bluuebunny/crossref_metadata_2025_split huggingface dataset:
An airborne study of vertical structure and microphysical variability within a small cumulus
Authors: Blyth A. M. , Latham J. 
Published: July 2010

AbstractOn 27 July 1981, as part of the CCOPE experiment, the University of Wyoming King Air research aeroplane made penetrations at six levels ranging from 590mb (‐4.9°C) to 770mb (7.2°C) through a nonprecipitating, unglaciated cumulus cloud whose top was at about 560 mb (‐7°C) and base about 780mb (8°C). the entire flight sequence—from the top downwards—took about six minutes. Principal measurements were of droplet size distribution N(d), number concentration N and liquid water content L, measured at 10 Hz (≃10m spatial resolution); drop‐count N′ (50Hz, ≃2m); temperature T. Also we calculated the fraction F of cloud base air in the mixture sampled (1Hz, ≃100m). the cloud was substantially subadiabatic throughout the volume studied. Paluch analyses, the observed air motions near cloud top, buoyancy profiles and the observed distribution of L and F with altitude demonstrated that the cloud was diluted principally by entrainment from cloud top. Considerable scatter was found in all microphysical and thermodynamic variables on all spatial scales. Large variations in L were primarily attributable to fluctuations in N and N′. Bimodal spectra were sometimes found at the interface between statistically smooth and highly variable regions. the breadth of the droplet spectra and the size of the largest droplets in the condensate spectrum were not systematically related to the degree of dilution. Calculations showed that a small fraction of the droplets (≃100 litres−1) exhibited superadiabatic growth of up to 4 m̈m diameter at the intermediate levels, but not near cloud base or cloud top. Support for the idea that droplets in lower concentrations (≃10 litre−1) grew even faster was provided by 1‐D probe measurements of droplets of up to 75 m̈m diameter in the central and upper regions of the cloud.
Evaporation from sparse crops‐an energy combination theory
Authors: Shuttleworth W. James , Wallace J. S. 
Published: July 2010

AbstractA one‐dimensional model is adopted to describe the energy partition of sparse crops. Theoretical development of this model yields a combination equation which describes evaporation in terms of controlling resistances associated with the plants, and with the soil or water in which they are growing. the equation provides a simple but physically plausible description of the transition between bare substrate and a closed canopy. Although the aerodynamic transfer resistances for incomplete canopies have, as yet, no experimental justification, typical values, appropriate to a specimen agricultural crop and soil, are shown to have limited sensitivity in the model. Processes which require further study if the equation is to be used to calculate evaporation throughout a crop season are also discussed.
Steady convection in pressure coordinates
Authors: Moncrieff M. W. 
Published: July 2010

AbstractConservative properties of steady flow in non‐hydrostatic pressure coordinates are used to formulate theoretical models of deep convection. the pressure coordinate analysis extends the range of analytic solutions previously obtained in height coordinates, because the effect of the variation of density with height is included and is more useful for comparison with observations and the implementation of dynamical cloud models in convective parametrization schemes. Previous models are made more realistic by including a non‐constant thermodynamic lapse rate. In the case of steering‐level convection, this is shown to be a simple reinterpretation of the constant lapse rate model, while for propagating convection there are more fundamental implications; downstream propagating solutions cannot exist if the net work done by the pressure field is zero, while upstream propagation, although dynamically possible, is not observed.
Remarks on the predictability properties of two‐ and three‐dimensional flow
Authors: Vallis Geoffrey K. 
Published: July 2010

AbstractThis paper discusses the relationship between certain well‐posedness results for the equations of motion and simple phenomenological arguments pertaining to the predictability of the flow fields. the barotropic and quasi‐geostrophic equations have been shown to be well‐posed under certain conditions. From this, it has been inferred that Lorenz's conjecture of finite predictability time for any scale of initial error is false. Such an inference is justified in the error energy may be made small by confining the error to small scales of motion. It is shown that this may be achieved, given finite bounds on the vorticity. It is also shown that there is no contradiction between essentially Kolmogorovian phenomenological arguments and the well‐posedness of the equations, since the conditions uder wich a finite predictability time is predicted by the former are those then phenomenological trubulence arguments and rigorous existence proofs imply that the predictability time of a barotropic fluid may be made as long as we wish if the initial error scale can be made small enough. Both sets of arguments also imply that enstrophy dissipation tends to zero as viscosity tends to zero. For a three‐dimensional fluid phenomenology implies a finite predictability time, and non‐zero energy dissipation as viscosity tends to zero, implying the ill‐posendness of the three‐dimensional Euler equations.
Secondary ice particle production during rime growth: The effect of drop size distribution and rimer velocity
Authors: Mossop S. C. 
Published: July 2010

AbstractThe rate of production of secondary ice particles during the growth of rime in a supercooled cloud at about ‐5°C is known to depend mainly upon the rate of accretion of large drops (diameter ⩾25 m̈m). New experiments have defined more clearly how ‘splinter’ production is affected by the rate of accretion of small drops (diameter ⩽12m̈m).The relationship between secondary ice production and rimer velocity is explored over a wider velocity range than before. At low velocities, splinter production persists to 0.55 ms−1 and probably lower. There is no evidence of a low‐velocity cut‐off as previously claimed. At high velocities, splinter production persists to velocities >5ms−1. This may have important implications for secondary ice production in hail clouds.
Observations of shade‐ring corrections for diffuse sky radiation measurements at the dead sea
Authors: Stanhill G. 
Published: July 2010

AbstractThe shade‐ring correction factor needed for measurements of diffuse irradiance at the Dead Sea averaged 1.41. Under normal near cloudless conditions, the anisotropy factor for sky radiance at the Dead Sea was in mid‐winter 14% greater than that calculated on the basis of clear sky radiance distribution measured in central England, rising to a 28% excess in mid‐summer. the relative strength of the circumsolar radiance calculated from the Dead Sea measurements was 1.54 compared with the value of 1.10 found to fit the data from nine other stations. the calculated angular width of the circumsolar zone at the Dead Sea, 0.63 radians, was, however, similar to that derived from data at other stations. Two possible reasons for the high degree of anisotropy are discussed. the correction factor was not influenced by the degree of cloud cover until over half the sky was clouded. On the very infrequent occasions of completely overcast skies the shade‐ring factor averaged 1.16, agreeing with the value calculated solely on the basis of the geometric view factor. the error in measurement of diffuse irradiance at the Dead Sea caused by uncertainties in the value of the shade‐ring correction was less than 5%, smaller than the uncertainty in the basic reference method of measurement.
A lagrangian analysis of scalar transfer in vegetation canopies
Authors: Raupach M. R. 
Published: July 2010

AbstractTo study the dispersion of scalar trace constituents such as heat, water vapour or CO2 from extensive sources within vegetation canopies, a Lagrangian approach is essential because of the need to account for the influence of travel time (as a fraction of the Lagrangian time scale) on the dispersion properties of marked fluid particles. A simple, analytic Lagrangian theory is developed for a canopy in which the turbulence is homogeneous. For a given scalar source distribution, predictions are obtained for mean scalar concentration, vertical flux, terms in the balance equation for vertical flux, and vertical diffusivities at first, second and third order. the predictions agree remarkably well with measurements of dispersion from an elevated plane source within a model plant canopy in a wind tunnel. the theory also explains the countergradient heat and CO2 fluxes observed in real forest canopies.
Evolution of potential vorticity in tropical cyclones
Authors: Wayne H. , Schubert  , Alworth Brian T. 
Published: July 2010

AbstractWe explore the simultaneous use of potential radius and potential temperature coordinates in the Eliassen balanced vortex model of tropical cyclones. This results in a simple flux form for the equation governing the inverse potential vorticity. the fluxes are accomplished by R and θ, which are given in terms of the angular momentum and heat sources. If the sources are specified functions of R and θ, analytic solutions for the time evolution of the potential vorticity distribution can be obtained. the solutions illustrate how latent heat release generates potential vorticity at low levels, destroys it at upper levels, and through vertical advection causes a deepening of the low‐level potential vorticity maximum and a pinching off of the upper‐level potential vorticity minimum. to recover the tangential wind and mass fields from the known potential vorticity, one must solve a second‐order nonlinear partial differential equation. Numerical solutions of this equation result in tangential wind fields which are similar in many ways to observed tropical cyclones.
On semi‐geostrophic flow over synoptic‐scale topography
Authors: Cullen M. J. P. , Chynoweth S. , Purser R. J. 
Published: July 2010

AbstractExisting semi‐geostrophic theories of flow over a two‐dimensional orographic ridge are extended using a geometrical interpretation of the equations. the method of solution allows information to be gained even when there are local violations of the scaling assumptions. the results show that the occurrence of many observed aspects of the flow, such as downslope winds, drag and flow separation, can be predicted. Quantitative assessment requires a three‐dimensional version of the model.
Comparison of conventional and transformed in the troposphere
Authors: Pfeffer Richard L. 
Published: July 2010

AbstractThe effect of synoptic‐scale transient eddies on the mean zonal current in the troposphere and lower stratosphere is examined using conventional and transformed Eulerian diagnostics. In each case the partial solution of the Eliassen‐Kuo diagnostic equation for the meridional circulation is obtained using as forcing functions only transient eddy (TE) fluxes of heat and momentum. This solution is then used to calculate the Coriolis force and the advective terms in the zonal mean momentum equation. the ‘transient‐eddy‐induced’ zonal momentum tendency is defined as the sum of these terms and the eddy flux terms in the zonal momentum equation. Although conventional and transformed Eulerian diagnostics give the same transient‐eddy‐induced momentum and kinetic energy tendencies, the interpretation of the mechanisms involved is different.It is found that the TE flux convergence of momentum, which is regarded as the torque in the conventional diagnostics, correlates better with the TE‐induced zonal momentum tendency in the troposphere and lower stratosphere than does the transient E‐P flux divergence, which is regarded as the effective torque in the transformed diagnostics. In the latter formalism, the Coriolis force acting on the residual meridional circulation is larger in magnitude than the E‐P flux divergence and is of opposite sign. the net zonal wind acceleration is given by an extremely small difference between these two large quantities and is largely opposite to the E‐P flux divergence. Moreover. the role of the TE heat flux in this formalism is found to be negligible, with the poleward heat flux at the boundary and in the interior inducing accelerations of almost equal magnitude and opposite sign.Some insight into the role of the transient E‐P flux divergence and its components is sought by examining a form of potential vorticity equation for the zonally averaged current, in which the residual meridional circulation has been eliminated. This relationship reveals the importance of the horizontal derivatives of the E‐P flux divergence in forcing zonal wind accelerations, and elucidates most vividly the role of the rotational stratification parameter in diminishing the impact of wave action at high latitudes in the middle troposphere. Examination of the numerical influence function corresponding to the differential operator which operates on the zonal momentum tendency in this equation reveals why the TE flux of heat, which peaks at a higher latitude and lower altitude than the TE flux convergence of momentum, is much less effective in accelerating the zonal current.
Impact of satellite‐based data on fgge general circulation statistics
Authors: Salstein David A. , Rosen Richard D. , Baker Wayman E. , Kalnay Eugenia 
Published: July 2010

AbstractTo assess the influence that data from satellites and other FGGE special observing systems can have on analyses of the large‐scale circulation, the NASA GLA analysis/forecast system was run in two different parallel modes. In the first, data from all of the FGGE observing systems were utilized (denoted the FGGE analysis), and in the second (the NOSAT analysis) only conventional upper air and surface reports were used. Global wind and temperature fields extracted from month‐long assimilations during the first Special Observing Period are similar in the two cases but showed some differences, especially over the southern hemisphere oceans where satellites play a significant role in filling data voids. Winds are a little stronger in general in the NOSAT case, suggesting a damping effect from the inclusion of satellite‐based data.The GLA model was also integrated for the same period without any data inserted (model CLIMATE run). an independent objective analysis based only on rawinsonde and pilot balloon data (STATION analysis) was performed as well. Stronger zonal winds in the model CLIMATE run and differences in features between the NOSAT and STATION cases attest to some influence of the GLA model and analysis technique on the resulting fields.Momentum and heat budget computations were performed for the FGGE, NOSAT and STATION cases. Integrated values of kinetic and potential energy terms in both zonal mean and eddy forms, as well as various conversions between terms, though similar among the cases, demonstrate overall a small decrease in the vigour of the circulation with the inclusion of satellite observations.
On Co2 climate sensitivity and model dependence of results
Authors: Mitchell J. F. B. , Wilson C. A. , Cunnington W. M. 
Published: July 2010

AbstractThe regional response of climate models to small perturbations is shown to be highly dependent on the unperturbed simulation. an experiment in which CO2 concentrations are doubled and sea surface temperatures are enhanced by 2 K has been carried out with two general circulation models which differ considerably in their control climates. the resulting changes in tropical precipitation in each model simulation are related to the increase in atmospheric water vapour which leads to enhanced precipitation in the main regions of low‐level atmospheric convergence. Since these regions of convergence occur in slightly different locations in the unperturbed simulations, the distribution of changes is also different.Differences in control simulations must be taken into account when comparing results from different models (for example, on doubling atmospheric CO2); otherwise unduly pessimistic conclusions may be reached concerning the consistency of model results. One may be able to make subjective allowance for the effect of known deficiencies in the unperturbed simulation on the model's response before using the simulated changes in, for example, impact studies.A detailed examination of one of the experiments reveals that the change in precipitation is limited by the heat balance of the atmosphere, and indicates the importance of treating accurately the radiative perturbation due to changes in water vapour. the magnitude of the model's response is shown to be consistent with that found in three‐dimensional climate models which include a simple representation of the ocean.
Large‐Eddy simulations of the neutral‐static‐stability planetary boundary layer
Authors: Mason P. J. , Thomson D. J. 
Published: July 2010

AbstractA series of large‐eddy simulations of the neutral‐static‐stability planetary boundary layer has been conducted. the simulations differ in the size of the computational domain and the scales represented by the subgrid‐scale turbulence parametrization. the flow eddies are always irregular but show an elongation in the direction of the local velocity shear vector. the dominant horizontal scales of the eddies increase with height in the boundary layer and become much larger than the boundary layer depth. All of this wide range of scales of motion is important in determining the gross boundary layer characteristics. the larger scales of motion have dynamics influenced by both the vertical and horizontal components of the earth's rotation. the flow statistics are compared with previous simulations and with high‐order closure models.
Water Vapour Transport Over Africa and the Atlantic Ocean During Summer 1979
Authors: Cadet D. L. , Nnoli N. O. 
Published: July 2010

AbstractThe water vapour transport over Africa and the eastern Atlantic Ocean during the 1979 summer is studied. the analysis is based on wind fields from the European Centre for Medium Range Weather Forecasts and humidity fields derived from a three‐layer precipitable water data set.The evolution of the bi‐weekly mean fields of water vapour flux in the surface to 850 mb layer shows the progressive penetration of moisture over West Africa during the summer. At low levels during the maximum activity of the African monsoon, the southerly flow penetrates up to 20°N and there is a large belt of westerlies around 10°N. the fluxes between 700 and 500 mb suggest the importance of the African easterly jet (AEJ) as a major artery for moisture for West Africa.Vertically integrated fluxes across different sections have been analysed. Across the equator at the longitudes of the Gulf of Guinea the flux shows a decreasing trend due to the northward propagation of the intertropical discontinuity over west Africa. Near 22°N, the flux is mainly from the north at the beginning of the summer and becomes southerly during surges of the monsoon. the flux from West Africa toward the Atlantic Ocean is large, indicating that moisture from the Gulf is transported upward and advected westward by the AEJ. the fluxes oscillate with two main periods, around 3‐5 days and 5‐7 days.Water vapour budgets have been estimated for boxes located over the Gulf of Guinea and West Africa. the Gulf of Guinea is a source of water vapour transported northward and westward by the trade winds. Over West Africa at low levels, moisture comes from the Gulf of Guinea. In the mid‐troposphere there is a strong easterly moisture flux associated with the AEJ and originating from central Africa. This moisture seems to come initially from the Gulf of Guinea. Because it is mainly divergent, the mid‐tropospheric flux may have little influence on rainfall over West Africa. the budget study also emphasizes the importance of evapotranspiration over the belt north of the Gulf of Guinea where water vapour is recycled and transported northward.
Two‐Dimensional Model Studies of Equatorial Dynamics and Tracer Distributions
Authors: Gray L. J. , Pyle J. A. 
Published: July 2010

AbstractA parametrization of Kelvin wave absorption in the equatorial stratosphere has been included in a two‐dimensional model of the atmosphere in order to improve the simulation of the semi‐annual oscillation. Additionally, a more detailed treatment of the momentum deposition associated with gravity wave breaking in the mesosphere has replaced the previous Rayleigh friction scheme. the model exhibits a semi‐annual reversal of the zonal winds at the equator in the stratosphere, with the westerly phase descending with time, as observed. the inclusion of the improved gravity wave parametrization has led to a number of significant improvements; in particular, the model also exhibits a semi‐annual oscillation in the mesosphere which is out of phase with that in the stratosphere. Meridional circulations associated with the westerly phase of the semiannual oscillation produce ‘double peak’ structures in a number of modelled tracer fields, including N2O, CH4 and H2O which compare well with observations by the SAMS and LIMS satellite experiments. These structures consist of a distinct minimum at the equator and double maxima in the subtropics; they are present for several months around each equinox. Inclusion of the more realistic westerly forcing has pointed to the need for additional easterly forcing in the model around each solstice. Further supporting evidence for the importance of momentum deposition associated with planetary waves in the easterly phase of the semi‐annual oscillation comes from the difference in double peaks between the northern hemisphere spring and autumn, as suggested in an earlier paper.
Eddy‐Forced Coherent Structures As A Prototype of Atmospheric Blocking
Authors: Haines Keith , Marshall John 
Published: July 2010

AbstractThe relevance of nonlinear free solutions of the equivalent barotropic vorticity equation known as ‘modons’ or ‘vortex pairs’ is reconsidered as a prototype of atmospheric blocking. It is argued that modons are highly appropriate reference solutions from which to consider the dynamics of blocks accounting for their local nature, their stability and longevity.Nonlinear resonance studies with an equivalent barotropic numerical model on a β‐plane channel demonstrate the ease and vigour with which vortex pairs can be excited by a vorticity‐forcing function of the appropriate form. Localized nonlinear structures which can be identified with modons exist on blocking timescales even in parameter ranges which allow stationary Rossby waves. Thecircumstances in which synoptic systems can provide an appropriate forcing function are investigated by studying the interaction between a modon and a train of travelling vortices. It is shownthat the anomalous transfer of potential vorticity induced by the straining of synoptic systems propagating in a diffluent jet is in a sense to maintain the modon against dissipation. Time sequences of the potential vorticity field from the equivalent barotropic model bear a remarkable resemblance to isentropic potential vorticity maps observed during a blocking episode and suggestthat much of the detail can be understood in terms of the passive deformation of baroclinically inactive weather systems.