bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meteorological and soil factors affecting evaporation from fallow soil
Authors: Penman H. L. , Keen B. A. 
Published: July 2010

AbstractUsing the conception of natural periods, for which the difference between rainfall and drainage can be equated to the evaporation, the mean daily rates of evaporation from a block of fallow soil at Rothamsted are examined for 94 periods varying in length from 13 to 45 days. In seeking correlations with single daily meteorological observations two types of treatment are employed. (1) The year is considered in three seasons of four months each—summer, winter and two equinoctial pairs of months—and it is shown that an almost complete description of evaporation can be obtained in terms of rainfall only, the nature of the correlation varying from season to season. (2) A general treatment is attempted in physical terms, considering evaporation as due to diffusion across a non‐turbulent boundary layer whose thickness is determined by wind velocity, the soil surface being assumed to be continuously at 100 per cent R.H. The general agreement between observed and predicted values is very good in winter. The summer data are shown to lie between the theoretical limits imposed by the assumptions of (i) continuous 100 per cent R.H. at the surface, and (ii) a steady retreat of the 100 per cent R.H. layer into the soil, i.e., no upward movement of liquid during the evaporation process. The considerable scatter in the data is attributed partly to the inadequacy of single daily meteorological observations but chiefly to the lack of knowledge of the conditions existing at the soil surface.
Cold and warm fronts in baroclinic waves
Authors: Hoskins B. J. , Heckley W. A. J. 
Published: July 2010

AbstractPrevious studies have shown how simple baroclinic waves may exhibit either a primary cold front or a primary warm front. In this paper it is shown that many of the quite realistic differences between the cold and warm fronts are a consequence of the forward tilt of the temperature wave with height. This forward tilt is proved to be a necessary feature of a growing baroclinic wave. Thus a dynamical distinction between cold and warm fronts is postulated.
Air flow over a two‐dimensional hill: Studies of velocity speed‐up, roughness effects and turbulence
Authors: Britter R. E. , Hunt J. C. R. , Richards K. J. 
Published: July 2010

AbstractWind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough, bell‐shaped, two‐dimensional hill, with height h and maximum slope 0.26, placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo = 0.02 h. Close agreement is found between the mean velocity and predictions obtained from Taylor's (1977) computational model and Jackson and Hunt's (1975) analytical linearized model, for locations at or upwind of the hill top but not in the wake. Examination of the models shows that the shear stresses are only important in an inner region close to the hill surface, so that, as suggested by Jackson and Hunt (1975), the perturbation to the mean flow outside this region is essentially inviscid. the theory shows that over very rough surfaces, such as wooded or urban terrain, the height of this inner region can be of the same order as the height of the roughness elements (so that in our experiments no measurements could be made in this region).In a second experiment flow over a smooth hill on a rough surface was studied. the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness (in this case rough to smooth). In the lee of a hill, however, the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate.Finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface. Calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field.
The quasi‐geostrophic equations: Approximation, predictability and equilibrium spectra of solutions
Authors: Bennett A. F. , Kloeden P. E. 
Published: July 2010

AbstractTwo well‐posed initial‐boundary value problems for the quasi‐geostrophic equations have been identified. the first is defined in a vertical annular cylinder with specified temperatures on the horizontal bottom and top surfaces. the second is defined in a box with periodic boundary conditions on the sides and with rigid bottom and top surfaces; bottom topography is included. Well‐posedness is established by theorems which determine conditions under which there exist unique solutions depending continuously on the initial and other data. the theorems are stated here, but proved elsewhere.Completely rigidly contained quasi‐geostrophic motion is in general an ill‐posed problem, due to over‐specification of circulation integrals around edges where vertical and horizontal boundaries meet.The theorems are used to infer (1) sufficient conditions for the convergence of finite‐element Galerkin approximations of Fix (1975) to exact solutions, (2) the predictability type of the solutions as defined by Lorenz (1969), and (3) that the long‐time high wave‐number spectra of the equations are steeper than the inertial ranges and the statistical equilibrium spectra of Kraichnan (1967). Implications for numerical circulation models are drawn.
On the mountain torque in barotropic planetary flow
Authors: Egger J. , Metz W. 
Published: July 2010

AbstractAn attempt is made to understand the long‐term balance of the total relative angular momentum M of an inviscid barotropic fluid forced by orography. the problem is treated by integrating the barotropic potential vorticity equation with the β‐plane approximation, and on the sphere, using spectral methods. First, a highly truncated system containing only the superrotational flow and one wave component is studied by analytical means. A fairly complete understanding of the behaviour and the climatic mean value of M is achieved. Then, less truncated systems with up to five zonal wave‐numbers are investigated by numerical integrations. It turns out that a climatic mean value can be ascribed to M if the integration is carried out for several weeks or more. It is demonstrated that this long‐term mean value can be estimated reasonably weil on the basis of the study of the highly truncated system. A possible application of these results to more realistic fluid systems is suggested.
Observations of condensate profiles over arctic leads with a hot‐film anemometer
Authors: Andreas Edgar L. , Williams Richard M. , Paulson Clayton A. 
Published: July 2010

AbstractDuring the AIDJEX Lead Experiment on the Arctic Ocean large‐amplitude, high‐frequency spikes were observed on the voltage signals of hot‐film sensors being used for turbulent velocity measurements near the water surface. Because over leads in winter temperature gradients are very steep and the super‐saturation extreme, condensate droplets can form and grow to measurable size even in the few seconds the air is over the lead. the voltage spikes resulted when these condensate droplets struck the hot‐films. We could, therefore, use the hot‐film information to determine not only turbulence quantities but also condensate concentration profiles and the flux of condensate droplets at the surface of leads. Condensate droplets were roughly 10 μm in diameter, concentrations within 20cm of the surface were usually 20‐80mg kg−1 (50‐220 droplets cm−3), and the condensate flux was of order 3mgm−2s−1.Non‐dimensional condensate profiles are well modelled by

where c* is a concentration scale and h, an estimator of the internal boundary layer height, is fetch dependent. the condensate flux is related to average quantities through the Nusselt number, Nuc, and the fetch Reynolds number, Rx: NUc

Because c* also depends on the condensate flux, the simplicity of the profile relation and this Nusselt number equation suggest two alternative ways to estimate condensate flux at the surface of leads from the measurement of bulk environmental parameters.
The impact of FGGE data coverage and improved numerical techniques in numerical weather prediction in the Australian region
Authors: Leslie L. M. , Mills G. A. , Gauntlett D. J. 
Published: July 2010

AbstractThis paper describes the results from an extensive series of experiments aimed at enhancing the skill of the Australian Numerical Meteorology Research Centre (ANMRC) limited area analysis/forecast system.Significant increases in model performance were achieved, in the sense of reducing S1, skill scores and in forecasting precipitation, in three ways: (1) improved data base since the beginning of FGGE; (2) the application of a more realistic lateral boundary specification, particularly nesting within a hemispheric forecast model; and (3) the reduction of truncation errors by either decreasing the grid spacing or (more efficiently) employing higher order difference operators.The improvement in skill is sufficiently large to suggest that when implemented operationally the quality of routine prediction of synoptic scale patterns over the Australian region will be considerably improved.
Tethered‐balloon observations of the structure of small cumulus clouds
Authors: Kitchen M. , Caughey S. J. 
Published: July 2010

AbstractThe turbulence and microphysical structures of small cumulus clouds have been studied in some detail using three turbulence probes and a droplet spectrometer attached to the tethering cable of a large (1300 m3) balloon. the airflow in and around clouds showed some evidence for a ‘P‐shaped’ circulation in the vertical plane and rotation in the horizontal plane. Power spectra of the vertical component of air motion both in and out of cloud and in the mixed layer below cloud base are described and contrasted. Mean turbulence characteristics (i.e. averaged over a few hours) strongly resemble those from the upper regions of the clear convective boundary layer but in the vicinity of clouds the turbulence field is considerably altered. Observations of the cloud droplet field near cloud top and the rate of dissipation of turbulent kinetic energy provide evidence that the entrainment and mixing of dry air proceed essentially inhomogeneously.
On the propagation of cold fronts
Authors: Manton M. J. 
Published: July 2010

AbstractThe assumption of steady two‐dimensional flow imposes constraints on the motion of a layer of cold air propagating through a body of warm air. Some general properties, such as the propagation speed of the front, can be deduced from consideration of the equations of motion away from the frontal region. Thus the differences between anafronts and katafronts are discussed.
Winter depression tracks and climatological jet streams in the Southern Hemisphere during the FGGE year
Authors: Physick W. L. 
Published: July 2010

AbstractA band‐pass filter transparent to fluctuations in the 2£5‐6 day period range is applied to a set of twice‐daily analyses covering the 1979 (FGGE year) winter of the Southern Hemisphere. Fields analysed include MSL pressure, 500mb height, 300mb wind, and the meridional heat flux due to transient eddies at 850mb. Variance maxima in these filtered fields indicate regions of high cyclonic activity, with favoured cyclolysis areas in the vicinity of the Antarctic coastline also showing up in the MSL pressure statistics. Using these results, supplemented by data on the distribution of cyclogenesis, we are able to identify the major depression tracks. In this analysis, extensive use is made of studies relating satellite‐observed cloud vortices to the various stages of cyclonic development. In general, it appears there was significantly more activity in the eastern hemisphere than in the western during the 1979 winter.By evaluating the terms in the time‐averaged zonal momentum equation (using the unfiltered data set), it is possible to assess the role of transient eddies in the maintenance of the time‐mean zonal flow. This analysis shows that Coriolis acceleration associated with poleward time‐mean ageostrophic flow at the tropopause level dominates the forcing of the jet centred around 25°S, but that convergence of eddy momentum flux maintains the higher latitude jet around 50°S. However, a significant contribution to the latter jet comes from poleward ageostrophic flow south of Africa.
Numerical simulation of the surge generated by the 1977 Andhra cyclone
Authors: Johns B. , Dube S. K. , Mohanty U. C. , Sinha P. C. 
Published: July 2010

AbstractThree different numerical models are used to simulate the surge generated by the 1977 Andhra cyclone. In each of these we simulate the effect of three days of wind‐stress forcing before landfall of the cyclone at the Andhra Pradesh coast. the analysis area in the first model includes the entire Bay of Bengal north of 6°N and utilizes a curvilinear boundary treatment to represent the coastlines. the second model is a coastal zone model extending along the east coast of India, again utilizing a curvilinear treatment of the coastline. In the third model, which again covers the entire Bay of Bengal, the coastlines are represented by a conventional stepwise procedure. Using available data on the Andhra cyclone as a guide in representing the effect of wind‐stress forcing in our models, we compare the predicted rise in the sea‐surface elevation obtained from each of these with estimates based on reports received from Andhra Pradesh after the disastrous flooding in that region. Each of the three models produces a qualitatively similar surge response. the slight quantitative differences are explained in terms of the different boundary treatments. the predicted peak surface elevation above mean sea‐level compares well with the estimated 5 m reported along part of the Andhra Pradesh coast south of Masulipatnam.
A comparison of laboratory measurements and numerical simulations of baroclinic wave flows in a rotating cylindrical annulus
Authors: Hignett By P. , White A. A. , Carter R. D. , Jackson W. D. N. , Small R. M. 
Published: July 2010

AbstractQuantitative and qualitative comparisons are made between laboratory measurements of rotating annulus flows and corresponding numerical model simulations. Two laboratory annuli, of similar dimensions but differing in instrumentation, are used. One contains a thermocouple array for temperature measurement: the other contains no sensor array but the working fluid is seeded with minute neutrally buoyant beads (600 m̈m diameter) which enable the horizontal velocity field to be measured. Each annulus has a rigid insulating lid in contact with the working fluid. the numerical model is a finite difference formulation based on the Navier‐Stokes equations for baroclinic flow of a Boussinesq liquid. Although the atmosphere and the laboratory annulus are both rotating baroclinic fluid systems, the forcing processes acting in the annulus are much simpler than those acting in the atmosphere, and may be accurately represented by established formulae: under a wide range of conditions no parametrizations of subgrid‐scale dynamical and diabatic processes are required. Comparison of numerical model results with laboratory measurements therefore enables the explicit dynamical formulation of numerical models of rotating, baroclinic flow to be verified to an extent which would be very difficult, if not impossible, to achieve using atmospheric data. Detailed quantitative comparisons for a steady wave flow reveal good agreement for major features of the temperature and horizontal flow fields, although a significant discrepancy in total heat flux is found. Qualitative comparisons are made by investigating the ability of the numerical model to reproduce the main flow types and phenomena of the laboratory system. Numerical simulations of intransitivity, hysteresis, wavenumber transitions, amplitude vacillation and a weak structural vacillation are described. Several suggestions for further comparative studies are made in conclusion.
A numerical and analytical study of atmospheric undular bores
Authors: Crook Norman A. , Miller Martin J. 
Published: July 2010

AbstractIn this paper the formation and structure of an atmospheric undular bore is examined with the aid of a numerical model and theoretical analysis. the numerical model is first used to simulate a density current propagating into an unstratified environment. A detailed comparison of the model results with existing theory shows that for a given pressure head the current can travel at a greater speed than that predicted by irrotational theory.When the density current is allowed to propagate into a low‐level stable layer it is found that for certain parameter regimes an undular bore forms ahead of the current. the results for two different types of stable layers are examined. For a layer with a step profile of potential temperature, comparison is made with both classical bore theory and the theory of density currents in two‐layer fluids and encouraging agreement is found. When a linear profile is specified in the stable layer it is found that energy‐conserving solutions can be obtained. the numerical fields are then compared with measurements of the morning glory, an undular bore observed in north‐eastern Australia, and again agreement is good.Finally, preliminary results of model simulations with stratification above the stable layer are discussed.
Vorticity balances in the tropics during the 1982‐83 El Niñio‐Southern oscillation event
Authors: Sardeshmukh Prashant D. , Hoskins Brian J. 
Published: July 2010

AbstractThe mean vorticity balances in the tropical atmosphere during December 1982 to February 1983, a season of extraordinary anomalies associated with the warming of the east equatorial Pacific Ocean, are determined using the 6‐hourly initialized and objectively analysed observations archived at the European Centre for Medium Range Weather Forecasts. the budgets are evaluated at one upper (150 mb) and one lower (850 mb) tropospheric level, with particular emphasis on the balance at 150 mb, near the level of maximum outflow associated with organized deep convection in the tropics.The balances at the upper and lower levels are found to differ qualitatively from one another. At 850 mb, the zonal flow is weak and the relative vorticity and its gradient small compared with that of the Coriolis parameter. the vorticity balance is therefore essentially a Sverdrup balance between the stretching and horizontal advection of planetary vorticity, and an assumption of linearity about a basic state at rest is not unreasonable. None of this applies, however, at 150 mb.At 150 mb, the balance is essentially nonlinear, and nearly inviscid, the primary balance obtaining between the stretching and advection of absolute vorticity by the time‐mean horizontal flow. Transients play a small though not insignificant role, but terms involving the vertical advection and twisting of vorticity are small enough to be neglected.The essentially nonlinear character of the upper tropospheric dynamics is highlighted by demonstrating the inability of a diagnostic barotropic model linearized about the observed steady zonal mean flow to simulate the anomalous flow in the central Pacific correctly. the idea of the expansion of material circuits in regions of strong convective outflow, leading to a rapid spin‐down of the local absolute vorticity, and the production of a region of almost zero absolute circulation, is of crucial importance. This is seen to be intimately related to the importance of nonlinearity.
Planetary wave‐mean flow interaction in the stratosphere: A comparison between northern and southern hemispheres
Authors: Shiotani M. , Hirota I. 
Published: July 2010

AbstractBy the use of stratospheric height and temperature field data obtained from the TIROS satellite, dynamical interaction between planetary waves and mean zonal winds in the stratosphere is investigated. Special attention is paid to differences between northern and southern hemispheres. an analysis is made for pressure levels from 70 to 0.4 mb during the period from June 1981 to May 1982. Eliassen‐Palm (E‐P) flux diagnostics are used as a powerful and useful tool to investigate the wave‐mean flow interaction.From winter to summer the seasonal marches of wave activity (measured by the E‐P flux) and of mean zonal wind are different between the two hemispheres. In the NH, wave activity varies intermittently with a characteristic timescale of about two weeks. Once the core of the stratospheric westerly jet shifts poleward due to a minor warming, the subsequent wave activity breaks the westerlies dramatically to replace them by the easterlies in association with the sudden warming, whilst in the SH wave activity in mid‐winter is quiet, corresponding to small time variations of the maximum westerly speed. In late winter the core of the stratospheric westerly jet suddenly shifts poleward and downward due to a wavenumber‐2 minor warming. After the shifting of the westerly jet the wave activity of wavenumber 1 is enhanced, and continues until early summer.On the basis of this observational evidence we discuss: (i) the seasonal evolutions of wave activity and the mean zonal wind; (ii) the interannual variability of the stratospheric circulations; and (iii) the time variation of wave activity.
Variance spectra of observed winds and initialized wind fields at the 500 mblevel over europe
Authors: Brown Philip S. , Robinson G. D. 
Published: July 2010

AbstractTwo‐dimensional scale (variance spectrum) analyses were made of the wind field at 500 mb over Europe and western Asia. Seven separate 20‐ to 30‐day periods, four in winter and three in summer, were investigated. On all occasions actual unmodified measured winds were used; on two of them the same techniques were applied to the interpolated and initialized data on a regular grid used by the National Weather Service in prognostic models. Standard analytical spectral analysis cannot be used on the unmodified observations; the method used involved iterative adjustment of a first guess spectrum to fit calculated variance and covariance functions.Some conclusions are: Our examination of the data does not unambiguously establish an ‘inertial range’ in the spectrum. the Taylor transformation of frequency to wavenumber is not reliable at scales more than about 1000 km. There are significant diurnal changes; in the summer periods they are not confined to the small unresolved scales.The Weather Service initialization‐interpolation procedure quantitatively removes variance at less than twice the grid scale, but also affects the spectrum in the resolved scales to a degree which might be significant in prognostic models.On two occasions there was evidence of widespread and persistent variance on a scale of about 350 km.
Measurements and predictions of flow and turbulence over an isolated hill of moderate slope
Authors: Mason P. J. , King J. C. 
Published: July 2010

AbstractField measurements of the mean flow and turbulence statistics in neutral static stability flow over an isolated, roughly circular hill, Blashaval, are presented. Blashaval rises approximately 100 m above the surrounding terrain and has a base diameter of about 800 m. the flow speed at 8 m over the summit is found to be increased by a factor of 1.7 over the upstream value and the flow direction reverses in the lee of the hill. the turbulence structure observed above the summit shows marked variations with height. the observed mean flow is compared with results from a model which makes a careful application of linear theory to real terrain. the turbulence measurements are compared with results from available theories.