,45(2):361-382

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Fossil Ground-Water Gradients in Arid Regional Sedimentary Basins     

John W. Lloyd  Mohamed H. Farag 《Ground water》1978,16(6):388-392

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The Hydrogeology and Utilization of Brines in El Salado, Chile     

John W. Lloyd 《Ground water》1974,12(2):72-77

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