bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vertical diffusion of aerosols over a city
Authors: McCormick R. A. , Kurfis K. R. 
Published: February 2007

AbstractVertical exchange coefficients for aerosol material, KA, were determined from measurements of atmospheric turbidity at λ = 0.5 μ following the motion of air flowing over Cincinnati, Ohio. Values of the coefficient for sensible heat, KH, were also obtained at the same time in some instances. Most of the values of KA were in the range 0.1 × 105 to 10 × 105 cm2 sec−1 with a marked seasonal variation of the average values. No significant variation of KA with height (100 to 600 m) was found.
Charge transfer between rigid spheres separated in an electric field
Authors: Latham J. , Freisen R. B. , Mystrom R. E. 
Published: February 2007

AbstractMeasurements have been made of the maximum separation X at which charge is transferred by means of a discharge process between two rigid spheres of radii r and R located in a uniform external electric field E. The experimental relationships between X, E, r and R are in good agreement with the calculations of Davis (1964). It was observed that for small separations charge transfer occurs even in the presence of weak external fields because the local field between the near surfaces of the spheres is greater than the external field strength by an amount that increases rapidly as their separation decreases.
The use of emissivity in atmospheric radiation calculations
Authors: Rodgers C. D. 
Published: February 2007

AbstractThe use of emissivity for calculating atmospheric radiation fluxes due to water vapour is investigated with a view to finding the most accurate way of using the approximation. It is shown that with care it is possible to adjust the emissivity so that errors in fluxes of less than 0·05 mW cm−2 are incurred, when compared with calculations using more accurate methods. This can be attained with the aid of a least squares fit of emissivity on calculated flux. ‘Laboratory’ type emissivities give errors of up to 1·3 mW cm−2.
Characteristics of billow clouds and their relation to clear‐air turbulence
Authors: Ludlam F. H. 
Published: February 2007

AbstractExisting theory of the stability of a stably stratified fluid containing a strong vertical shear suggests that unstable waves may develop when the curvature of the velocity profile changes sign and the Richardson number is somewhere less than 1/4. Some observations are described which show the properties of atmospheric billow clouds formed in travelling amplifying waves (transverse to the shear vector), on occasions when these conditions appear to be met. Static instability seems to arise in parts of the wave‐pattern where layers are inverted, and to cause a convective overturning, which may halt the wave development. The most pronounced waves occur in the upper troposphere in association with jet streams, in layers of strong wind shear which are usually dry. They probably only rarely produce clouds, and may more frequently be responsible for the clear‐air turbulence encountered by aircraft. The associated relative air velocities occur over a range of scales: up to about 1 km in the convective regions, and up to the several km associated with the billow wave‐lengths, with magnitudes of up to 10 m sec−1 or more.
An experimental investigation of the selective ion‐capture theory of cloud electrification
Authors: Abbas M. A. , Latham J. 
Published: February 2007

AbstractMeasurements made of the charges acquired by water drops and smooth ice spheres suspended in electric fields and exposed to streams of positive ions only, negative ions only, and ions of both signs present in equal and unequal concentrations were found to be in excellent quantitative agreement with the equations of Whipple and Chalmers. Electrical masking was probably responsible for the slightly increased charging obtained when the experiments were repeated with ice spheres of irregular surface structure. The charges acquired by drops falling through ion streams in electric fields are explicable in terms of the Wilson process.
Cross‐pollination between fields of sugar beet
Authors: Chamberlain A. C. 
Published: February 2007

AbstractTheoretical and experimental data on the travel and deposition of small particles in the atmosphere are used to calculate the cross‐pollination between neighbouring plots of sugar beet grown for seed.If two 20 acre plots are situated at a distance apart of 1,000 m the number of pollen grains falling on one plot which come from the other is about 4 × 10−3 of the number which come from the plot itself. The effect of varying the size and separation of the plots is calculated, and a very approximate estimate of the contribution from background sources of pollen is given.The calculations are made for average meteorological conditions. In moderately unstable conditions the proportion of cross‐pollination between plots is likely to be reduced by about 25 per cent.
Glacier resurgence at the Atlantic/sub‐Boreal transition
Authors: Mercer J. H. 
Published: February 2007

AbstractSome mountain glaciers in both the Northern and Southern Hemispheres advanced in late Atlantic and early sub‐Boreal time, between about 5,200 and 4,600 radiocarbon years ago, and several in the Southern Hemisphere reached their greatest post‐glacial extents. This suggests that the cool phase was as severe as at the start of the sub‐Atlantic (ca. 2,800 radiocarbon years ago), but many botanists believe that the fluctuation was weak. Much botanical evidence indicates that the cool phase was followed by renewed warmth and divided the Hypsithermal Interval into two parts of unequal length.
Horizontal and vertical air motion and precipitation growth, within a shower
Authors: Browning K. A. , Harrold T. W. , Whyman A. J. , Beimers J. G. D. 
Published: February 2007

AbstractTwo Doppler radars have been used to measure simultaneously the vertical and horizontal velocity components within an isolated air mass shower. Precipitation growth was found to be restricted to a small region of gently rising air within which the vertical and horizontal air velocities relative to the shower rarely exceeded 1 m sec−1. Ice crystals within the updraught were balanced by it; graupel particles developed during descent through it. The growth rate of the graupel was consistent with a cloud liquid water content about half the adiabatic value. As in many showers studied using Doppler radar, the updraught was restricted to the upper parts of the shower. The descent of the graupel beneath the updraught was associated with weak downdraughts and a local increase in the horizontal winds relative to the shower.
Global spread of volcanic dust from the Bali eruption of 1963
Authors: Dyer A. J. , Hicks B. B. 
Published: February 2007

AbstractThe global spread of volcanic dust from the Mt. Agung eruption of 17 March 1963 is assessed on the basis of the decrement of direct solar radiation. The initial injection at 8°S lodged an equatorial reservoir in the stratosphere at a height of 22–23 km. Most of the dust remained in the Southern Hemisphere, but a significant fraction entered the lower Northern Hemisphere stratosphere. Seasonal effects appeared in both hemispheres, the apparent dust amounts showing a ‘winter’ maximum of constant amplitude in any one season with a poleward progression of 40 cm sec−1 between 30° and 90° latitude. At 15°N, seasonal effects were also evident but significantly out of phase with the sequence at higher latitudes, suggesting a hand‐over in the horizontal transport process at 20°–30° latitude.Whilst the ‘winter’ maxima in the Northern Hemisphere were almost identical in amplitude for 1963 and 1964, the Southern Hemisphere data showed a significant reduction in dust amount over these years. The latter effect can be shown to imply an updraught in the lowest 2 km of the equatorial stratosphere of about 0·02 cm sec−1. By continuity, the poleward outflow from this circulation would be consistent with the observed rate of poleward progression. It is speculated that the seasonal effects could arise from an annual oscillation of the axis of this meridional circulation.Attempts to relate the observations by a diffusion model are less convincing, but in the absence of more direct information, no firm conclusion can be drawn. The paucity of suitable radiation data for equatorial regions severely limits the extent to which inferences can be made.
Seasonal and year‐to‐year ozone variations from soundings over South‐Eastern Australia
Authors: Pittock A. B. 
Published: February 2007

AbstractSeasonal mean vertical distributions of ozone obtained with Mast‐Brewer electrochemical ozone sondes are presented for Aspendale (38°S, 145°E) from winter 1965 through winter 1967. They reveal a winter‐spring maximum at the 30 to 40 mb level and a marked seasonal variation in the 100 to 350 mb region. Transient and standing eddy transport of ozone is found to be important at some levels, while vertical motion plays a significant role. The zonally averaged mean meridional transport could at most be comparable with the transient eddy term in some seasons. Year to year variations between corresponding seasons are found to be large and significant in all seasons. Large variations in the ozone content of different altitude layers occur in opposite senses, and apparently systematic patterns of change with altitude and time are found for Aspendale and also for Boulder, Colorado (40°N, 105°W). These could be related to the quasi‐biennial oscillation of other atmospheric properties. The data are not considered sufficient to establish representative climatological means.
Similarity theory and geostrophic adjustment
Authors: Gill A. E. 
Published: February 2007

AbstractThe length and velocity scales appropriate to geostrophic adjustment are discussed for both neutral and lapse conditions. Similarity arguments based on these scales lead to (i) an improved derivation of the relation between geostrophic and surface winds for the neutral case and (ii) the result that, in lapse conditions, the Coriolis force does not affect the relation between geostrophic and surface winds to the first order. Nevertheless a region of weak geostrophic adjustment may be defined. The case of inversion conditions is also discussed.
On the earth's core ‐ mantle interface
Authors: Hide R. 
Published: February 2007

AbstractRecent work on the magnetohydrodynamics of the liquid core of the Earth and on the interaction between core motions and the overlying solid mantle has yielded a number of novel results. A new type of magneto‐hydrodynamic wave has been discovered through an attempt to explain the geomagnetic secular variation; the nature of the horizontal stresses at the core‐mantle interface that are implied by the ‘decade’ fluctuations in the length of the day has been elucidated; and evidence pointing to a previously unsuspected correlation between the Earth's gravitational and magnetic fields has been found. Global‐scale undulations in level of the core‐mantle interface that are so shallow (a kilometre or so) as to be unresolvable by contemporary seismological techniques are strongly implied by some of these results.
The temperature fluctuations in stable stratification
Authors: Okamoto M. , Webb E. K. 
Published: February 2007

AbstractThe intensity and spectrum of temperature fluctuations recorded at a height of 2 m over flat grassland in stable conditions are examined. Thr results show a demarcation between two distinct régimes, ‘ turbulent ’ for Ri less than a critical value of about 0.2 and ‘ quiet ’ for larger Ri.The magnitude of the temperature fluctuations, scaled relative to z δz, is comparatively large in the turbulent régime, decreases as Ri increases towards the critical value, and remains small in the quiet régime. The temperature, while always of a typically turbulent character in the turbulent régime, is of variable behaviour in the quiet régime ‐ intermittently quiescent with occasional isolated smooth pulses (usually negative), or wave‐like with assorted frequencies, or turbulent.In the turbulent régime, the spectrum approximates to the − 5/3 power form for normalized frequencies nz/U greater than 0.6. In the quiet régime, the form of the spectrum varies unpredictably from one occasion to another.
Non‐linear baroclinic instability of a continuous zonal flow
Authors: Drazin P. G. 
Published: February 2007

AbstractIn this theoretical paper, Eady's linear model of baroclinic instability of a zonal basic flow of an inviscid non‐conducting Boussinesq fluid in quasi‐geostrophic motion is extended by consideration of non‐linearity. The method of normal mode cascade is used to find the non‐linear development of a slightly unstable linear disturbance. Amplitude vacillations are found, similar to some observed in experiments on a differentially‐heated rotating annulus. Interactions of the zonal flow and non‐linear waves are described analytically and related to instability of the westerlies in mid‐latitudes.
Dynamics of disturbances on the Intertropical Convergence Zone
Authors: Bates J. R. 
Published: February 2007

AbstractThe dynamics of disturbances on a theoretically derived Intertropical Convergence Zone (ITCZ) are studied.Radiative cooling over a hemisphere is parameterized by a Newtonian cooling law, relative to a radiative equilibrium temperature which decreases from Equator to Pole. Release of latent heat of condensation in the Tropics is treated as a function of convergence in the planetary boundary layer.The zonally symmetric field of motion which evolves in response to these sources of energy shows a concentrated region of rising motion near, but not at, the Equator. The associated low‐level wind field possesses a strong cyclonic shear.Asymmetric perturbations periodic in longitude are introduced by means of truncated Fourier series. The wavelengths are chosen to correspond to maximum instability in the ITCZ, and as such are too small to permit baroclinic instability in middle latitudes. In this way, the stability of the low latitude flow is examined while excluding middle latitude perturbations.The low‐level wind field in the vicinity of the ITCZ is found to be barotropically unstable, the wavelength of maximum growth rate being about 2,000 km. The corresponding e‐folding time is found to be of the order of two days, depending on the frictional and heating coefficients.The perturbations are allowed to grow to finite amplitude. In the initial stages of growth, the Reynolds stresses supply most of the perturbation energy. At the mature stage, the energy is provided mainly by direct conversion of condensationally produced eddy available potential energy. Further growth is then limited by frictional dissipation of kinetic energy.The mean flow is in turn influenced by the disturbance through the mechanisms of Reynolds stresses, eddy conduction and the modification of the mean flow condensational heating through boundary‐layer pumping. The influence is seen on the mean temperature and zonal wind fields, and may extent to latitudes poleward of where the perturbation amplitude in situ has decreased to zero.A framework is thus provided for viewing tropical disturbances as an integral component of the general circulation of the atmosphere.
The effect of wind shear on a puff
Authors: Richards J. M. 
Published: February 2007

AbstractThis paper corrects Hall's work in the light of more complete experiments which have established that a thermal is merely a special case of a buoyant puff. The general theory, presented here, applies to any isolated buoyant or non‐buoyant puff in shearing surroundings of uniform potential density.This theory is then applied to the case of constant mass deficit and constant wind shear, and solutions are obtained in the form of algebraic equations and simple definite integrals. When these solutions are evaluated numerically, using experimentally determined constants, it is found that the ratio of the coefficients of vertical transport of momentum and heat attributable to the puff lies in the range 0.27 σ to 0.7 σ approximately, where σ is the (small) proportion of the area of the horizontal plane through any height which is occupied by puffs. Also, realistic variation of the angle of spread of puffs is found to produce a very considerable effect on the depth of the convective layer. Only narrow puffs rise far.
Atmospheric frontogenesis models: Some solutions
Authors: Hoskins B. J. 
Published: February 2007

AbstractIn this paper are presented some solutions of analytic models in which large‐scale velocity fields act on initially large‐scale distributions of temperature. Phenomena very similar to atmospheric fronts both surface and upper tropospheric are described. At the surface front there is a tendency to form discontinuities in velocity and temperature in a finite time. The upper tropospheric front and its jet stream are associated with the descent of a tongue of stratospheric air. The main assumption underlying the models is the justifiable one of geostrophic balance across but not along the front.
The effect of variable target reflectivity on weather radar measurements
Authors: Rogers R. R. 
Published: February 2007

AbstractWeather radar signals fluctuate because of relative motions among the scatterers; these fluctuations must be accounted for in quantitative reflectivity measurements. The standard theory of weather signal fluctuations assumes targets of fixed reflectivity. In actual measurements, signals from a volume in space and over a short period of time are combined to yield an overall reflectivity measurement. Within this measurement region the reflectivity may not be constant, in which case the standard‐fluctuation theory will not strictly apply.It is shown that the theory can readily be extended to include reflectivity variations. Models of the reflectivity structure are introduced to assess the effects of these variations on reflectivity measurements. If the measurement is made by averaging the signal and applying the standard theory, it will tend to underestimate the actual target reflectivity whenever variations are present except for the special case of a radar with a quadratic receiver response. If reflectivity is measured by selecting the maximum intensity level from a sample of size N and applying standard theory, it will tend to overestimate the actual target reflectivity when variations are present. The variance of the measurement is increased by reflectivity variations, whether averaging or peak‐detecting is employed. These effects are expected to introduce only small errors (less than 5 dB) in all but extreme cases of reflectivity variations, but such errors can be significant in applications of radar to problems in hydrology or communications, where high accuracy of measurements is required.
Parameterized processes in the surface boundary layer of an atmospheric circulation model
Authors: Delsol F. , Miyakoda K. , Clarke R. H. 
Published: February 2007

AbstractA general circulation model is modified successively by adding five new features in the lower boundary layer; namely, (i) a different roughness parameter over land and sea, (ii) a Monin‐Obukhov type treatment of the turbulent transfer process in the constant‐flux layer, (iii) a Richardson number dependent parameterization for Ekman layer process, (iv) a diurnal variation of insolation, and (v) heat conduction into the soil. To assess the effect of each, the experiments are repeated by gradually increasing the complexity of the model. The circulation model has relatively low horizontal grid resolution and 9 vertical levels, and it is applied to a winter case for 14 day predictions. The results indicate that the sophistication of the boundary layer physics does not produce a particularly large effect on the synoptic scale prediction until about 7 days. Its effect may become large after 10 days. One noteworthy result is that the effect of the diurnal variation of insolation is not great for the free atmosphere but an influence is effectively transferred in the vertical, if the Richardson number dependent parameterization for the Ekman layer process is incorporated. The entire study is a preliminary test, the purpose of which is to determine the relative magnitude of each effect. A detailed comparison with observed data was not attempted.
Structure of the atmosphere in the vicinity of large‐amplitude Kelvin‐Helmholtz billows
Authors: Browning K. A. 
Published: February 2007

AbstractData are presented for 17 separate occurrences of Kelvin‐Helmholtz billows in the upper troposphere for which the crest‐to‐trough amplitude exceeded 200 m. The billows were detected in clear air by means of high‐power radar. The associated mesoscale patterns of static stability, vertical wind shear, and Richardson number have been derived from sequences of hourly radiosondes tracked by precision radar. Every occurrence of billows was found to be closely associated with well‐defined, local, wind‐shear maxima. In some cases the shear was as strong as 9 m s−1 per 200 m. The minimum value of the Richardson number when evaluated over layers 200 m deep was usually found to be in the range 0.15–0.3.
Raindrop interactions and rainfall rates within clouds
Authors: Brazier‐Smith P. R. , Jennings S. G. , Latham J. 
Published: February 2007

AbstractExperiments showed that when a pair of water drops of raindrop dimensions collide and separate in air at their relative terminal velocities satellite drops are generally produced. Although the numbers and sizes of satellites resulting from individual interactions are highly variable a typical event produces about 3 satellites each having a volume of 0.04 ViVj/(Vi + Vj), where Vi and Vj are the volumes of the parent drops.A full stochastic treatment is presented of the development of rainfall in a volume within a cloud where water is being released by condensation at a constant rate J. The production of satellites and an experimentally verified expression for the coalescence efficiency ε are incorporated into these calculations. Computations are made of the variation with time of the cloud water content, C, the rainwater content, L, the radar reflectivity, Z, the rainfall rate, P, and the drop‐size distribution. The calculations show that the crucial parameter in governing the intensity and duration of rainfall is J, and that the microphysical processes are of secondary importance; C, L and P are all insensitive to ε and the production of satellite drops. The influence upon rainfall development of the break‐up of large raindrops on attaining their maximum size within a cloud is found to be even less than that of the satellites.The drop size distribution after several minutes of growth is insensitive to the initial spectrum but is markedly dependent upon ε and the production of satellites, which tend eventually to produce a bimodal spectrum. The radar reflectivity increases very rapidly with time (typically by about an order of magnitude every 2 1/2 minutes) and depends quite strongly on ε, but is unaffected by the production of satellites.
Observation of Kelvin‐Helmholtz billows and their mesoscale environment by radar, instrumented aircraft, and a dense radiosonde network
Authors: Hardy K. R. , Reed R. J. , Mather G. K. 
Published: February 2007

AbstractOn 19 February 1970, a T‐33 jet aircraft, equipped with fast‐response meteorological instruments, obtained measurements of a wave structure and clear air turbulence. The clear air structure was simultaneously detected with a sensitive 10·7 cm wavelength radar at Wallops Island, Virginia. From a special network of radiosonde stations with separations of about 100 km, the detailed mesoscale synoptic conditions associated with the clear air structures were determined. The turbulence and wave structure occurred between heights of 2 and 3 km within an upper level frontal zone which had advanced well ahead of the surface cold front. The wave pattern consisted of two‐dimensional Kelvin‐Helmholtz billows. The billow velocity was close to the mean wind velocity of the sheared layer, and the Richardson number for the layer was about 0·15 which is consistent with the criterion for instability based on theoretical and wind tunnel results. The most intense turbulence occurred where the billows were rolling up or breaking.