bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aircraft measurements of humidity in the low stratosphere over southern England 1972–1976
Authors: Cluley A. P. , Oliver M. J. 
Published: February 2007

AbstractA frost point hygrometer installed in a Canberra aircraft of the Meteorological Research Flight has been used to make measurements of humidity in the high troposphere and low stratosphere. The results from 60 flights over southern England in the period 1972 to 1976 are reported. It is shown that above some level in the stratosphere the humidity mixing ratio (h.m.r.) becomes independent of height; the average h.m.r., by mass, in this region was (3.1±0.3)10−6. An annual oscillation in stratospheric h.m.r. of amplitude 0.4 × 10−6 and significant at the 5% level is found. The measurements are compared with an average h.m.r. of (1.9±0.2)10−6 derived from previous MRF measurements made in 1954 and 1955.
A parameterization scheme for non‐convective condensation including prediction of cloud water content
Authors: Sundqvist Hilding 
Published: February 2007

AbstractA model for non‐convective condensation processes has been developed. The model allows condensation to begin before relative humidity reaches 100%. The liquid water content of clouds is a prognostic variable of the model. The rate of condensation is a function of relative humidity and moisture flux convergence. The micro‐physical processes involved in the formation of clouds and precipitation are parameterized by assuming that the rate of precipitation formation is a function of the amount of cloud water. Evaporation from falling rain is taken into account.Quantitative tests with the model indicated that it yields reasonable evolution times and water content of clouds, and gives reasonable precipitation amounts.
Spectral distribution of solar radiation. I: Direct radiation
Authors: McCartney H. A. , Unsworth M. H. 
Published: February 2007

AbstractMeasurements of the spectral distribution of direct solar radiation, made in both wide and narrow wavebands, are reported. The measurements suggest that the wavelength dependence of aerosol attenuation in central England, in summer, can generally be described by a power law with wavelength exponent of about 1.7. Attenuation of visible radiation is reported in terms of an integral turbidity coefficient, τv, and is shown to depend to some extent on air mass origin, air masses from the continent being more turbid than maritime air masses. The mean value of τv a is 0.31 with a range of 0.05 to 0.6. The ratio of visible to total direct irradiance is found to be a linear function of τv, the constants of linearity being functions of zenith angle. From these relationships a semi‐empirical model is developed enabling spectral irradiance, visible irradiance and total solar irradiance to be estimated from arbitrary values of turbidity and zenith angle.
The application of the Rayleigh–Gans approximation to scattering by polydispersions
Authors: Box M. A. , Lo S. Y. , McKellar B. H. J. , Reich M. 
Published: February 2007

AbstractThe possibility of analysing data on light scattering by polydisperse aerosols using the Rayleigh–Gans approximation is considered. We show that this approximation may be used to determine the mean radius of a polydispersion from measurements of light scattered in the near‐forward direction by correcting for the systematic errors involved. However, neither the absolute normalization of the phase function nor the multispectral extinction data may be usefully analysed by this method to obtain the mass loading.
A pilot study of concomitant changes in total ozone and atmospheric general circulation
Authors: Newell Reginald E. , Wu Mao‐Fou 
Published: February 2007

AbstractCorrelation between monthly total ozone anomalies from long‐term monthly means shows a pattern with latitude that is consistent with the concept of Hadley cell circulation modulation. The anomalies are positively correlated with temperature at middle latitudes. Long‐term trends appear to be related to changes in the overall intensity of the Hadley cell circulation and in tropospheric meridional temperature gradients.
A numerical study of tornadogenesis in a rotating thunderstorm
Authors: Smith R. K. , Leslie L. M. 
Published: February 2007

AbstractThe structure and dynamics of tornadoes and the mechanisms leading to their formation are explored in the context of an axi‐symmetric numerical model of a tornado cyclone. The paper extends a recent study of tornadogenesis by the authors to include explicit representation of moisture effects.The calculations show that the distribution of buoyancy in the updraught of a severe ‘supercell’ thunderstorm can account for the generation and maintenance of an intense tornado when the level of rotation in the storm is within the observed range of values. The simulated vortex extends to high levels in the cloud but maximum swirling velocities occur within the lowest kilometre or two above the ground in concordance with recent Doppler radar observations.For a fixed vertical distribution of ambient temperature and moisture, the vortex strength is sensitive to the imposed circulation: if the latter is too small, the cloud updraught rotates weakly but there is no evidence of a vortex or a funnel cloud; if it is too strong, a vortex and its associated funnel cloud may form but terminate aloft. This explains why only a few apparently suitable thunderstorms spawn damaging tornadoes.The effects of surface friction on vortex strength and structure are studied in some detail and the results suggest that the terminating inflow layer at the ground may have a less important control on the vortex dynamics than has hitherto been supposed.
Catastrophes and resilience of a zero‐dimensional climate system with ice‐albedo and greenhouse feedback
Authors: Fraedrich Klaus 
Published: February 2007

AbstractAn ‘almost trivial’ climate system of geometrical dimension zero is analysed. It consists of the global energy storage which is balanced by the globally averaged net radiation (solar input minus infrared emission) with ice‐albedo and greenhouse feedbacks included. This nonlinear and time‐dependent climate system is formulated as a gradient system of a potential. It can be analysed without explicit time integration according to catastrophe theory, so that the resilience of the system, due to changes of the external parameters and due to variations of the state variable, can be determined. For the ice‐albedo or the greenhouse feedback alone, two equilibrium solutions appear: the stable ones are attractors, characterizing the present day interglacial; the unstable ones define a lower or an upper bound, respectively, for temperature changes to be absorbed by the systems. Beyond thresholds of external parameters (fold catastrophes) no equilibria exist, so that the systems attain the states of ‘deep freeze’ and ‘desert heat’, respectively. The two feedbacks combined lead to three equilibria, the stable interglacial being bounded by two unstable solutions, beyond which initial temperature values tend towards the ‘deep freeze’ or ‘desert heat’. External parameter changes can lead to structural instability occurring at fold lines, which meet at the cusp catastrophe. Outside the fold and cusp catastrophes only unstable equilibria appear, from which initial temperature values tend towards ‘desert heat’ or ‘deep freeze’ situations.
Dew and thermal lag: A model for cocoa pods
Authors: Monteith J. L. , Butler D. R. 
Published: February 2007

AbstractDew forms on cocoa pods after sunrise when the dew‐point temperature of air in the canopy rises faster than the surface temperature of the pods. Exchanges of heat and water vapour are estimated by treating a pod as an isothermal body with homogeneous thermal properties. Two treatments of this simple model are discussed. First, the heat balance equation is simplified to a form which allows the environmental limits for condensation to be derived explicitly. Second, the equation is solved numerically to find the duration and mean depth of wetness as a function of environmental variables. Consistent with observation, the thermal lag of the pod is about 1 to 3K; condensation to a depth of 10 to μm occurs when air at sunrise is almost saturated and windspeed is light.Condensation on cocoa pods is likely to be significant in the spread of Black Pod, a serious fungal disease.
A coupled ocean‐atmosphere experiment: The ocean response
Authors: Wells N. C. 
Published: February 2007

AbstractA mixed layer ocean model, which includes the effects of advection and salinity, is coupled to an atmospheric general circulation model of the southern hemisphere. The response of the ocean model is compared with observations and shown to be successful in simulating the pattern of heating occurring during the summer season, in subtropical and middle latitudes.The sensitivity of the model to changes in atmospheric circulation, advection and salinity is assessed.
Observations of downwind development of wind speed and variance profiles at Bognaes and comparison with theory
Authors: Peterson Ernest W. , Jensen Niels Otto , Højstrup Jørgen 
Published: February 2007

AbstractObservations of atmospheric flow over a change in surface roughness are reported. Both wind speed and turbulence characteristics were measured. Although the observation site departed from the ideal assumed in roughness change models, it was found that the predictions of ‘second‐order closure’ models are consistent with the observed flow.
On the use of an analytic solution in estimating eddy viscosity distribution and water vapour flux in a mature hurricane
Authors: Evans H. P. , Davies D. R. 
Published: February 2007

AbstractAn analytic solution, in p coordinates, of the dynamical equations of a mature hurricane system is used to determine the p dependence of eddy viscosity coefficients for an assumed quasi‐stationary and axisymmetric phase. The solution is based on: (i) eddy viscosity coefficients K1 and K2, describing respectively horizontal and vertical transfers of momentum, expressed as general functions of p; and (ii) the premise that the radial variation of the magnitudes of the tangential and radial components of velocity are of similar form. This leads to an integral equation for the tangential velocity. Explicit expressions for K1 and K2 are finally obtained by choosing power law forms, in the p variable, which lead to good agreement of the tangential velocity solution with observed distributions. By using this (inverse) method of calculating K1 and K2, the whole eddy system, ranging from eddies created by the very strong velocity shear close to the sea surface to those connected with violent cloud convection, is described by continuous mathematical functions. The associated temperature and condensation heating distributions are then calculated from the hydrostatic relation and the thermodynamic equation. To complete the model an integral water vapour flux condition relates the sea surface temperature to prescribed humidity conditions at the outer boundary of the model.
Eddy flux measurements using an instrumented powered glider
Authors: Milford J. R. , Abdulla S. , Mansfield D. A. 
Published: February 2007

AbstractAn instrumented powered glider was used to measure eddy fluxes of heat and water vapour within the planetary boundary layer in summer over southern England. The errors involved in the method are analysed; it appears that individual 25km runs can give heat fluxes to±15W m−2 and latent heat fluxes to ±25W m−2.The significance of individual runs was tested for internal consistency, against budget methods and, for heat fluxes, against tethered balloon measurements. With a well‐marked inversion and winds more than 5m s−1, heating rates agreed within 0.2K h−1. With light winds the discrepancies were larger; these are attributed to sampling problems. Latent heat fluxes could not be compared with budgets usefully, mainly because of the great variability encountered early in the day. The humidity measurements show the gradual establishment of the mixed layer. They show that sampling of the mean state of the boundary layer by single ascents, or of fluxes by 25km runs, may give misleading results.In light winds and deep boundary layers the heat flux carried by scales less than 3.5km was reduced, whereas the larger‐scale latent heat flux was increased, in each case by a factor of 2.
Structure parameters in the atmospheric surface layer
Authors: Bradley E. F. , Antonia R. A. 
Published: February 2007

AbstractThe behaviour of structure parameters, relating turbulence properties to other turbulence properties, has been determined from atmospheric surface layer data obtained over both land and ocean. The ratio of momentum flux to turbulence energy is found to decrease significantly as the instability increases. Structure parameters relating heat and moisture fluxes to variances of temperature and humidity fluctuations, respectively, also exhibit a strong stability dependence, under unstable conditions. Monin‐Obukhov similarity for these parameters seems to be satisfied by only part of the data examined. Neutral values of these parameters are smaller than corresponding values obtained in the laboratory boundary layer. Possible reasons for this difference are discussed.
Wind direction statistics and lateral dispersion
Authors: Sawford B. L. 
Published: February 2007

AbstractEulerian observations of wind direction fluctuations in slightly unstable conditions are analysed in terms of Taylor's statistical theory of dispersion which, with the Hay‐Pasquill assumption of similar shapes for Lagrangian and Eulerian spectra, relates the standard deviation of the crosswind material distribution, σy, to the standard deviation of fluctuations in wind direction, σθ. The dependence of the predicted cross‐wind dispersion parameter, S=σy/(σθx), where × is the distance downwind from the source, on travel time, T, is examined, and it is concluded that the data are well represented by an empirical form originally proposed by Draxler to fit observed crosswind dispersion.In contrast to direct dispersion observations, the present data show little scatter and unambiguously demonstrate that the common assumption of an exponentially decaying correlogram results in a less accurate representation. In particular, the exponential form approaches the large‐time limit, S2 α 1/T, too rapidly, and thus may be expected to perform poorly in extrapolating from a limited range of data.The consistency of the Draxler form in representing both the Eulerian measurements presented here, and direct Lagrangian dispersion observations, serves to support not only the form itself, but also, indirectly, the Hay‐Pasquill hypothesis.Evidence of a correlation between the intensity and scale of turbulence is also presented, which, if confirmed over a larger range of atmospheric stability conditions than considered here, will be very useful for estimating dispersion from wind statistics.
A numerical simulation of BOMEX data using a turbulence closure model coupled with ensemble cloud relations
Authors: Yamada Tetsuji , Mellor George L. 
Published: February 2007

AbstractA one‐dimensional version of a simplified second‐moment turbulence closure model, coupled with a recently developed cloud model, is used to simulate BOMEX (Barbados Oceanographic and Meteorological Experiment) data. Partial differential equations for the turbulence energy and a master length scale are solved. Simulated mixing ratios of water vapour, virtual temperatures and horizontal wind speeds are compared with observations. Horizontal wind speeds agree quite well; however, simulated temperature and mixing ratio of water vapour at the end of the fourth day are about 2K and 1.5 g kg−1 higher, respectively, than corresponding observations; possibly this is due to the fact that the surface temperature used in the simulation is too high. Mean liquid water, cloud volume, liquid water variance, turbulence energy and eddy viscosity coefficients are presented, but data for these variables are not available for comparison. Surface momentum, heat and moisture fluxes are also presented and are compared with data. Sensitivity studies indicate that the simulated mixing ratios of water vapour agree best with observations when both vertical wind and horizontal advection obtained from the data are included.The present study is encouraging, although further research is required to improve the model and to develop confidence in its predictive capability.
Theory of the sunpillar
Authors: White R. 
Published: February 2007

AbstractThe radiance distribution predicted by classical physical models of the sunpillar is calculated. It is shown that the loci of constant tip angle calculated by Stuchtey differ from loci of constant radiance only as a result of variation of the reflection coefficient with arc distance from the source. At least at low source elevations, crystals oscillating about a horizontal equilibrium position are more efficient as pillar producers than those rotating about horizontal C6 axes, but there is no conclusive evidence that the latter never produce pillars. It is shown that the variation of the cross‐sectional area of the incident beam has important effects, such as production of a minimum radiance at the source. Neglect of this factor by recent workers casts doubt on some of their conclusions.No evidence is found to suggest that the classical models need replacement: tentative suggestions are made that diffraction, transfer effects, and modes other than external reflection in crystals rotating about horizontal C6 axes may enhance the formation of pillars at higher source elevations.
The angular distribution and interception of diffuse solar radiation below overcast skies
Authors: Steven M. D. , Unsworth M. H. 
Published: February 2007

AbstractThe angular distribution of diffuse radiation was measured from May 1976 to May 1977 with a set of purpose‐built actinometers. Radiance distributions for 98 overcast hours were fitted well by an expression similar to the conventional function for a ‘standard overcast sky’ (SOC). However, values of the coefficient b averaged 1.23, significantly smaller than for the SOC (b = 2). Expressions for the interception of diffuse irradiance by sloping planes are discussed.
A case study of a subsynoptic disturbance in a polar outbreak
Authors: Oerlemans J. 
Published: February 2007

AbstractA subsynoptic disturbance, occurring in an outbreak of polar air over northwestern Europe, is studied by using routine observational data. The disturbance showed a characteristic length scale of about 150km, a time scale of 4 hours, caused a surface pressure drop of only 1 mb, but brought up to 20 mm of precipitation in the coastal region of the Netherlands.The observational analysis suggests that the disturbance was a warm‐core system driven by latent heat release and triggered by forced lifting along the coastline, which activated a weak trough filled with potentially unstable air.
The blocking of middle latitude westerly winds by planetary waves
Authors: Austin J. F. 
Published: February 2007

AbstractA study of hemispheric data suggests that the splitting of westerly winds by blocking anticyclones is initially due to simple interference between stationary planetary waves with very large amplitudes but normal phases. A simple model is then used to investigate Green's hypothesis that the blocking anticyclone, once formed, can be maintained by baroclinic waves travelling in the split jet. The results are in good agreement with observations, particularly the vertical structure. A resonance seems likely at zonal wavenumber four.
A two‐dimensional numerical study of horizontal roll vortices in the neutral atmospheric boundary layer
Authors: Mason P. J. , Sykes R. I. 
Published: February 2007

AbstractThe dynamics of large‐scale, horizontal roll vortices in the neutral planetary boundary layer are investigated by means of a two‐dimensional numerical model. The rolls are assumed to be two‐dimensional and are calculated explicitly, while small‐scale turbulence is parametrized by a mixing‐length hypothesis. Although buoyancy effects are never negligible in the atmosphere, the assumptions of the turbulence modelling are supported by atmospheric observations of large eddies which are highly elongated in a direction close to that of the geostrophic wind, together with the observed partitioning of turbulence energy between the large eddies and a distinctly smaller scale. The results indicate a strong sensitivity to the roll orientation, and also the presence of a slow variation on the Coriolis timescale.
Diurnal and seasonal variation of convection in the wind‐mixed layer of the ocean
Authors: Woods J. D. 
Published: February 2007

AbstractBuoyant convection in the wind‐mixed layer of the ocean provides a source of turbulent kinetic energy that is restricted to a layer whose depth, C, is equal to, or less than, H, the depth of the mixed layer. At night C = H, and convection contributes significantly to deepening the mixed layer by turbulent entrainment. During most of the day, when the rate of heat input by the Sun exceeds the rate of surface heat loss by evaporation, conduction and long wave radiation, C < H and convection does not contribute to entrainment. When C < H, C = D, the thermal compensation depth, whose magnitude is independent of any consequences of turbulent mixing or entrainment. D can be calculated from a model of solar energy absorption in the ocean. Such a model is used to determine the diurnal variation of D at selected locations. The shape of this variation (a ‘top hat’ distribution) suggests the use of two parameters Dmin (the noon value) and P10 (the proportion of each day for which D < 10m). The seasonal and meridional variations of these parameters reveal the corresponding variations in the contribution of convectively generated turbulent kinetic energy to mixed layer deepening by turbulent entrainment. The parameter P10 can be used to take account of the daytime quenching of convection by the Sun in climate models that do not resolve the diurnal cycle.
Mass divergence in tropical weather systems Paper II: Large‐scale controls on convection
Authors: McBride John L. , Gray William M. 
Published: February 2007

AbstractComposited summertime deep cumulus convective weather systems are investigated over three tropical oceans. The occurrence and intensity of the convection are governed by various large‐scale forcing mechanisms, such as ITCZ convergence, easterly waves, and differences in diabatic heating between the disturbance and its clear or mostly cloud‐free surrounding region. Vertical profiles of divergence and vertical velocity for the weather systems are analysed from the point of view of trying to establish the relative importance of each large scale control on convection.The dominant forcing in the Western Pacific and the GATE region is ITCZ convergence, with important secondary roles being played by differential radiative‐convective heating, easterly waves and convective feedback. In the Western Atlantic trade wind region there is no contribution from ITCZ convergence; the vertical motion of a typical weather system is consequently much weaker than in the other regions.In all three regions the contribution to vertical velocity from frictional convergence is shown to be quite small.A large diurnal modulation of convection is observed. In the GATE region a diurnal variation is documented for the low‐level convergence into the ITCZ. A physical mechanism is proposed to explain this phenomenon.It is shown that the actual observed vertical motion of the summer‐time tropical oceanic weather systems comes from a combination of forcing mechanisms and does not result from any individual large‐scale control acting by itself. It is important that any idealized picture of tropical weather systems be broad and flexible enough to account for the large regional and multi‐scale forcing mechanism differences which exist. A simple ‘easterly wave’ or ‘ITCZ’ model of organized tropical convection is inadequate.