bluuebunny/crossref_metadata_2025_split huggingface dataset:
Turbulent transfer mechanisms in the atmospheric surface layer
Authors: McBean G. A. , Miyake M. 
Published: February 2007

AbstractThe objective of this study was to investigate the turbulent transfer mechanism near the surface. ‘Direct’ measurements of the turbulent fluxes of momentum, heat, and moisture were made in the atmospheric surface layer 2 m above a grass surface at Ladner, Canada.The spectral correlation coefficients were considered to be a measure of the transfer efficiency as a function of scale size. For momentum transfer the efficiency decreased at all scales as instability increased. It is postulated that this was due to greater amounts of momentum being transferred in bursts of short duration, thus making the spectral correlation coefficient, averaged over sufficient time, smaller.The Ladner results for heat transfer showed that its transfer efficiency increased at all scales when instability increased. The ratio of the transfer efficiency of heat to that of momentum was greater than 1 for most scales, even for near neutral stratifications, and increased to between 2 and 3 for more unstable conditions.The efficiency of moisture transfer was usually smaller than that for heat transfer and was found to depend on the correlation between moisture fluctuations and those of temperature.
The generation of available potential energy by sensible heating in Southern Ocean cyclones
Authors: Bullock B. R. , Johnson D. R. 
Published: February 2007

AbstractEstimates of the generation of available potential energy by sensible heating in the boundary layer for two extratropical cyclones in the Southern Ocean are presented. Boundary layer frictional dissipation is also estimated to contrast the relative importance of the storm's energy source by diabatic process with its sink by frictional effects. In the storm area of 2,000 km radial extent, representative average generation estimates by the sensible heating and frictional dissipation are 0.5 and 2.1 W m−2, respectively, for the late developing stage. In the occluding stage, the generation increased to 0.9 W m−2 and the frictional dissipation increased to 6.2 W m−2. The generation to frictional dissipation ratio of 1:3 and 1:7 for the two stages indicate that the in situ diabatic source of storm available potential energy is significant in the cyclogenetic stage but that its importance decreases as the storm decays.Because of the paucity of data in the Southern Ocean a simplified model to estimate the sensible heat flux is developed in this study. The model estimates the upward flux through the sea‐air interface for the synoptic scale from analyses of the depth of the adiabatic boundary layer, the surface pressure and the sea surface temperature.
Observations on certain features to be seen in a photograph of haloes taken by Dr. Emil Schulthess in Antarctica
Authors: Tricker R. A. R. 
Published: February 2007

AbstractA more complete theory than has been available before of the Lowitz arc and its associated upward pointing companion, is given. The theory of the supralateral arc to the halo of 46° is also given and it is shown that, at least in the case of the halo photographed, the suggestion put forward by Hastings (1920a) about the nature of the halo of 46° is untenable. It follows that his explanation of the arcs of contact to this halo have also to be revised. Alternative explanations are put forward.
Spectral characteristics of surface‐layer turbulence
Authors: Kaimal J. C. , Wyngaard J. C. , Izumi Y. , Coté O. R. 
Published: February 2007

AbstractThe behaviour of spectra and cospectra of turbulence in the surface layer is described within the framework of similarity theory using wind and temperature fluctuation data obtained in the 1968 AFCRL Kansas experiments. With appropriate normalization, the spectra and cospectra are each reduced to a family of curves which spread out according to z/L at low frequencies but converge to a single universal curve in the inertial subrange. The paper compares these results with data obtained by other investigators over both land and water.Spectral constants for velocity and temperature are determined and the variability in the recent estimates of the constants is discussed. The high‐frequency behaviour is consistent with local isotropy. In the inertial subrange, where the spectra fall as n−5/3, the cospectra fall faster: uω and ωθ as n−7/3, and uθ, on the average, as n−5/2. The 4/3 ratio between the transverse and longitudinal spectral levels is observed at wavelengths of the order of the height above ground under unstable conditions and at wavelengths of the order of L/10 under stable conditions. This lower isotropic limit is shown to be governed by the combined effects of shear and buoyancy on small‐scale eddies.
Diurnal wind variations in Antarctica
Authors: Hisdal V. 
Published: February 2007

AbstractFor the three Antarctic ice shelf stations considered (Norway Station, Maudheim, and Halley Bay) it is shown that from spring to autumn a systematic diurnal variation of the mean vector wind at the surface exists. Different factors that may be responsible for this variation are discussed. The results seem to agree well with the assumption that in areas far from the ice front (the seaward edge of the ice shelf) the main cause is the larger net gain of momentum in the lowest layers during the middle of the day, while closer to the ice front there is an additional effect of the varying contrast between the air temperature over the sea and over the ice shelf.
Wind profiles and change of terrain roughness at Risø
Authors: Panofsky H. A. , Petersen E. L. 
Published: February 2007

AbstractThe Risø 125 m tower is situated on a narrow peninsula, surrounded by bays of varying width. The resulting surface roughness changes are clearly reflected by ‘kinks’ in the measured wind profiles, whose characteristics depend on the wind direction. The height of the lowest kink for water‐to‐land trajectories is in good agreement with theory.The roughness lengths computed for the immediate surrounding of the tower vary with wind direction in a manner consistent with terrain features. However, the roughness lengths of the water estimated from the profiles are unrealistically small.The mean profiles obtained when the trajectory passes over relatively homogeneous terrain are represented quite well by wind profile expressions that are usually applied only in the surface layer.
On the variance spectra and spatial coherences of equatorial winds
Authors: Parker D. E. 
Published: February 2007

AbstractThe variance spectra of daily zonal and meridional winds in the troposphere and lower stratosphere over Gan (00°41′S, 73°09′E) were investigated. The total zonal variance considerably exceeded the total meridional variance at all the levels studied except the surface. In the upper troposphere the total zonal variance had a marked peak caused almost entirely by effects with periodicities greater than 10 days. The variance due to 4‐ to 5‐day meridional effects usually had a maximum slightly below the tropopause. However, at all the levels investigated this variance fluctuated considerably with time although without showing any long‐term regularities. Some specific 4‐day meridional motions at 150 mb over the equatorial regions between Gan and East Africa appeared to progress westward with a zonal wavelength of between 10,000 and 12,000 km.The vertical coherence of daily tropospheric winds over Gan was found to be weak on a scale of several km. Correlation coefficients between daily tropospheric winds over Gan and corresponding winds over Port Victoria (04°37′S, 55°27′E) were found to be small except for part of the upper troposphere.
Spectra of the temperature and humidity fluctuations in the marine boundary layer
Authors: Warner J. 
Published: February 2007

AbstractThe results are given of the analysis of temperature and humidity fluctuations observed from an aircraft in 61 runs at heights of 30–550 m above the open sea in conditions of active convection in the south‐east Trades. The dimensionless temperature fluctuations varied with ( − z/L)−1/3 for scale heights from about 0·2 to 2 but thereafter showed little change with height. The spectra obeyed the −5/3 power law for dimensionless frequencies in excess of about 0·3. The variance of virtual potential temperature showed a maximum at a lower dimensionless frequency than the variance of vertical air velocity observed during the same series of observations.
The use of Nimbus 4 radiance and radio‐sonde data in the construction of stratospheric contour charts
Authors: Aanensen C. J. M. 
Published: February 2007

AbstractThe construction of 10, 3 and 1 mb contour charts using thicknesses derived from Nimbus 4 selective chopper radiometer (SCR) measurements is described. Examples of such charts during the 1972 stratospheric warming period are given. Heights and deduced gradient winds obtained from these charts were compared with radio‐sonde and rocket observations. At 10 mb the average heights using satellite measurements exceeded those from radio‐sondes by 5 dam in a ‘quiet’ period and by 14 dam in the warming period, the greatest difference occurring in the area of warming. Rocket data showed the average height difference increased upwards to some 40 dam at 1 mb. Consideration of derived gradient winds supported the impression that the shape of contours is better than the spacing. Though there is evidence of increased error on the occasion of major warmings it is concluded that the method described produces realistic charts.
A note on the relationship between large scale energy functions and characteristics of climate
Authors: Smith R. F. T. 
Published: February 2007

AbstractA study has been made of large‐scale energy functions using 500 mb height and 500–1,000 mb thickness data for 1954–1956 and associated synoptic charts in order to consider further the relationship between blocking anticyclones and eddy kinetic energy (K′) as proposed by Everson and Davies (1970). For the winter of 1955–1956, K′ displayed much larger amplitude variations with a longer period than those for the winter 1954–1955. The difference in weather was also quite marked, the 55–56 winter being dominated by blocking anticyclones whilst the 54–55 winter was comparatively mild. The onset of large‐scale blocking activity generally coincided with minima of K′ as anticipated.It was further found that a minimum of K′ coupled with a relatively low value of zonal kinetic energy (K̄) and a significant land‐sea temperature contrast was generally followed by European blocking, whereas a minimum of K′ in other circumstances was not.
The influence of evaporation and drop‐interactions on a rainshaft
Authors: Brazier‐Smith P. R. , Jennings S. G. , Latham J. 
Published: February 2007

AbstractCalculations have been made of the variations with fall‐depth z of the liquid water content, L, rainfall rate, p, radar reflectivity, Z, drop concentration, NT, and raindrop size distribution n(r), within a steady‐state rainshaft as a result of the evaporation and interaction of the drops. The interactions were described by a generalized stochastic equation which takes account, as described by Brazier‐Smith, Jennings and Latham (1973), of the variation of coalescence efficiency ε with drop radii R, γ and the fact that satellite drops are produced when drops separate after collision. The relative humidity is assumed to fall linearly from 100 per cent at cloud base (z = 0, T = 8°C) with a gradient β. The lapse rate within the rainshaft was taken to be 8°C km−1 and the initial size distribution was generally given by the Marshall‐Palmer equation. Calculations were made for 3 different situations in order to isolate the physical processes which most affect the rainfall: (1), evaporation without interaction; (2) interaction without evaporation; (3) both interaction and evaporation.The calculations for Case (1) indicate that the numbers of drops in all size classes are diminished with increasing Z̄, with a preferential reduction at the small‐radius end of the spectrum. In Case (2) the interactions of the raindrops introduce considerable detail into n(r), with bimodal curves associated with satellite drop production, the highly efficient consumption of small drops by larger ones and the variations of ε and fall‐velocity V with drop‐radius γ.The main feature of the calculations for Case (3) is the rǒle of coalescence in preserving within the spectrum a considerable amount of liquid water that would otherwise be lost by evaporation. For example, whereas the rainwater content at z = 1·5 km for β = 20 per cent km−1 and Lo = 1·0 gm m−3 is 0·28 gm m−3 if interactions are absent, their presence elevates L to 0·57 gm m−3 at this level. This retention effect is significant for all values considered of β, L, p, and the initial slope of the raindrop size distribution (varied from half to twice that of the Marshall‐Palmer equation). It is also found that the structure introduced into the size distributions as a result of interactions is partially smoothed out by evaporation, which replaces a substantial proportion of the smallest drops consumed by coalescence.
Stability of the Rossby‐Haurwitz wave
Authors: Hoskins B. J. 
Published: February 2007

AbstractA spectral method is used to integrate the primitive equations for the motion on a sphere of a shallow layer of fluid with a free surface. A simple Rossby‐Haurwitz wave of zonal wavenumber 4 is found to change its form little over 24 days, whilst one of wavenumber 8 breaks down completely in 5 days. Inspired by the integrations, the barotropic stability of a wave to a perturbation composed of another wave and a zonal flow is considered. The theory suggests that waves of zonal wavenumber greater than 5 may be unstable because the feedback of the perturbation on itself is positive. Those of wavenumber 5 and less are stable, the feedback being negative. The theory and the general barotropic instability of Rossby waves is tested by integrations of the non‐divergent barotropic model, in which the wave is perturbed by a zonal flow. Some agreement with theory is found. Waves of zonal wavenumber 8 rapidly break down to produce jets in the same direction as the perturbation zonal flow. The stability of these jets is also examined.
A stochastic model of ice particle multiplication by drop splintering
Authors: Chisnell R. F. , Latham J. 
Published: February 2007

AbstractA stochastic model is developed which describes the increase in ice particle concentrations resulting from the splintering of supercooled drops on freezing. Analysis of the experimental evidence suggests that significant splintering occurs at least for drops with diameters in the range 50 to 200 μm. At time t = 0 one such drop freezes and ejects r ice splinters. Each of these splinters may be captured by another water drop in the same size range at any subsequent time, which in turn will freeze and eject a further r splinters, and so on. Consideration of the probability that a particular capture will take place at a particular time yields an expression for m(t), the estimated number of particles existing at time t,m(t) = (r2e(r‐1)t/τ − 1)/(r − 1),Where τ is the mean lifetime of an ice splinter. It is stressed that by considering the probability of a collision occurring at any time after the birth of a splinter, far higher estimates of the population are obtained than from a non‐stochastic model.Calculations show that the largest ice particle multiplication factors measured by Mossop et al. (1972), of order 104, can be produced in the available time if the value of r for the splintering size range is 5 or 6. Analysis of the experimental evidence suggests that such a value for r is possible.
The accuracy of radar‐derived rainfall measurements in hilly terrain
Authors: Harrold T. W. , English E. J. , Nicholass C. A. 
Published: February 2007

AbstractA weather radar has been used to measure rainfall over hilly terrain in north Wales. The radar was a standard Plessey Type 43S, which has a wavelength of 10 cm and a beam width to half power points of 2°. Measurements were compared with those based on a raingauge network consisting of 62 tipping bucket gauges distributed over 1,000 km2. This density of gauges was inadequate to define the hourly areal rainfall sufficiently accurately on some occasions and in these circumstances the radar‐derived pattern was used to interpolate between the gauges so as to obtain an ‘optimum’ estimate of the actual sub‐catchment rainfall which was then used to evaluate the accuracy of the radar measurement.Errors in the radar estimates were excessive unless the radar was calibrated hourly using raingauge measurements from one site. The accuracy was further increased when the horizontal drift of the rain in the wind between the radar beam and the calibration site was allowed for. Using these procedures, the mean percentage difference regardless of sign, Y, between the radar and optimum estimates of three‐hourly rainfall over sub‐catchments of typically 50 km2 varied from about 15% close to the calibration site to about 20% at a distance of 20 km. Differences decreased as the period of integration was increased; Y was 13% for 6 hour periods compared with 20% for 2 hour periods. Y also varied with the area of comparison. For point measurements hourly estimates differed by 37% but over an area of 500 km2 around the calibration site they differed by about 13%.The main causes of error in the radar measurements seem to be (i) variations in the drop size distribution relation, (ii) the spatial variation in the growth (or evaporation) which occurred between the beam and the ground and (iii) the horizontal drift of the rain in the wind. Probably all of these factors, but in particular (ii), are more important in the hilly terrain of this study than would be the case in flatter terrain. A further factor contributing to the differences between the radar and optimum estimates was the (unavoidable) error in each optimum estimate of the actual rainfall.The accuracy of the radar estimates decreased markedly if the beam intersected the melting layer. The increased errors were reduced by introducing an empirical correction factor which is a function of the range of the sub‐catchment from the radar and the height of the melting layer, but the spatial and temporal variations of the melting layer were such that it was not possible to obtain the same accuracy as when the beam was entirely within rain.
A comparison of grid‐point and spectral methods in a meteorological problem
Authors: Doron E. , Hollingsworth A. , Hoskins B. J. , Simmons A. J. 
Published: February 2007

AbstractIntegrations of the shallow water equations on the sphere using a second order finite difference method and a spectral method are compared. By increasing the resolution, a good estimate of the exact solution may be made, thus allowing an estimate of the accuracy of each integration. The particular initial conditions used are a Rossby wave of zonal wavenumber 4 which moves with little change in shape or amplitude and a Rossby wave of zonal wavenumber 8 which undergoes large changes within 5 days. All the models perform reasonably for the wavenumber 4 integration. A 5° times; 3° grid for the finite difference simulation is insufficient to resolve the breakdown in wavenumber 8 despite there being 9 points per zonal wavelength. A spectral model with a truncation at wavenumber 16 uses less storage and takes the same computing time as the grid‐point model. However, it is able to predict quite accurately the breakdown.
The sizes of the stratospheric volcanic particles over south‐east Australia after Mt. Agung's eruption in 1963
Authors: Neumann J. 
Published: February 2007

AbstractAssuming an air layer of geometric thickness L, a particle number density N, particles of uniform radius a and density ϱ, the optical depth of the particle layer is τ = πa2 QNL, Q being the extinction efficiency factor. The total mass M of the particles in a vertical air column of unit cross‐section is M = (4/3)πa3ρNL. The ratio of the two quantities is M/τ = 4aϱ/3Q.The above ratio is applied to data of τ for the observed 20% reduction in direct solar radiation over south‐east Australia about mid‐1963, reported by Dyer and Hicks. For M, an estimate given by Deirmendjian is used. It is inferred from the above ratio that a particle radius of a few tenths of one micron leads to a Q value such that the values for the radius and for Q are mutually consistent with the Mie scattering theory. If we assume much smaller radii, we run into contradiction with the latter. We thus conclude that most of the extinction must have been effected by particles of radii of about the same magnitude as the wavelengths where the bulk of the solar radiation energy resides. We estimate that the particle concentration may have been about 5 cm−3 and that absorption by the particles was probably very small.
The production of sub‐micron ice fragments by water droplets freezing in free fall or on accretion upon an ice surface
Authors: Bader M. , Gloster J. , Brownscombe J. L. , Goldsmith P. 
Published: February 2007

AbstractIn an attempt to explain the excess concentration of ice crystals over ice nuclei in some maritime cumulus clouds, laboratory experiments were carried out to determine whether sub‐micron ice particles are produced when water droplets freeze in free fall or on riming. The results show that not enough ice fragments are produced when the droplets freeze in free fall but that the numbers of sub‐micron particles ejected during riming may go some way towards explaining the large concentrations of ice crystals in maritime cumulus clouds.
Polar lows: The development of baroclinic disturbances in cold air outbreaks
Authors: Mansfield D. A. 
Published: February 2007

AbstractThe formation of small disturbances in cold air outbreaks over the north‐east Atlantic is shown to be due to baroclinic instability. A case study of two such disturbances shows their growth rate, wavelength and phase speed to be very close to the predictions of the baroclinic theory. Surface friction is shown to have a very important effect; strong surface winds enhancing the friction and severely reducing the growth rate. Heating from the sea surface also reduces the growth rate. It is concluded that these lows will develop only when the surface winds are light and where the air flow is not parallel to sea‐surface isotherms, thus explaining their rarity compared to that of cold air outbreaks and providing more discriminating criteria for forecasting their development.
Simulation of three‐dimensional turbulence with given second‐order statistical structure
Authors: Lindberg William R. , Thompson Rory O. R. Y. 
Published: February 2007

AbstractA method is presented for generating a turbulent, three‐dimensional flow field with correct mean flows, Reynolds' stresses, and energies, along with boundary layer structure. The details of the simulation of turbulent plane Poiseuille flow are given as an example. Plane Poiseuille flow was chosen because it is a useful model for many applications, and has available reliable and extensive measurements. All nine of the components of the spectral matrix are included, from actual measurements, along with incompressibility, a sheared mean flow, and measured boundary‐layer structure of the turbulence. The results appear to be realistic, and the statistical structure imposed is adequate for a variety of turbulence studies of three‐dimensional flows, in particular turbulent dispersion. Compared with finite‐difference methods for solving the dynamic flow equations, with comparable resolution, the method presented here requires some two orders of magnitude less storage, and some four orders of magnitude less computer time.