bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of volcanic eruptions on global turbidity, and an attempt to detect long‐term trends due to man
Authors: Dyer A. J. 
Published: February 2007

AbstractFollowing a brief discussion of early radiation measurements and the interpretation of the effects of volcanic eruptions in the light of current knowledge of the stratosphere, recent radiation data from USSR, Japan, USA and Australia are examined. Whilst the effects of the Agung eruption are clearly seen on a global scale, the analysis yields no convincing evidence for a recent world‐wide increase in atmospheric turbidity. The need for extreme measurement accuracy is emphasized in the context of long‐term atmospheric monitoring.
Multi‐level measurements of turbulence over the sea during the passage of a frontal zone
Authors: Bryant G. W. , Browning K. A. 
Published: February 2007

AbstractA Doppler radar technique originally proposed by Lhermitte (1968) has been used to measure the horizontal components of turbulence simultaneously at closely spaced height intervals from an altitude of 80m to 2500m. The observable range of turbulence scales was between about 200m and 5000m. Observations were made over the sea, with the radar situated on the Isles of Scilly, to minimize the effects of in‐homogeneities in terrain.The measurements reported in this paper were made during the passage of a warm frontal zone with strong surface winds; they show the change with height in the structure of turbulence simultaneously in both the planetary boundary layer and a free shear zone situated some way above it. Below 600m, in the planetary boundary layer, the two horizontal components of turbulence were rather similar in intensity, the total variance of horizontal velocity in the observed spectral range decreasing from 1·7m2s−2 at 80m to less than 0·1m2s−2 at 700m. For much of the observed spectral range the turbulence spectra were of the form kS(k) α k−n, with n decreasing from 1·2 below 300m to 0·7 at 700m. The lapse rate was slightly less than dry adiabatic in the planetary boundary layer with broken cloud above 300m, consistent with slight stability below 300m and some instability above. The decrease in the value of n is thought to have been due to the decrease of stability with height. The spectral scale λm increased with height reaching a value of 1·6km at 900m. Above the boundary layer for most of the time there was a placid layer several hundred metres deep and this was surmounted by a free shear layer in which the variance of velocity increased again to typically 0·5m2s−2. In the free shear layer the horizontal components of turbulence resolved parallel and perpendicular to the local shear vector were rather similar in intensity at scales less than 500m but were markedly unequal at scales between 500m and 2km. This is consistent with the occurrence of Kelvin‐Helmholtz billows with a wavelength of 1 to 2km.The Doppler radar measurements also enabled the vertical flux of horizontal momentum to be calculated. The quantity −u′w′ was found to decrease from about 0·2m2s−2 in the planetary boundary layer to about 0·01m2s−2 in the placid layer, before increasing again to about 0·1m2s−2 in the free shear layer. The energy dissipation rate ϵ was estimated from the turbulence spectra in those cases where the spectral slope n was not greatly different from 2/3. Values of ϵ decreased from 10cm2s−3 at 400m to 2cm2s−3 in the placid layer, before increasing to a second maximum of about 20cm2s−3 in the free shear zone. The rate of mechanical production of turbulence was calculated from the Doppler radar measurements of momentum flux and shear and it was found to vary with height in a rather similar manner to ϵ.
The simulation of particle motion in the atmosphere by a numerical random‐walk model
Authors: Hall C. D. 
Published: February 2007

AbstractOf all the models of turbulent motion that are based on a random‐walk technique, the simplest are ones which simulate individual particle trajectories. The accuracies of two such models are assessed by applying them to low‐level diffusion in the atmosphere. It is found that one based on a Markov‐Chain principle predicts particle concentrations over short and medium ranges which are consistent with observation. Calculations are extended to include dispersion in unstable conditions, and by postulating the dependence of several important turbulence parameters on z/L, it is possible to derive a physically realistic model.
An attempt to predict the anomalies in the monthly mean sea level pressure field a month ahead
Authors: Colgate M. G. 
Published: February 2007

AbstractThis article investigates an eigenvector technique for predicting monthly surface pressure anomalies over a network of grid points covering most of the Northern Hemisphere from the previous months' surface pressure anomalies. Eigenvector analyses on archival monthly surface pressure anomalies enabled the anomalies to be represented by natural components whose coefficients were used as predictors in linear regression models for estimating the next month's surface pressure anomaly at each of the grid points.The results show that most of the predictive value was provided by about the first ten natural components accounting for the highest proportion of monthly surface pressure variance. They gave weak, but significant, predictions even after allowing for long period climatic trends, and for persistence of surface pressure anomalies from one month to the next.Further investigation was carried out to discover the nature of the relationships, and these results are also presented.
A spectral barotropic model in horizontal empirical orthogonal functions
Authors: Rinne Juhani , Karhila Vesa 
Published: February 2007

AbstractA limited area barotropic vorticity equation model is integrated using a representation in terms of 57 horizontal empirical orthogonal functions. No boundary conditions are applied; the inflow and outflow of weather systems are absolutely free. The length of the time step in a normal centred scheme can be as much as 10 hours. With a time step of 6 hours, the model was integrated up to ten days without any smoothing, and the energy and enstrophy terms still had reasonable values. The skill of the forecasts is at least as good as, probably better than, comparison finite difference forecasts.The present climatological functions were transformed to make them closer to two‐dimensional harmonics. About half of the new functions resembled two dimensional harmonics; their wave lengths were about 3000–5000km.
Vertical wind shear measurements in the lower stratosphere
Authors: Cadet D. 
Published: February 2007

AbstractDuring two flight series of superpressure constant‐level balloons conducted in the lower stratosphere by the Laboratoire de Météorologie Dynamique, the vertical wind shear vector over 100 metres has been measured. It has been found from a record of almost two months that the r.m.s. wind shear is about 1·5 × 10−2s−1. The shear can reach 5 × 10−2s−1 in association with a breakdown of the stably stratified flow. From the records of wind shear vectors over 100 metres, 15 wind shear hodographs have been drawn which in turn have been divided in two groups. In the first group, the shear vector keeps a constant direction with time and in the second one it rotates anticlockwise with a 7 to 8·5 hour period suggesting the existence of gravity‐inertia waves in the flow. The modulus of the wind shear oscillates with a similar period but this feature is found whichever the group to which the hodograph belongs.
Turbulent fluctuations in convective conditions
Authors: Caughey S. J. , Readings C. J. 
Published: February 2007

AbstractThe dependences of the standard deviations of temperature (σr), total horizontal and vertical velocities (σuH and σw respectively) on local parameters are investigated in the atmospheric boundary layer. Useful expressions are obtained that enable rough estimates of σw and σT to be made in the bulk of the boundary layer.
The use of a multipoint filter as a dissipative mechanism in a numerical model of the general circulation of the atmosphere
Authors: Francis P. E. 
Published: February 2007

AbstractA multipoint filter for use as a dissipative mechanism in a numerical model is formulated, and some of its properties discussed. The results of three numerical experiments are compared, of which one employs a non‐linear diffusion term, another has the filter applied in the zonal direction only, and the third employs the filter in both zonal and meridional directions. The simulated climatology of the filtered experiments is seen to be significantly better in some respects than that of the experiment using a diffusion term.
A monthly analysis of the global wind stress and the ocean transports predicted from a numerical model
Authors: Bye J. A. T. , Noye B. J. , Sag T. W. 
Published: February 2007

AbstractThe monthly wind stress fields over the oceans have been calculated from marine climatic data incorporating the effect of thermal stability. The resulting angular momentum balance due to frictional torques indicates that the drag coefficients used in the study are essentially correct. A half‐yearly oscillation of zonal wind stress in high temperate latitudes in the southern hemisphere is clearly evident. The curl of the wind stress computed from the wind stress data has been used as the driving for a numerical model of the transports of a homogeneous flat‐bottomed world ocean. The variations of the ocean transports obtained are comparable with the rather sparse data except in the case of the Circumpolar Current and the Gulf Stream.
Electric field growth in thunderclouds
Authors: Winn William P. , Byerley L. G. 
Published: February 2007

AbstractWe have constructed a balloon‐borne instrument for measuring the magnitude of the horizontal component of the electric field in thunderclouds. It consists of two hollow, copper spheres 15cm in diameter held 2cm apart. The spheres spin about an axis that can be described as the perpendicular bisector of the line segment between the centres of the spheres. The sinusoidally‐varying charge that is induced on the spheres by an electric field is amplified and telemetered to ground. The amplifier and telemetry transmitters are located inside one of the spheres. The spheres also serve as the telemetry antenna. The time behaviour of the electric field in the cloud is substantially different than that at the ground. The effects of corona discharge from the ground and of the finite conductivity of the air outside the cloud seem to be negligible in the presence of the intense field near a region of charge inside a cloud. Measurements of electric field intensities inside a cloud just before and after a lightning flash when combined with measurements at the ground can be used to obtain an approximate value for the total quantity of charge in a region of cloud just before it is partially discharged by lightning. In two cases the charge just before lightning was estimated to be −120C and −160C. During a brief interval in one of our flights the electric field at the balloon reflected the time behaviour of the electric field in the cloud; the electric field increased linearly with time between lightning flashes.
The role of eddies in atmospheric water vapour transport
Authors: Wu Mao‐Fou 
Published: February 2007

AbstractIt is demonstrated by applying a theory developed by Starr that the mean meridional circulations cannot transport atmospheric water vapour across surfaces of constant mean values of water vapour mixing ratio, and that the work of transferring the moisture from zonal regions of surplus to those of deficit must therefore be accomplished by eddy components of motion.
Evaporation and advection II: evaporation downwind of a boundary separating regions having different surface resistances and available energies
Authors: McNaughton K. G. 
Published: February 2007

AbstractUsing the model and methods developed in Part I of this study, it is shown that steady‐state evaporation, downwind of a sharp boundary separating uniform regions with constant but different surface resistances and available energies, can be written as

where ϕx is a dimensionless ‘exchange function’ that decreases from unity to zero as distance increases downwind of the boundary. The symbols have their conventional meanings and the primes signify upwind values. The form of ϕx depends on the profiles of wind speed and effective diffusivity, and on the downwind surface resistance and temperature via the parameter γrs/(s+γ).Empirical expressions for ϕx are obtained from a known solution of the atmospheric diffusion equations assuming power law forms of the wind speed and effective diffusivity profiles and from a simple model assuming perfect vertical mixing and constant wind speed beneath an impermeable inversion base. These may give some indication of the form and magnitude of ϕx at small and at large distances respectively.
Determination of surface stress from vertical‐velocity spectra
Authors: Moravek D. , Panofsky H. A. , Weber A. 
Published: February 2007

AbstractMany recent measurements of vertical‐velocity spectra in the atmospheric boundary layer are combined in order to derive the dependence of the maximum of the logarithmic spectrum, normalized by surface stress, on stability. An empirical equation is suggested which fits the observations and has the proper limiting form for free convection. It is suggested that this equation can be used to derive surface stresses from relatively simple measurements of the most energetic part of the spectrum, and from a stability parameter.
Airflow and hail growth in supercell storms and some implications for hail suppression
Authors: Browning K. A. , Foote G. B. 
Published: February 2007

AbstractMultiple radar and aircraft observations of a damaging supercell hailstorm in northeastern Colorado are synthesized to show that the airflow and hail growth conformed in many respects to earlier models derived by the lead author. Some features that before had to be inferred indirectly are now substantiated and elaborated upon by direct observation. As a result of our increased confidence in certain aspects of the model we have been able to draw implications regarding the feasibility of suppressing hail by different means.The observations indicate that an important stage in the growth of large hail is the entry of hailstone embryos into the edge of an intense updraught. These embryos are grown near the storm's right flank and get carried around the forward flank under the influence of a strong environmental airstream which divides at the stagnation point and flows around on either side of the main updraught. The main updraught itself is characterized by a weak‐echo vault and the embryos grow into large hail as they follow a simple up‐and‐down trajectory over it.The vault takes on added significance in that it is a symptom of inefficiency in the conversion of cloud water to precipitation. Paradoxically it is this very inefficiency that encourages the growth of large hail by minimizing the effects of competition for the available supercooled droplets. Those recirculating embryos that find their way to the edge of the vault via the embryo curtain are seen to compete unfairly by being the first to encounter the undepleted cloud water in the vault. It is difficult to suppress their growth artificially because seeding in the main updraught at economical rates produces particles that rise above the hail growth region before they can have any significant influence on the available water.The existence of a large vault implies that the flow field is so restricting the number of embryos re‐entering the main updraught that they may be sweeping up only a small proportion of the overall cloud water. Thus there is a danger that, if a mode of seeding were used which caused additional embryos to re‐enter the updraught along with the re‐entering natural embryos, this would lead to the production of additional large hailstones. Hence, at least for some storms, doubt is cast on the credibility of the competing embryo hypothesis for hail suppression, according to which the generation of additional embryos by seeding is supposed to promote competition for a restricted amount of cloud water to the extent that none can grow large.
Tropical forcing of atmospheric motions in a numerical model
Authors: Rowntree P. R. 
Published: February 2007

AbstractThe effects of tropical forcing on the atmosphere have been isolated in two general‐circulation models – one hemispheric, one global – by eliminating other zonally asymmetric forcing such as mountains and extratropical ocean/land thermal contrasts. Tropical surface temperatures were found to force upper tropospheric geopotentials in the tropics and geopotentials throughout the troposphere in middle and high latitudes with little scale dependence up to about wavenumber 5. In the hemispheric experiment the tropical forcing generated Rossby–Haurwitz waves similar to tesseral harmonics with 3 or 5 nodes between the poles; the associated phase agreement between tropical forcing and the tropical and extratropical response was also a dominant feature of the global experiment despite the more complicated structure of the forcing field. Some aspects of the results are explicable by wave propagation theory including a strong dependence on wavenumber of the geopotential response in the tropical lower troposphere.
The approximation of particulate scattering coefficients in the determination of total ozone
Authors: Basher R. E. 
Published: February 2007

AbstractFor the purpose of total ozone measurement, the atmosphere's particulate scattering spectrum in the 305 to 340 nm interval is approximated by a parabolic function. The inclusion of this function in the usual total ozone equations gives rise to expressions which allow the experimental determination of the “true” total ozone as well as the otherwise unknown expansion coefficients of the function.The theory can be both illustrated and tested by the graphical methods which are described. The parabolic model is found to be very well supported by an experimental data sample. Of note is the finding that this sample's double wavelength‐pair total ozone values differ from the true total ozone value by as much as 0.024 atm‐cm. Some implications of the theory are discussed.
Interpretation of 8–13μm measurements of sea‐surface temperature
Authors: Cogan James L. 
Published: February 2007

AbstractThe difference between the true sea‐surface temperature and that inferred from satellite measurements of infrared radiances when viewing vertically through a cloud‐free atmosphere may be estimated to a useful accuracy for the 8–13μm radiometers of Defense Meteorological Satellite Program satellites. A simple parametric formula is developed that gives the difference to within ±0.6 K of that computed by a numerical method of solving the equation of radiative transfer. A comparison with data suggests that accuracies ⩽1.3K may be achieved relative to the actual value. Further work is necessary to confirm this accuracy because of an apparent discrepancy in the satellite data.
The flux‐angle distribution of momentum as determined from propeller anemometer measurements
Authors: Weiss A. , Allen L. H. 
Published: February 2007

AbstractFlux‐angle distributions of momentum derived from measurements of a UVW propeller anemometer were compared with results from a three‐component sonic anemometer and were found similar. Under unstable and near neutral conditions, momentum fluxes were negative both at small angles of attack for updraughts and at large angles of attack for downdraughts. At other angles of attack, the momentum flux‐angle distribution was always positive. A flux‐angle distribution algorithm is presented which shows the relative contribution made by each angle of attack of the flow to the total flux.
Thermally driven vortices: A numerical study with application to dust‐devil dynamics
Authors: Smith R. K. , Leslie L. M. 
Published: February 2007

AbstractThis paper describes a series of numerical experiments designed to explore the close interplay between the rotational, the pressure gradient, and the buoyancy, force fields in concentrated vortex flows driven thermally by heating from below. The calculations are motivated by a desire to understand the dynamics of dust‐devils and to provide a theoretical framework in terms of which both past and future observations of these vortices may be interpreted.In the model, a vortex is generated along the vertical axis of a cylindrical region of fluid bounded by a rigid (no‐slip) lower boundary, and a sidewall consisting of a rigid, impermeable upper portion and a rotating, porous, lower portion through which fluid at ambient temperature enters the cylinder and acquires rotation. The flow is driven by maintaining a circular portion of the lower boundary at a fixed temperature above ambient and fluid is allowed to enter or leave the cylinder normally through the upper boundary. For a cylinder of given size, the flow behaviour depends on the magnitudes of two nondimensional parameters which characterize the strength of the thermal forcing and of the imposed rotation. According to the sizes of these, flows with axial downflow on part or all of the axis of rotation are possible and, in some cases, a closed cell of reversed flow is possible. In each case it is possible to give a complete description of the force field balance which combines to produce the particular flow pattern.The calculations go a long way to providing an understanding of the main features of dust‐devils as observed in a careful and detailed study by Sinclair and corroborate well with the experimental results of Fitzgarrald in relation to laboratory vortices. In particular, we show how rotationally induced axial pressure gradients can supplement buoyancy forces in accelerating the vertical flow in dust‐devils as appears necessary to explain the large vertical accelerations observed near the ground in these vortices.
On the use of Taylor's translation hypothesis for diffusion in the mixed layer
Authors: Willis G. E. , Deardorff J. W. 
Published: February 2007

AbstractDiffusion measurements in a modelled mixed layer support the equivalence of an instantaneous line‐source concentration field without a mean wind and a continuous point source with a mean wind when use is made of Taylor's translation hypothesis. Taylor's hypothesis as applied to mixed‐layer diffusion appears to break down in this type of flow for values of s̀u/U > 0.5, where s̀u is the horizontal turbulence velocity component and U is the uniform mean wind. Variations in expected levels of cross‐wind integrated concentration are presented as a function of height and distance downstream from the source for a sampling duration of 4zi/U, where zi is the mixed‐layer depth.
An analysis of Manley's central England temperature data: I
Authors: Dyer T. G. J. 
Published: February 2007

AbstractManley's (1974) temperature data for central England are subjected to analyses which suggest that they should be treated as a set of monthly time series. Secular variation is found for the months October to April inclusive. Extended methods dealing with spectral analysis are used to focus attention on the mainly longer‐period oscillations. Oscillations of lengths 10–12 and 22–25 years are suggested for some months. Burg's maximum entropy spectral method has been used to resolve signals in the very low frequencies. The combined variance associated with these oscillations is shown to increase for months near mid‐year when the sun has its maximum north declination and to decrease for months on either side of June and July to a minimum when the sun has greatest south declination. Furthermore, the variance associated with months when the sun changes direction in declination and crosses the equator appears to receive boosts.