Diagnostic Quantities Research Articles

Assessment of mesoscale eddy parameterizations for a single‐basin coarse‐resolution ocean model

In this study we explore the ability of three parameterization schemes to represent mesoscale eddies' effects in a single, idealized ocean basin. We first carry out an eddy‐resolving simulation with an ocean general circulation model (GCM). The three schemes tested are the traditional Fickian diffusion and the Green‐Stone (GS) and Gent‐McWilliams (GM) parameterizations. Evaluation of the divergence of the eddy heat flux from the reference simulation in the time‐averaged thermal balance shows that eddies contribute significantly to the balance only in a geographically limited area adjacent to the western boundary around the separation point of the midlatitude jet. For this region, diagnostic tests are carried out comparing the local properties of the eddy heat flux evaluated from the fine‐resolution eddy‐resolving reference simulation with the parameterized fluxes diagnosed according to the three schemes. Evaluation of the Fickian diffusion shows that the components of the eddy heat flux are not down the temperature gradient in about half of the domain. The GS parameterization is assessed by examining the relative orientation of the isopycnal surface and the eddy heat flux vector. The relative orientation falls outside the range implicitly assumed by the GS parameterization in about half of the domain. Similarly, the GM scheme simulates the wrong sign for the divergence of the eddy heat flux in about half of the domain. Comparison of the divergences predicted with the schemes in the most energetic subdomain of the western region shows that all of them have some skill but does not identify any one scheme as being superior to the others, and two of them, GS and GM, fail in the western boundary current by predicting the wrong sign of the divergence. The incorrect orientation of the eddy heat flux vector in the test of the GS scheme implies that mean flow kinetic energy is an important source of eddy energy, and this is a likely reason why the GS and GM schemes do not do better. We carry out a further assessment of the parameterization schemes by implementing them in an ocean GCM in coarse‐resolution experiments, thus mimicking the actual procedure used in climate simulations. All the parameterization schemes can be tuned to reproduce with some accuracy some of the climatological diagnostic quantities, hence their relative success in climatological coarse‐resolution simulations. However, once again, no one scheme is noticeably better than the others. We note that our results only apply to parameterizations of eddies generated in western boundary currents and their extensions.

Diagnosing ozone loss in the extratropical lower stratosphere

Chemical ozone loss in the Southern Hemisphere lower stratosphere during winter and spring 1996 is investigated using a three‐dimensional chemical transport model. Model diagnostic quantities are developed to determine the underlying chemical mechanisms controlling the distribution of ozone. These diagnostic tracers quantify the ozone change due to individual catalytic cycles or reaction mechanisms that form or destroy ozone. Results from these tracers confirm the importance of halogens not only in the development of the ozone hole but also in midlatitude ozone depletion of which almost 50% is due to cycles involving halogens. The dominant chemical ozone loss mechanism in the middle latitudes is due to the cycle whose rate determining step involves the bimolecular collision between HO2 and O3. Observational evidence from ozonesonde measurements shows substantial ozone depletion in the polar subvortex region (altitudes below ∼14 km). These measurements also indicate that this ozone depletion must be due, at least in part, to in situ chemical ozone loss. Model results show that over a quarter of the ozone depletion associated with the ozone hole resides at subvortex altitudes. Diagnostic tracers designed to quantify ozone loss occurring above and below the subvortex transition altitude show that the majority of this ozone depletion is in situ ozone loss. Furthermore, at altitudes below the subvortex transition, polar ozone loss is efficiently transported to middle latitudes, where it contributes to midlatitude ozone decline.

Variational Assimilation of Precipitation Data and Gravity Wave Excitation

Abstract The degree of imbalance forced by deep convection in a three-dimensional variational analysis scheme (3DVAR) is examined. Simulated surface precipitation rates are used with various degree of errors together with different background atmospheric fields. Dynamical imbalances are defined only for the fastest timescales associated with gravity waves and diagnosed according to the implicit normal mode framework. Local measures of ageostrophic perturbations are also considered over rainy areas. Slow timescale perturbations on internal gravitational modes introduced by convection during 3DVAR are also monitored using temporal evidence of their presence. The diagnostic quantities used here are more appropriate for deep vertical scales where Machenhauer's balance scheme can be justified but must be used with care when discussing possible imbalance for shallow vertical gravity modes (especially for mesoscale data assimilation). These diagnostic measures are not actually used as an explicit constraint in t...

AN IMPROVED COMPOUND ESTIMATOR FOR ROBUST REGRESSION

ABSTRACT Advances in statistical computing software have led to a substantial increase in the use of ordinary least squares (OLS) regression models in the engineering and applied statistics communities. Empirical evidence suggests that data sets can routinely have 10% or more outliers in many processes. Unfortunately, these outliers typically will render the OLS parameter estimates useless. The OLS diagnostic quantities and graphical plots can reliably identify a few outliers; however, they significantly lose power with increasing dimension and number of outliers. Although there have been recent advances in the methods that detect multiple outliers, improvements are needed in regression estimators that can fit well in the presence of outliers. We introduce a robust regression estimator that performs well regardless of outlier quantity and configuration. Our studies show that the best available estimators are vulnerable when the outliers are extreme in the regressor space (high leverage). Our proposed compound estimator modifies recently published methods with an improved initial estimate and measure of leverage. Extensive performance evaluations indicate that the proposed estimator performs the best and consistently fits the bulk of the data when outliers are present. The estimator, implemented in standard software, provides researchers and practitioners a tool for the model-building process to protect against the severe impact from multiple outliers.

Regression Diagnostics for Binomial Data from the Forward Search

Summary. We suggest a simple robust method for the detection of atypical and influential observations in binomial data. Our technique is based on a forward search procedure which orders the observations from those most in agreement with a specified generalized linear model to those least in agreement with it. The effectiveness of the forward search estimator in detecting masked multiple outliers, and more generally in ordering binomial data, is shown by means of three data sets. Plots of diagnostic quantities during the forward search clearly show the effect of individual observations on residuals and test statistics. These examples reveal the strength of our method in showing the structure of the data in a way which is more simple and effective than it would be by using standard deletion diagnostic procedures.

Quality Criteria Development within the Fourth Framework Research Programme: Computed Tomography

The Quality Criteria concept has recently been extended to Computed Tomography with the European Guidelines on Quality Criteria for CT (EUR 16262) produced under the 4th Framework Research Programme in a Concerted Action. The adaptation of the quality criteria to CT has become necessary due to the relatively high collective dose which derives from CT within Europe, where in some countries it accounts for more than one third of the total collective dose from diagnostic X ray examinations, whilst representing only about 2-4% of all examinations. The Guidelines include diagnostic requirements specifying anatomical/diagnostic image quality criteria for six main groups of examinations: cranium, face and neck, spine, chest, abdomen and pelvis, and bones and joints. The image criteria refer to characteristic features of imaged anatomical structures with a specific degree of visibility. Two diagnostic reference dose quantities have been defined on the basis of measurements of the Computed Tomography Dose Index (CTDI).

Radial basis function approximations as smoothing splines

Radial basis function methods for interpolation can be interpreted as roughness-minimizing splines. Although this relationship has already been established for radial basis functions of the form g( r)= r α and g(r)=r α log (r) , it is extended here to include a much larger class of functions. This class includes the multiquadric g( r)=( r 2+ c 2) 1/2 and inverse multiquadric g( r)=( r 2+ c 2) −1/2 functions as well as the Gaussian exp (−r 2/D) . The crucial condition is that the Fourier transform of g(| x|) be positive, except possibly at the origin. The appropriate measure of roughness is defined in terms of this Fourier transform. To allow for possibility of noisy data, the analysis is presented within the general framework of smoothing splines, of which interpolation is a special case. Two diagnostic quantities, the cross-validation function and the sensitivity, indicate the accuracy of the approximation.

Objective fronts

AbstractThis paper addresses the long‐standing problem of plotting atmospheric fronts objectively. A thermodynamic definition of a front is proposed. Time‐independent diagnostic quantities are then devised according to this definition. These can be computed from any gridded dataset. Fronts are then plotted, without human intervention, by utilising standard graphics package facilities, such as contouring, to represent the diagnostics. The methodology includes applying threshold criteria to erase automatically fronts which are thermally weak. By tuning these criteria a good match with subjective fronts is obtained. In addition, the objective surface fronts very often coincide with troughs in surface pressure, implying that a thermodynamic definition is sufficient. The objective front‐plotting is further developed to recognise split fronts, and ana‐ and kata‐front characteristics. Many examples are presented; these illustrate how objective fronts are potentially a very powerful tool for both forecasting and research. At the Joint Centre for Mesoscale Meteorology plots and animations showing objective fronts have been produced on a daily basis for many months now. Copyright © 1998 Royal Meteorological Society

An Empirical Method for Optimal Robust Regional-Residual Separation of Geophysical Data

Prior to interpretation and further analysis, many datasets must first be separated into regional and residual components. Traditional techniques are either subjective (e.g., graphical methods) or nonrobust (e.g., all least-squares based methods). Bathymetric data, with their broad spectrum, pose serious difficulties to these traditional methods, in particular those based on spectral decomposition. Spatial median filters offer a solution that is robust, objective, and often defines regional components similar to those produced graphically by hand. Characteristics of spatial median filters in general are discussed and a new empirical method is presented for determining the width of the robust median filter that accomplishes an optimal separation of a gridded dataset into its regional and residual components. The method involves tracing the zero-contour of the residual component and evaluating the ratio between the volume enclosed by the surface inside this contour and the contour's area. The filter width giving the highest ratio (or mean amplitude) is called the Optimal Robust Separator (ORS) and is selected as the optimal filter producing the best separation. The technique allows a unique and objective determination of the regional field and enables researchers to undertake reproducible separations of regional and residual components. The ORS method is applied to both synthetic data and bathymetry/topography of the Hawaiian Islands; ways to improve the technique using alternative diagnostic quantities are discussed.

The Antarctic Circumpolar Current as a Waveguide for Rossby Waves

Abstract Results from the Fine Resolution Antarctic Model suggest that much of the eddy activity in the Southern Ocean takes the form of eastward propagating wavelike structures, and there is evidence from altimetry that this may be true of the real Southern Ocean. In the model, eastward propagating waves in the core of the Antarctic Circumpolar Current (ACC) are separated by a sharp boundary from westward propagating waves to the north. The theory of Rossby wave interactions with a zonal, barotropic current predicts complicated behavior involving the formation of strongly nonlinear critical layers associated with Reynolds stress divergences. The ACC is neither truly zonal, nor is it barotropic, but diagnostic quantities suggested by the idealized models show similar dynamics occurring in this more complicated situation. This interaction between mean flow and Rossby waves may be crucial to understanding how the ACC interacts with bottom topography.

Preparation, Characterization and99mTC Radiolabeling of Polyethylene glycol - coated Vesicles

Poly (ethylene glycol) - coated lipid vesicles of average diameter ∼200nm containing glutathione (GSH) were prepared by extrusion under pressure through polycarbonate filters, external GSH removed by chromatography on Sephadex G50, and the vesicles concentrated to a final lipid concentration of ∼ 60 mM using Millipore 10,000 NMWL low-protein-binding regenerated cellulose ultrafiltration units. Vesicles were subsequently radiolabeled with diagnostic quantities of technetium-99m (99mTc) - 740 Mbq (20 mCi) - using the ability of non-reduced hexamethylpropylene-amineoxime (HM-PAO) in the presence of tin (Sn) to transport 99mTc across the lipid bilayer. The use of Millipore filters represents a gentle, relatively rapid and simple method to concentrate lipid vesicles without causing loss of entrapped marker or affecting the efficiency of subsequent radiolabeling. Once external GSH was removed, vesicles retained >97% of their contents over a period of ∼ 4 months when stored at 4°C. The radiolabeling of the lipid vesicles using HM-PAO was unaffected by temperature, lipid composition or lipid phase state, but was critically dependent upon the ratios of HM-PAO, Sn and 99mTc.

Deletion diagnostics for transformations of time series

Deletion diagnostics are derived for the effect of individual observations on the estimated transformation of a time series. The paper uses the modified power transformation of Box and Cox to provide a parametric family of transformations. Inference about the transformation parameter is made through regression on a constructed variable. The effect of deletion of observations on residuals and on the estimate of the regression parameter are obtained. Index plots of the diagnostic quantities are shown to be highly informative. Structural time series modelling is used, so that the results readily extend to inference about regression on other explanatory variables.

Experiments with Non-Normal-Mode Initialization of a Shallow-Water Limited-Area Model: Impact of Relaxation, Orography, and of an Extended Linearization Including Most of the β Terms

A non-normal-mode initialization scheme, that is, an initialization scheme that does not require an explicit computation of the normal modes of the linearized equations, is considered. Such a scheme is applied to a shallow-water limited-area model on a stereographic projection, for which the computation of the normal modes is too expensive due to nonseparability. The numerical tests for the initialization concern the problem of relaxation toward constant or time-variable boundary conditions, the consistency of the initialization scheme with the semi-implicit scheme of the model, and the effect of orography. The scheme is then applied to a similar limited-area model but with a stretched grid, whose domain is greatly extended in latitude with the regular grid domain being located at its center. Numerical tests are performed for the initialization of this model to assess the impact of using a more comprehensive linearization including most of the β terms. Certain diagnostic quantities, used to test the convergence of the initialization scheme, are computed during the simulations.

Diagnostic Modeling of the Indian Monsoon Onset. Part I: Model Description and Validation

Abstract A new type of diagnostic model is developed and applied to the study of the onset of the Indian summer monsoon. The purpose of the model is to aid in the analysis of interactions between the physical processes that affect the monsoon onset. The model is one-dimensional and consists of a single atmospheric column coupled to an ocean mixed layer. The atmospheric component of the model includes representations of all the physical processes typically included in general circulation models, except that the fields of vertical motion and horizontal advection are specified at each time step from observational data rather than predicted. With these time-dependent observational inputs, the model is then integrated numerically to produce consistent profiles of atmospheric temperature and humidity, together with energy budget components and other diagnostic quantities. The atmospheric model is based on the thermodynamic energy equation and a conservation equation for water. Parameterizations of the effects o...

Computerized acquisition and evaluation of whole blood aggregometry data

A special-purpose software package has been developed to acquire and analyze analog signals from a whole blood aggregometer. Up to four independent blood samples can be analyzed simultaneously or with arbitrary delays in time. The user menu ensures porper calibration prior to each measurement and provides a real-time graphic display of the signals. From analog/digital converted data, several “derived diagnostic quantities” are calculated. They are constructed with the aim to mimic the process of visual inspection of aggregometry curves and thus place the intuitive diagnostics of blood platelet function on a quantitative basis.

Dynamics of a Rapid Cloud Band Development over Southeastern Australia

Abstract On the night of 27–28 August 1985, a cloud band associated with a cold front dramatically broadened over southeastern Australia, leading to unforecast rain and overforecast daytime temperatures. This paper presents a detailed synoptic description of this event, describes the vertical circulations leading to cloud band development, and, by means of back trajectory analysis, determines the origins of air parcels entering the cloud band. The analyses which were used in this diagnostic study were prepared using an intermittent insertion incremental limited-area data assimilation system. The consistency and coherence of the diagnostic quantities calculated from these analyses demonstrates the value of linking the analyses with a dynamic forecast model, even with the relatively coarse resolution of 250 km used in this study. It is shown that, following the reorganization of the jet patterns over Western Australia (WA), pressure falls lead to an amplification of the surface pressure trough and the accel...

Intermittent coronary sinus occlusion in humans: Pressure dynamics and calculation of diagnostic quantities : Schreiner W, Neumann F, Schuster J, et al: Cardiovas Res 22:277–286,1988

Intermittent coronary sinus occlusion in humans: Pressure dynamics and calculation of diagnostic quantities : Schreiner W, Neumann F, Schuster J, et al: Cardiovas Res 22:277–286,1988

Computation of derived diagnostic quantities during intermittent coronary sinus occlusion in dogs.

The haemodynamic responses to pressure controlled intermittent coronary sinus occlusion (PICSO) were recorded intraoperatively in dogs. After analogue-digital conversion the data for coronary sinus pressure were submitted to numerical analysis for detection of systolic and diastolic envelopes and their subsequent fitting by a non-linear model. From the model variables derived quantities, such as plateau and rise times, were constructed so as to resemble the most important features of coronary sinus pressure rise during each occlusion-release cycle. The derived quantities were then monitored during all consecutive cycles throughout the entire experiment. In each dog the measurements were taken during normal coronary artery perfusion, left anterior descending coronary artery infarction, and reperfusion. The analysis comprise time course, stability, and physiological correlates of the derived quantities, on some of which a closed loop regulation may be based. Predicted plateaus (systolic and diastolic) and mean integrals (systolic and diastolic) were found to be stable quantities which, on subaveraging of about five successive estimates, yielded a 10% accuracy on the mean. By contrast, the rise times required subaveraging of about 15 cycles to achieve the same relative stability. It is concluded that, on subaveraging, derived quantities lend themselves for closed loop regulation input. Thus this quantitative assessment of numerical coronary sinus pressure analysis, as obtained from animal data, may lay the basis for future human application.

Intermittent coronary sinus occlusion in humans: pressure dynamics and calculation of diagnostic quantities.

Pressure controlled intermittent coronary sinus occlusion (PISCO) was applied in 30 patients undergoing coronary artery bypass surgery. The occlusion and release times were manually adjusted according to visual control of the intraoperatively monitored coronary sinus pressure. In six patients the coronary sinus measurements were additionally digitised with a personal computer before postoperative mathematical analysis, which comprised automatic detection of systolic peaks, diastolic troughs, and the calculation of derived quantities. The purpose of the analysis was (a) to assess quantitatively human coronary sinus pressure dynamics, (b) to determine whether visual control and interpretation of coronary sinus pressure rise could be replaced by a mathematical model, and (c) to ascertain whether the occlusion and release cycle lengths were adequate. Numerical estimates for intraindividual and interindividual spread of calculated quantities were produced, the mathematically obtained results were related to a possible physiological interpretation, and the most efficient method of statistical analysis was ascertained. These results form the numerical basis for a closed loop adjustment of pressure controlled intermittent coronary sinus occlusion cycling.

Stress calculations for assemblies of inelastic speres in uniform shear

Previous work on assemblies of inelastic, frictional disks is extended to three dimensions in a molecular-dynamics study of steady shearing flow of an idealized granular material consisting of equal-sized spherical particles that are smooth but inelastic. Cumulative time and space averages are calculated for several diagnostic quantities including the kinetic and potential energy densities, the R.M.S. (deviatoric) velocity and both the kinetic and potential contributions to each component of the stress tensor. Under steady-state shearing deformation the kinetic-energy-density (granular temperature) generally is found to increase as the solids fraction is decreased and decrease as the binary-collision coefficient-of-restitution is decreased. For constant coefficient-of-restitution interactions the calculated stresses increase generally with the square of the strain rate, with exceptional behavior noted at extremes in solids loadings. The general trends of the calculated stresses and velocities are in substantial agreement with the Lun et al. linearized perturbation of Chapman-Enskog theory for slightly inelastic spheres. However, some significant differences are noted at very low (ν 0.5) solids fractions. A variable coefficient-of-restitution interaction interaction model (decreasing as the impact velocity increases) results in calculated stresses that deviate from the constant coefficient-of-restitution behavior in a manner similar to that predicted by Lun and Savage. The calculated stresses are in rough agreement with experimental measurements; however, the calculated shear-stress to normal-stress ratio for spheres with coefficients of restitution between 0.8 and 0.95 are significantly below experimentally measured values for glass and polystyrene beads in annular shear cell tests. Based on effects seen in two-dimensional calculations, the inclusion of interparticulate friction and particle rotations are expected to significantly reduce the discrepancy.