bluuebunny/crossref_metadata_2025_split huggingface dataset:
A mesoscale semi‐implicit numerical model
Authors: Seaman Nelson L. , Anthes Richard A. 
Published: July 2010

AbstractA three‐dimensional semi‐implicit mesoscale numerical model based on the Navier‐Stokes equations is described and tested. Numerical techniques for achieving numerical stability with long time steps are discussed. In simulating flow over mountains the model accurately reproduces the results of an explicit model. Low vertical resolution causes moderate damping of the orographically forced responses, but adjustment rates are not seriously affected. the model is stable with time steps six times those of a similar explicit model and its computational efficiency is about three times greater.A cross‐section version is used to examine the response characteristics. With four layers in the vertical, the phase speeds of external gravity waves with wavelengths 8 Δx to 30 Δx are slowed to 50% to 85% of the analytic phase speeds, respectively. Even so, simulations with eight and sixteen layers show that the semi‐implicit model reproduces the features of simulations with the explicit model and has comparable mass and energy conservation characteristics.Adjustment rates of the mass and momentum fields towards a steady state are studied for mountain wave and jet stream circulations. Despite the reduced gravity wave phase speeds, root‐mean‐square error calculations show very little difference between the semi‐implicit and explicit models. This is attributed to the fact that most of the adjustment is effected by relatively slow internal modes which are not greatly slowed in the semi‐implicit model. the verification that the semi‐implicit model produces adjustments between mass and momentum fields about as well as an explicit model is an important step in ensuring that the semi‐implicit technique can be successfully applied to mesoscale forecasting.
Estimating return values of environmental parameters
Authors: Carter D. J. T. , Challenor P. G. 
Published: July 2010

AbstractReturn values of an environmental parameter, such as wind speed or wave height, are frequently estimated from an extreme value analysis of observed annual maxima assuming that the parameter is identically distributed throughout the year. Environmental data generally have considerable within‐year variation. an indication of the error in return values resulting from this assumption is obtained by analysing monthly maxima of wave height and wind speed data. It appears that the assumption leads to an underestimation of return values.
Synoptic‐scale forcing of coastal lows: Forced double kelvin waves in the atmosphere
Authors: Bannon Peter R. 
Published: July 2010

AbstractGill (1977) has interpreted the coastal lows of southern Africa as atmospheric coastal Kelvin waves. the lows are trapped horizontally next to the steep slopes of the Great Central Plateau by Coriolis forces and vertically by a low‐level inversion. This hypothesis is tested and extended using two linear models.A barotropic primitive‐equation analysis on an equatorial beta‐plane models the generation of these waves. an impermeable eastern boundary is included to reflect the blocking of the low‐level flow below the coastal inversion by the orography. Results of the linear analysis suggest that the formation of the coastal lows may be explained in terms of the scattering of eastward‐propagating synoptic‐scale disturbances at the meridional boundary. the boundary response is structurally similar to a Kelvin wave. At the frequencies of interest, no zonally propagating Rossby waves are excited. Further, in contrast to the case of a western boundary, the equatorial response is negligible.A two‐layer, f‐plane model enables the dynamics of the layer of fluid below the interior inversion to be incorporated. At the period of the synoptic forcing (six days), the boundary response is a maximum along the escarpment and decays exponentially from it. the e‐folding distance is slightly less than the appropriate Rossby radius of deformation. These results, together with observations, suggest that the coastal low and its companion low over the interior may be interpreted as forced internal double Kelvin waves.The possible application of these results to foehn (chinook) winds and lee cyclogenesis is mentioned.
An observational study of primary and secondary billows in the free atmosphere
Authors: James P. K. , Browning K. A. 
Published: July 2010

AbstractA case study is presented showing the kinematic structure of a train of large‐amplitude billows associated with a strongly sheared layer of high static stability in the upper troposphere. the observations were obtained using a high‐power microwave Doppler radar with a range resolution of 30 m. A beamwidth resolution almost as good as this was achieved at the ranges of interest using a 25 m paraboloid aerial. the resulting detailed measurements revealed the kinematic structure of secondary billows of wavelength 350m growing on the back of primary billows of wavelength 4.2km. the secondary billows were regions of moderate turbulence, the outer scale of which was small compared with the radar resoluton. Streamers of cirrus ice particles were present in the region of interest and these served as tracers showing how the billows perturbed the flow over a considerable depth above and below the primary billows.
Aircraft measurements of solar and infrared radiation and the microphysics of cirrus cloud
Authors: Paltridge G. W. , Platt C. M. R. 
Published: July 2010

AbstractProfiles of the upward and downward solar and infrared flux densities and of the downward beam radiance at 11 μm are reported for six cirrus cloud decks over Socorro, New Mexico. the data are used to derive empirical relations between vertical ice‐water path (obtained from simultaneously measured particlesize distributions) and solar absorptance, solar albedo, broad‐band infrared flux emittance and the 11μm beam emittance. As a guide, for ice‐water paths of about 75 gm−2 where the infrared emittances are approaching unity, the solar albedo is about 0.4, the solar absorptance is of the order of 0.15 and the geometrical thicknesses are between 1.5 and 2.5 km. Within an individual cloud there is little variation of particle size distribution with height, but the geometrically thicker clouds favour large particles. No icecrystal shape information is available, but the observed relation between albedo and emittance suggests that theoretical treatment of cirrus ice particles as ‘cylinders’ is better than treatment as ‘equivalent spheres’.
A field study of radiation fog in meppen, West Germany
Authors: Choularton T. W. , Fullarton G. , Latham J. , Mill C. S. , Smith M. H. , Stromberg I. M. 
Published: July 2010

AbstractA field study of the microphysical properties of a radiation fog was conducted in Meppen, West Germany, on 17 February 1978. It is described and interpreted in terms of the prevailing meteorological conditions.Pronounced periodic fluctuations in liquid water content (intervals ∼70s) were observed at times in the radiation fog. It is suggested that these were a result of convective motions in the form of Bénard cells. the drop size distributions were broad, containing drops of radii up to 25 μm. Calculations indicate that these larger drops cannot be produced by radiative cooling from the fog top. It is argued that these large drops may have been produced either by large supersaturation fluctuations near the fog top, resulting from downwards entrainment of warmer moister air, or by convective motions causing a fraction of the larger drops to make several excursions to the radiative cooling region near the fog top. the radiation fog was observed to clear when cloud was advected over the site. It is suggested that this was due mainly to eddy diffusion and gravitational sedimentation of drops to ground, after radiative cooling from the fog top had been severely curtailed by the cloud layer.
Estimating solar radiation income from ‘bright’ sunshine records
Authors: Revfeim K. J. A. 
Published: July 2010

AbstractThe potential of Campbell‐Stokes records of sunshine hours has not been exploited. Since 1924 various forms of the Angstrom equation have been used to estimate mean daily global radiation from the mean daily fraction of possible ‘bright’ sunshine. the Angstrom equation gives an equal radiation weight to all hours of sunshine and consequently the relationship is weak. As measured by the Campbell‐Stokes instrument ‘bright’ sunshine may be measured and recorded within individual hours from the hour markings on the card. Most observers routinely add up the sunshine measured for individual hours to give the daily total of sunshine hours.Adding monthly mean fractions of ‘bright’ sunshine within each hour, weighted by the cosine of the mid‐hour zenith angle and a mid‐hour atmospheric transmission, gives standardized radiation hours which are quite precisely related to mean daily direct radiation. Making assumptions about the effects of atmospheric scattering and absorption allows calculation of diffuse radiation income as well. Thus a proper use of the information content of sunshine records can give good estimates of direct, diffuse and global radiation. These may be used in the absence of other radiation records or for the direct/diffuse partitioning of radiation as recorded by solarimeters or pyrheliometers.
Apparent absence of the quasi‐biennial oscillation in sea level pressure in the south indian and south atlantic oceans
Authors: Dyer T. G. J. 
Published: July 2010

AbstractMonthly mean sea level pressure over the Indian and South Atlantic oceans can be represented adequately by a few uncorrelated pressure fields derived using principal component analysis. Apart from a major, and general, field both zonal and meridional compensatory pressure systems appear to occur over this region of the Southern Hemisphere (approximately 10°W to 60°E and 20.5°S to 40.5°S). the time series of these fields were submitted to spectral analyses, and apart from an oscillation centred at 20 months in the third component there was no evidence suggesting the existence of the quasi‐biennial oscillation in the pressure data. This result conflicts with those for rainfall over southern Africa, and sea level pressure and sea surface temperature around Australia.
Generation of coastal lows by synoptic‐scale waves
Authors: Anh Nguyen Ngoc , Gill A. E. 
Published: July 2010

AbstractA model is presented in which eastward propagating synoptic waves interact with a meridional escarpment. It is shown that, under suitable conditions, trapped waves are produced at the escarpment, the dominant wave being poleward propagating. This model is intended to represent the generation of coastally trapped disturbances like those found in southern Africa.
Thermodynamic dissipation and the global climate system
Authors: Paltridge Garth W. 
Published: July 2010

AbstractThe principle of maximum thermodynamic dissipation (minimum entropy exchange) suggested by Paltridge with reference to the earth‐atmosphere climate system concerns selection of a particular steady state from a spectrum of possible steady states of a system whose boundary properties are functions of internal behaviour. the physical basis of such selection is suggested in terms of the system's non‐linear response to natural fluctuations. the explanation is sufficiently general that the principle presumably applies to a broad class of non‐linear (i.e. multiple steady state) systems.With reference to the specific climate model of the earlier papers, it is pointed out that the regional or zonal ‘boxes’ of that model must be regarded as strictly zero‐dimensional; so that the earlier discussion involving a concept of upper boundary temperature was incorrect. the model is used to generate the zonalaverage climates of perpetual January and perpetual July. This leads to a determination of the seasonal change zonal‐average time constants of the climate system, which range from a minimum of about nine months at 30°N latitude to a maximum of about five years at 50°S latitude.
Further application of the theory of stochastic perturbation of deterministic systems to simple climate models
Authors: Benzi Roberto , Pandolfo Joseph P. , Sutera Alfonso 
Published: July 2010

AbstractA previous paper (Sutera 1981) considered the effect of stochastic perturbation on the long‐term behaviour of a highly idealized energy‐balanced model of zero spatial dimension. It was shown that, in the presence of stochastic perturbations, transitions between different stable equilibria, or ‘climates’, of the model become possible. the expected time for a stochastically perturbed model solution to leave the attractor basin of a stable equilibrium is called the ‘exit time’. the ‘exit time’ must be considered as an important new parameter characterizing model behaviour.In order to illustrate the methodology described in Sutera (1981) we apply these general considerations to a spatially one‐dimensional Budyko‐Sellers model. In fact, using two different heat capacity formulations, we test the sensitivity of such a model to stochastic perturbations. an interesting physical result, common to both versions of the model, is that, if the noise level is confined below a certain value, then the solution corresponding to an ‘ice‐covered earth’ will never be experienced.
Buoyancy effects on the turbulent transport processes in the lower atmosphere
Authors: Ueda Hiromasa , Mitsumoto Shigeki , Komori Satoru 
Published: July 2010

AbstractBuoyancy effects on the turbulent transport processes in the atmospheric boundary layer above the surface layer have been investigated. Direct measurement of heat flux and wind and temperature profiles was made by sonic anemometers and the continuous ascending and descending operation of a kitoon, to determine the eddy diffusivity of heat and the local Richardson number. the present results, along with those of a parallel study on the stratified turbulence structure in a laboratory experiment were examined by comparison with previous results in the surface layer. Under stable conditions significantly different stability dependence in the surface layer and the layer above it is recognized; in the layer above the surface layer the eddy diffusivity of heat. KH, along with the ratio of the eddy diffusivities of heat and momentum, KH/KM, decrease remarkably with the gradient Richardson number, Ri, reaching a value of KH/KHO = 0.01 at Ri = 1 and under strongly stable conditions the ratio KH/KHO varies as (Ri)−2, while in the surface layer the ratio KH/KM remains constant or decreases slightly. This contrasting behaviour in the surface layer and the layer above is presumed due to the modification of the turbulence structure and so the turbulent transport processes by the presence of the ground, as indicated by Gibson & Launder (1978). Under unstable conditions the ground effect is not so significant that results of the present observation along with the laboratory experiment may be applied to the entire region of the atmosphere. the ratios of KH/KHO and KH/KM increase as the stratification shifts from neutral to weakly unstable conditions. the ratio KH/KM takes a peak value of about 3 at Ri ∼ −0.2 and then falls gradually with increasing instability and attains the value of unity at Ri ∼ −10.0. This fact together with the increase of Km/KMO with increasing [Ri] results in a constant value of the ratio KH/KHO equal to about 6.0.
Kolmogorov constants for structure functions in turbulent shear flows
Authors: Antonia R. A. , Chambers A. J. , Satyaprakash B. R. 
Published: July 2010

AbstractKolmogorov constants in the inertial sub‐range expressions for the second‐order velocity structure function and the one‐dimensional spectrum of the streamwise velocity fluctuation have been estimated for both laboratory turbulent free shear flows and the atmospheric surface layer. A unique relation between the spectral constant α1, and the structure function constant is expected when the Reynolds number is infinitely large. the relation is found to be inadequate in both the laboratory and the atmosphere where values of α1, obtained via the structure function are, on average, smaller by about 15% than spectral estimates of α1. For the present atmospheric data the average estimate, from the second‐order structure function data, of α1 is about 0.54 in reasonable agreement with an estimate from the skewness of the structure function. the additive constant in the r3 law is approximately zero for the laboratory data.
Radiation conditions for the lateral boundaries of limited‐area numerical models
Authors: Miller M. J. , Thorpe A. J. 
Published: July 2010

AbstractAttention is focused on the use of numerical formulations of the Sommerfeld radiation condition δΦ/δt + cδΦ/δx = 0 as a lateral boundary condition. This numerical boundary condition which originally used the leap frog scheme (Orlanski 1976) is shown to be made more accurate by the use of the upstream method. In this form it is tested in a two‐dimensional model of a density current and is stable. the boundary becomes effectively transparent to incident disturbances, even under the severe test of allowing the density current head to propagate upstream and through the boundary, thus changing initial inflow to strong outflow.An analysis is presented of various extrapolation and radiation boundary conditions, involving calculation of their accuracy for waves and more general solutions. the leading terms in the truncation error are compared, and for general disturbances some have second order accuracy, while for solutions of the wave equation, it is shown that the radiation condition is third order. It can be made fourth order, for both leapfrog and upstream differencing, by the use of an extrapolation formula to give a better numerical estimate for c. This condition derives its greater accuracy from the use of values at seven (space and time) gridpoints, in contrast to the original scheme which used four, and standard extrapolation formulae which use, at most, three points.
Radar and raingauge observations of orographic rain over south Wales
Authors: Hill F. F. , Browning K. A. , Bader M. J. 
Published: July 2010

AbstractEight detailed case studies are summarized to clarify the structure and mechanism of orographically enhanced frontal rain over hills of modest height. the observations were obtained as part of a field project in south Wales in which data from a 3‐dimensionally scanning radar were combined with autographic raingauge data. the results show that the generation of orographic rain is consistent with Bergeron's seeder‐feeder mechanism, according to which raindrops from upper‐level (seeder) clouds wash out small droplets within low‐level (feeder) clouds formed over the hills. It is demonstrated that the orographic enhancement is strongly influenced by the low‐level wind speed. the largest enhancement of rainfall occurred in association with strong winds, and also high relative humidity, below 2km. the radar showed that over 80% of the enhancement occurred in the lowest 1.5 km above the hills. It also showed that the periods of enhanced rainfall were associated with the passage of pre‐existing areas of precipitation. the precise value of the upwind rainfall rate was rather unimportant in influencing the orographic increment provided the rainfall rate upwind exceeded about 0.5mmh−1, These findings are compared with the results of theoretical calculations based upon the washout model of Bader and Roach.
The effect of cirrus of varying optical depth on the extraterrestrial net radiative flux
Authors: Platt C. M. R. 
Published: July 2010

AbstractA simple model has been used to investigate the effects on the net radiation at the top of the atmosphere of a change in cirrus optical depth at various latitudes. the model employs relationships between the cloud solar albedo and the cloud infrared emittance which are based on theoretical considerations and also supported by recent observations. the model is used to predict the change in net radiant flux at the top of the atmosphere with a unit change in cloud amount and with a change in cloud emittance. Generally, tropical and mid‐latitude cirrus clouds cause a warming effect until the optical depths become large. For optical depths greater than about 12 for tropical cirrus, and about 5 for mid‐latitude cirrus, an increase in cloud will cause a cooling tendency.The importance of specifying the correct albedo‐emittance relationships is emphasized by a comparison of the solar reflection properties of cirrus using two different theoretical models; one model envisages cirrus as composed of ice (or water) spheres and the other as composed of long ice cylinders. Recent observations tend to support the cylinder model.
Inertial capture of particles by obstacles in form of disks and stellar crystals
Authors: Prodi F. , Caporaloni M. , Santachiara G. , Tampieri F. 
Published: July 2010

AbstractThe process of cloud droplet capture by falling plate‐like ice crystals has been reproduced in the laboratory by impacting streams of monodisperse spherical particles (2 < R < 22 μm) onto disk‐shaped and star‐shaped fixed obstacles in the range between viscous and potential flow. the particles collected on the upwind surface of the obstacles are counted using an optical microscope. A collection efficiency is determined for the different planar shapes under the specific experimental conditions.For the disk shape the results have been compared with those from the potential and viscous flow theories. They show that collection efficiencies computed from the potential flow theory are not representative of the actual efficiencies. Comparison with the viscous flow theory shows that in the range 0.8 < Nstk < 2 the theory fits the experimental data well. Non‐zero efficiencies have been found for Nstk lower than the theoretical cut‐off, while for Nstk < 4 the collection efficiencies are lower than theoretically predicted. This difference has been interpreted in terms of the hydrodynamic interactions between the particle and the obstacle.For the planar shapes, the collection efficiencies regularly increase with the Stokes number and depend on the surface area distribution in the models. the values of the collection efficiencies are always higher than those of the disks of equal area.
The interaction between an internal gravity wave and the planetary boundary layer. Part I: The linear analysis
Authors: Einaudi F. , Finnigan J. J. 
Published: July 2010

AbstractUsing the data obtained at the Boulder Atmospheric Observatory (BAO), we have analysed a gravity wave‐turbulence event, which occurred on 18 September 1978. A 300m tower was equipped with various sensors at eight different levels and provided information on the vertical structure of the disturbance to an unprecedented degree. These data were complemented by measurements from a nearby microbarograph network which allowed us to determine the period and horizontal wavelength of the disturbance. It was the rather accurate determination of the period of the gravity wave and its near monochromaticity that made possible the utilization of the phase average operator in separating the periodic and turbulent components of the field variables. In this paper, we concentrate on describing the wave field and on comparing it with a linear model, deferring to a second paper the discussion of the effect of the periodic disturbance on the coexisting turbulence. We show that a linear model adequately describes the observed parameters (period and horizontal wavelength) and the vertical structure of the fluctuations in the temperature and horizontal and vertical velocity components.