bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mesoscale structure of a polar low with strong upper‐level forcing
Authors: Browning K. A. , Dicks E. M. 
Published: February 2007

AbstractDry air descending within the circulation of a polar low was observed to give a striking signature in the echo return from an upward‐looking VHF radar. Data from this radar, along with weather‐radar data, satellite imagery and output from limited‐area and mesoscale versions of the Met Office Unified Model, are synthesized to depict the mesoscale structure of the weather system. The polar low had a compact vortex centred near 3 km, a cold core below this level, and a warm core above. Attribution of quasi‐geostrophic forcing showed that on the larger scale the polar low was dominated by upper‐level forcing. The detailed mesoscale analysis showed that the polar low, during its mature phase, was affected by a stratospheric intrusion that brought air from near tropopause level down to 3 km to give the striking signature in the VHF radar echo pattern. The echo pattern also suggested that thin tongues of this stratospheric, or near‐stratospheric, air were penetrating slantwise down a further several hundred metres, above the shallow cloud constituting the southern end of an archetypal cloud head. It is argued that this may be a locally important region of mixing between air originating near the tropopause and the boundary layer. In more general terms, the study demonstrates the ability of the operational mesoscale model to represent various small‐scale features. The study also helps in developing the interpretation of the patterns of clear‐air radar echo observed with VHF radar.
Life cycle of Sahelian mesoscale convective cloud systems
Authors: Mathon Vincent , Laurent Henri 
Published: February 2007

AbstractThis paper provides an eight‐year high‐resolution climatology of Sahelian mesoscale convective systems (MCSs) during the summer. MCSs are defined as convective cloud clusters larger than 5000 km2. They are extensively tracked from METEOSAT full‐resolution infrared images (time resolution 0.5 h and spatial resolution about 5 km). The method enables every MCS to be tracked throughout its entire lifetime. For each time step, the MCS location and its morphological and radiative characteristics are computed for three different brightness temperature thresholds. The methodology is presented, evaluated and compared with previous studies using low‐resolution data.Statistical MCS distributions, diurnal cycle and spatial variability of MCS characteristics are analysed on the basis of this high‐resolution tracking. It is shown that a few large and long‐lived cloud clusters contribute most of the total cloud cover. Sahelian cloud clusters propagate westward at a greater speed when very deep convection is well developed. The diurnal organization of the convection has been analysed, and has proved that the merging of MCSs is partly explained by the actual merging of independent convective entities, whereas the splitting of MCSs is mostly associated with weakening of convection. The importance of mesoscale convective complexes for the total MCS coverage has also been studied.
Cloud‐base fluxes in the cumulus‐capped boundary layer
Authors: Grant A. L. M. 
Published: February 2007

AbstractA closure for the fluxes of mass, heat, and moisture at cloud base in the cumulus‐capped boundary layer is developed. The cloud‐base mass flux is obtained from a simplifed turbulence kinetic energy (TKE) budget for the sub‐cloud layer, in which cumulus convection is assumed to be associated with a transport of TKE from the sub‐cloud layer to the cloud layer.The heat and moisture fluxes are obtained from a jump model based on the virtual‐potential‐temperature equation. A key part of this parametrization is the parametrization of the virtual‐temperature flux at the top of the transition zone between the sub‐cloud and cloud layers.It is argued that pressure fluctuations must be responsible for the transport of TKE from the cloud layer to the sub‐cloud layer.
Atmospheric multiple equilibria and non‐Gaussian behaviour in model simulations
Authors: Hannachi A. , O'Neill A. 
Published: February 2007

AbstractMultiple equilibria from general circulation models (GCMs) are investigated via Gaussian mixture models. The cross‐validation technique based on bootstrap, used to find the possible number of clusters, is shown to have a tendency to display a bias in the number of clusters when the sample is not statistically independent. The method is shown, however, to give satisfactory results when applied with a strategy based on statistical independence. The mixture model is successfully applied to a few dynamical systems and data from the UK Universities Global Atmospheric Modelling Programme (UGAMP) GCM. The same analysis is then carried out and applied to the wintertime 500 mb geopotential height field taken from a 50‐year run of the Hadley Centre HadAM3 GCM. Three regions, the North Pacific‐American, the North Atlantic, and the northern hemisphere are investigated for nonlinear circulation regimes. It is shown that the model displays robust regime behaviour over the North Pacific‐American sector, while only marginal regime behaviour is observed over the North Atlantic, and no trace of hemispheric regimes.
The GEOS ozone data assimilation system: Specification of error statistics
Authors: Štajner Ivanka , Riishøjgaard Lars Peter , Rood Richard B. 
Published: February 2007

AbstractA global three‐dimensional ozone data assimilation system has been developed at the Data Assimilation Office of the NASA Goddard Space Flight Center. The Total Ozone Mapping Spectrometer (TOMS) total ozone data and the Solar Backscatter Ultraviolet/2 (SBUV/2) partial ozone profile observations are assimilated. The assimilation, into an off‐line ozone transport model, is done using the global Physical‐space Statistical Analysis Scheme. This system became operational in December 1999.A detailed description of the statistical analysis scheme and, in particular, of the forecast‐ and observation‐error covariance models is given. A new global anisotropic horizontal forecast‐error correlation model accounts for a varying distribution of observations with latitude. Correlations are largest in the zonal direction in the tropics where data are sparse. Forecast‐error variance is assumed to be proportional to the ozone field. The forecast‐error covariance parameters were determined by maximum‐likelihood estimation. The error covariance models are validated using χ2 statistics.The analysed ozone fields in the winter 1992 are validated against independent observations from ozone sondes and the Halogen Occultation Experiment (HALOE). The difference between the mean HALOE observations and the analysis fields is less than 10% at pressure levels between 70 and 0.2 hPa. The global root‐mean‐square difference between TOMS observed and forecast values is less than 4%. The global root‐mean‐square difference between SBUV observed and analysed ozone between 50 and 3 hPa is less than 15%.
Diagnosis and adaptive tuning of observation‐error parameters in a variational assimilation
Authors: Desroziers Gerald , Ivanov Serguei 
Published: February 2007

AbstractFollowing the a posteriori diagnosis approach proposed by some authors, a practical computation of the expectation of sub‐parts of the value of a cost function at the minimum is shown to be feasible by using a randomization technique based on a perturbation of observations or background fields. These computations allow the tuning of observation‐error weighting parameters by applying a simple iterative fixed‐point procedure. The procedure is first tested in a simplified variational scheme on a circular domain and then in a similar scheme but with the addition of the vertical coordinate. The relationship between the proposed approach and the Generalized Cross Validation is also shown. A test in the French Action de Recherche Petite Echelle Grande Echelle (ARPEGE) three‐dimensional variational framework with both simulated observations and background fields is finally performed. It shows that a complete description of observation‐error parameters can be retrieved with only a few iterations and, thus, at a reasonable cost.
A satellite radiance‐bias correction scheme for data assimilation
Authors: Harris B. A. , Kelly G. 
Published: February 2007

AbstractRecently, much progress has been made in the direct assimilation of satellite radiance measurements in numerical weather‐prediction systems. In order to use radiances from the TIROS Operational Vertical Sounder (TOVS), biases between the observed radiances and those simulated from the model first guess must be corrected. The original scheme for TOVS radiance‐bias correction at the European Centre for Medium‐Range Weather Forecasts utilized a global scan correction, and a linear air‐mass correction, with the observed radiances from the Microwave Sounding Unit channels 2, 3 and 4 as predictors. The new scheme differs in two fundamental ways. Analysis of radiance data shows a significant residual scan bias which depends strongly on latitude for some channels. The new scheme applies a latitudinally dependent scan correction to take this into account. The air‐mass predictors are now computed from the background field, since the background field contains a more consistent representation of the air mass and surface characteristics than the observed microwave radiances. Four new predictors are used, 1000–300 hPa thickness, 200–50 hPa thickness, model surface skin temperature and total precipitable water. In particular, the skin‐temperature predictor is able to differentiate between ocean and sea‐ice, performing much better than the old scheme in the winter hemisphere. The use of model predictors is a change in philosophy away from correction of the observations to correction of the computed forward radiances. This leads to a natural extension where the gradient of the bias correction can be taken into account in variational retrieval schemes.
A gravity‐wave induced quasi‐biennial oscillation in a three‐dimensional mechanistic model
Authors: Lawrence Bryan N. 
Published: February 2007

AbstractPrevious two‐dimensional model simulations using the Hines parametrization of unresolved gravity waves have produced long‐period oscillations in the tropics. Such oscillations include the quasi‐biennial oscillation (QBO) and the semi‐annual oscillation (SAO). In this paper simulations with a three‐dimensional mechanistic model are reported which show an even more realistic representation of the QBO. These simulations show the expected dependence of the period of the QBO on the momentum flux entering the stratosphere, but also show a hitherto unreported dependency of the period on the upper boundary condition. In these simulations the dependency is linked to changes in mesospheric vertical velocities associated with the SAO.
The role of sea‐salt particles as cloud condensation nuclei over the remote oceans
Authors: Mason B. J. 
Published: February 2007

AbstractIf recent measurements of the fluxes of sea‐salt particles over the oceans as a function of wind speed are extrapolated to include the smallest particles detected over the oceans and in laboratory experiments on bursting bubbles, the flux F of particles having radii between r0 = 0.1 μm and r μm at 80% relative humidity may be represented by F = 2U3.5(e−0.2r0) – e−0.2r) m−2) s−1, where U is the near‐surface wind speed in m s−1. The flux of particles of r ≤ 5 μm in winds of 16 m s−1 is 20 000 m−2s−1. The corresponding local rate of production by air bubbles bursting in the foam patches of breaking waves that occupy, on average, only 5% of the ocean surface at this wind speed is 40 cm−2s−1. The average concentration of particles over the sea area producing whitecaps is:

where vr is the deposition velocity for particles of radius r. In winds of 16 m s−1 the total concentration of sea‐salt particles is calculated to be 40 cm−3. These, and the fluxes and concentrations calculated for other wind speeds, are consistent with measurements made at sea and in the laboratory by many scientists during the last 50 years.Recently O'Dowd et al. have reported on sea‐salt particles of dry radius as small as 0.03 μm, with radius 0.06 μm at 80% relative humidity and mass 5 × 10−16 g. If the above equation is extended to include such small particles, it predicts a total concentration of 60 cm−3 in winds of 17 m s−1, fairly close to the reported 70 cm−3.In general these computed and observed concentrations of sea‐salt particles are adequate to account for observed droplet concentrations in clouds over remote oceans uncontaminated by continental aerosols. However, on rather rare occasions droplet concentrations in maritime cumulus exceed 100 cm−3. Observations are cited to suggest that, in such cases, sea‐salt nuclei may be augmented by biogenic particles originating at the sea surface and by sulphate/sulphuric acid nuclei produced by the absorption of derivatives of dimethyl sulphide in cloud droplets.Locations such as Hawaii and Tasmania are occasionally contaminated by continental or local pollution which may account for the rare reports of droplet populations being as high as 400 cm−3.
Measures of skill and value of ensemble prediction systems, their interrelationship and the effect of ensemble size
Authors: Richardson David S. 
Published: February 2007

AbstractEnsemble forecasts provide probabilistic predictions for the future state of the atmosphere. Usually the probability of a given event E is determined from the fraction of ensemble members which predict the event. Hence there is a degree of sampling error inherent in the predictions. In this paper a theoretical study is made of the effect of ensemble size on forecast performance as measured by a reliability diagram and Brier (skill) score, and on users by using a simple cost‐loss decision model. The relationship between skill and value, and a generalized skill score, dependent on the distribution of users, are discussed. The Brier skill score is reduced from its potential level for all finite‐sized ensembles. The impact is most significant for small ensembles, especially when the variance of forecast probabilities is also small. The Brier score for a set of deterministic forecasts is a measure of potential predictability, assuming the forecasts are representative selections from a reliable ensemble prediction system (EPS). There is a consistent effect of finite ensemble size on the reliability diagram. Even if the underlying distribution is perfectly reliable, sampling this using only a small number of ensemble members introduces considerable unreliability. There is a consistent over‐forecasting which appears as a clockwise tilt of the reliability diagram. It is important to be aware of the expected effect of ensemble size to avoid misinterpreting results. An ensemble of ten or so members should not be expected to provide reliable probability forecasts. Equally, when comparing the performance of different ensemble systems, any difference in ensemble size should be considered before attributing performance differences to other differences between the systems.The usefulness of an EPS to individual users cannot be deduced from the Brier skill score (nor even directly from the reliability diagram). An EPS with minimal Brier skill may nevertheless be of substantial value to some users, while small differences in skill may hide substantial variation in value. Using a simple cost‐loss decision model, the sensitivity of users to differences in ensemble size is shown to depend on the predictability and frequency of the event and on the cost‐loss ratio of the user. For an extreme event with low predictability, users with low cost‐loss ratio will gain significant benefits from increasing ensemble size from 50 to 100 members, with potential for substantial additional value from further increases in number of members. This sensitivity to large ensemble size is not evident in the Brier skill score. A generalized skill score, dependent on the distribution of users, allows a summary performance measure to be tuned to a particular aspect of EPS performance.
Liquid water path variability in unbroken marine stratocumulus cloud
Authors: Wood Robert , Taylor Jonathan P. 
Published: February 2007

AbstractLiquid water path variability in unbroken marine stratocumulus clouds is examined using a simple adiabatic model and both ground‐based and airborne observations. Observations from FIRE suggest that fluctuations in liquid water path at scales smaller than around 60 km can be modelled reasonably well as a function of fluctuations in cloud‐base height. A simple adiabatic model of cloud liquid water content with a normally distributed cloud base and constant inversion height results in liquid water path distributions that compare favourably with observations. Further, it is shown how cloud‐base height fluctuations can be predicted from the sub‐cloud turbulent fluctuations of temperature, specific humidity and their covariance. The relative importance of these three contributing terms is assessed. Aircraft observations of these fluctuating variables are used to predict the widths of liquid water path distributions observed radiometrically. The observations also suggest that the standard deviation of cloud‐base height and hence liquid water path variability increases with increasing boundary‐layer depth. The model liquid water path distributions could be used to derive plane‐parallel albedo biases and offer a possible framework for future parametrizations of subgrid‐scale variability in general circulation models.
Alternative implementations of the semi‐Lagrangian semi‐implicit schemes in the ECMWF model
Authors: Cullen M. J. P. 
Published: February 2007

AbstractAn important issue for the future development of global models is the degree of implicit solution required for optimum performance, and whether this will change the relative cost‐effectiveness of spectral and finite‐difference models. This is explored by using a predictor‐corrector integration scheme in the European Centre for Medium‐Range Weather Forecasts model, where both steps are integrated using the current semi‐implicit procedure. This is equivalent to taking a first iteration towards a fully implicit scheme, using the existing semi‐implicit method as a preconditioner. The results show that benefit can be obtained provided that both the nonlinear part of the gravity‐wave terms and the semi‐Lagrangian trajectory are recalculated. This suggests that more fully implicit schemes will be beneficial in numerical models. However, the cost of elliptic solvers will not dominate as significant recalculation of tendencies will be required at each iteration.Another strategic issue is the robustness of semi‐Lagrangian schemes at high resolution. These are the only advection schemes that preserve monotonicity that are available for spectral models. As resolution is increased, solutions of the equations always contain motions with the wind direction varying rapidly along the trajectory. These are typically not well treated at current operational resolutions, but limit the time step that can be used with semi‐Lagrangian schemes. We illustrate the effect of selective damping of these motions, which may be desirable until much higher resolutions are reached.
Influenza viruses and MAP kinase cascades – Novel targets for an antiviral intervention?
Authors: Ludwig Stephan 
Published: February 2007

AbstractInfluenza virus infections still pose a major threat to human and animal health worldwide. On one hand, like any other viral pathogen influenza viruses are strictly dependent on their host cell for efficient replication. On the other hand cells respond to infection by mounting an innate immune program to fight the invader. This constant battle between the virus and the host‐cell is also reflected on the level of the intracellular signalling events that are induced upon infection. While these signalling pathways are primarily initiated as a cellular defence program, the virus has acquired the capability to exploit some of these activities to support its replication. This review aims to illustrate this principle with regard to the diverse functions of different MAP kinase cascades during influenza virus infection. Some of these cascades act within cell protective pathways while others are required for efficient viral replication and thus, may serve as novel targets for antiviral intervention.
Human T cell leukemia virus type 1 Tax‐induced signals in cell survival, proliferation, and transformation
Authors: Silbermann Katrin , Grassmann Ralph 
Published: February 2007

AbstractHuman T cell leukemia virus type 1 (HTLV‐1), a delta‐retrovirus, causes an aggressive malignancy of T lymphocytes called adult T cell leukemia/lymphoma and stimulates permanent cell growth in culture. The virus encodes a nonstructural regulatory protein, Tax, which is both transforming in cell culture and oncogenic in vivo. This multifunctional protein controls viral transcription and in multiple ways interferes with cellular control of survival, proliferation, and genomic stability. Tax, by activation of NF‐κB, AP‐1, and other transcriptional pathways, enhances expression of cellular genes encoding cytokines (e.g. IL‐13, IL‐15), cytokine receptors (e.g. IL‐2Rα), and antiapoptotic factors (Hiap‐1, Bcl‐xL, OX40), leading to altered signal transduction (e. g. Jak/Stat, PI3K, Caspase 3/7). Cellular proliferation is stimulated by direct targeting of the cell cycle kinase (Cdk4, Cdk6) holoenzymes, repression of Cdk inhibitors, and the functional inactivation of the tumor suppressor p53. Finally, Tax, by promoting genomic instability through interference with DNA‐damage signaling, checkpoint control (G2/M, mitotic spindle assembly), chromosome segregation, and cellular DNA repair pathways could contribute to malignant conversion of infected cells.
HIPIMS: Die neue PVD‐Technologie
Authors: Münz W.‐D. 
Published: February 2007

AbstractHIPIMS (High Power Impulse Magnetron Sputtering) stellt die neueste Entwicklung auf dem Gebiet der PVD‐Puls‐Sputter‐Technik dar. Unter dem Einfluss extrem hoher Puls‐Leistungen (4–6 MW) gelingt es, Gasentladungen zu erzeugen, die der weithin bekannten Arc‐Entladung, unter völliger Vermeidung von Droplets, sehr ähnlich sind. Hohe Metallionen‐Konzentrationen und Mehrfach‐Ionisierung tragen dazu bei, dass besonders dichte, homogene Schichten mit hoher Haftfestigkeit abgeschieden werden. Die industrielle Realisierung steht noch am Anfang. Mittlerweile sind bereits erste, auf HIPIMS spezialisierte Beschichtungsanlagen im Markt erhältlich. Erste Ergebnisse mit CrN–Schichten mit einer Härte von HV 3000 weisen auf das hohe Potential dieser neuen Technologievariante hin.
Preparation of dibasic acid‐containing soy phospholipids by chemical and enzyme‐catalyzed transesterification and evaluation of their surface‐active properties
Authors: Das Soma , Das Kali Pada , Bhattacharyya D. K. 
Published: February 2007

AbstractThe preparation of dibasic acid‐containing soy phospholipid was made by transesterification reaction with alkyl ester of diabasic acid with both lipase and alkoxide as a catalyst. The extent of incorporation of a dibasic acid varied with the molecular size of the dibasic acid. The extent of incorporation in soy phospholipids was 4–13% in the case of adipic acid and 9–20% in the case of sebacic acid. The surface‐active properties of these modified soy phospholipids were examined and were found to be different from those of the original (unmodified) soy phospholipid. The interfacial properties such as critical micelle concentration (CMC), γCMC, surface excess concentration Γmax, and minimum area per molecule (Å), and thermodynamic parameters such as standard free energy of micellization, were found to depend on the hydrophobic part of the dibasic acids.