bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tropical Pacific Ocean model error covariances from Monte Carlo simulations
Authors: Alves O. , Robert C. 
Published: August 2006

AbstractAs a first step towards the development of an Ensemble Kalman Filter (EnKF) for ocean data assimilation in the tropical oceans, this article investigates a novel technique for explicitly perturbing the model error in Monte Carlo simulations.The perturbation technique involves perturbing the surface zonal stress. Estimates of the characteristics of the wind stress errors were obtained from the difference between zonal wind fields from the NCEP and ECMWF re‐analyses. In order to create random zonal wind stress perturbations, an EOF analysis was performed on the intraseasonally time‐filtered difference between the two re‐analysis products. The first 50 EOFs were retained and random wind stress fields for each ensemble member were created by combining random amounts of each EOF.Ensemble runs were performed using a shallow‐water model, with both short forecasts and long simulations. Results show covariance patterns characteristic of Kelvin wave and Rossby wave dynamics. There are interesting differences between covariances using short forecasts and those using long simulations. The use of the long simulations produced non‐local covariances (e.g. negative covariances between east and west Pacific), whereas short forecasts produced covariances that were localized by the time it takes Kevin and Rossby waves to travel over the forecast period and the scales of spatial covariance in the wind stress errors.The ensembles of short forecasts produced covariances and cross‐covariances that can be explained by the dynamics of equatorial Rossby and Kevin waves forced by wind stress errors. The results suggest that the ensemble generation technique to explicitly represent the model error term can be used in an EnKF. Copyright © 2005 Royal Meteorological Society
A multivariate balance operator for variational ocean data assimilation
Authors: Weaver A. T. , Deltel C. , Machu E. , Ricci S. , Daget N. 
Published: August 2006

AbstractIt is common in meteorological applications of variational assimilation to specify the error covariances of the model background state implicitly via a transformation from model space where variables are highly correlated to a control space where variables can be considered to be approximately uncorrelated. An important part of this transformation is a balance operator which effectively establishes the multivariate component of the error covariances. The use of this technique in ocean data assimilation is less common. This paper describes a balance operator that can be used in a variable transformation for oceanographic applications of three‐ and four‐dimensional variational assimilation. The proposed balance operator has been implemented in an incremental variational data assimilation system for a global ocean general‐circulation model. Evidence that the balance operator can explain a significant percentage of background‐error variance is presented. The multivariate analysis structures implied by the balance operator are illustrated using single‐observation experiments. Copyright © 2005 Royal Meteorological Society
A pre‐operational variational data assimilation system for a non‐hydrostatic model at the Japan Meteorological Agency: formulation and preliminary results
Authors: Honda Y. , Nishijima M. , Koizumi K. , Ohta Y. , Tamiya K. , Kawabata T. , Tsuyuki T. 
Published: August 2006

AbstractA new variational data assimilation system for a non‐hydrostatic model is being developed at the Japan Meteorological Agency (JMA) for operational use. Known as the JMA non‐hydrostatic model variational data assimilation (JNoVA) system, it mainly functions as a four‐dimensional variational data assimilation system, although it has an option to be used as a three‐dimensional system.The set of control variables consists of initial conditions of unbalanced horizontal winds, large‐scale components of potential temperature and surface pressure, unbalanced temperature and pseudo relative humidity. In the control variable transformation, hydrostatic balance and geostrophic balance are considered explicitly and the effect of the surface friction is also considered implicitly. When calculating the background‐error covariances by the NMC method, a low‐pass filter is introduced to remove noise in potential temperature and surface pressure that degrades the quality of the balanced winds. The cut‐off wavelength of the low‐pass filter is set to 300 km, which is the scale at which the model's kinetic energy spectrum transits to the shallower slope characterizing mesoscale motions.An adjoint model of the JMA non‐hydrostatic model has been developed from scratch by hand for this system. Although some of the physics are simplified, all physical processes except the radiation are considered.A preliminary data assimilation experiment with the JNoVA has been done for a heavy rainfall event. The results show that the quantitative precipitation forecast (in terms of the intensity, timing and position of the event) from the analysis by the JNoVA is improved over the forecast from the analysis by a four‐dimensional variational system that employs the JMA hydrostatic spectral model. Copyright © 2005 Royal Meteorological Society
Ensemble Kalman filtering
Authors: Houtekamer P. L. , Mitchell Herschel L. 
Published: August 2006

AbstractAn ensemble Kalman filter (EnKF) has been implemented at the Canadian Meteorological Centre to provide an ensemble of initial conditions for the medium‐range ensemble prediction system. This demonstrates that the EnKF can be used for operational atmospheric data assimilation.We show how the EnKF relates to the Kalman filter. In particular, to make the ensemble approximation feasible, we have to use a fairly small ensemble with many less members than either the number of model coordinates, or the number of independent observations, or the (unknown) dimension of the dynamical system. To nevertheless obtain good results, we must (i) counter the tendency of the ensemble spread to underestimate the true error, and (ii) localize the ensemble covariances. The localization is severe and leads to imbalance in the initial conditions.The operational EnKF is used to investigate to what extent our system respects the underlying hypotheses of both the Kalman filter and its ensemble approximation. In particular, we quantify the imbalance in the initial conditions and the magnitude of the model‐error component. The occurrence of imbalance constrains the ways in which time interpolation can be performed and in which parametrized model error can be added. With this study we hope to obtain and provide guidance for further improvements to the EnKF. Copyright © 2005 Royal Meteorological Society
Convective‐scale assimilation of radar data: progress and challenges
Authors: Sun Juanzhen 
Published: August 2006

AbstractActive research has been carried out in recent years to assimilate high‐resolution observations into numerical models to improve precipitation forecasting. Considerable progress has been made although great scientific and technological challenges still exist. This paper reviews techniques used in convective‐scale data assimilation research. Experiences in the assimilation of radar observations into high‐resolution numerical models are presented. A number of future challenges in convective‐scale data assimilation are discussed. Copyright © 2005 Royal Meteorological Society
Opportunities for enhanced collaboration within the data assimilation community
Authors: McLaughlin Dennis , O'Neill Alan , Derber John , Kamachi Masafumi 
Published: August 2006

AbstractRecent advances in sensor technology, telecommunications and computation open up new possibilities for the application of data assimilation concepts across the Earth sciences. As a result, the data assimilation community is expanding beyond meteorology and oceanography to include representatives from climatology, hydrology, atmospheric chemistry, ecology and other disciplines. This development offers new opportunities for collaboration between the operational and research sides of the community. Opportunities exist not only in traditional forecasting applications, but also in areas such as reanalysis, model diagnosis, development of new model parametrizations, and observing‐system design. Disciplinary scientists from outside the traditional data assimilation community are starting to appreciate that data assimilation can provide an integrated view of earth processes over a range of time and space scales. Operational data assimilation groups have special expertise and capabilities that are needed by newcomers to the field. If the scope of the operational community expands to include a wider range of applications, the entire field will likely benefit from new ideas, new resources, and increased visibility and recognition. Copyright © 2005 Royal Meteorological Society
Assimilation of MIPAS observations using a three‐dimensional global chemistry‐transport model
Authors: Baier F. , Erbertseder T. , Morgenstern O. , Bittner M. , Brasseur G. 
Published: August 2006

AbstractMIPAS observations are assimilated using a modified version of the chemistry‐transport model ROSE to derive consistent global chemical analyses of the stratosphere. Due to different retrieval schemes applied, available MIPAS datasets are expected to differ in quality and coverage. In this study we investigate the sensitivity of the data assimilation scheme to two different sample datasets. ENVISAT/MIPAS baseline observations of H2O,O3,HNO3,CH4,N2O and NO2, covering October–November 2003, are considered. Sequential assimilation is performed using an optimum interpolation scheme with error propagation. It is shown that all assimilated model species benefit significantly from observations. Results are analysed using observation minus first‐guess error statistics and are additionally compared to UARS/HALOE data. Optimized assimilation parameters are derived using χ2 diagnostics. Two different MIPAS data products are examined: the European Space Agency operational product and the Institute for Meteorology Karlsruhe (IMK) scientific product. Assimilation results show some significant differences with respect to the dataset type used. For example, regions with increased stratospheric H2O concentrations near the tropical tropopause are only present when IMK data are applied. Both datasets are found to be well suited for global assimilation experiments to study the chemistry and dynamics of the middle atmosphere. Copyright © 2005 Royal Meteorological Society
Ensemble data assimilation for an eddy‐resolving ocean model of the Australian region
Authors: Oke P. R. , Schiller A. , Griffin D. A. , Brassington G. B. 
Published: August 2006

AbstractThe Bluelink Ocean Data Assimilation System (BODAS) is an ensemble optimal interpolation system applied to a global ocean general‐circulation model with 10 km resolution around Australia. BODAS derives estimates of forecast‐error covariances (FECs) from a stationary 72‐member ensemble of intraseasonal model anomalies. The FECs are localized around each observation to reduce the negative effects of sampling error and to increase the rank of the ensemble. The FECs have characteristics that reflect the length‐scales and the anisotropy of the ocean circulation in different regions. BODAS assimilates in situ and satellite‐derived observations of temperature, salinity and sea‐level anomaly. Results from a 13‐year ocean re‐analysis demonstrate that the reanalysed fields are often in very good agreement with withheld observations, and provide a good synoptic representation of the eddy field around Australia. Copyright © 2005 Royal Meteorological Society
Treating strong adjoint sensitivities in tropical eddy‐permitting variational data assimilation
Authors: Hoteit I. , Cornuelle B. , Köhl A. , Stammer D. 
Published: August 2006

AbstractA variational data assimilation system has been implemented for the tropical Pacific Ocean using an eddy‐permitting regional implementation of the MITgcm. The adjoint assimilation system was developed by the Estimation of the Circulation and the Climate of the Ocean consortium, and has been extended to deal with open boundaries. This system is used to adjust the model to match observations in the tropical Pacific region using control parameters which include initial conditions, open boundaries and time‐dependent surface fluxes. This paper focuses on problems related to strong adjoint sensitivities that may impede the model fit to the observations. A decomposition of the velocities at the open boundaries into barotropic and baroclinic modes is introduced to deal with very strong sensitivities of the model sea surface height to the barotropic component of the inflow. Increased viscosity and diffusivity terms are used in the adjoint model to reduce exponentially growing sensitivities in the backward run associated with nonlinearity of the forward model. Simplified experiments in which the model was constrained with Levitus temperature and salinity data, Reynolds sea surface temperature data and TOPEX/POSEIDON altimeter data were performed to demonstrate the controllability of this assimilation system and to study its sensitivity to the starting guesses for forcing and initial conditions. Copyright © 2005 Royal Meteorological Society
Multi‐model fusion and error parameter estimation
Authors: Logutov O. G. , Robinson A. R. 
Published: August 2006

AbstractA robust and practical methodology for multi‐model ocean forecast fusion has been sought. Present regional ocean forecasting systems adapt and evolve in response to modelled processes. This makes it imperative that a forecast combination methodology be adaptive and capable to operate with a small sample of past validating events. To this end, we consider an extension of maximum‐likelihood error parameter estimation to multi‐model predictive systems, and utilize the resulting methodology for adaptive Bayesian model fusion. The methodology consists of the following three general steps: (a) parametrization of forecast uncertainties through either a suitable parametric family (e.g. covariance models) or through a low‐rank approximation (e.g. flow‐dependent error subspaces); (b) update of uncertainty parameters via maximum likelihood; and (c) combining model forecasts based on their uncertainty parameters via maximum likelihood. In order to implement step (b), we have extended the maximum‐likelihood error parameter estimation methodology to multi‐model forecasting systems using the expectation‐maximization technique, with the true state‐space vector at observation locations treated as missing data. With only one forecasting model, the procedure reduces to the standard maximum‐likelihood error parameter estimation. The proposed multi‐model fusion methodology neglects cross‐model error correlations in order to gain the capability to work with a small sample of past events. We illustrate the methodology with a two‐model forecasting example (HOPS, ROMS) within the framework of the real‐time forecasting experiment held in Monterey Bay during 2003. Copyright © 2005 Royal Meteorological Society
Is routine vaginal examination necessary for asymptomatic women attending sexual health services?
Authors: Lee D M , Chen M Y , Bradshaw C S , Fairley C K 
Published: August 2006

The aim of this study was to determine whether our sexual health service could be streamlined by dispensing with routine vaginal examination of asymptomatic women, without missing important diagnoses. This was an audit of asymptomatic women presenting to the centre who had had a Papanicolaou (PAP) smear in the previous two years. Of the 421 women who were eligible, no abnormalities were found on genital inspection in 392 (93%) individuals. Abnormalities detected on clinical examination included one case (0.2%) with mucopurulent cervicitis that tested positive for Chlamydia trachomatis, four (1%) with warts or molluscum contagiosum, and one with an asymptomatic genital ulcer of unknown cause. Dispensing with the vaginal examination in asymptomatic women who have had a speculum examination as part of biennial cervical screening may be appropriate in settings where sensitive non-invasive testing for sexually transmitted infections (STI) is in use and STI prevalence is low.
HIV testing in Scotland. Are we meeting the standard? BASHH Scotland National Audit 2004
Authors: Ross F , Wardle D , Currie A , Baguley S 
Published: August 2006

Most sexually transmitted infections (STIs) are associated with increased risk of HIV transmission. The draft Scottish Sexual Health Strategy (2003) proposed that 'HIV testing [should be] offered to all GUM clinic attendees not known to be HIV infected who present with a new STI. … Reasons for non-uptake should be recorded.' We performed a national audit comparing practice in Scottish genitourinary (GU) medicine services against these standards. The results show that practice is highly variable but overall in 2004 Scottish GU medicine clinics were failing to meet the strategy standard.
Nondestructive Field Testing of Installed Weatherproofing Sealant Joints—Questions and Answers
Authors: Huff D 
Published: August 2006

Abstract
With current expectations for building exteriors to prevent all air and water entry into the building interior, the need for a near pertect seal of weatherproofing sealant joints has reached new levels of intensity. The need for better field tests has increased accordingly. To reach these goals, ASTM Standard C-1521-02a [1] has been developed and adopted. The practice outlines a nondestructive procedure. This procedure provides an examiner of the joint the option of inducing an artificial strain to the sealant bead using a blunt instrument so that the sealant is subjected to a stress at the bond line typical to the anticipated cyclic movement endured by the sealant during the normal service life of the joint. The advantage of this methodology is that it allows an unlimited amount of testing to be conducted. While the procedure does not specify a specific instrument to induce the strain, a device able to accomplish this procedure in a uniform, controlled, and calibrated fashion has been developed. The paper outlines a description of the device and its capabilities. The paper also provides a discussion of the use of statistical sampling when the option of 100 % testing is not feasible or required. The author believes that the future of field testing of installed weather proofing sealant joints should include enhanced nondestructive procedures. Continued field use, research, and development are essential in the quest for a near perfect building seal.
Proactive Mitigation of PCTFE-Related Ignition Hazards in Oxygen Systems: I. Development of a Voluntary Consensus Standard Specification to Control Property Variation in Finished PCTFE Parts
Authors: Waller JM , Julien HL , Newton BE , Beeson HD 
Published: August 2006

AbstractRevelations of dimensional instability in polychlorotrifluoroethylene (PCTFE) semifinished articles and finished parts raised concerns that leaks or part failure could occur during service, leading to catastrophic component or system failure, especially in high-pressure gaseous oxygen systems where flow friction, flow resonance, or kindling chain ignition mechanisms are operative. These concerns culminated in the release of an internal NASA Kennedy Space Center Problem Advisory and a Government-Industry Data Exchange Program Problem Advisory on PCTFE. Release of the advisories coincided with a task group study examining the factors contributing to property variation in PCTFE. More specifically, the effect of resin grade, process route, annealing method, and machining on dimensional stability, molecular weight, and crystallinity was determined. To better control dimensional stability, for example, a Biot-Fourier method is described that allows calculation of the time needed for PCTFE parts of known geometry to reach thermal equilibrium during annealing. A voluntary consensus material specification was then implemented to control properties in finished PCTFE parts used in aerospace applications.
Domestic iterated one-point extensions of algebras by two-ray modules
Authors: Bobiński Grzegorz , Skowroński Andrzej 
Published: August 2006

Abstract
In the paper, we introduce a wide class of domestic finite dimensional algebras over an algebraically closed field which are obtained from the hereditary algebras of Euclidean type , n≥1, by iterated one-point extensions by two-ray modules. We prove that these algebras are domestic and their Auslander-Reiten quivers admit infinitely many nonperiodic connected components with infinitely many orbits with respect to the action of the Auslander-Reiten translation. Moreover, we exhibit a wide class of almost sincere domestic simply connected algebras of large global dimensions.
On representation theory and the cohomology rings of irreducible compact hyperkähler manifolds of complex dimension four
Authors: Guan Daniel 
Published: August 2006

Abstract
In this paper, we continue the study of the possible cohomology rings of compact complex four dimensional irreducible hyperkähler manifolds. In particular, we prove that in the case b
2=7, b
3=0 or 8. The latter was achieved by the Beauville construction.
Absolutely continuous functions of several variables and diffeomorphisms
Authors: Hencl Stanislav , Malý Jan 
Published: August 2006

Abstract
In [4], a class of absolutely continuous functions of d-variables, motivated by applications to change of variables in an integral, has been introduced. The main result of this paper states that absolutely continuous functions in the sense of [4] are not stable under diffeomorphisms. We also show an example of a function which is absolutely continuous with respect cubes but not with respect to balls.
Surface diffusion of Pb on clean Si surfaces
Authors: Dolbak Andrey , Zhachuk Ruslan , Olshanetsky Boris 
Published: August 2006

AbstractPb diffusion on clean Si(111), (100), and (110) surfaces was studied by Auger electron spectroscopy and low energy electron diffraction in the temperature range from 100 to 300°C. It is shown that lead transport along sillicon surfaces takes place via the mechanism of solid-phase spreading with a sharp moving boundary. The temperature dependence of the Pb diffusion coefficients on Si(111), (100) and (110) surfaces have been obtained. A Si(110)-4×2-Pb surface structure has been observed for the first time.
Magnetic phases in UNi2Si2
Authors: Svoboda Pavel , Javorský Pavel , Honda Fuminori , Sechovský Vladimír , Menovsky Alois 
Published: August 2006

AbstractThe tetragonal compound UNi2Si2 exhibits in zero magnetic field three different antiferromagnetic phases belowT N=124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q z). Two additional order-order magnetic phase transitions are observed below T N, namely atT 1=108 K and T 2=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi2Si2 single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi2Si2.