bluuebunny/crossref_metadata_2025_split huggingface dataset:
A systematic error in the measurement of frost point using a Meteorological Office Mk 3 hygrometer
Authors: Oliver M. J. , Cluley A. P. 
Published: February 2007

AbstractA series of laboratory and airborne experiments were undertaken to investigate a possible systematic error in the measurement of frost point using a Meteorological Office Mk 3 hygrometer. It was found that temperature gradients in the hygrometer thimble could cause the temperature sensor to read frost points too low by over 2 degC. The error was greater at low thimble temperatures. A table of corrections is presented for frost points in the range −40 to −85°C.
Measurements of turbulence by an instrumented aircraft in a convective atmospheric boundary layer over the sea
Authors: Nicholls S. 
Published: February 2007

AbstractThe turbulence measurement instrumentation system installed on the Meteorological Research Flight Hercules aircraft is described and discussed with particular reference to the measurement of atmospheric boundary layer parameters. As an illustration, the structure of a simple, shallow, unstable boundary layer over the sea is discussed. Semi‐organized motions, perhaps in the form of convective rolls or bands aligned roughly parallel to the wind direction, are shown strongly to influence the transport of water vapour and momentum above the surface layer. Where possible, measurements are compared with previous results.
On the concept of available potential energy
Authors: Pearce R. P. 
Published: February 2007

AbstractThe available potential energy of the atmosphere is defined as the property of the atmosphere for which the source is energy generated by the distribution of the heat sources and sinks, i.e. their deviations from the mean heating rate, and the sink its conversion to kinetic energy; the unavailable potential energy is defined as having as its source the mean (uniform) heating rate and its sink the energy made available for conversion by the heating distribution, i.e. the APE source. These definitions lead to an expression for the APE which, to a good approximation, is proportional to the global mean temperature variance. This partitions into zonal and eddy components and, in addition, a component involving the mean temperature distribution in the vertical. Associated with the latter is a source term determined by the mean heating distribution in the vertical and sink terms corresponding to its conversion to the other two components, these terms being proportional to the conversions to KE. This additional component is referred to as the static stability component of available potential energy (SAPE). The zonal and eddy components, which depend on the temperature variance on isobaric surfaces, are together referred to as the baroclinicity component of the APE.The relationship between this form of the APE and that proposed by Lorenz is discussed in detail. The physical interpretation of the conversion between zonal and eddy APE, associated mainly with poleward heat (enthalpy) transport down the mean meridional temperature gradient is found to have its analogue in the conversion from the static stability component to the other two components which is associated with upward heat transport down the vertical temperature gradient. The concepts are illustrated for a numerical simulation of the life cycle of an idealized baroclinic wave. It is further shown that this definition of APE extends quite naturally to the description of the energetics of dry and moist convection and its conversions can be calculated without difficulty even if there exist regions in which the lapse rate is dry adiabatic. The roles of frictional and non‐frictional heating in the general atmospheric circulation are discussed and, finally, comments are made on the concept of adiabatic mass redistribution and the definition of a reference state for APE in the light of the approach adopted here.
Direct evaluation of aerosol mass loadings from multispectral extinction data
Authors: Box Michael A. , McKellar Bruce H. J. 
Published: February 2007

AbstractWe derive a formula for the evaluation of the total volume of aerosol in a column, and hence for the aerosol columnar mass loading, from multispectral extinction data. This formula is exact in the ‘anomalous diffraction’ approximation, and reasonably accurate for Mie scattering, over a fairly wide range of refractive indices typical of real aerosols.
Numerical simulations showing the role of the downdraught in cumulonimbus motion and splitting
Authors: Thorpe Alan J. , Miller Martin J. 
Published: February 2007

AbstractThe results of two numerical simulations are presented. The first shows the classic deviatory motion of a multicell system, to the right of the mean tropospheric wind. The second, having a more highly sheared environment, produces a storm which splits into two after the formation of a wedge‐shaped downdraught outflow.Both simulations highlight the important role played by the downdraught dynamics in establishing a regenerative forcing mechanism. In the higher shear case the updraught core exhibits a large downshear slope with rain falling into the inflow region, thus producing a split updraught core and eventually two distinct cells.The strength and direction of the relative inflow lead to the different structures and life histories of the two storm systems. The importance of the flow relative to the cell is demonstrated by considering the effects of Galilean transformations of the coordinate system.
The steady‐state format of global climate
Authors: Paltridge G. W. 
Published: February 2007

AbstractIt can be proved for certain small‐scale convective heat transfer processes that the preferred steady‐state mode is one of maximum entropy production. The constraint is more or less equivalent to one of maximum kinetic energy dissipation or of maximum convective heat transport. Evidence is accumulating that the same constraint may apply on the much larger scale of the earth‐atmosphere system. The concept is accepted as the basis of a purely thermodynamic model of the mean annual global climate. The model allows a prieri calculation of the broad‐scale geographic distributions of cloud, surface temperature, horizontal energy fluxes in the ocean and in the atmosphere, net radiant energy inputs, etc. The agreement with observation strongly supports the basic concept. It suggests also that, to the extent allowed by the degrees of freedom in the dynamics, the partition of atmospheric and oceanic energy flow is determined by a requirement to equalize the local dissipations in the two media.
A numerical investigation of variations in the drag coefficient for air flow above water waves
Authors: Taylor P. A. , Gent P. R. 
Published: February 2007

AbstractNumerical predictions of the drag coefficient for air flow above a train of monochromatic water waves are presented. The air is assumed to be neutrally stratified, and the water surface aerodynamically rough, characterized by a local small‐scale roughness length Zo associated primarily with capillary waves. Details of the numerical model are described in an earlier paper. The variation of the drag coefficient with wave slope and with the ratio of wave phase speed to friction velocity is analysed. The applicability of the results to the sea is discussed in relation to the many observations of the drag coefficient.
Separation effects in Ekman layer flow over ridges
Authors: Mason P. J. , Sykes R. I. 
Published: February 2007

AbstractTwo‐dimensional numerical integrations of the Navier‐Stokes equations for flow of an Ekman layer ove a ridge on a range of length scales corresponding to large Rossby numbers are presented. The results are compared, where appropriate, with numerical solutions of the triple deck equations of boundary layer flow For steady flow agreement is good and, as predicted by triple deck theory, the net change in total force or the domain is small for homogeneous flow. An increase in force arises either through gravity wave radiation when triple deck predictions agree well, or when the ridge is sufficiently steep to give eddy shedding.
Destruction at the ground and the diurnal cycle of concentration of ozone and other gases
Authors: Garland J. A. , Derwent R. G. 
Published: February 2007

AbstractSeveral gaseous pollutants show marked diurnal variations, with daily maxima and nightly minima of concentration. The nocturnal decrease is held to be due to deposition at the ground, with isolation of the lowest layers of the atmosphere from the air above by the nocturnal inversion. In the morning, deep mixing is re‐established and brings material down to the surface from higher layers. Ozone exhibits this behaviour clearly and is convenient to study as an example, but it has been suggested by some authors that changes in the rates of gas‐phase reactions that produce and destroy ozone are responsible for the daily cycle of concentration. We have studied the destruction of ozone at the surface and conclude that this process can probably explain the nocturnal decline of concentration near the ground.Deposition rates for ozone were deduced from profiles of concentration, windspeed and temperature measured over grassland in southern England. The mean deposition velocity was 0.58cms−1 by day and 0.29cms−1 by night. The aerodynamic and surface components of resistance both increased at night, but the behaviour of the surface resistance was not consistent with stomatal control.Observations of the nocturnal decrease of ozone concentration at the same site are reported. A computer simulation of the behaviour of ozone, with a description of the nocturnal boundary layer due to Wyngaard, duplicated the major features observed, and a procedure for predicting the height of the mixed layer and the rate of decline of ozone concentration at the ground gave good agreement with observations on many occasions.The nocturnal behaviour has important consequences for the measurement of mean concentrations in the atmosphere, and for long‐range transport. Observation of the daily cycle of concentration may indicate the likely importance of the surface sink for many gases.
Measurements of the kinematics of natural hailstones near the ground
Authors: Lozowski E. P. , Beattie A. G. 
Published: February 2007

AbstractHigh speed photography of 48 natural hailstones falling in a hailshaft near the ground has led to new results concerning the vertical, horizontal and tumbling motions of quasi‐conical hail in the size range 0.5 to 1 cm. The relation vz = 12.43 D1/2 max provides an estimate (±1.5ms−1) of the sea level fall speed of these hailstones, while deviations from this relation and variations in the horizontal velocity components indicate the possible influence of air turbulence, particle shape and density, and tumbling motion on the free‐fall hailstone kinematics. At least one third of the hailstones were tumbling or oscillating while falling.
Annual and semiannual waves in the temperature of the mesosphere as deduced from Nimbus 6 PMR measurements
Authors: Crane A. J. 
Published: February 2007

AbstractThe annual and semiannual waves in zonal mean temperature in the mesosphere are analysed using data from the Nimbus 6 pressure modulator radiometer (PMR). The observation that the annual temperature cycle in the extratropical upper mesosphere has almost exactly opposite phase to the solar cycle and explains over 90% of the total variance suggests that the mechanism which maintains the temperature structure is very closely linked with the annual solar cycle. The occurrence of a peak in the semiannual oscillation around 64° latitude in the southern hemisphere contrasts with an amplitude maximum nearer to the pole in the northern hemisphere, reflecting the different characteristics of sudden warmings between the hemispheres which are the cause of this wave. In the upper mesosphere the semiannual wave has similar phase at all latitudes. This gives rise to a pronounced semiannual wave in the global mean temperature of the upper mesosphere.
The polar low as an extratropical CISK disturbance
Authors: Rasmussen E. 
Published: February 2007

AbstractIt is suggested that the polar low is basically a thermal instability phenomenon much akin to a small tropical cyclone. A quasi‐geostrophic model is employed in order to find small‐scale unstable CISK‐forced disturbances in a barotropic basic flow with a vertical structure similar to that actually observed during a polar air outbreak. Case studies of some polar low developments in some ways support a convective hypothesis according to which the polar low is driven by latent heat released in convection clouds.
Forecasting and general circulation results from finite element models
Authors: Cullen M. J. P. , Hall C. D. 
Published: February 2007

AbstractA 5‐level global model is described in which finite element methods are used to describe the variations of fields in the horizontal. Three versions of the model are used: two use velocity components as dependent variables but differ in horizontal resolution; the third uses stream function and velocity potential. The results show that the finite element models are competitive with existing finite difference models but proper comparison is difficult because of the large effect of certain special features of the models, for instance the treatment of the poles. The change in dependent variable has a much greater impact on the results than a change in resolution with no change in formulation.
A one‐dimensional time‐dependent model for small cumulus
Authors: Ryan B. F. , Lalousis P. 
Published: February 2007

AbstractA one‐dimensional cloud model with a variable radius has been developed. The model is capable of being tuned to give internal cloud properties (such as liquid water content) that are in reasonable agreement with field observations. Unlike many other one‐dimensional cloud models, the cloud base rises only slowly over the lifetime of the cloud. The model is compared with two other types of one‐dimensional model: a steady‐state model and an Eulerian time‐dependent model.
A diagnostic study of the long‐term balance of kinetic energy of atmospheric large scale motion over the British Isles
Authors: Holopainen E. O. , Eerola K. 
Published: February 2007

AbstractCalculations of the various terms in the kinetic energy budget of the atmosphere were carried out for the area of the British Isles using aerological data for the period 1974–76. The residual term (‘dissipation’) necessary to balance the equation is interpreted as representing the forcing effect of sub‐grid scale processes. The results are compared with earlier calculations for the same area, and with corresponding results for the area of North America.The results show that the annual mean dissipation of kinetic energy in the boundary layer (below 850 mb) is 3.4 Wm−2, which is considerably larger than that found for the area of North America. The corresponding values for winter, spring, summer and autumn are 6.2, 2.3, 2.0 and 3.2 Wm−2, respectively.Results for the British Isles in the free atmosphere are very different from those for North America. Whereas there is, on average, generation of kinetic energy by pressure forces (−V.▽Φ > 0) and net export of kinetic energy over North America, the contrary is true over the British Isles.The mean residual term in the kinetic energy equation over the British Isles is relatively small between about 850 and 400 mb. However, higher up, the term is definitely positive, indicating (if interpreted physically) an energy input from sub‐grid scales to the synoptic scale: a situation opposite to that prevailing, in the annual mean, over North America. It is suggested that this ‘negative viscosity’ phenomenon may in general be typical for diffluent flows (such as are found in the exit areas of jet streams) and could be due to horizontal and vertical convergence of momentum flux associated with jet streaks and other sub‐grid scale phenomena.
On the broadening of a droplet distribution by turbulence near cloud base
Authors: Manton M. J. 
Published: February 2007

AbstractThe effect of turbulence on the development of the distribution of droplets growing by condensation in a cumulus cloud is investigated. Both small scale and large scale turbulence are shown to produce some broadening of the distribution. Turbulence with high vertical coherence is found to generate a bimodal distribution for which the dispersion increases with height above cloud base while the mean radius increases slowly.
Numerical weather prediction for GATE
Authors: Krishnamurti T. N. , Pan Hua Lu , Chang Chia Bo , Ploshay Jeff , Walker David , Oodally A. Wahed 
Published: February 2007

AbstractThe results of a few numerical weather prediction experiments that utilize GATE data are presented. Aside from some simple forecasts based on single‐level models, experiments with a multilevel model examine the roles of some of the physical processes. They include the influences of diurnally varying radiative effects, effects of cloud feedback on shortwave and longwave radiation, the heat balance of land surfaces, and the influence of West African orography in the 3‐ to 4‐day range of numerical weather prediction. Data sources for these experiments include surface and upper air observations from the World Weather Watch, GATE ships, upper winds from commercial aircraft, low‐ and high‐level cloud winds from geostationary satellites, winds from GATE research aircraft, and special surface observations from a ship data collection. The data analysis is based on a successive correction method where a subjective interface is also incorporated. The initial data are further subjected to a static as well as a dynamic initialization process.The major results are that single‐level forecasts are very promising with this data set if they are carried out at 700 mb. The multilevel adiabatic experiment produces very poor predictions due to lack of adequate vertical coupling between the lower and the upper troposphere and due to its inability to describe the broad‐scale monsoons. The diurnally varying heat balance of the earth's surface and cloudiness in radiative calculations appear to be important in the 3‐ to 4‐day range of prediction of African disturbances. In this paper we show some interesting vertical structure diagrams of African waves based on the results of numerical weather prediction, which exhibit a close similarity to the structures of composite GATE disturbances constructed by Professor R. J. Reed and his associates.
Katabatic winds: A field case study
Authors: Manins P. C. , Sawford B. L. 
Published: February 2007

AbstractResults of a case study of katabatic winds utilizing tethered balloon profiling equipment are presented and discussed. The data are unique in the detail they provide of both vector wind and potential virtual temperature throughout the flow.It is concluded from the data that the one‐dimensional models so far proposed in the literature are inappropriate. Direct computation shows that the divergence of radiation responsible for cooling the air is much smaller than the surface radiation flux used in these models. The inadequacy of these models is not due to the underlying assumption of temporal invariance, but rather the implication is that the flow is significantly three dimensional.Use of surface stress as the retarding stress in the dynamical balance is also shown to be erroneous, at least so long as ambient wind does not assist the katabatic flow. The stress between the flow and the ambient air is much more important and this stress is inextricably tied in with the downslope development of the flow which is thus inferred to play a major part in the dynamics of katabatic winds.Katabatic flow is an example of an internal mixing process. The data are shown to suggest a critical gradient Richardson number of about 1/4 for the maintenance of internal mixing above slope flows.
Non‐selective absorption by atmospheric water vapour at visible and near infrared wavelengths
Authors: Tomasi Claudio 
Published: February 2007

AbstractMeasurements of the atmospheric optical thickness at ‘window’ wavelengths in the visible and near infrared region have been obtained from data of direct solar radiation through clear and hazy atmospheres. At these wavelengths, the weak attenuation of the atmosphere is due to Rayleigh scattering, non‐selective absorption by water vapour and extinction by particulate matter.Since non‐linear dependence may exist between the particulate matter optical thickness and the preci‐pitable water vapour, seasonal sets of atmospheric optical thicknesses have been selected, which present linear and direct correlation with the precipitable water vapour, at each wavelength. Thus the slope of the regression line of optical thickness on precipitable water vapour is the sum of (i) the non‐selective absorption coefficient of atmospheric water vapour and (ii) the linear variation coefficient of the particulate matter optical thickness as a function of precipitable water vapour. The latter coefficient has been evaluated at the various wavelengths for each set of data, by examining the spectral series of data in terms of Angström's expression and determining linear relationships between atmospheric turbidity parameters and precipitable water vapour. Each monochromatic estimate of the non‐selective absorption coefficient of water vapour has been obtained as the difference between the slope of the regression line and the linear variation coefficient of the particulate matter optical thickness. The resulting estimate has been related to the vertical distribution of absolute humidity, in order to determine the mass absorption coefficient of water vapour at unit air pressure.
Evaluation of empirical expressions for the estimation of hourly and daily totals of atmospheric longwave emission under all sky conditions
Authors: Arnfield A. J. 
Published: February 2007

AbstractMeasurements of hourly totals of atmospheric longwave emission, made during summer and autumn seasons in southern Ontario, are used to evaluate the performance of several empirical estimation equations. Under clear sky conditions, the formulae of Swinbank and of Idso and Jackson gave similar results, with daily totals estimated to within measurement error, but with systematic deviations in hourly values which resembled those reported in earlier studies. The timing of these errors, however, suggests that previous hypotheses for such deviations may be invalid. The accuracy of estimates made with the formula of Brunt depended very strongly upon the regression parameters selected. Under all sky conditions, use of the Idso and Jackson formula, with adjustment for cloud type and amount following Bolz, yielded estimates of variable accuracy on an hourly basis, but daily (and similar period) totals are estimated with an error similar to that of the original measurements.
Velocity spectra and cospectra and integral statistics over Arctic leads
Authors: Andreas Edgar L. , Paulson Clayton A. 
Published: February 2007

AbstractFrom the high frequency velocity measurements of the AIDJEX Lead Experiment we derive estimates of u and w spectra and uw cospectra both above Arctic leads and over relatively smooth pack ice. The measurements over the leads are unique for two reasons: they were made within a geophysical internal boundary layer (IBL) resulting from a large step change in surface temperature; and all were made within 50cm of the surface.The intense mixing within the IBL and the nearness of the measurements to the surface affect the shapes of all the over‐lead spectra and cospectra. The u and w spectra have rounded peaks and no inertial subrange. The cospectra contain substantial energy at frequencies typically in the inertial subrange. Coherence spectra are greater than zero out to nondimensional frequencies of order ten. Despite the anisotropy of their origin, however, normalized spectra and cospectra plotted against the nondimensional frequency fz/U and grouped according to Reynolds number collapse into single curves.The integral statistics (w2/ − uw)1/2 and (u2/ −uw)1/2 have values smaller than those usually reported, as a consequence of both the mixing and the low measurement height.