bluuebunny/crossref_metadata_2025_split huggingface dataset:
A numerical study of radiation fog with an explicit formulation of the microphysics
Authors: Brown R. 
Published: February 2007

AbstractA model of radiation fog is described containing an explicit formulation of the microphysics of the condensation process. The coupling between the radiative and microphysical processes within the model means that apart from the specification of the turbulence and CCN spectrum it is deterministic.Results are presented which indicated that:
The drop‐size distribution is sensitive to the CCN concentration but not to the presence of large CCN.
Radiative loss from the drops can have a significant effect upon their growth.
The drop‐size distribution is very sensitive to reductions in the condensation coefficient to a value below 0.033.
Differences between observed and model drop‐size distributions are attributed to an underestimate in the model of the level of mixing within a mature fog.
Measurements of nitric oxide in the stratosphere of the Southern Hemisphere
Authors: Roy C. R. , Galbally I. E. , Ridley B. A. 
Published: February 2007

AbstractVertical profiles of NO in the stratosphere above Mildura, Australia (34°S, 142°E), were obtained in December 1977 using a balloon‐borne chemiluminescent detector. The average mixing ratio increased from about 0.2 ppbv at 10 km to 0.45 at 20 km and to about 7 ppbv at 33 km. The results are in good agreement with a profile obtained in the USA (32°N, 96°W) during October 1977 with the same instrument. It is suggested that the stratospheric NO distribution may, at low latitudes, be symmetric about the equator. The NO measurements and earlier chemical‐filter HNO3 measurements made at Mildura are compared to recent chemical model predictions.
A non‐linear atmospheric long wave model incorporating parametrizations of transient baroclinic eddies
Authors: White A. A. , Green J. S. A. 
Published: February 2007

AbstractNumerical experiments with a simple spectral model of tropospheric long waves are described. The model is based on the 2‐parameter, β‐plane, quasi‐geostrophic equations and a coarse truncation is applied. Transient baroclinic eddy motion is represented parametrically using transfer coefficient expressions which are extensions of those proposed by Green in 1970 for zonal average formulations. The long waves are forced directly by externally specified diabatic and orographic functions. Zonal average diabatic forcing is also applied. When the eddy flux parametrizations act on the zonal fields only, realistic steady states are obtained if a coarse meridional truncation is applied, but explicit baroclinic instability occurs if higher meridional modes are included. Explicit baroclinic instability is suppressed if the parametrizations act also on the long wave fields; and in this case it is found that diabatic forcing of the largest scales of motion is the most important generator of stationary long waves in the model. Various reformulations are considered, and the problem of devizing better transient eddy parametrizations is discussed.
Mesoscale observations of upstream blocking
Authors: Manins P. C. , Sawford B. L. 
Published: February 2007

AbstractAnalysis of detailed tethered balloon soundings simultaneously undertaken at two sites in a valley shows that blocked (i.e. near stagnant) flow upwind of the ridges is characterized by a critical internal Froude number, Fr = uaH−1(gγa/θr)−1/2 of approximately 1.6. For Fr above this value the air in the valley is swept out by ambient wind. Otherwise blocking to near ridge height is observed. Here ua is ambient wind speed measured above ridge height H, g is acceleration due to gravity, θr a reference potential virtual temperature and γa the ambient vertical gradient of this quantity.
A note on the paper by P. J. Sellers and J. G. Lockwood, ‘A computer simulation of the effects of differing crop types on the water balance of small catchments over long time periods’
Authors: Shuttleworth W. J. , Gash J. H. C. , Sellers P. J. , Lockwood J. G. 
Published: February 2007

AbstractArguments are presented suggesting that the difference between predicted interception loss given by the multi‐layer MANTA model and the single source Rutter model, reported by Sellers and Lockwood (1981), are primarily related to differences in the treatment of aerodynamic transfer in saturated conditions. The reinterpretation is important in that, assuming the treatment used in the MANTA model is correct, changes in effective source position generate an unexpectedly large change in effective aerodynamic resistance. Attention is also drawn to features present in results given by the MANTA model operating in dry conditions which require further investigation.
Airflow over hills of moderate slope
Authors: Carruthers D. J. , Choularton T. W. 
Published: February 2007

AbstractA three‐layer model is presented. This describes the flow on an inversion capped boundary layer over hills of moderate size and slope. The linearized vorticity equation is solved using non‐linear boundary conditions. The pressure field developed in the boundary layer is used to calculate a modified inner region velocity field (Jackson and Hunt 1975).A low level inversion with height I, ≲ 2h is found to decrease the speed‐up near the ground. When I ≳ 2h the flow of the inversion layer shows an increasing tendency to be subcritical; this leads to a much increased speed‐up. Increasing the stability of air above the inversion increases the asymmetry of the flow. This causes an upwind lull and a subsequent rapid increase in the flow speed with very high wind speeds at the summit and downwind.Comparison of the theory with simple observations made on Great Dun Fell, Cumbria shows encouraging agreement.
Aircraft measurements of wave momentum flux over the Colorado Rocky Mountains
Authors: Lilly Douglas K. , Nicholls J. M. , Kennedy Patrick J. , Klemp Joseph B. , Chervin Robert M. 
Published: February 2007

AbstractResults are presented from a programme designed to measure the momentum flux associated with standing gravity waves over the central Rocky Mountains of North America. The purpose was to determine momentum losses from the westerlies as they cross a mountainous section of the northern hemisphere where wave drag is believed to be substantial. The data from one to three instrumented aircraft, operating on 20 flight days, mostly during January to March of 1973, are in reasonably good conformity with linear wave theory and also correlate well with surface measurements of downslope winds. Downward westerly momentum flux averaged 0.5 ‐ 1.0 dynes cm−2 (0.05 ‐ 0.1 Pa). The mean westerly flow on the flight days was near the climatological mean for the period of the project, although the mean flow over this period as a whole was much weaker than the climatological mean.
The daytime planetary boundary layer: A new interpretation of Wangara data
Authors: Manins P. C. 
Published: February 2007

AbstractThe efficacy of a simple encroachment model of mixed‐layer growth is explored by simulating two disparate days of the Wangara Experiment. The inclusion of thermal winds is shown to be essential if temperature, height and vector wind of the mixed layer are to be predicted with accuracy. In strong wind shears, additional growth due to the stress between the mixed layer and the air above evidently occurs and this is included by a new closure, invoking mean‐flow energetics (termed ‘the Froude dynamics’ approach).Simulation of Day 12 supports the new model showing that even when averaged over (say) the central four hours of that day, the interfacial stress is expected to have been 30% larger than the surface stress. In conditions of convective heating and light winds the model predicts that negligible entrainment occurs. Growth is by encroachment only. This is confirmed by the simulation of Day 33.Working from the turbulence kinetic energy equation, the closure problem for the Froude dynamics model is solved by a ‘catastrophe’ interpretation in which the normal state is one of no entrainment. Turbulence kinetic energy generated at the surface is dissipated and used to redistribute fluid within the mixed layer. Only when the Froude number, Fr, of the mixed layer exceeds a value of unity does entrainment occur such that the normal state is restored. Here Fr = |Δu|2θvo/gh ΔθV and Δu is the velocity jump, Δθv the virtual potential temperature jump (reference value θvo) at the top of the mixed layer which is of height h; g is acceleration due to gravity. There are no adjustable or tunable parameters involved.
Field studies of the effect of entrainment upon the structure of clouds at Great Dun Fell
Authors: Baker M. B. , Blyth A. M. , Carruthers D. J. , Choularton T. W. , Fullarton G. , Gay M. J. , Latham J. , Mill C. S. , Smith M. H. , Stromberg I. M. , Caughey S. J. , Conway B. J. 
Published: February 2007

AbstractA description is given of experiments and calculations performed to investigate the effect of the entrainment of undersaturated air upon the microphysical structure of cap clouds at Great Dun Fell, Cumbria. Three case studies are presented: in I the properties of the cloud were essentially adiabatic; II provided evidence for mixing intermediate between the homogeneous and extreme inhomogeneous types; in III the mixing was extremely inhomogeneous. Consistent with this picture, the time constant for turbulent erosion of the entrained parcels of air is significantly greater in II than in III. Spectral changes observed in II and III agree well with predictions from a diffusive model of mixing (Baker and Latham 1982).
The climatological minimum in tropical outgoing infrared radiation: Contributions of humidity and clouds
Authors: Warren Stephen G. , Thompson Starley L. 
Published: February 2007

AbstractSatellite observations of outgoing terrestrial infrared (IR) radiation as a function of latitude exhibit a minimum near the equator 20–40 Wm−2smaller than peaks in the subtropics. We attempt to dissect the causes of the dip through calculations with a spectrally‐detailed multi‐level radiative transfer model. Roughly one third of the dip can be attributed to the latitudinal variation of atmospheric water vapour; the remainder apparently is due to latitudinal variations in cloud amount and (especially) cloud‐top height. However, inclusion of clouds as given by published climatologies enhances the clear‐sky dip only slightly. Thus, about one half of the dip is essentially unexplained. We suspect the explanation is that near‐equatorial cirrus and cumulonimbus heights are too low in the cloud climatology, emphasizing the need for a better cloud climatology.Since tropospheric humidity variations have a strong effect on clear‐sky outgoing IR, empirical studies which correlate cloud with IR variations may overestimate the effect of clouds on outgoing IR if cloud amount is correlated with relative humidity.The effect of humidity variations on outgoing IR suggests that a measure of tropospheric humidity be incorporated explicitly in the parametrization of outgoing IR for simple climate models.
Stratospheric water vapour over Australia
Authors: Hyson P. 
Published: February 2007

AbstractMeasurements of stratospheric water vapour over Australia (Mildura, 34°S 140°E) during the period 1977–1979 indicate a mean mixing ratio between 15 and 21 km of 2°4p.p.m.m. The record since 1973 shows a quasi‐biennial oscillation with a peak to peak amplitude of 2 p.p.m.m. in the 15–21 km height interval. The latter appears well correlated with 50–30 mb equatorial westerlies.
Inland convection and energy transfers in a sea breeze model
Authors: Richiardone R. , Pearson R. A. 
Published: February 2007

AbstractAvailability of potential energy in inland convection and in a sea breeze circulation are compared using a formulation of P. C. Manins and J. S. Turner for the convectively mixed atmospheric boundary layer, and a numerical model of a sea breeze. Entrainment processes during the mixed layer growth appear to affect both the convective scale and the mesoscale, decreasing the amount of potential energy available to the convective scale yet increasing the potential energy available at the mesoscale. The kinetic energy content of the sea breeze cell is explained in terms of a constant efficiency for the conversion of available potential energy inside a cell whose horizontal dimension increases in time. Results of numerical experiments indicate that the current value of the temporally integrated buoyancy flux at the ground is the most important parameter for the sea breeze flow. This parameter determines the strength of the flow as well as the inland movement of the sea breeze front.
Solar radiation in dense saharan aerosol in Northern Nigeria
Authors: Brinkman A. W. , McGregor James 
Published: February 2007

AbstractMeasurements of normal incidence and global irradiance were made during the periods November to December 1977 and November 1978 to February 1979. Aerosol density was monitored in terms of turbidity, derived from the normal incidence record. A daily mean turbidity was calculated and used to trace variations in aerosol density over the season. Values ranged from 0–09 to 2–16 with average values of 0–44 and 0–47 for the two measurement periods respectively. A simple model was devised which related the diffuse irradiance to the turbidity and a parameter which described the angular dependence of scattering. This model demonstrated that significant differences existed between the optical properties of the local background aerosol and the dense Saharan aerosol periodically transported by the Harmattan wind. One such period of dense aerosol, when the visibility was reduced throughout most of Nigeria, is presented as a case study. The reduction was particularly severe in the north, where visibility fell below 500 m and an associated drop in air temperature of up to 6 °C occurred. Diurnal variations in turbidity were observed during periods of dense aerosol, although during the clearer periods diurnal variations were not evident. Some broad‐band spectral measurements of normal incidence irradiance were taken which indicated that extinction in both the dense Saharan and background aerosols was spectrally neutral.
A random walk model of dispersion in the diabatic surface layer
Authors: Ley Anne J. , Thomson D. J. 
Published: February 2007

AbstractA two‐dimensional random walk atmospheric dispersion model applicable to a passive pollutant within the surface layer in all stability conditions is described. Numerical concentration profiles from the model are shown to be in good agreement with experimental data. Lagrangian statistics from the model are compared with Lagrangian similarity theory, and the variation of the similarity constant c with stability is studied. The similarity properties of the root‐mean‐square cloud height σ2 are also investigated.
Stratospheric tracer transport: A modified diabatic circulation model
Authors: Rogers C. F. , Pyle J. A. 
Published: February 2007

AbstractWe describe a model for stratospheric tracers in which transport consists of advection by the mean diabatic circulation and chemical eddy transport arising from longitudinal variations in in situ sources and sinks. The ozone distribution is reproduced well by the model and all species show interesting variations with longitude. The limitations of the model are discussed; we speculate that the most important of these is the neglect of transient contributions.
Aircraft measurements of the humidity in the lower stratosphere from 1977 to 1980 between 45°N and 65°N
Authors: Foot J. S. 
Published: February 2007

AbstractResults are presented of measurements of humidity in the lower stratosphere from a Canberra aircraft of the Meteorological Research Flight using a manually operated frost point hygrometer. From 1977 to 1980, observations were taken routinely between 45 and 65°N so it has proved possible to study both temporal and latitudinal variations. The most striking feature emerging from these analyses is the decrease in variability with increasing latitude. Overall the results appear to indicate that (a) the subtropical jet stream is an important source as well as sink of water vapour to this region; (b) that there may be a sink of water vapour in polar regions; and (c) that the influence of sudden warming events can be detected in water vapour changes at latitudes greater than 50°N. No explanation for an apparently greater probability of unusually high humidity in the north in this range has been possible.
Transport of water vapour in a stratosphere‐troposphere general circulation model. I: Fluxes
Authors: Allam R. J. , Tuck A. F. 
Published: February 2007

AbstractThe fluxes of water vapour in the upper troposphere and lower stratosphere of a general circulation model have been calculated. Although the results are probably affected by some model characteristics, particularly the vertical resolution, they suggest that ingress of water vapour to the stratosphere may occur by large‐scale eddy motions above the core of the subtropical jet stream, as well as by vertical motion through the tropical tropopause. The latter motion occurs predominantly in the equatorial western Pacific and Indian Ocean, and is connected with the monsoon circulation.
On the non‐hydrostatic equations in pressure and sigma coordinates
Authors: Miller M. J. , White A. A. 
Published: February 2007

AbstractThe non‐hydrostatic equations governing the inviscid, adiabatic motion of a perfect gas are formulated using pressure as vertical coordinate; and M. J. Miller's 1974 approximate quasi‐non‐hydrostatic pressure coordinate equations are derived by applying a systematic scale analysis and power series expansion. The derivation makes clear that these equations are the pressure coordinate counterparts of the anelastic height coordinate equations obtained by Y. Ogura and N. A. Phillips in 1962. The two sets cannot be interconverted by coordinate transformation and so they are not physically equivalent; but the differences are small at the order of validity of both sets. Consideration of a quasi‐hydrostatic approximation emphasizes the non‐hydrostatic character of Miller's equations. Sigma coordinate quasi‐non‐hydrostatic equations are obtained by direct transformation of the pressure coordinate forms, and consistent energy equations are derived for both sets. Convenient diagnostic partial differential equations for the geopotential field are obtained for both pressure and sigma coordinate forms. As shown by Miller, the quasi‐non‐hydrostatic formulation does not permit vertically propagating acoustic waves. Horizontally propagating acoustic waves (Lamb waves) are in general allowed, but can be removed from the pressure coordinate system by applying suitable boundary conditions. Some aspects of the treatment of the Lamb wave problem are corrected in this study. The quasi‐non‐hydrostatic sigma coordinate system permits Lamb waves, but it may still be considered suitable for convective and (especially) mesoscale modelling with or without orography. The possible use of the quasi‐non‐hydrostatic system in large‐scale theory and modelling is also discussed.
On the accuracy of general circulation statistics calculated from FGGE data—a comparison of results from two sets of analyses
Authors: Lorenc A. C. , Swinbank R. 
Published: February 2007

AbstractBy comparing statistics from two independent sets of analyses, and relating the differences seen to known characteristics of the analysis system, an indication is given of the likely accuracy of typical general circulation statistics calculated from FGGE data. The analyses compared are those made by the European Centre for Medium Range Weather Forecasts using the main delayed mode observations, and those made in near real time by the Meteorological Office FGGE analysis system. Examples are given of the accuracy of both zonal means and geographical distributions, for basic time mean fields, for derived fields such as divergence, variances and fluxes, and for budget calculations.It was found that qualitative agreement between the two sets of statistics was very good, even in the tropics and southern hemisphere. Quantitative agreement was also in general good; most of the systematic differences could be traced to known characteristics of the analysis systems.
The response of a nonlinear, time‐dependent, baroclinic model of the atmosphere to tropical thermal forcing
Authors: Grose W. L. , Blackshear W. T. , Turner R. E. 
Published: February 2007

AbstractA multi‐level, sigma coordinate, primitive equation atmospheric model has been utilized to study both the tropical and extratropical response to an isolated region of steady thermal forcing in the tropics. The nonlinear response during the first 28 days of the simulation is described. The response can be generally characterized by two distinct components. The first component is a quasi‐stationary disturbance which extends eastward and poleward away from the source region along a ‘great circle’ path. The structure of this disturbance is essentially barotropic away from the source region. The second component is a growing baroclinic wave propagating zonally at mid‐latitudes. Significantly, this disturbance is apparently the result of baroclinic instability induced by the quasi‐stationary wavetrain. The discussion is predominantly heuristic in form and relies heavily on graphical presentation and quasi‐geostrophic theory to interpret the response and individual components of the thermodynamic energy and momentum equations.
An application of the Langevin equation for inhomogeneous conditions to dispersion in a convective boundary layer
Authors: De Baas Anne F. , Van Dop Han , Nieuwstadt Frans T. M. 
Published: February 2007

AbstractDispersion in one dimension is simulated by the Langevin equation dW = −(W/TL)dt + dμ, where W is the velocity of the particle (hypothetical fluid element), TL the Lagrangian time scale and dμ the random velocity increment induced by forces exerted by the turbulence on the particle during dt. The moments of dμ in the Langevin equation in inhomogeneous conditions can be determined, by requiring that for large times the density distribution of the particles is the same as that of the air. In our numerical experiment the Langevin equation with the above‐defined moments is applied to diffusion in the convective boundary layer. Profiles of the moments of the vertical turbulence velocities, U(z), n = 1, 2, 3, are based on measurements and scaled by convective scaling; TL is assumed constant. Particles are released at several heights, with an initial velocity distribution that has the same moments as the Eulerian turbulence velocity distribution at that height. At the boundaries reflection conditions are imposed. Our results are extensively compared with water‐tank experiments of Willis and Deardorff, wind‐tunnel experiments of Poreh and Cermak, field experiments by Briggs and a model of Baerentsen and Berkowicz. The mean height and variance of the particles, the concentration field as a function of down‐wind distance and height, and ground level concentrations are presented. They agree very well with observations of dispersion in the convective boundary layer.
On the local rate of turning of wind direction
Authors: Lecluyse A. , Neumann J. 
Published: February 2007

AbstractFrom the equations of horizontal motion an equation is derived for the local rate of change of wind direction. The derivation retains the nonlinear and frictional terms, in addition to the horizontal pressure gradient and Coriolis terms. The resulting equation can be briefly described as comprising two groups: in the first ‘group’ we have the constant term −f(f= Coriolis parameter; −f= rate of directional turning of ‘inertial’ wind); the second group is the sum of several variable terms which thus ‘modulate’ the fundamental term −f. The modulation can result in changes both in the magnitude and sense of rotation.In the discussion, the relative importance of the various terms is considered for two flows: sea breeze and synoptic‐scale flow, including an estimate of magnitude of contribution of the frictional term.