bluuebunny/crossref_metadata_2025_split huggingface dataset:
A net long‐wave radiometer
Authors: Paltridge G. W. 
Published: February 2007

AbstractAn ordinary net radiometer may be converted to a long‐wave instrument using black polythene as a filter to reject the short‐wave solar radiation. The polythene is formed into a spherical shell enclosing the radiometer, and the shell is spun continuously to neutralize the effect of short‐wave heating. Sample records are discussed.
Lamb waves in a nearly isothermal atmosphere
Authors: Bretherton F. P. 
Published: February 2007

AbstractIf the variations in sound speed c (z) and wind u (z) with height z are not too great, there is a mode of propagation of acoustic waves in the atmosphere in which the wave energy E (z) decreases exponentially with z with a scale c02/(2 – y) g (about 16 km), and the phase speed cm is given approximately by(about 300 m s−1).
The lunar semidiurnal wind variations at Hongkong and Uppsala
Authors: Haurwitz B. , Cowley Ann D. 
Published: February 2007

AbstractThe lunar semidiurnal variations of the wind at anemometer level are determined from 67 years of Hongkong data and 84 years of Uppsala data. The amplitudes agree in order of magnitude with theory, but they do not show the theoretically expected increase with latitude. The tidal wind vectors turn in the direction opposite to that predicted by the theory, confirming earlier determinations at five other stations.
Some aspects of linear lee wave theory for the stratosphere
Authors: Berkshire F. H. , Warren F. W. G. 
Published: February 2007

AbstractCertain theoretical features of high altitude lee waves for some simple two‐dimensional models are described. It is shown that some of these allow an intense local radiation of lee waves in a nearly vertical beam into the high stratosphere (similar to the leakage upwards of short radio waves in a familiar electromagnetic theory). Some associated quasi‐resonance phenomena are noted.
The Sheffield meteor wind experiment
Authors: Müller H. G. 
Published: February 2007

AbstractAn account is given of the development and application of a system for the study of high altitude winds using the radio meteor method. Three main subjects have been investigated : atmospheric tides and short term wind oscillations possibly resulting from internal atmospheric gravity waves, wind shears in the meteor zone and finally the nature of drifts obtained with the spaced receiver ionosonde technique. The Sheffield system has been steadily expanding and current developments as well as other projects linked with the Sheffield experiment are described.
Experimental measurements of the collection efficiencies of ice crystals in electric fields
Authors: Latham J. , Saunders C. P. R. 
Published: February 2007

AbstractExperimental studies have been made of the aggregation of ice crystals of mean diameter about 5 μm upon an ice sphere of diameter 0.2 cm at the same temperature. The growth rate was found to be roughly independent of temperature over the range − 7°C to − 27°C and increased with electric field strength E to exceed the field‐free value by about 15 per cent, 40 per cent and 80 per cent in fields of 500, 1,000 and 1,500 V cm−1 respectively. At higher values of E the growth‐rate was reduced because of the ejection of clusters of ice crystals from the aggregate, probably under the influence of the intense electric forces. An appreciable amount of aggregation was observed at temperatures as low as − 37°C, in the presence or in the absence of electric fields.Absolute values of collection efficiencies at a velocity of 3 m s−1 were determined at the temperatures − 7°C, − 11°C, − 17°C and − 27°C. In the absence of an electric field collection efficiencies of about 0.3 were determined at all temperatures studied. Experiments with charged ice crystals indicated that electric fields increase the growth rate by increasing the adhesion efficiency and not the collision efficiency.
A case study of frontal behaviour using a 10‐level primitive equation model
Authors: Benwell G. R. R. , Bushby F. H. 
Published: February 2007

AbstractThe predicted air motion and precipitation patterns obtained from a 10‐level primitive equation model of the atmosphere are presented for comparison with the observed patterns analysed by isentropic and Doppler radar techniques for the same occasion by Browning and Harrold (1969). There is considerable agreement over the scales of motion which it is possible to predict using the model though it is possible that further refinement in the handling of friction and topography and of the cloud physics can improve the predicted overall large‐scale distribution of rainfall.
Mid‐tropospheric frontogenesis
Authors: Bosart L. F. 
Published: February 2007

AbstractMid‐tropospheric frontogenesis is investigated for a case study in which special three‐hourly rawinsonde data are available. Isentropic analyses are made by objective means. Isentropic trajectories lead to the three‐dimensional description of the velocity field in space and time. Potential vorticity is used to check trajectories and to distinguish stratospheric from tropospheric air.Miller's frontogenesis equation is applied in two and three dimensions to an intensifying mid‐tropospheric baroclinic zone. Frontogenetical and frontolytical regions arising from twisting, horizontal confluence, vertical shear of vertical velocity and ageostrophic contributions are delineated. Typical frontogenesis magnitudes are 2°C (100 km)−1 (3 hr)−1 and 2°C (km)−1 (3 hr)−1 in two and three dimensions respectively.Previous observations of the extrusion of stratospheric air into the troposphere are confirmed.A synoptic sequence common to many occurrences of mid‐tropospheric frontogenesis is described. A simple explanation is given of the initial development of a thermally indirect circulation accompanying the early frontogenesis. Mid‐tropospheric frontogenesis seems to accompany the extrusion of stratospheric air into the troposphere during which momentum, potential vorticity, ozone and radioactivity are transported downward and southward.
An operational linear lee wave model for arbitrary basic flow and two‐dimensional topography
Authors: Vergeiner I. 
Published: February 2007

AbstractA partial survey of recent theoretical work on the flow over obstacles is presented. A model for linear, stationary mountain waves with arbitrary basic flow and two‐dimensional topography is described in detail. It contains the option of a nonlinear lower boundary condition. The wave drag is computed by three methods and the complete flow field is obtained. The sensitivity of the solutions to small changes of the upstream flow is demonstrated as a critical factor limiting the applicability of the model. The strong downslope wind storms of the Boulder area are briefly discussed in the general context of foehn phenomena. Computations indicate that resonance lee waves do not seem to be part of the mechanism of these winds.
A diagnosis of adiabatic production and destruction of kinetic energy by the meridional and zonal motions of the atmosphere
Authors: Kung E. C. 
Published: February 2007

AbstractAdiabatic production and destruction of kinetic energy by the meridional and zonal motions of the atmosphere at different latitudes from 20° to 70°N were investigated with twice‐daily observed wind and geopotential data over North America during a one‐year period.At the lower latitudes kinetic energy is produced by the meridional motion and destroyed by the zonal motion; while in the middle and higher latitudes, functions of meridional and zonal winds are reversed. Despite the general smallness of the meridional wind, the magnitude of – v δϕ/δy is comparable to that of – u δϕ/δx. As the result of the characteristic latitudinal distribution of – u δϕ/δx and – v δϕ/δ y, the resultant kinetic energy generation – V. ∇δ is maximum at the subtropical latitudes and minimum at the middle latitudes.
Momentum absorption by vegetation
Authors: Thom A. S. 
Published: February 2007

AbstractMeasurements were made in a wind‐tunnel of the drag on elements of a simply‐structured artificial crop, and of the wind profiles above and within the crop. Analysis demonstrates
that the drag force on an element of such an array can be calculated from the profile of the turbulent shear flow within the array, using the known (and unmodified), wind‐tunnel value of the drag coefficient of the individual element;
that the zero‐plane displacement (d) of an aerodynamically rough surface can be identified with the level of action of the drag on its elements; and
that von Kármán's constant = 0.41 ± 0.03.
The relation z0 = 0.36 (h – d) is suggested for the roughness parameter of vegetation of height h.Calculated values of the drag force, f, on unit column of a real stand of beans in the field, using individual‐element drag coefficients (Cd) and measured wind speeds, give f = 3.5 τ0 where τ0 is the downward momentum flux derived from the shape of the wind profile above. On the evidence of conclusion (i) and the dense and complex nature of the bean canopy, the factor 3.5 is attributed to mutual sheltering of neighbouring canopy elements rather than as evidence that the Cd – values are modified by turbulent shear flow.For the artificial crop, and for the real crop, recognition of the wind‐speed dependence of the individual‐element drag coefficients gives values of eddy viscosity, KM, almost constant in the height range h/3 < z ⩽ h and significantly larger than those found when constant drag coefficients are assumed. Constant KM within a crop canopy is consistent with the wind profile u(z)/u(h) = {1 + α(1 – z/h)}−2: an explicit expression is given for the parameter α.
The freezing of raindrops falling through strong electric fields
Authors: Smith M. H. , Griffiths R. F. , Latham J. 
Published: February 2007

AbstractSupercooled water drops of radius around 2 mm and temperature ranging from 0 to −12°C were detached from a support and could be disrupted as they subsequently fell into a region of intense electric field. Photographs showed that whereas no freezing occurred if the drops were not disrupted the fraction of drops that froze increased steadily from 0 at about −5°C to around 0.6 at –10°C if they were disrupted. The passage of a spark to the drops during disruption did not affect the freezing probability. Studies were made on about 200 drops.A series of experiments on bulk supercooled water and drops suspended from mechanical supports indicated that nucleation was initiated by means of cavitation. This conclusion was reinforced by high speed photographs showing the production and collapse of cavity bubbles when disruption occurred and indicating strongly that freezing initiated from the sites of these bubbles at the time of their collapse.
Nucleation of water drops by Brownian contact with AgI and other aerosols
Authors: Sax R. I. , Goldsmith P. 
Published: February 2007

AbstractAitken‐sized (0.01μm) particles of AgI, CuI, and ‘contaminated’ Ag2O were able to nucleate various sized water droplets in free fall (20–80μm in radius) by a direct, diffusive (Brownian) contact mechanism. The AgI aerosol was found to be the most efficient nucleator, showing a probability of 100 per cent at −16°C, 50 per cent at about −14°C, and 1 per cent at −11°C. These nucleation characteristics for AgI can be modelled from heterogeneous nucleation theory if the value of the contact parameter is assumed to be 0.70. Ag2O, passing through carrier tubing previously contaminated with iodine, was found to be only a slightly less efficient nucleating agent than AgI. CuI was found to have a nucleating efficiency corresponding to that which would theoretically be expected from an aerosol with a contact parameter of 0.55. Aerosols of the ‘pure’ oxides of silver, platinum, and chromium were unable to cause nucleation (to within detectable limits) at temperatures as low as −18°C. Auxiliary experiments indicated that the AgI aerosol had a small, but finite (10−5), nucleating efficiency at −5°C. Aitken‐sized particles of AgI did not lose their nucleating ability when captured at temperatures higher than 0°C.It is postulated that contact nucleation by the Brownian capture of Aitken particles may be an important enough process in the atmosphere to contribute significantly to the large amounts of ice which have been observed at relatively high (−10°C) temperatures in some clouds.
Observations of lee waves by high‐power radar
Authors: Starr J. R. , Browning K. A. 
Published: February 2007

AbstractA very high‐sensitivity 107 mm radar has been brought into operation for meteorological studies of airflow within the optically clear (or cloudy) atmosphere. One application of this radar has been to observe the detailed three‐dimensional structure of lee waves, using backscatter from both refractive index inhomogeneities and cirrus ‘clouds’ as means of tracing the pattern of airflow. This paper presents case studies showing how the radar has revealed the structure of lee waves downwind from the Welsh mountains. One of the case studies illustrates a steady‐state wave pattern, another illustrates an unsteady pattern with waves varying in orientation and wavelength, another illustrates a strongly damped wave pattern, and a final one illustrates two families of waves co‐existing at different altitudes. The radar method is shown to provide a direct and elegant technique for measuring lee wave properties. Although it depends on the presence of naturally occurring targets to trace the airflow pattern, such targets are found to be abundant in situations of strong lee wave activity.
A numerical model of the Adriatic for the prediction of high tides at Venice
Authors: Finizio C. , Palmieri S. , Riccucci A. 
Published: February 2007

AbstractThe present study deals with the application of a physical mathematical model of the Adriatic Sea to the problem of predicting the sea level variations at Venice. The equations of motion are considered. Taking into account the peculiar topography of the region, a unidimensional model of the Adriatic Sea is formulated. The conditions for the computation stability are determined; a first test of the model is carried out by computing the variation in time of some fundamental quantities like the mass and energy of the basin. Thereafter, the main effects due to the geometry of the basin are studied by using ideal ‘wind quanta’. Agreement is found between the results of the model and those obtained by means of classical hydrodynamics. Applications of the model to actual cases of sea level rise at Venice follow. Finally, on the basis of a critical analysis of the results, some considerations on the predictability of the phenomenon and on the requirements of the predicted meteorological fields are offered.
Momentum, mass and heat exchange of vegetation
Authors: Thom A. S. 
Published: February 2007

AbstractVegetation is treated as a complex surface roughness to which the transfer of mass or heat encounters greater aerodynamic resistance, γP, than the transfer of momentum, γD. The excess resistance (γP – γD) is equated to B/u*, where B−1 is the non‐dimensional bulk parameter introduced by Owen and Thomson (1963) and used by Chamberlain (1966, 1968). A general expression is obtained for B−1 in terms of the exchange characteristics of the individual elements of a vegetative canopy: this expression does not contain the surface roughness parameter Z0.Using exchange coefficients of individual bean leaves (Thom 1968) and the bulk momentum absorption properties of a particular bean crop (Thom 1971) the relation B−1 = (constant) u*1/3 is derived. With u* in cm s−1, the constant is 1.35 for heat exchange and transpiration, 2.18 for CO2 exchange, and 1.13 for evaporation from the crop when wet. It is suggested, partly on the basis of the lack of dependence of B−1 on z0, that the same set of equations may provide a first approximation to B−1 for many types of vegetation.Demonstrated are (i) that Monteith's (1963) method of extrapolating to zero wind speed to determine representative surface values of vapour pressure and of temperature (es and Ts) is much more rigorous if extrapolation is made to u = −B−1u* rather than to u = 0; and (ii) that the surface resistance γS, proportional to (ew(Ts) − es) (Monteith 1965) exceeds the bulk physiological, or stomatal, resistance γST of vegetation by an amount {1 − (Δ/γ).β}.B−1/u*, significant only when the Bowen ratio β is less than about 3/4(γ/Δ). (γ = 0.66 mb °C−1; Δ = dew/dT.) In particular, for B−1 = 4 and β = 0: (i) γST = 1/3 to 1/2 of γS; and (ii) use of γS with γD in the Penman equation (instead of γS, with which γD is compatible) overestimates λE by about 15 per cent.
Baroclinic instability of an idealized model of the polar night jet
Authors: McIntyre M. E. 
Published: February 2007

AbstractThe zonal current u(z), considered by Murray (1960, Section 4), as a model for the polar night jet in the lower stratosphere, has no shear in the model troposphere, and constant vertical shear uz in the stratosphere, u being a continuous function of z. The Richardson number is large. It is shown that this zonal current is always unstable, in the absence of dissipation, to small‐amplitude wave disturbances of essentially the same kind as those found in the theories of Charney and Eady. But, for numerical parameter values appropriate to the base of the polar night jet, predicted growth rates are small, and the disturbances have high zonal wave number (say 5 to 10) and are not very deep (several km at most).
A radiometer‐sonde for observing stratospheric emission due to water vapour in its rotational band
Authors: Brewer A. W. , Thomson K. P. B. 
Published: February 2007

AbstractA balloon‐borne instrument is described which measures the downward flux from atmospheric water vapour in the 20–60 μm region. The instrument uses a thermistor bolometer as the infra‐red sensor. A special infra‐red filter composed of beryllium oxide embedded in polyethylene provides the desired optical characteristics for the instrument.In‐flight energy calibration is carried out with two reference black bodies. The radiometer‐sonde is flown in conjunction with a conventional radiosonde, which provides atmospheric temperature, and pressure data for the ascent. Results have been obtained from 3 ascents. In the stratosphere the observed flux is consistent with the flux calculated for a water vapour mixing ratio of 2 × 10−6, and using published spectral data. The divergence of the flux corresponds to cooling at a rate of 0.4°C/day.
Direct measurement of vapour pressure and its fluctuations using fine thermocouples
Authors: Polavarapu R. J. 
Published: February 2007

AbstractAn instrument was developed to measure directly vapour pressure and temperature and their fluctuations compared to a moving average sampling line of 10 min. Copper‐constantan thermocouples of 75 μm in diameter are used for the measurement of fast fluctuations in dry‐ and wet‐bulb temperatures and a thermistor (100 kω at 25°C) for the measurement of mean wet‐bulb temperature. By applying the thermocouple voltages to a specially designed operational amplifier circuit, the vapour pressure is obtained as output voltage of the operational amplifier. The output voltage varies linearly with vapour pressure in the range 5‐40 mb. The values of the input and feed back resistances were theoretically determined by relating the output voltage with the Regnault's psychrometric equation. Field measurements showed that the power spectra of temperature and water vapour pressure followed −5/3 law in the frequency range 0.2 – 2.0 Hz.
The spatial variability of eddy fluxes in the constant flux layer
Authors: Dyer A. J. , Hicks B. B. 
Published: February 2007

AbstractAt the 1970 International Comparison of Turbulence Instruments held at Tsimlyansk, U.S.S.R., a large number of momentum and heat flux measurements were obtained simultaneously with two Fluxatrons. The data are analysed from the point of view of spatial variation of eddy fluxes, bearing in mind the limitations of the sensors, the variability of the eddy fluxes themselves, and the possibility of errors due to tilt. It is concluded that, at the Tsimlyansk site, the variation of heat and momentum fluxes both in the vertical (4 – 14 m) and the horizontal (1 – 150 m) is of the order 10 per cent or less. This result is in accord with traditional opinion, and provides a satisfactory experimental basis for the concept of a ‘constant flux layer’.
An investigation of the structure of baroclinic waves using three‐level streak photography
Authors: Douglas H. A. , Hide R. , Mason P. J. 
Published: February 2007

AbstractA new technique, based on streak photography of tiny neutrally buoyant particles, for studying the three‐dimensional structure of patterns of thermal convection in a rotating fluid annulus has been devised and employed in a series of new experiments on theaxisymmetric andnon‐axisymmetric régimes offlow.Ofparticular interest in connection with the energetics of atmospheric motions and transfer processes are the experimental determinations of the depth dependence and time variations of salient features of the horizontal flow patterns of fully‐devslopedbaroclinic wavesand their theoreticalinterpretation.
The critical condition for the maintenance of turbulence in stratified flows
Authors: Arya S. P. S. 
Published: February 2007

AbstractTheoretical models for predicting the critical Richardson number for the maintenance of turbulence in a stratified atmosphere are re‐examined in the light of recent observations. It is proposed that the critical condition may first arise from the failure of the maintenance of steady shear in the presence of buoyancy forces. An expression for the critical flux Richardson number is derived from the consideration of the equations of Reynolds stress and turbulent energy. This gives a range of 0.15 – 0.25 for Rfer, in agreement with the results of direct observations.
Aerial explorations of the low‐level cross‐equatorial current over eastern Africa
Authors: Findlater J. 
Published: February 2007

AbstractAn instrumented light aircraft has been used to investigate the low‐level cross‐equatorial current over eastern Africa. Using Doppler radar wind‐finding equipment the core of the current has been located and explored on four separate days, and the main features of wind, temperature, cloud and moisture content distribution have been determined. Mean fields of horizontal and vertical shear have been derived, and patterns of divergence and vertical motion around the core of the current have been deduced.
A simple climatological model of the dynamics and energetics of the nocturnal circulation at Lake Victoria
Authors: Fraedrich K. 
Published: February 2007

AbstractThe local atmospheric night‐time circulation at Lake Victoria (East Africa) is simulated by a simple model which is cylindrically symmetric. It consists of an upper layer (linearized, steady state, hydrostatic, incompressible, saturated over the lake) above a surface boundary layer (constant flux layer, log + lin profile). Analytical solutions are derived for the dynamical, energetical, and hydrological parameters. They mainly depend on the surface temperature difference between land and lake, which is the driving mechanism of the motion, and the choice of representative mesoscale transport coefficients Km, Kh. The results are compared with the climatological features of the nocturnal circulation.
The propagation and transfer properties of steady convective overturning in shear
Authors: Moncrieff M. W. , Green J. S. A. 
Published: February 2007

AbstractA conservative quantity is found as an integral of a component of the vorticity equation and used to formulate a non‐linear theory of steady, two‐dimensional convection in shear. The steering‐level and propagation speed are determined in terms of a Richardson number and a density‐scaling parameter. Case studies indicate a favourable agreement between theory and observation, especially where the Richardson number is of order unity. The parcel theory of convection is extended and the importance of the horizontal pressure gradient as a control on the updraught intensity is discussed quantitatively. Heat and momentum transfer laws are obtained in terms of the mean flow parameters, and define a non‐Fickian transfer.