bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural convection in water over an ice surface
Authors: Townsend A. A. 
Published: February 2007

AbstractA tank of water with an ice‐covered bottom and an upper surface maintained at about 25°C provides a simple way of studying the disturbance of a layer of stably‐stratified fluid by convective motion in an underlying layer of unstable fluid. Observations of temperature fluctuations and of the motion of dye streaks and suspended particles show that vigorous overturning is confined to a thin layer on the ice‐covered bottom, from which emerge rising columns of buoyant fluid. the columns penetrate a region of constant mean temperature (3·2°C) which occupies about two‐thirds of the tank volume but are deflected horizontally as they reach the region of stable stratification. the layer just beyond the farthest penetration of the columns is remarkable for large and continuous fluctuations of temperature, apparently caused by internal gravity waves excited by the impacts of columns on the stable fluid. Calculations show that the disturbance from an impulse at the interface spreads comparatively slowly into the stable fluid and the observed concentration of wave energy can be explained if the life‐time of each ripple is limited by energy loss either by ‘wave breaking’ or by viscous forces. Shallow layers with strong internal wave motion may occur in the atmosphere near the interface between an upper region of stable fluid and a lower region in convective motion.
Evaporation and evapotranspiration in southern nigeria
Authors: Chapas L. C. , Rees A. R. 
Published: February 2007

AbstractData are presented on a 4‐weekly basis over the two years 1961 and 1962 for evaporation from three types of evaporation pan, and an evaporation estimate by Penman's method. Evapotranspiration was estimated by the methods of Penman, Blaney‐Criddle, Thornthwaite, and Garnier's modification of Thornthwaite's method. Grass covered lysimeters receiving only rainfall gave actual evapotranspiration, or were watered daily to give potential evapotranspiration. Actual evapotranspiration measurements are compared with theoretical estimates.Potential evapotranspiration is overestimated by Thornthwaite's method and slightly underestimated by that of Penman. the true value is about 120 cm annually with a marked seasonal variation which follows the bi‐modal radiation cycle. Actual evapotranspiration is 50 cm less than this, marked departure from the potential rate occurring during the main and subsidiary dry seasons.
A note on the relationship between net radiation and solar radiation
Authors: Davies J. A. 
Published: February 2007

AbstractLinear relationships between daytime net radiation (Rn) and solar radiation (Q) have been determined for West Africa and for selected stations throughout the world. For three West African stations.Rn = 0·612 Q −28And for fourteen stations throughout the worldRn = 0·617 Q −24Where Rn and Q are in g cal cm−2 day−1.The surfaces represented have albedos ranging from 0·20 to 0·30. On average, net radiation is 55 per cent of the solar radiation. Values for a heating coefficient β, inferred from the relationships, lie between 0·14 and 0·30. The results are not consistent with some previous work. The application of the relationship to estimating evaporation and potential evapotranspiration is discussed.
The turbulent transport of heat and water vapour in an unstable atmosphere
Authors: Dyer A. J. 
Published: February 2007

AbstractMicro‐meteorological data acquired during five expeditions to carefully chosen sites are analysed to determine the flux‐gradient relation for the transfer of heat and water vapour in the lower atmosphere. The analysis takes the form of a direct assessment of the Monin‐Obukhov universal functions φH and φW. Data for φH were available from all five expeditions, and for φW from two of these.It was found that φH = φW over the whole of the z/L range available, indicating an identity in mechanism for the turbulent transport of heat and water vapour over a freely evaporating surface. Over the range 0.02 < |z/L| < 0.6, both φH and φW were found to vary approximately as |z/L|−1/3. In this range of |z/L|, Priestley's H* was assessed as 1.15·0.07 and Crawford's E* as 1.10·0.12. This value of H* leads to the formulae H = 21.2 δθ3/2 and E = 51.7 δq δθ1/2 where E and H are in mWcm−2, δθ is the potential temperature difference (°C) and δq the specific humidity difference (gm kg−1) between 1 and 4 metres height. For |z/L| > 0.2, φH was found to vary as |z/L|−1/2. Insufficient data limited the value of the corresponding analysis for φW Excellent agreement was found between the φH and φW data, and φ‐curves assessed from a previous shape‐function analysis (Swinbank and Dyer 1967). The empirical relation φ = (1–15 z/L)−0·55 agrees with the experimental values of φH and φW over the whole of the |z/L| range to within a few per cent, thus permitting numerical evaluation of φ.
Momentum and mass transfers in the surface boundary layer
Authors: Pruitt W. O. , Morgan D. L. , Lourence F. J. 
Published: February 2007

AbstractResults are presented from six micrometeorological studies conducted over a grass turf at Davis, California, in 1966 and 1967. Highly reliable surface drag and evaporation data from very sensitive lysimeters of 6·1 m diameter afforded excellent opportunity to evaluate several parameters important to aerodynamic‐prediction equations.For the six studies the mean von Kármán constant, k, ranged from 0·40 to 0·44, strongly supporting continued acceptance of k at around 0·42.The Monin‐Obukhov (1954) universal ϕM function was found to vary as ∣Ri∣−1/3 under near‐free convection, indicating significantly greater diabatic profile effects than suggested in the form of the KEYPS profile as given by Sellers (1965).Empirical relationships providing excellent fit to experimental data for the range −3·5 < Ri < 0·3, were ϕM = (1–16 Ri)−1/3 and ϕM = (1 + 16Ri)1/3 respectively for unstable and stable conditions. For ϕw corresponding expressions were ϕw = ·885 (1–22 Ri)−.40 and ϕw = ·885 (1+34 Ri).40.The ratio KW/KM showed a systematic drop from 1·13 at neutral to a value around 0·75 under strongly stable conditions, which conflicts with recent reports of no change of KH/KM within a wide range of stable conditions (Laykhtman and Panomareva 1969; Webb 1970; Oke 1970). The UCD results are in general agreement with the literature in that KW/KM systematically increased with increasing instability. In the range 0 > Ri > −2·0, KW/KM increased from 1·13 to 1·6.No expressions relating ϕM and ϕW or KW/KM to z/L are presented due to uncertainties in Davis z/L data. However, use of Davis Ri data in several published z/L (Ri) relationships, allowed a limited comparison with results of previous studies.
Modified quasi‐geostrophic equations using geometric height as vertical coordinate
Authors: White A. A. 
Published: February 2007

AbstractA quasi‐geostrophic β‐plane set using geometric height as vertical coordinate is derived without the conventional assumption that fractional changes of basic state potential temperature over a scale height of the atmosphere are small. Although the hydrostatic, continuity and vorticity equations contain terms not present in the usual set, and the rigid horizontal boundary condition is modified, the form of the implied potential vorticity equation in terms of the stream function is the same as before. Some of these conclusions are extensions to the nonlinear case of results obtained in 1968 by Lindzen in a linearized analysis. the modified equations have reasonable integral conservation properties. As regards accuracy they are closely comparable with the quasi‐geostrophic pressure coordinate equations, but since rigid horizontal boundary conditions are easily applied exactly in the modified set the most nearly equivalent pressure‐based system is evidently a (quasi‐geostrophic) σ‐coordinate set rather than the p‐coordinate set. the modified rigid horizontal boundary condition has the property of allowing for the change in the apparent vertical when a coordinate transformation to a frame moving with a uniform zonal velocity relative to the β‐plane is carried out. Application of the modified equations to an f‐plane baroclinic instability problem reveals a dependence of stability properties on the height‐averaged flow Uo as well as the shear (as found also in 1947 by Charney and by Geisler and Dickinson in 1975 in β‐plane analyses), the dependence on Uo being most marked for the longer waves.
Dynamics of stationary ultra‐long waves in middle latitudes
Authors: Bates J. R. 
Published: February 2007

AbstractThe dynamics of stationary ultra‐long waves in middle latitudes are studied using a set of approximate linear equations for small perturbations about a zonal flow. the equations are derived by an expansion procedure based on the assumptions of planetary scales of variation and small mean superrotation. the zero‐order equations reduce to a vertical structure equation containing no meridional derivatives. Analytical solutions are obtained for forced stationary waves in a model atmosphere consisting of three continuous layers, representing the troposphere, the lower stratosphere and the upper stratosphere.The waves are generated by thermal and topographic forcing in the model troposphere and propagate wave energy at zonal wavenumbers 1 and 2 into the upper stratosphere, where they are damped by Newtonian cooling. General relationships are found involving the zero‐order fluxes of sensible heat and wave energy. These greatly clarify the dynamics of the waves, particularly in the lower stratospheric layer which links the regions of generation and dissipation.Taking realistic values of the parameters for northern middle latitudes in winter, the solutions for wavenumbers 1 and 2 show good agreement with observation. an examination of the sensitivity of the solution to changes in various model parameters shows that the meridional flux of heat by ultra‐long waves in the troposphere is extremely sensitive to changes in the stratospheric wind profile and static stability. Since these waves are known observationally to account for a large fraction of the total poleward heat transport in northern middle latitudes in winter, a dynamical mechanism is suggested whereby variations in solar ultraviolet radiation or changes in the ozone content of the upper atmosphere could lead to climate change.
Swell waves at Saint Helena related to distant storms
Authors: Cartwright D. E. , Driver J. S. , Tranter Joyce E. , Charnock H. 
Published: February 2007

AbstractThis paper discusses the relationship between a frequency‐time plot of energy density of swell, from records taken at St Helena in December 1970 and January 1971, and meteorological records of distant storms. A similar exercise in 1969 had suggested that some of the swells originated from the southern hemisphere, even possibly from the Pacific Ocean, but wave amplitudes were all very low. Higher waves were recorded in the present exercise, but all the major events in the energy spectra were attributable to northern hemisphere storms, a few minor events only to the southern hemisphere, and none to the Pacific Ocean. It is concluded that large northwesterly storms in the area southeast of Newfoundland are probably responsible for the spectacular ‘rollers’ which are frequently reported from St Helena.
Deuterium in hailstones collected on 29 November 1972
Authors: Roos D. v. D. S. , Schooling H. , Vogel J. C. , Triegaardt D. O. 
Published: February 2007

AbstractThe deuterium content of more than 400 samples cut from 34 hailstones was determined. These hailstones came from three storms the structures of which were studied by radar. the range in values of deuterium excess (δD) of about 60‰ (extending as low as −86‰) was compatible with the moist adiabatic model only if a significant increase in δD of atmospheric vapour occurred at some stage. Individual growth layers were concluded isotopically uniform. Opaque ice was associated with relatively low δD, especially for the bulk of the hailstones beyond the embryo stage. the correlation found between SD and crystal size was used to derive the relationship between δD and ambient temperature. It was hence concluded that embryos mostly grew between 6 and 7km above ground level. Hailstones of all sizes acquired most of their mass between 7 and 8 km (−20 to −25°C) during the early stages of the severe storms when radar echo tops reached up to 16km. However, during later stages most of the growth occurred during descent. Hailstones from places no more than a few kilometres apart in one storm were concluded 10 have grown in very different conditions: while some must have experienced updraughts in which the speed in the environment of the hailstone increased steadily with time, others encountered an updraught that pulsated with a period of about 8min. Updraught maxima often occurred at about 7.5km, approaching values of 40ms−1.
Stratospheric water vapour measurements over Australia 1973–1976
Authors: Hyson P. 
Published: February 2007

AbstractResults are presented of measurements of stratospheric water vapour over Mildura (34°S 140°E) Australia. The mean mixing ratio between 15 and 21 km is approximately 2–7ppm and is closely approximated below 15km by an exponential profile with a height constant of 2–4km.
Infrared fluctuation hygrometry in the atmospheric surface layer
Authors: Raupach M. R. 
Published: February 2007

AbstractThis paper describes a single‐beam infrared fluctuation hygrometer, operating in the 2.7 μm water vapour band. By restricting attention to frequencies making up the atmospheric eddy spectrum, a calibration equation for fluctuations is obtained which is independent of moderately stable instrumental gain parameters. A transmission function appropriate to this type of hygrometer is obtained from the random statistical model of band absorption, and shown to imply: (i) a weak but significant dependence of the calibration upon mean humidity; (ii) a very small contribution to transmission fluctuations from temperature fluctuations, which can often be neglected but which may require correction when the Bowen ratio is high. A suitable calibration method is outlined. The results of a field trial over a shallow lake demonstrate the hygrometer's reliability and operational effectiveness for experimental periods of many weeks, and lead to an estimate of 0.88 for the Kolmogorov coefficient for humidity fluctuations.
Instability of planetary waves and zonal flows in two‐layer models on a sphere
Authors: Frederiksen J. S. 
Published: February 2007

AbstractA study is made of the stability of finite amplitude planetary waves by themselves and together with zonal flows in two‐layer quasi‐geostrophic models on a sphere. Critical amplitudes for incipient instability of baroclinic waves, growth rates, perturbation streamfunctions and momentum fluxes are obtained and are compared with the corresponding properties for barotropic waves in the nondivergent barotropic model. The change in the growth rates, perturbation streamfunctions, momentum and heat fluxes due to the superposition of basic planetary waves on zonal flow profiles is examined in two‐layer quasi‐geostrophic models. The presence of the long planetary waves is found to produce regions of preferential development of cyclones and anticyclones. The position of the most intense development, downstream from the long wave troughs or ridges depending on the basic flow profile, is shown to be related to Phillips's criterion for incipient instability. It is also found that the largest of all the growth rates is increased in the presence of baroclinic waves but decreased in the presence of barotropic waves and it is concluded that baroclinic instability, rather than barotropic instability, is the most important factor in the unpredictability of largescale atmospheric motions. Barotropic waves, however, produce larger changes in the disturbance stream‐functions, momentum and heat fluxes; in particular, when superimposed on solid body rotation zonal flow profiles, they may produce zonally averaged perturbation momentum fluxes with both poleward and equatorward components. The presence of planetary waves in the basic profile removes the short wave instability cutoff characteristic of two‐layer quasi‐geostrophic models with purely zonal flow basic profiles.
The diffuse solar irradiance of slopes under cloudless skies
Authors: Steven M. D. , Unsworth M. H. 
Published: February 2007

AbstractThe diffuse irradiance of slopes relative to the diffuse irradiance of a horizontal surface is calculated by integrating the mean radiance distributions of cloudless skies in Britain for a wide range of solar elevations, azimuths and slope angles. There is reasonable agreement with measurements reported from a number of stations; discrepancies are probably due to errors in measurements and to the influence of aerosol on the radiance distributions. A simple model of the diffuse irradiance of slopes, which takes account of circumsolar radiation, is proposed, and agrees well with integrated values of irradiance.
Transient synoptic systems as mechanisms for meridional transport: An observational study in the southern hemisphere
Authors: Tucker G. B. 
Published: February 2007

AbstractA classification of satellite cloud vortices compiled for the southern hemisphere by Streten and Troup is used to provide an inventory of the incidence of various stages in the life‐cycle of depressions as a function of latitude. These figures are then allied with estimated meridional transient eddy fluxes of both heat and momentum to assess the varying effectiveness of the systems during their life‐cycles as mechanisms of meridional transport, in comparison with the net contribution from other transient systems (travelling long waves and temporal variations in stationary waves). The developing stage of the cloud vortex is shown to be associated with a strong poleward heat flux, decreasing with the age of the system, with only a small (poleward) contribution from other transient mechanisms. For momentum, the developing stage is associated with a moderate poleward flux and the mature stage with relatively little net flux, while strong equatorward transport occurs during the decaying stage. A major poleward momentum flux is attributed to other transient mechanisms, particularly in the upper troposphere. The results are consistent with the hypothesis that the occurrence at preferred latitudes of different stages in the life‐cycle of systems is a major factor controlling the latitude profile of meridional transient eddy flux. A postulated meridional eddy flux distribution within a frame of influence for a mid‐latitude disturbance during its life‐cycle, when related to the broad‐scale zonal current, can account for salient features in the observed global distribution of meridional eddy fluxes of both heat and momentum. An indirect toroidal circulation is inferred when such a system interacts with the mean zonal current, and other synoptic implications are discussed.
A cloud parametrization scheme derived from GATE data for use with a numerical model
Authors: Slingo Julia M. 
Published: February 2007

AbstractA cloud parametrization scheme which allows for low, medium, high and convective clouds has been developed from GATE data for use in the Meteorological Office 11‐layer tropical model. The problems involved in using synoptic observations to derive methods of predicting clouds are discussed. Only limited success was obtained in relating observed cloud amounts to relative humidity and atmospheric temperature structure. The restrictions imposed on the cloud scheme by the model's resolution and by its inability to produce a perfect simulation are considered. In the light of these difficulties a simple approach was adopted based on the assumption that condensation on the smallest scales is part of a larger‐scale condensation regime related to the synoptic scale situation. The scheme has been designed to reproduce the main features of a cloud field by relating the large‐scale meteorological features associated with a cloud distribution to model variables. Low, medium and high cloud amounts are determined from a quadratic relationship with relative humidity. Low cloud has also been related to the temperature lapse rate in an attempt to model the persistent areas of sub‐tropical stratocumulus occurring under inversions. A relative humidity relationship is inappropriate for convective cloud which has, therefore, been related to the convective mass flux calculated in the convection scheme of the model. The scheme has been reasonably successful in predicting the cloudiness associated with the ITCZ and the NE. and SE. trades. The cloud fields showed a good degree of coherence from day to day and there were no signs of unrealistic feedbacks between radiation, cloud and dynamics.
On the vertical structure of damped steady circulation in the tropics
Authors: Geisler J. E. , Stevens Duane E. 
Published: February 2007

AbstractThis paper presents an analysis of the vertical structure of steady motion in a dissipative tropical atmosphere forced by steady isolated diabatic heating. Vertical modes appropriate to the problem are obtained, and the forcing is projected onto these modes. With the use of an analytic expression obtained by Gill (1980) for the horizontal structure, these modes are summed to obtain the amplitude and the vertical structure of the response in the region to the east of the heating.
Equatorial waves in steady zonal shear flow
Authors: Plumb R. Alan , Bell Robert C. 
Published: February 2007

AbstractThe properties of equatorial Kelvin and mixed Rossby‐gravity waves are investigated in an equatorial beta‐plane model of the lower stratosphere. The basic state and wave amplitudes are assumed to be independent of time; the waves are dissipated by thermal and/or mechanical damping.Particular emphasis is placed on the forcing of the mean flow by the waves. In agreement with earlier studies the latitudinal structure of the mean flow forcing is found to be sensitive to the dissipation mechanism; when the mean state is one of no zonal motion the easterly mixed Rossby‐gravity wave‐induced acceleration of the zonal flow is zero on the equator when only thermal dissipation acts, but maximizes on the equator when dissipation is included. This latter property is also found in the presence of equatorial jets.Results from this model, with its explicit resolution of the wave structure, are compared with those from the multiple‐scales approach of Boyd; good agreement is found.
Simulations of an observed stratospheric warming with quasigeostrophic refractive index as a model diagnostic
Authors: Butchart N. , Clough S. A. , Palmer T. N. , Trevelyan P. J. 
Published: February 2007

AbstractA three‐dimensional primitive equation model of the stratosphere and mesosphere is described. The model was forced at its lower boundary by observed 100 mb height fields for the wavenumber 2 stratospheric warming period of February 1979, and correctly simulated the reversal of the high latitude circulation. This behaviour contrasts with earlier model simulations of wavenumber 2 warmings in which forcing of a climatological zonally symmetric initial circulation by a stationary wave perturbation led to an initial reversal of the circulation in low latitudes. In a series of idealized experiments we show that wave‐wave interaction played no essential role in this simulation and that the ingredients leading to its success were firstly the non‐climatological initial wind structure and secondly an imposed longitudinal phase speed for the upward propagating planetary wave at the lower boundary. These studies also demonstrate that in the prewarming period the direction of propagation of planetary wave activity, as represented by integral curves of the so‐called Eliassen‐Palm flux, may be qualitatively described by the WKBJ limit of the quasi‐geostrophic potential vorticity equation. In this limit, the Eliassen‐Palm flux is simply related to the zonal mean refractive index, leading to two complementary diagnostics for studying wave, mean‐flow interaction.