bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal variability of temperature, salinity, velocity, vorticity and sea level in the central Gulf of California, as inferred from historical data
Authors: Ripa P. , Marinone S. G. 
Published: February 2007

AbstractHistorical data from 17 cruises into the Guaymas basin, central part of the Gulf of California, are globally analysed. Temperature, across‐gulf integrated velocity, sea level, and salinity have a significant seasonal cycle. The last variable has an important semi‐annual component, presenting four extremes per year. The others are mainly annual, reaching their maximum values in summer and their minima in winter.By interaction with the atmosphere, the central gulf is gaining heat and losing fresh water during the whole year, on a monthly‐mean time scale (the only exception is an unimportant gain of fresh water in August). This implies net heat and salinity fluxes into the open ocean, through the gulf's mouth.Temperature and salinity vertical gradients at the surface are well correlated with atmospheric forcing, through turbulent diffusion of heat and salt. Average velocity correlates with the along‐gulf wind stress with zero lag, as if frictionally dragged in a surface layer, with a short relaxation time. Seasonal sea‐level changes are mainly caused by the thermal expansion of the water column.Horizontal processes (advection and diffusion) are as important as, or more important than, vertical diffusion for both heat and salt balances in the upper layers.Vorticity, the across‐gulf derivative of the velocity field, does not show a seasonal cycle. Its contribution to the instantaneous geostrophic velocity and surface elevation near each coast is larger than that due to the across‐gulf average velocity.
Airflow over a two‐dimensional escarpment. I: Observations
Authors: Pitts R. O. , Lyons T. J. 
Published: February 2007

AbstractObservations of forced flow over the highly asymmetric topography of the Darling Scarp, Western Australia, are presented. These are typified by shallow surface gradient winds of 10–20 m s−1 with an inherent critical level aloft and a stable layer produced through nocturnal radiational cooling. The observations highlight a topographically induced hydraulic jump, lee waves or vertically propagating hydrostatic waves depending on the upwind stability and wind profile. The vertically propagating waves and hydraulic jump are observed to produce accelerated flow down the escarpment.
Regimes in the wintertime circulation over northern extratropics. I: Observational evidence
Authors: Molteni Franco , Tibaldi Stefano , Palmer T. N. 
Published: February 2007

AbstractRegimes of the northern extratropical circulation in winter are identified in this paper as clusters of atmospheric states in a low‐dimensional phase space generated by the leading EOFs of eddy geopotential fields. In order to define the clusters, our algorithm seeks points corresponding to local maxima for the density of atmospheric states; subsequently, a cluster is defined around each density maximum as that portion of the phase space in which the observed density can be locally approximated by a unimodal function. Two analyses were performed, using a 5‐dimensional and a 3‐dimensional space respectively, and they provided consistent results. Six clusters were found. the largest cluster includes 40% of the fields in our sample; its centroid is close to the climatological winter state, but it possesses a positive projection on the Pacific‐North American (PNA) pattern. the other five clusters represent anomalous flow regimes and include 52% of the fields. One of them shows a low amplitude of the planetary waves; the remaining four represent states with large wave amplitude but different phases. the variability between clusters accounts for the bimodality in the amplitude of planetary waves detected in previous observational studies. Our analysis reveals that this bimodality is much enhanced in the region of the phase space where the PNA index is negative, and the separation among the clusters is stronger. Finally, frequencies of transitions between clusters are presented, which show an asymmetric behaviour in the transitions between regimes with low and high amplitude of planetary waves.
Nieuwstadt's stable boundary layer revisited
Authors: Derbyshire Stephen H. 
Published: February 2007

AbstractCurrently no theory of the stably stratified atmospheric boundary layer (SBL) is generally accepted as definitive even for idealized cases. Nieuwstadt's theory, though a promising candidate, faces objections relating to upper boundary and steady‐state conditions, internal wave effects and the consistency of the model outside the strong‐stability limit. the aim of this paper is to examine the objections, improve the model, draw further deductions and compare with numerical models.We shall deduce from Nieuwstadt's model that Bo = RfcG2|f|/√3, where Bo is the surface buoyancy‐flux, G the geostrophic wind speed, f the Coriolis parameter and Rfc the critical value of the flux Richardson number Rf. Higher‐order expansion shows this value is an upper bound corresponding to the stable limit L/h → 0. This is consistent with a similar bound on Bo derived from independent energy arguments. By contrast, within present idealizations there is no bound on the surface cooling rate.Comparisons with a new series of large eddy simulations (LES) and other numerical models support the interpretation of Nieuwstadt's SBL as an idealized limiting case. the theory explains from first principles the observed sensitivity to small slopes. Interaction between sharp inversions and slopes may cause turbulence in thin layers. Coupling with the surface boundary conditions is a likely cause of intermittent turbulence, and explains features of Brost and Wyngaard's second‐order closure study. the formal singularity at the top of the SBL gives time‐scales for approach to inertial and heat equilibrium. Both, for separate reasons, are O(|f|−1).A natural extension to moderately stable and near‐neutral conditions agrees well with numerical model results, and provides a complete prediction of SBL structure from given surface heat flux and synoptic pressure gradient. the near‐neutral regime is narrow at high Rossby number. Comparison with LES supports both the local scaling approach and the gross predictions of the theory. the model gives insight into the limitations of Rossby‐similarity formulae. In particular, restrictions of domain size hd (or similar background stability effects) may not become negligible even when h/hd → 0. Hence matching to neutral conditions is important in predicting even quite stable boundary layers. Wave effects, though non‐local in some respects, do not fundamentally change the Nieuwstadt picture for the mean structure. Retention in the model of the original value for Rfc is recommended even if wave radiation perturbs local Rf.In summary, the adapted Nieuwstadt theory seems to provide a definitive framework for the idealized SBL, from which other ‘perturbation’ effects may be assessed. the value of Bo/G2|f| gives a criterion for (a) quasi‐steady or (b) intermittent SBL regimes.
Comments on ‘Numerical models of the raingauge exposure problem, field experiments and an improved collector design’ by C. K. Folland (October 1988, 114, 1485–1516)
Authors: Sevruk B. 
Published: February 2007

AbstractDirect field comparisons of precipitation gauges (PG) are difficult and costly. For this reason the development of correction models such as Folland's, based on wind tunnel tests, is very valuable. This note draws attention to some new wind tunnel data on the airflow over several types of gauge. the new data are in much better agreement with those of Robinson and Rodda (1969) than with those of Green and Helliwell (1972) supporting Folland's preference for the former data. In addition, the new data provide support for Folland's assumption that the airflows over the 5‐inch and Hellmann gauges are similar, though this appears to be more or less accidental.
The information content of data from satellite sounding systems: A simulation study
Authors: Eyre J. R. 
Published: February 2007

AbstractThe potential of the TIROS Operational Vertical Sounder (TOVS) and the Advanced TOYS (ATOVS) for providing information on the vertical profiles of atmospheric temperature and humidity is investigated. the theoretical performances of these systems are examined primarily in terms of their ability to contribute information to a numerical weather prediction (NWP) system. the covariance of retrieval error expected from an optimal nonlinear inversion scheme, which retrieves simultaneously all the atmospheric and surface variables which significantly affect the measured radiances, is calculated theoretically and compared with the covariance of error assumed in the prior information which constrains the inversion. Performance is assessed for different combinations of radiometers, corresponding to present and future operational systems, and for different sets of assumed conditions: in the atmospheric profile, the cloud conditions, the surface characteristics and the assumed prior knowledge of these variables.The potential performance of ATOVS is shown to be a considerable improvement on the present TOVS in many respects. the value of retaining a combined infrared and microwave system is confirmed. It is demonstrated that, although the ability of these sounding systems to improve on an NWP model's analyses of temperature and humidity is rather limited, the potential for improving on the analysis of layer quantities is much greater.Some new ideas are presented for extending current retrieval methods to accommodate the additional problems presented by ATOVS data. Methods are proposed for treating the effects of microwave surface emissivity and cloud liquid water in a simultaneous inversion.
The Meteorological Office analysis correction data assimilation scheme
Authors: Lorenc A. C. , Bell R. S. , Macpherson B. 
Published: February 2007

AbstractA major revision is described to the analysis component of the Meteorological Office data assimilation scheme for both the global and the regional numerical weather prediction models. Initialization by repeated insertion of data and divergence damping is retained but a more flexible modified successive‐correction scheme replaces optimum interpolation for the analysis step. The scheme is derived as an approximate iterative solution to a general equation for the optimal analysis. Within iterations, the analyses of each model variable are performed sequentially and multivariate increment fields are derived for dynamical balance at intermediate stages. The horizontal influence area of data is substantially increased, giving a beneficial impact in data‐sparse regions. All data contribute to the analysis at each gridpoint within their radius of influence. The observation weights are recalculated every model time‐step, allowing asynoptic data to be used at their true valid time, though this feature is found to have only slight impact on forecasts. Each analysis is factorized into a vertical step, then into a horizontal step. The structure of each is described in detail, with system parameters listed in appendices.Results of two kinds are presented. Sensitivity experiments highlight the effects of some individual constituents of the scheme; operational trials against the old scheme reveal the impact of the whole system. The new analyses are better balanced and lead to a better short‐period forecast, especially for the wind field. Medium‐range impact is clearly beneficial in the southern hemisphere but ambiguous in the northern hemisphere. Precipitation forecasts in the regional model are improved.
Concentration fluctuation measurements in a dispersing plume at a range of up to 1000 m
Authors: Mylne K. R. , Mason P. J. 
Published: February 2007

AbstractA series of tracer experiments studying concentration fluctuations in a dispersing plume of pollutant in the atmosphere at ranges of between 50m and 1000m is described. Experiments were conducted on three different field sites in near‐neutral or slightly convective meteorological conditions. The results show time series which are characterised by the intermittent occurrence of periods of fluctuating non‐zero concentrations, interspersed by periods of essentially zero concentration. The spectrum of concentration fluctuations is found to display inertial subrange behaviour, characterised by a −2/3 power law when nS(n) is plotted against frequency n, where S(n) is the variance (of the fluctuation) per unit frequency interval. The spectral peak frequency varies with distance from the source. In all cases the clipped‐normal probability density function (PDF) provides a reasonable fit to the concentration PDF. The exponential PDF is less flexible in fitting a wide range of experimental conditions, but is slightly superior for some short range examples. In the alongwind direction it is found that, although there is a rapid initial decrease in fluctuation intensity with distance, the intensity seems to approach an approximately constant non‐zero value at long range. In cross‐sections of the plume the variation of fluctuation statistics is dominated by the varying proportion of time during which the concentration is essentially zero. Conditional statistics, calculated from significantly non‐zero concentrations only, show only slight variations across the plume.
Atmospheric gravity waves and the ‘Rissaga’ phenomenon
Authors: Monserrat S. , Ibbetson A. , Thorpe A. J. 
Published: February 2007

AbstractThe atmospheric forcing of large sea‐level oscillations (up to 1.5 m amplitude with about a 10 min period) in some bays and inlets of the Balearic Islands is described using simultaneous measurements of pressure and sea‐level elevation in the port of Ciutadella (at the end of a large and narrow inlet) during 5–7 July 1989. The influence of atmospheric pressure oscillations on these large sea‐level variations, locally known as ‘rissaga’, is investigated. Coherence and cross‐correlation functions reveal that the large oscillations in the inlet are associated with and probably forced by a 10 min gravity wave in the atmosphere. The effect of longer‐period waves on the inlet is seen in the well‐known inverted barometric effect, forcing small oscillations in the water level of just some centimetres. These latter waves have a period of around 50 min and an unusually large amplitude of some 3 mb. The phase spectrum between sea level and pressure suggests that the inlet may behave as a damped harmonic oscillator which, during rissaga, is externally forced by the atmospheric pressure oscillations.
Morphology and density of ice accreted on cylindrical collectors at low values of impaction parameter. I: Fixed deposits
Authors: Levi L. , Nasello O. B. , Prodi F. 
Published: February 2007

AbstractThe morphology and density of ice depositions grown on fixed cylinders are studied in the ranges of Macklin's parameter, X, and of the Stokes number, K, of 0.5 <X<7μ ms−1 K−1 and 0.8° K £3.2 respectively.For K<3, the deposit morphology was characterized by concave growth fronts and inward direction of lateral feathers. For larger K‐values, the growth fronts changed to convex profiles, and ice feathers to an outward direction.The density was measured in the first millimetre of rime, using the X‐ray micrography technique. The stagnation‐region density (θ = 0) was found to depend on X only, the ρ(X) curve being independent of the K‐value. For X<2, ρdecreased slowly down to ρ ±; 0.3gcm−3, probably approaching a limiting value.The results ‘off the stagnation region’ depend on K. For K<3, air gaps appear between lateral feathers and ρdecreases with the angular distance, from the stagnation line. For K > 4, the air‐gap effect was reduced to the very flanks of the deposit, and ρwas nearly independent of θ. The possible dependence of the observed behaviour on the shadow effect, generating air gaps, and on the supposed variation with θ of the droplet impact speed is discussed. It is shown that experimental aspects of deposit morphology agree well enough with stochastic model results obtained by previous authors, some differences probably being related to the oversimplification of the model, where the droplet spectrum is represented by the median volume droplet radius.Relations between the morphology and density of the deposit and between these properties and the parameters X and K are discussed.
Observation of a quasi‐periodic oscillation due to gravity waves in a shallow radiation fog
Authors: Duynkerke Peter G. 
Published: February 2007

AbstractQuasi‐periodic oscillations with a period of about 40 min are observed in visibility, temperature, water vapour, wind speed and long‐wave radiation during the fully developed stage of a shallow radiation fog. These oscillations were observed up to a height of about 60 m, whereas the fog extended up to a height of about 30 m. An interpretation of the oscillations is given in terms of gravity waves, which are rather typical under these very stable conditions.
A Preliminary Morphology of Precipitation Systems In Tropical Northern Australia
Authors: Keenan T. D. , Carbone R. E. 
Published: February 2007

AbstractA preliminary morphology of convective systems observed in the vicinity of Darwin, Australia is presented. Several types of tropical convection during monsoonal and break‐season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk Richardson number. A significant spectrum of convective activity ranging from low shear and low Convective Available Potential Energy (CAPE), to high shear and moderate to high CAPE, typical of mid‐latitude severe storms, is identified. Significant differences between monsoonal flow and break‐season systems are apparent. the formation of convective lines perpendicular to the low‐level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features. Convective‐scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer (PEL).The motion of the break‐season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental PEL flow. Deviations from this balance are hypothesized, to result in the observed ‘propagating’ and ‘non‐propagating’ or slow‐moving modes. Examples of these modes are given, showing the classical continuous development of new cells in a balanced state along the leading edge of long‐lived squalls and, in the propagating case, the discontinuous development of new cells on the cold pool ahead of the squall.
Two‐Layer Solutions to Long's Equation For Vertically Propagating Mountain Waves: How Good Is Linear Theory?
Authors: Durran Dale R. 
Published: February 2007

AbstractFinite‐amplitude solutions for infinitely deep stratified flow over orography are obtained for upstream conditions with uniform wind and a two‐layer static‐stability structure. the flow within each layer is governed by Long's equation. the governing equations are solved using a semi‐analytic model with an open (radiation) boundary condition in the upper layer. A simplified, computationally efficient form of the finite‐amplitude radiation upper‐boundary condition is presented and utilized in the two‐layer calculations.When the higher stability is in the lower layer, finite‐amplitude effects may produce large‐amplitude waves in circumstances where linear theory predicts a weak response. the relationship between the continuously stratified system and shallow‐water hydraulic theory is explored, and an expression is derived for the effective Froude number in unbounded continuously stratified flow. In those cases producing the strongest finite‐amplitude response, the flow undergoes a transition from subcritical to supercritical just to the lee of the mountain crest.When the higher stability is in the upper layer, the finite‐amplitude response is also sensitive to the location of the stability interface. the dependence of the solution on the height of the interface is, once again, different from that predicted by linear theory. the interface height that produces the strongest response increases as the mountain height increases. These results support the idea, originally suggested through the analysis of linear multi‐layer models, that the vertical phase shift between the ground and the tropopause has an important influence on the strength of downslope windstorms. the optimal phase shift for finite‐amplitude waves cannot, however, be reliably determined from linear theory.
The Parametrization of Rainfall Interception In GCMs
Authors: Johannes Dolman A. , Gregory David 
Published: February 2007

AbstractExperiments with a one‐dimensional version of the Meteorological Office's 11‐layer GCM are used to derive a simple calibrated subgrid parametrization of rainfall interception by the Amazonian rain forest. Two interception parametrizations, both incorporating subgrid variability of precipitation within a GCM grid box are presented and tested, and compared with observations made at a single location. the 1‐D model is a fully interactive atmospheric column and incorporates all the GCM physics but is forced at its boundaries by climatic data. the interception losses appear to be sensitive to what fraction of area in the GCM grid box is covered by the rain and to the precise formulation of the interception process. the implications for the parametrization of the wet area in a GCM grid box are discussed and suggestions are made as to how to parametrize the fraction of wetted area in a GCM grid box.
Exergy in meteorology: Definition and properties of moist available enthalpy
Authors: Marquet Pascal 
Published: February 2007

AbstractThe exergy of the dry atmosphere can be considered as another aspect of the meteorological theories of available energies. The local and global properties of the dry available enthalpy function, also called flow exergy, were investigated in a previous paper.The concept of exergy is well defined in thermodynamics, and several generalizations to chemically reacting systems have already been made. Similarly, the concept of moist available enthalpy is presented in this paper in order to generalize the dry available enthalpy to the case of a moist atmosphere. It is a local exergy‐like function which possesses a simple analytical expression where only two unknown constants are to be determined, a reference temperature and a reference pressure.The moist available enthalpy,am, is defined in terms of a moist potential change in total entropy. The local functionamcan be separated into temperature, pressure and latent components. The latent component is a new component that is not present in the dry case. The moist terms have been estimated using a representative cumulus vertical profile. It appears that the modifications brought by the moist formulation are important in comparison with the dry case. Other local and global properties are also investigated and comparisons are made with some other available energy functions used in thermodynamics and meteorology.