bluuebunny/crossref_metadata_2025_split huggingface dataset:
A storm surge model for the Australian region
Authors: Hubbert G. D. , Leslie L. M. , Manton M. J. 
Published: February 2007

AbstractA depth‐integrated ocean‐current model is developed to simulate currents and sea surface elevations on the Australian continental shelf. the nonlinear advective terms are included and the equations of motion are solved using an efficient split‐explicit finite difference scheme, which yields accurate and stable results. the model predictions are compared with observations over a four‐day period of both surface elevations and currents in Bass Strait during the passage of a typical cold front in April 1984.
Entrainment instability and vertical motion as causes of stratocumulus breakup
Authors: Weaver C. J. , Pearson R. 
Published: February 2007

AbstractEntrainment instability is thought to be a cause of stratocumulus breakup. At the interface between the cloud and the overlying air, mixtures may form which are negatively buoyant because of cloud droplet evaporation. Quantities devised to predict breakup, δ2, X and δm, are obtained from aircraft observations and are tested against cloud observations from satellite. Often, the parameters indicate that breakup should occur but the clouds remain, sometimes for several days. One possible explanation for breakup is vertical motion from passing synoptic cyclones. Several cases suggest that breakup is associated with the downward vertical motion from the cold air advected behind an eastward moving cyclone.
Simulating giant hailstone structure with a ballistic aggregation model
Authors: Lozowski E. P. , Brett M. , Tait N. , Smy T. 
Published: February 2007

AbstractA ballistic aggregation model designed for thin film simulation in microelectronics has been adapted to simulate the rime growth behaviour of hailstones. The model is able to account for both lobe development and the occurrence of large air bubbles and voids. The microstructures predicted by the model and those observed in a thin section of a giant hailstone are seen to be both qualitatively and quantitatively similar, lending some support to the possibility that certain large hailstones may grow by the accretion of low density rime with subsequent soaking.
On the concept of exergy and available enthalpy: Application to atmospheric energetics
Authors: Marquet Pascal 
Published: February 2007

AbstractThe available enthalpy is an early form of the modern thermodynamic concept of exergy, which is the generic name for the amount of work obtainable when some matter is brought to a state of equilibrium with its surroundings by means of reversible processes.It is shown in this paper that a study of the hydrodynamic properties of available enthalpy leads to a generalization of the global meteorological available energies previously introduced by Lorenz, Dutton and Pearce. A local energy cycle is derived without approximation. Moreover, static instabilities or topography do not prevent this theory from having practical applications. The concept of available enthalpy is also presented in terms of the potential change in total entropy. Using the hydrostatic assumption, limited‐area energetics is then rigorously defined, including new boundary fluxes and new energy components. This innovative approach is especially suitable for the study of energy conversions between isobaric layers of an open limited atmospheric domain.Numerical evaluations of various energy components are presented for a hemispheric field of zonal‐average temperature. It is further shown that this new energetic scheme realizes a hierarchical partition of the components so that the smallest of those available enthalpy reservoirs are almost of the same magnitude as the kinetic energy. This is actually the fundamental property that induced Margules to define the primary concept of available kinetic energy in meteorology.
Regional air pollution, with special emphasis on Europe
Authors: Smith F. B. 
Published: February 2007

AbstractThe state of acidifying air pollution in Europe is reviewed, as is the ability and limitation of models to simulate concentrations and depositions. The lack of complete quality in emission data is often a significant problem in these modelling studies. Nevertheless, models, for all their uncertainties, can play an important, if not totally reliable, role in assessing the origins of acidic depositions on any area. Although emissions have changed over the years, generally having decreased over the last decade, the time trend in measured depositions appears to indicate no very simple response to these overall decreases: the unequal changes in different parts of the continent and year‐to‐year changes in weather preclude such simplicity. The total impact of acid deposition on the environment, which is reviewed, depends not only on the average magnitude but also on the range of magnitudes of the depositions, and in particular on the occurrence of severe episodes. Some discussion of the probability distribution function is given.
A diagnostic study of winter diabatic heating in the Mediterranean in relation to cyclones
Authors: Shay‐El Y. , Alpert P. 
Published: February 2007

AbstractDiabatic heating and net condensation rates during winter are calculated over the Mediterranean and surrounding areas from the 1982‐88 ECMWF initialized analyses using the residual method for the heat and moisture budgets. The steady‐state contributions over the Mediterranean are found to be prominent as in the tropics, but contrary to the case of the tropics the transients contributions in the Mediterranean, attributed to cyclonic activity, are not at all negligible.A composite Cyprus low was constituted from 67 typical cyclones in the eastern Mediterranean. The diabatic heating and net condensation distribution indicate vigorous sea fluxes especially in the lee of the Turkish mountains over the Aegean Sea where the air‐sea contrast is maximized. In contrast with other regions, the maximum in the vertical profile of diabatic heating due to latent heat release is found at a lower altitude of about 850 hPa. It is suggested that this fact has important implications in modelling Mediterranean cyclones.
Morphology and density of ice accreted on cylindrical collectors at low values of impaction parameter. II: Rotating depositsxs
Authors: Prodi F. , Levi L. , Nasello O. B. , Lubart L. 
Published: February 2007

AbstractThe morphology and density of deposits grown on rotating cylinders of 0.5 cm radius, collecting droplets of median volume radius Δ = 10 μm, are studied. The wind speed and temperature are regulated so that Macklin's parameter and Stokes number are 0.5 < X < 7 μm m s−1 K−1 and 0.8 < K < 3.2 respectively. The knobby structure typical of rotating deposits is shown to form after the formation of the first 0.5–1 mm rime layer. Pronounced lobes, separated by wide entrances are observed at K < 3. Entrances change into air gaps for larger K values, as is shown also by comparison with previous results obtained for K > 4.Rime density measurements are made by the X‐ray micrography technique. The first rime layer and the lobe interior density is represented by a ρ(X) curve located between those of Prodi and Levi and Macklin. The former is approached by the experimental point at X = 6.5, K = 3.2. The mean deposit density is evaluated by averaging the results obtained by scanning the X‐ray micrographs, at different distances d from the point of deposit initiation. The mean density is shown to decrease markedly with d for K ± 3, as a consequence of the knobby structure, so that the average density of deposits 3–4 mm thick approaches Macklin's curve. This effect is very much reduced for K > 4, where lobes are separated by thin air gaps.These results are discussed by taking into account the shadow effect, and its dependence on K. Formulae for ρ(X) for different values of K and deposit thickness are proposed.
The structure of turbulence in a coastal atmospheric boundary layer
Authors: Shao Yaping , Hacker Jörg M. , Schwerdtfeger Peter 
Published: February 2007

AbstractThis study, based on airborne observations obtained during the Upper Spencer Gulf experiments in South Australia, investigates the structure of turbulence in a coastal boundary layer, which represents an extreme situation of horizontal inhomogeneity. The development of the coastal boundary layer under mainly onshore wind conditions, which is characterized by the formation of a convective thermal internal boundary layer (TIBL), is illustrated using cross‐sections of potential temperature, sensible‐heat fluxes and turbulent kinetic energy. The similarity of turbulence within the TIBL and the effectiveness of local scaling for inhomogeneous conditions are examined. It is suggested that, even in advective conditions, turbulence can be considered as being in local equilibrium. By introducing a simple TIBL model, local similarity relationships can be linked to external parameters. Some turbulence properties, such as the variance of vertical velocity, are found to be determined by three external parameters: the surface heat flux over land, the onshore wind speed and the thermal stability of the approaching airflow.
An Idealized Simulation of the Indian Monsoon Using Primitive‐Equation and Quasi‐Equilibrium Models
Authors: Mawson M. H. , Cullen M. J. P. 
Published: February 2007

AbstractAn idealized simulation of the Indian monsoon is performed using a prescribed heat source representative of the time‐averaged latent heating due to convection over India, and a simple representation of the east African orography. A quasi‐equilibrium model is used to solve this problem in three dimensions on a sphere. the model is shown to be able to simulate the cross‐equatorial flow and monsoon circulations driven by this problem and to be in good agreement with parallel integrations carried out with a hydrostatic primitive‐equation model except in areas affected by orographically forced gravity waves. the solutions given by these time‐dependent models are in good agreement with those found by using linearized steady‐state equations.
Potential Vorticity Index Vacillation In the 1978/79 Winter: Its Relation to Teleconnection Patterns
Authors: Weng Heng‐Yi 
Published: February 2007

AbstractA potential vorticity (PV) index is defined as a measure of the zonally averaged, raid‐latitude PV gradient on the 300 K isentropic surface in the northern hemisphere, and use is made of the 1978/79 wińter ECMWF FGGE Hl‐b data set to study the evolution of that index and its relation to teleconnection patterns of 500 mb geopotential‐height anomaly. This index vacillates with a dominant period of about two weeks. For some time lags, the isoline patterns of the cross‐correlation function between the PV index and 500mb geopotential‐height anomalies are similar to some teleconnection patterns studied by several investigators using large climatological data sets. Scandinavia, Greenland and the Pacific are important centres of ‘action’ in the northern hemisphere in the 1978/79 winter. the formation of blocking highs at these locations occurs at rather specific phases during the vacillatory evolution of the PV index, especially as the flow transits from a low to a high PV index.When the above study is duplicated using a zonal mean wind gradient at 500mb as a zonal index, the results do not reflect the teleconnection patterns as crisply as the PV index does for the FGGE year.
Reply to Comments By C. B. Moore and B. Vonnegut: Further Analysis of Two Regions of Charge During Initial Thunderstorm Electrification
Authors: Dye J. E. , Jones J. J. , Weinheimer A. J. , Winn W. P. 
Published: February 2007

AbstractIn response to the comments of Moore and Vonnegut we have thoroughly re‐examined the aircraft and radar measurements made in two small thunderstorms in New Mexico originally reported by Dye et al. (1988). Our conclusions remain the same. Although pressure altitude was used instead of geometric altitude in one case and distance labels were interchanged for a vertical section used to illustrate the other case, improved calculations for the particle image measurements and the ice particle collision rate show that the two regions of charge were in or near locations with appreciable supercooled liquid water, ice particle concentrations and graupel, and also near the top of reflectivity cores as originally stated. As before, we conclude that, given this spatial correlation of the inferred charge with ice particles and liquid water, the observations are consistent with what is expected from the non‐inductive ice‐collision charge separation mechanism of thunderstorm electrification. However, because the data are incomplete we cannot preclude the possibility that one of the regions of charge (on 15 August 1984) was the result of positive ions being attracted to the cloud by a downward‐directed field, as suggested by Moore and Vonnegut.
An Integrated View of the 1987 Australian Monsoon and Its Mesoscale Convective Systems. I: Horizontal Structure
Authors: Mapes Brian , Houze Robert A. 
Published: February 2007

AbstractThis observational study is organized around three issues: the forcing of the monsoon flow by embedded deep convection, the thermodynamic conditions that support the convection, and the structures of the mesoscale convective systems (MCSs) that constitute much of the deep convection.The monsoon convective cloudiness occurred predominantly offshore, over the earth's warmest waters. Week‐long periods of widespread deep convection caused cycles of monsoon spin‐up, culminating in tropical‐cyclone formation. Momentum transports by the convection also created smaller‐scale vortex pairs in the upper troposphere.Sounding data suggest that the convection was modulated by low‐level processes, not by large‐scale deep forced ascent. Triggering by mesoscale boundary‐layer cold‐pool boundaries and coastlines determined specifically where convection occurred, while several positive feedbacks acted to keep regional thermodynamic conditions favourable. Hence monsoon convection, once initiated, persisted as self‐exciting ‘superclusters’, composed at any instant of many distinct MCSs.The observed MCSs all contained areas of deep convection and stratiform precipitation areas. Stratiform precipitation usually evolved in place from convective cells, although precipitation also occasionally fell from overhanging anvils created by upper‐level shear. the MCSs within similar synoptic wind environments tended to have similar mesoscale structures. This fact reflects the effects, illustrated herein, of environmental winds upon the relative motions of cold pools (which trigger new convective cells) and stratiform precipitation areas (which evolve from old convective cells).
On the behaviour of baroclinic waves undergoing horizontal deformation. I: The ‘RT’ phase diagram
Authors: Bishop Craig H. 
Published: February 2007

AbstractNon‐modal baroclinic wave growth in an idealizsed flow comprising baroclinic shear and horizontal confluence is considered. It is shown how a general semi‐analytic solution may be derived for the evolution of non‐modal waves with uniform potential vorticity in this ‘mixed’ basic state. The solution is new. It represents a synthesis of baroclinic waves with pure deformation solutions.For a given initial wavelength the solution is capable of describing an infinite number of distinct non‐modal developments. To overview this large variety, phase diagrams, dubbed ‘RT’ diagrams, have been developed. The diagrams depict the evolution of vertical structure for a wide range of initial conditions. Some specific solutions with relevance to type B cyclogenesis and the potentially destablizing effect of deformation are discussed.
A case study of lee waves over the Lake District in northern England
Authors: Shutts Glenn , Broad Adrian 
Published: February 2007

AbstractThe structure and intensity of stationary, orographically‐forced over the Lake District and northern Pennines on he afternoon of 26 November 1991 is determined through a combination of field observations and high‐resolution numerical modelling. Observations were provided by the Meteorological Office's C130 aircraft at four different levels and by five radisondes (of differing ascent rates) released in rapid succession from an observing station located on the Cumbrian coast. Vertical velocity was inferred from both of these data sources and, with the help of satellite imagery, it was possible to build up a comprehensive picture of the lee wave structure.In addition, a non‐hydrostatic primitive equation model was run with a 2‐km grid, covering a 180‐km square region of the northern Pennines, in an attempt to simulate the gravity wave motion observed. The model was initialized with an upstream profile formed by merging a descent profile obtained from the aircraft with one from the sondes. The model orography was defined using a terrain height data‐set with 500‐m resolution and with some smoothing to the model grid. After about four hours of integration the model achieves a quasi‐steady state with strong lower‐tropospheric lee waves.Verification on the model response was sought by comparing the vertical velocity in the model along the paths of the aircraft and sondes with that actually deduced from the observations. The overall agreement of the simulated amplitude and phase of the lee waves with that observed is very encouraging—as found in a different case study (Shutts 1992). The success of the model in predicting lee wave motion gives strong support for the use of these models for the development of gravity‐wave‐drag parametrization schemes.The domain‐averaged surface frictional stress was found to be much larger than the wave drag, and consistent with the high roughness lengths likely in the case of mountainous terrain.
Effective resistance to sensible‐ and latent‐heat flux in heterogeneous terrain
Authors: Blyth E. M. , Dolman A. J. , Wood N. 
Published: February 2007

AbstractNumerical‐weather‐prediction models resolve mean variable at the scale of their grid length only. Effective surface parameters must, therefore, be used to relate the mean properties of humidity, temperature and wind speed to the mean surface fluxes. The effective parameters can be calculated using a model with a finer grid. In this paper effective aerodynamic and surface resistances to sensible‐and latent‐heat flux for a surface which varies over a horizontal scale of one kilometre are calculated from a two‐dimensional model with a grid size of 30m, and compared with simpler averaging techniques. The averaging techniques considered include taking the mean of the aerodynamic and surface resistance in parallel or in series, the mean of the solutions given by these two, and a heuristic model that treats the different surface covers independently but assumes that they are exposed to the same mean meteorological variables at a blending height. The heuristic model consistently estimates the effective resistances to within 25% but, in comparison to the other methods, requires more information. For heterogeneous surfaces, the effective parameters for momentum and sensible‐ and latent‐heat transfer do not bear the same relationship to each other as they do for homogenous surfaces. Effective parameters for each type of flux, therefore, have to be calculated separately. In situations where negative sensible‐heat fluxes occur over rough ground, the effective resistance to sensible‐heat flux can be very large, becoming underfined in the extreme case where the area‐average sensible‐heat flux is zero.
On the response of the tropical atmosphere tio large‐scale deforestation
Authors: Eltahir E. A. B. , Bras R. L. 
Published: February 2007

AbstractRecent studies on the Amazon deforestation problem predict that removal of the forest will result in a higher surface temperature, a significant reduction in evaporation and precipitation, and possibly significant changes in the tropical circulation. Here, we discuss the basic mechanisms contributing to the response of the tropical atmosphere to deforestation. A simple linear model of the tropical atmosphere is used in studying the effects of deforestation on climate. It is suggested that the impact of large‐scale deforestation on the circulation of the tropical atmosphere consists of two components: the response of the tropical circulation to the negative change in precipitation (heating), and the response of the same circulation to the positive change in surface temperature. Owing to their different signs, the changes in predicted temperature and precipitation excite competing responses working in opposite directions.The predicted changes in tropical circulation determines the change, if any, in atmospheric moisture convergence, which is equivalent to the change in run‐off. The dependence of run‐off predictions on the relative magnitudes of the predicted changes in precipitation and surface temperature implies that the predictions about run‐off are highly sensitive, which explains, at least partly, the disagreement between the different models concerning the sign of the predicted change in Amazonian run‐off.
The exchange of atmospheric ammonia with vegetated surfaces. II: Fertilized vegetation
Authors: Sutton M. A. , Fowler D. , Moncrieft J. B. , Storeton‐West R. L. 
Published: February 2007

AbstractMeasurements of the exchange of gaseous ammonia (NH3) have been made over fertilized plant canopies using micrometeorological techniques. The NH3 exchange over ungrazed grassland and arable crops was examined in a range of environmental conditions: a bidirectional exchange of ammonia was observed, with warm dry conditions favouring emission (NH3 fluxes up to 24 ng m−2s−1) and cool wet conditions favouring deposition (fluxes in the range 1–35 ng m−2s−1). Limited measurements made when the ground was frozen suggest an increased surface resistance may occur in these conditions (Measured Rc up to 80 s m−1), resulting in reduced rates of deposition.The fluxes are contrasted with measurements over unfertilized vegetation, and it is suggested that the net canopy exchange is the combined result of leaf surface, stomatal and soil exchange processes; the increased tendency of fertilized vegetation to emit ammonia is attributed to the larger fixed nitrogen concentrations in these ecosystems. The bidirectional fluxes may be related to the existence of ammonia compensation points. Estimates of the stomatal compensation point for fertilized croplands were in the range 1‐7 μg NH3m−3, though because of deposition to leaf surfaces, this frequently does not control net fluxes. The Mean surface concentration of ammonia X(z'o), or canopy compensation point, was therefore also estimated and found to vary, with environmental conditions, in the range 0‐3 μg m−3. A simplified procedure is used to estimate the net annual exchange of ammonia over an example fertilized crop in the British Isles. This predicts an emission of fixed nitrogen of less than 1 kg per hectare, which is the net result of emission and deposition throughout the year.