bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atmospheric and surface variations during westerly wind bursts in the tropical western pacific
Authors: Fasullo John , Webster Peter J. 
Published: July 2010

AbstractAn analysis is made of variations in both the surface energy balance and the regional atmospheric dynamic and thermal structure during 44 westerly wind bursts (WWBs) in the western equatorial Pacific Ocean from 1979 to 1995. The study assesses winds, convective available potential energy, cloud properties, precipitation, surface temperature, and surface heat flux while distinguishing between brief (5–25 day periodicity) and sustained (30–90 day) WWBs. Datasets used in the study include fields from the NCEP/NCAR and ECMWF re‐analyses, and satellite retrievals of clouds (ISCPP), precipitation (MSU), moisture (TOVS), and surface solar flux.Both brief and sustained WWBs, by definition, experience strong low‐level westerly winds that typically induce an increased surface latent‐heat flux of approximately 30 W m−2. Enhanced cloud thickness, precipitation, and upper tropospheric easterly wind anomalies accompany surface westerly winds, though maxima in winds lag those in clouds and precipitation by about one day for brief WWBs and four days for sustained events. WWBs of both types experience strong seasonality, occurring frequently in all seasons except boreal summer.Important distinctions between brief and sustained WWBs can also be made. Westerly anomalies typically extend above 200 hPa during brief WWBs but are generally confined to the lower troposphere (below 400 hPa) for sustained events. Sustained WWBs are also preceded by a quiescent period of reduced cloud thickness and surface winds that is accompanied by strong incident solar flux. Convective instability, as judged by a variety of techniques, increases by approximately 30% during this quiescent period. Brief WWBs do not include the precursory surface warming or convective destabilization of sustained WWBs. Notwithstanding the warming episodes before the events, sustained WWBs are associated with a net surface cooling approximately 40% larger than brief WWBs.The relationship between brief and sustained WWBs and the phase of the Madden‐Julian Oscillation (MJO) (as judged from outgoing long‐wave radiation) is also examined. Results support the classification of events as ‘brief’ and ‘sustained’ as used in this study, with brief WWBs occurring frequently during both wet and dry phases of the MJO, while sustained WWBs occur uniquely during the MJO wet phase. The association of brief and sustained WWBs with the MJO is shown to be independent of the El Niiio Southern Oscillation phase. It is therefore proposed that some, but not all, WWBs may be viewed as the surface signature of the MJO and that the mechanisms responsible for the MJO play an integral role in the formation and sustenance of sustained WWBs.
Dissipative heating in climate models
Authors: Fiedler B. H. 
Published: July 2010

AbstractThe various strategies towards dissipative heating in meteorological models are reviewed. The strategies are implicit formulations, explicit formulations, and exclusion. A thermodynamic formulation based on dry static energy, which has long been used in hydrostatic models, implicitly includes dissipative heating. Many modem non‐hydrostatic mesoscale models, being based on potential temperature, do not include any dissipative heating. The National Center for Atmospheric Research community climate model (CCM3) explicitly formulates the dissipative heating for the resolved motion, which is based upon potential temperature, but, uses the implicit formulation for the sub‐grid motion.Those who want to use the mesoscale‐model formulation as a cloud‐resolving climate model are advised to consider the effect of dissipative heating. We show a dry radiative‐convective model, formulated without dissipative heating, in which climate equilibrium occurs with a net inward radiative flux of about 18 W m−2at the top of the atmosphere, and a surface temperature that is 8 K too low.
On the accuracy of the semi‐geostrophic approximation
Authors: Cullen M. J. P. 
Published: July 2010

AbstractThe semi‐geostrophic model has been widely used to understand atmospheric flows such as fronts and developing cyclones. However, there have been a number of demonstrations of its lack of accuracy. This paper presents theory and computations to demonstrate that the semi‐geostrophic model is an accurate approximation to the primitive equations either on horizontal scales larger than the Rossby radius of deformation or when the ratio of horizontal to vertical scales is greater than f/N.
The ECMWF operational implementation of four‐dimensional variational assimilation. II: Experimental results with improved physics
Authors: Mahfouf J.‐F. , Rabier F. 
Published: July 2010

AbstractA comprehensive set of physical parametrizations has been linearized for use in the European Centre for Medium‐Range Weather Forecasts (ECMWF's) incremental four‐dimensional variational (4D‐Var) system described in Part I. The following processes are represented: vertical diffusion, subgrid‐scale orographic effects, large‐scale precipitation, deep moist convection and long‐wave radiation. The tangent‐linear approximation is examined for finite‐size perturbations. Significant improvements are illustrated for surface wind and specific humidity with respect to a simplified vertical diffusion scheme. Singular vectors computed over 6 hours (compatible with the 4D‐Var assimilation window) have lower amplification rates when the improved physical package is included, due to a more realistic description of dissipative processes, even though latent‐heat release contributes to amplify the potential energy of perturbations in rainy areas. A direct consequence is a larger value of the observation term of the cost‐function at the end of the minimization process when improved physics is included in 4D‐Var. However, the larger departure of the analysis state from observations in the lower‐resolution inner‐loop is in better agreement with the behaviour of the full nonlinear model at high resolution. More precisely, the improved physics produces smaller discontinuities in the value of the cost‐function when going from low to high resolution. In order to reduce the computational cost of the linear physics, a new configuration of the incremental 4D‐Var system using two outer‐loops is defined. In a first outer‐loop, a minimization is performed at low resolution with simplified physics (50 iterations), while in the second loop a second minimization is performed with improved physics (20 iterations) after an update of the model trajectory at high resolution. In this configuration the extra cost of the physics is only 25%, and results from a 2‐week assimilation period show positive impacts in terms of quality of the forecasts in the Tropics (reduced spin‐down of precipitation, lower root‐mean‐square errors in wind scores). This 4D‐Var configuration with improved physics and two outer‐loops was implemented operationally at ECMWF in November 1997.
The vertical resolution sensitivity of simulated equilibrium temperature and water‐vapour profiles
Authors: Tompkins Adrian. M. , Emanuel Kerry. A. 
Published: July 2010

AbstractVariability of atmospheric water vapour is the most important climate feedback in present climate models. Thus, it is of crucial importance to understand the sensitivity of water vapour to model attributes, such as physical parametrizations and resolution. Here we attempt to determine the minimum vertical resolution necessary for accurate prediction of water vapour.To address this issue, we have run two single‐column models to tropical radiative—convective equilibrium states and have examined the sensitivity of the equilibrium profiles to vertical resolution. Both column models produce reasonable equilibrium states of temperature and moisture.Convergence of the profiles was achieved in both models using a uniform vertical resolution of around 25 hPa. Coarser resolution leads to significant errors in both the water vapour and temperature profiles, with a resolution of 100 hPa proving completely inadequate. However, fixing the boundary‐layer resolution and altering only the free‐tropospheric resolution significantly reduces sensitivity to vertical resolution in one of the column models, in both water and temperature, highlighting the importance of resolving boundary‐layer processes. Additional experiments show that the height of the simulated tropopause is sensitive to upper‐tropospheric vertical resolution.At resolutions higher than 33 hPa, one of the models developed a high degree of vertical structure in the vapour profile, resulting directly from the complex array of microphysical processes included in the stratiform cloud parametrization, some of which were only resolved at high resolutions. This structure was completely absent at lower resolutions, casting some doubt on the approach of using relatively complicated cloud schemes at low vertical resolutions.
On the wave‐activity invariants and stability of the two‐layer shallow‐water semi‐geostrophic model
Authors: Ren Shuzhan 
Published: July 2010

AbstractAlthough the two‐layer shallow‐water semi‐geostrophic (TLSWSG) model has been proven to be an important tool for the investigation of the dynamics of anisotropic and baroclinic flow in frontal zones, its general instability mechanism, however, has not been well understood. In light of recent work on the stability of the one‐layer SWSG model, this issue is re‐examined in this paper by extending a body of well developed theorems in the two‐layer quasi‐geostrophic (QG) model to the TLSWSG model. The generalized linearized TLSWSG model equations with respect to a parallel basic state are presented first. Conservation equations for two small‐amplitude wave‐activity invariants analogous to pseudo‐momentum and pseudo‐energy densities in QG dynamics are derived and then used to examine the stability of a parallel basic state. It is found that the TLSWSG model possesses two kinds of stability conditions: Arnold's first stability condition in the interior, plus conditions on lateral boundaries, and Arnold's second stability condition. In contrast to previous work, Ripa's ‘subsonic’ condition \documentclass{article}\pagestyle{empty}\begin{document}$ \[\left({\left({U_{G1},U_{G2} } \right)\max < \sum\nolimits_{j = 1}^2 {\left({{1 \mathord{\left/ {\vphantom {1 {cj}}} \right. \kern-\nulldelimiterspace} {cj}}} \right)^{ - 1} } } \right) \] $\end{document}, where UG1 and UG2 are basic flows at two levels and Cj is the phase speed of gravity waves at the jth level) is found to be unnecessary, and the underlying physical reasons, associated with the coastal Kelvin waves in the model, are given. It is also found that the phase speed of unstable normal‐mode disturbances of slow motion satisfies Howard's semi‐circle theorem.The energy—Casimir method is applied to derive small‐ and finite‐amplitude wave‐activity invariants and corresponding stability criteria for non‐parallel basic states. It turns out that the stability criteria for non‐parallel basic states include not only those for parallel basic states but also conditions associated with the anisotropy of basic flow. The nonlinear stability analyses in this work help us to understand the failure of the energy—Casimir method in deriving finite‐amplitude stability criteria in the continuously stratified semi‐geostrophic model.
Some field experiments on the interaction of plumes from two sources
Authors: Davies B. M. , Jones C. D. , Manning A. J. , Thomson D. J. 
Published: July 2010

AbstractSome experiments to measure concentration fluctuations downwind of two tracer sources in the atmospheric surface layer are described and the results presented. Fast response detectors were used. The sources were at a height of 4 m and the experiments were restricted to short ranges where the flow and turbulence can be assumed to be approximately homogeneous for the purpose of predicting the dispersion. The results are analysed to show the downwind evolution of the intensity of fluctuations for each source separately and to show how the correlation between the concentrations from the two sources varies with downwind distance and source separation. The variation of the intensity of fluctuations and the correlation with averaging time is also explored. Results support the idea of a universal behaviour when suitably scaled.
A method for estimating the analysis error variance in a physical space data assimilation system
Authors: Rushøjgaard Lars Peter 
Published: July 2010

AbstractThe error variance of a meteorological analysis is an important quantity, both as a measure of confidence in the analysed product, and as an initial condition for the forecast error variance in a cycling data assimilation system. Modem assimilation systems that rely on global solutions of the analysis equations typically do not include an estimate of this quantity, even though the equation for the full analysis error covariance matrix is well‐known. The reason is that this equation is far too costly to implement directly. In this article we analyse the analysis error covariance equation of the Kalman filter, and we propose a computationally efficient method for estimating the analysis error variance, i.e. the diagonal elements of the covariance matrix. The estimate is shown to be conservative in the sense that the analysis error variance is overestimated everywhere. We illustrate the performance of the method in the context of simple two‐dimensional analysis experiments as well as in a global, three‐dimensional ozone data assimilation system. These experiments show that both quantitatively and qualitatively the method captures the main features of the variance calculated by the full covariance equation at a small fraction of the cost.
Observation and background adjoint sensitivity in the adaptive observation‐targeting problem
Authors: Baker Nancy L. , Daley Roger 
Published: July 2010

AbstractRecent observation‐targeting field experiments, such as the Fronts and Atlantic Storm‐Track Experiment (FASTEX) and the NORth Pacific Experiment (NORPEX), have demonstrated that by using objective adjoint techniques it is possible, in advance, to identify regions of the atmosphere where forecast‐error growth in numerical forecast models is maximally sensitive to the error in the initial conditions. 'Qpically, such techniques produce a field of the sensitivity of some aspect of the forecast to the analysis field. This analysis sensitivity field is then used to identify promising targets for the deployment of additional observations during the flight‐planning phase of field experiments. While FASTEX and, particularly. NORPEX had a number of successful ‘hits’, where the addition of dropsondes reduced the forecast error, there were also failures.None of the objective techniques have involved any consideration of the characteristics of the data‐assimilation systems used in the analysis of the targeted observations. In particular, the interaction with the background field, interactions with other observations, and the background‐ and observationerror characteristics have been ignored. This can lead to potential mis‐sampling, conflict with other observations, and inefficient use of aircraft and expendables.In this study, the adjoint of a simplified data‐assimilation system is used to determine directly the sensitivity of the forecast aspect to the observations and the background field. The procedure is illustrated by using simplified linear contexts such as the one‐ and two‐dimensional horizontal univariate problem and the one‐dimensional direct radiance assimilation problem. Adaptive targeting tools, such as a single‐observation sensitivity map and a marginal observation sensitivity vector, are devised and tested. The possibility of determining when the forecast would be sensitive to the background field and/or the observations is demonstrated. Such dependencies are shown to be a function of the specified observation‐ and background‐error variances, the characteristic scales of analysis sensitivity vector and background‐error correlations, and the properties of forward (observation) operators.Although the present experiments concerned simplified assimilation systems and observation networks, extension of the technique to real situations is quite feasible. Obtaining the adjoint of a full three‐dimensional variational assimilation system is straightforward; moreover, the target areas are small and contain relatively few observations so the computational requirements are modest.Finally, the data‐assimilation adjoint theory can be used for a posteriori assessment of those sources of forecast error which are due to errors in the initial analysis.
The use of tovs observations for the identification of tropopause‐level thermal anomalies
Authors: Fourrié Nadia , Claud Chantal , Donnadille Jérǒme , Cammas Jean‐Pierre , Pouponneau Béatrice , Scott Noelle 
Published: July 2010

AbstractThe evolution of tropopause‐level thermal patterns is generally not well represented by the conventional observational network, especially over the oceans. An alternative is provided by satellite observations which are global and frequent. In particular, from the TIROS‐N (Television Infra‐Red Observation Satellite) Operational Vertical Sounder (TOVS) which flies on‐board National Oceanic and Atmospheric Administration satellites, an estimate of the temperature of the lower stratosphere (TLS) can be derived using the Improved Initialization Inversion algorithm. In this study, the degree of reliability of TLS for describing tropopause‐level thermal structures and variations is examined. For three intensive observation periods (16, 17 and 18) of the Fronts and Atlantic Storm‐Track Experiment, conducted in January and February 1997 over the North Atlantic Ocean, TLS fields are described; their advantage, compared with the use of raw microwave data, is illustrated; TLS variations are also studied in connection with other dynamical variables which can be obtained by the French Action de Recherche Petite Echelle Grande Echelle operational model analysis. Finally, the suitability of TLS as a possible forecasting aid over mid‐oceanic regions is promoted.
Properties of the arctic tropopause
Authors: Highwood E. J. , Hoskins B. J. , Berrisford P. 
Published: July 2010

AbstractA climatology of Arctic tropopause properties is derived using European Centre for Medium‐Range Weather Forecasts Re‐analyses, and is shown to be consistent with that from the Historical Arctic Radiosonde Archive. It is demonstrated that the thermal tropopause is generally easy to define from the temperature profile, even in the polar night, in contrast with the situation in Antarctic winter. In winter, the tropopause tends to have higher pressure and temperature in the western hemisphere and lower values in the eastern hemisphere. In summer the situation is more zonally symmetric with the higher pressure and temperature tropopause region near the pole. Strong annual cycles are seen in both temperature and pressure. these cycles being out of phase temporally. It is hypothesized that the tropopause temperature is largely determined by the approximately isothermal lower‐stratospheric temperature, while the pressure is more strongly influenced by changes in the tropospheric lapse rate due to dynamical mechanisms. The multi‐decade radiosonde dataset (1965–1990) shows some evidence of a long‐term trend in tropopause properties. The wintertime tropopause pressure has decreased by approximately 14 mb per decade, while that in other seasons has decreased by around 5 mb per decade. The tropopause temperature only shows a significant trend during winter, having decreased by 1.6 K per decade since 1965. These changes are discussed in relation to changes in ozone and greenhouse gases, and the strength of the stratospheric vortex. In particular, the winter tropopause properties appear to be strongly correlated with the Arctic Oscillation Index.
Surface resistance in atmospheric flow
Authors: Sutcliffe R. C. 
Published: July 2010

AbstractThe formula for surface resistance to atmospheric flow, F = ρκV2s, where Vs is the velocity of the surface wind, ρ the density, and κ a non‐dimensional constant, was proposed by G. I. Taylor, on an analogy with flow in pipes. In pipes, the value of κ was 0.004, and Taylor gave a mean value of 0.0025 for κ in the case of flow of air over the ground. In this paper the value of κ was deduced from actual observed distributions of wind velocity at different heights, obtained by pilot balloons, no assumption being made as to the nature of eddy viscosity. The mean value of κ so deduced is 0.006 over land, and 0.0004 over the sea.
Sonographic description and classification of tendinous involvement in relation to tophi in chronic tophaceous gout
Authors: de Ávila Fernandes Eloy , Sandim Gabriel B. , Mitraud Sônia A. V. , Kubota Edson S. , Ferrari Antonio J. L. , Fernandes Artur R. C. 
Published: July 2010

AbstractObjectiveTo describe and classify the varied ultrasound features of tendinous involvement in relation to tophi in chronic tophaceous gout so that they are better recognised.MethodsUltrasound images of 138 affected areas from 31 patients with chronic tophaceous gout were analysed using high-quality broadband linear transducers. The relationship between tendon and tophi was classified, and the inter-observer agreement regarding classification was analysed.ResultsTophi envelopment in the tendon was the most frequent characteristic (45%) followed by no relationship between tophi and tendon (41%), tophi at the insertion site of the tendon (7%), extrinsic compression (6%) and tophi within the tendon (1%). The inter-observer concordance on classification of the relationship between tophi and tendon was measured using McNemar’s test withP < 0.001 (χ2 = 30.0, degree of freedom = 9) and kappa test = 0.627 (P < 0.001), indicating substantial inter-observer concordance.ConclusionTophi generally envelope the tendon or there is no relationship between them. Tophi can also be found at the insertion site of the tendon, cause extrinsic compression or be located inside the tendon. There is substantial inter-observer agreement for ultrasound classification of tendon involvement by tophi. This study contributes to diagnostic elucidation and shows the diverse characteristic forms of tendon involvement by tophi.
Substance use among middle school students: Associations with self‐rated and peer‐nominated popularity
Authors: Tucker Joan S. , Green Harold D. , Zhou Annie J. , Miles Jeremy N.V. , Shih Regina A. , D’Amico Elizabeth J. 
Published: July 2010

ABSTRACTAssociations of popularity with adolescent substance use were examined among 1793 6–8th grade students who completed an in‐school survey. Popularity was assessed through both self‐ratings and peer nominations. Students who scored higher on either measure of popularity were more likely to be lifetime cigarette smokers, drinkers, and marijuana users, as well as past month drinkers. Self‐rated popularity was positively associated with past month marijuana use and heavy drinking, and peer‐nominated popularity showed a quadratic association with past month heavy drinking. These results extend previous work and highlight that popularity, whether based on self‐perceptions or peer friendship nominations, is a risk factor for substance use during middle school. Given the substantial increase in peer influence during early adolescence, prevention program effectiveness may be enhanced by addressing popularity as a risk factor for substance use or working with popular students to be peer leaders to influence social norms and promote healthier choices.