bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of 500 mb anomalies in long‐range forecasting
Authors: Ratcliffe R. A. S. 
Published: February 2007

AbstractAn objective method of predicting the category of 15‐day and monthly rainfall and mean temperatures in terms of terciles and quintiles over England and Wales is developed. The method selects those areas in the Northern Hemisphere where anomalies on 500 mb monthly mean charts preceding warm months have been significantly different from the anomalies in the same areas preceding cold months at the same time of year. For this purpose data over the period 1945‐72 have been used and Welch's test has been applied to assess the significance of the difference between the two means.Having found the areas which have been significantly different before warm and cold months, the anomalies at all grid points within these areas are added for each year of the data, taking due account of sign, and the years then ranked in terms of the total anomalies. The result is a list with most of the cold years at the top, the average ones in the middle and the warm ones at the bottom. If the same procedure is carried out on current data and the current month included in the ranking, a forecast of the probable temperature category can be made.A similar procedure is used for rainfall, and for both elements on the 15‐day time scale. A test involving some 250 forecasts over a period of a year shows excellent results.
Calculations of electric field growth, field structure and charge distributions in thunderstorms
Authors: Illingworth A. J. , Latham J. 
Published: February 2007

AbstractCalculations have been made of the electrical evolution of a thundercloud under the action of various precipitative charging mechanisms. the cloud is cylindrical, with a defined width and depth. the finite dimensions of the cloud permit the distributions of axial field and charge to be calculated. This was not possible with the infinite parallel‐plate cloud model employed by earlier workers, which in any event has been shown to provide greatly exaggerated rates of field growth.The calculations take into account various criticisms of other precipitative treatments. These features include the important effects of the dependence of the charge transfer, under an inductive mechanism, on the charge carried by the larger of the two colliding particles and the angle defining their point of separation. Levitation, ionic dissipation and multiple collisions of cloud particles with precipitation are also discussed and shown to be unimportant in situations of interest.It is found that the water‐water inductive charging mechanism is quite inadequate to explain thundercloud electrification. the available experimental evidence is insufficient to permit a conclusion to be drawn concerning the importance of the corresponding water‐ice mechanism.Two established mechanisms which appear to be capable of producing breakdown fields in the available time ‐ although only marginally ‐ both involve collisions between hail pellets and ice crystals. These are the inductive mechanism and the thermoelectric mechanism. Although these two processes are about equally powerful, the details of the predicted field‐growth rates, the field structure and the charge distributions under these two mechanisms are quite different. Analysis of the available field evidence is consistent with the inductive theory in some cases and the thermoelectric theory in others. However, a combination of these two processes appears to be consistent with all the evidence, and to provide a tenable theory of thundercloud electrification.
Measurements of the deposition coefficient for ice, and its application to cirrus seeding
Authors: Choularton T. W. , Latham J. 
Published: February 2007

AbstractTwo techniques have been used to measure the deposition coefficient β for water vapour molecules onto ice formed from distilled water, from 0·01M HCl and from 0·1M HCl. One involved measurement of the evaporation rates of ice spheres at laboratory pressure. the other involved measurement of the equilibrium temperature achieved by a shell of ice surrounding a resistor within which electrical power was being dissipated at a known rate; this experiment was conducted at low pressures (< 10−2torr). Measurements of β were made over the temperature range −37 to −9°C.It was found that for pure ice β increased from 10−3 at −37°C to 5 × 10−3 at −9°C. Similar temperature dependency was found for the ice specimens formed from HCl solutions, but the values of β were lower at all temperatures. This reduction was greater for the more contaminated ice.The measured values of β were employed in calculations of the distance which cirrus crystals will fall through undersaturated air below cloud base. Various humidity structures and temperature distributions were considered. For a particularly well‐documented case it was calculated that crystals of dimensions 80 and 300 μm will survive a fall of about 0·5 and 2·3 km respectively; these predictions are consistent with observation. These two values of survival depth are greater than the Maxwellian values (β = 1) by factors of about 3 and 1·2, respectively. It is concluded that in most situations the persistence of a stream of cirrus crystals is not profoundly affected by these new values of β but that in conditions conducive to the formation of middle‐level cloud the survival depths may be substantially increased.
Standard distributions of clear sky radiance
Authors: Steven Michael D. , Unsworth M. H. 
Published: February 2007

AbstractDiffuse radiation from cloudless skies varies with solar height and atmospheric turbidity but its angular distribution remains generally characteristic of single scattering. It was found that when sky radiance measurements, N, were normalized with respect to horizontal diffuse irradiance, Sd, the angular distributions of N/Sd were remarkably independent of atmospheric turbidity. This enabled standard distributions of normalized sky radiance, based on a long series of measurements on clear skies, to be drawn up for different solar zenith angles. Due to the difference between radiometric and photometric units these distributions are not comparable with previously published luminance distributions. Departures due to variation in atmospheric turbidity, of the radiance distributions from the proposed standards, were analysed and found to be small for the range of turbidities (τα from 0·1 to 0·5) normally encountered in Britain.
Evaluation of the aerodynamic method of determining fluxes over natural grassland
Authors: Saugier B. , Ripley E. A. 
Published: February 2007

AbstractProfiles of wind speed, temperature, humidity, and CO2 content up to a height of 6.5 m were measured over a period of several months above natural grassland in an area with an average fetch of 2km. Profile shapes have been analysed in relation to atmospheric stability.In unstable conditions, temperature and CO2 profiles exhibit similar shapes and depart more from logarithmic than does the wind profile. All profiles are relatively well described by existing empirical stability corrections.In stable conditions all profiles have approximately the same shape: they depart from the logarithmic profile at moderate stabilities and return to it at strong stabilities. However, the oft‐quoted log‐linear profile does not provide a very good fit.Empirical stability corrections have been used to develop a generalized aerodynamic method for flux computation. This method tends to underestimate (by up to 20%) fluxes during unstable conditions and to overestimate (by up to 40%) in moderately stable conditions. These results stem from a comparison of aerodynamic and Bowen ratio estimates of sensible heat flux. They are in essential agreement with the analysis of profile shapes.The drag coefficient of vegetation may be predicted from the leaf area index. This allows the use of a simplified aerodynamic method, based on measurements of wind speed at one level and of temperature (or H2O or CO2) at two levels.
The influence of drop size distribution on the production of secondary ice particles during graupel growth
Authors: Mossop S. C. 
Published: February 2007

AbstractThe production of secondary ice particles when a moving body gathers rime in a supercooled cloud at −5°C has been studied for various drop size distributions. It is found that the rate of production of ice ‘splinters’ depends not only upon the concentration of large drops (⩾about 24 μm diameter) but also upon the concentration of small drops (⩽about 13μm) in the cloud.
Spectral distribution of solar radiation. II: Global and diffuse
Authors: McCartney H. A. 
Published: February 2007

AbstractMeasurements of the spectral distribution of global and diffuse solar radiation made in both wide and narrow wavebands are reported. Relationships between the ratio of diffuse to global irradiance, α, in both the visible and total solar wavebands, and atmospheric turbidity and zenith angle are developed. Narrowband measurements are analysed to yield relationships between α and spectral turbidity in the waveband 400–800 nm. The measurements indicate that atmospheric turbidity has a greater influence on both the magnitude and shape of diffuse irradiance than of global. The biological implications of the results are briefly discussed.
Three‐dimensional lee‐wave pattern
Authors: Gjevik B. , Marthinsen T. 
Published: February 2007

AbstractSatellite photographs are analysed to study the lee‐wave patterns generated by isolated islands in the Norwegian Sea and the Barents Sea.In situations where the wave motion is confined to the lower atmosphere (trapped waves) the waves are located within a wedge‐shaped wake behind the islands. Both the diverging wave type, where the crests are orientated outwards from the centre of the wake, and the transverse wave type, where the crests are nearly perpendicular to the wind direction, are observed. The former wave type is, however, the more common.In certain situations a long single‐crested wave is observed at Jan Mayen. The wave appears on photographs as a straight lane in the cloud layer. In one case it extends sideways from the island to a distance of about 350km. Wave kinematics is used to obtain the phase lines for a steady wave pattern for different atmospheric models. The theory is found to explain some important features of observed wave forms.
Penetrative convection at the top of a growing boundary layer
Authors: Mahrt L. 
Published: February 2007

AbstractMotions at an entraining interface of a growing mixed layer are ideally partitioned into large eddies, such as plumes and thermals which act to distort the interface, and smaller scale turbulence responsible for entrainment through the interface.Influences of horizontal entrainment and pressure effects on the depth of penetration of large eddies into the stratified free flow are examined. This penetration plays an important role in the initiation of cumulus at the mixed layer top and modifies the turbulence energy balance and entrainment rate there. For example, previous models predict the entrainment rate to depend on the cube of the fundamental velocity scale at a stratified interface and linearly on this velocity scale with vanishing stratification (free entrainment). The present development, which includes specific roles of penetrating elements, suggests a possible intermediate quadratic regime corresponding to weak inversion strength.
Microphysics and dynamics of clouds associated with mesoscale rainbands in extratropical cyclones
Authors: Matejka Thomas J. , Houze Robert A. , Hobbs Peter V. 
Published: February 2007

AbstractMeasurements obtained with research aircraft in clouds associated with various types of mesoscale rainbands in extratropical cyclones have been examined together with radar data and other detailed measurements. The analyses have yielded information on the structure and microphysical characteristics of the clouds and the nature of the vertical air motions in the clouds associated with each type of mesoscale rainband, and schematic models of the different mesoscale rainbands have been constructed.In clouds accompanying warm frontal rainbands, ice particles formed above the warm front, probably in shallow convective cells, and fell into the stable air mass below, where they grew by aggregation and helped glaciate stratiform clouds.Warm sector rainbands resembled squall lines. A younger, convectively active rainband occurred just ahead of an older, less convectively active one. The younger rainband contained both cloud liquid water and ice particles, and ice particles were growing by riming. The older rainband was nearly glaciated, with ice particles growing by aggregation.Narrow cold frontal rainbands were located along the convergence lines at the advancing edges of cold frontal zones. Each was associated with a convective updraught, 1 to 5 km wide and 1 to 3ms−1 in magnitude, and a similarly narrow downdraught. The core of the updraught contained young, developing cloud, with much higher cloud liquid water content and lower ice particle concentration than in its immediate surroundings. Ice particles grew by aggregation and were heavily rimed. Wide cold frontal rainbands (several tens of kilometres in width) occurred when lifting above a cold front was enhanced to several tens of centimetres per second. Clouds in this region consisted of supercooled water and ice and contained embedded convective elements. Below the cold front, high concentrations of ice particles grew by aggregation.Prefrontal surges of cool and dry air occurred above the warm front and ahead of the cold front in occluded cyclones. A surge rainband, resembling a wide cold frontal rainband, occurred at the leading edge of the surge and was followed by a field of convective elements. These elements, sometimes arranged in lines, were in various stages of development.Postfrontal rainbands were lines of convective clouds located well behind a cold front. They may have been associated with secondary fronts and sometimes appeared to behave as organized convective systems.
Correction of flux measurements for density effects due to heat and water vapour transfer
Authors: Webb E. K. , Pearman G. I. , Leuning R. 
Published: February 2007

AbstractWhen the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived.If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre‐dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required.If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required.These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.
The transport of minor atmospheric constituents between troposphere and stratosphere
Authors: Robinson G. D. 
Published: February 2007

AbstractMeasurements of the water vapour content of air in the upper troposphere and lower stratosphere are reviewed. They are interpreted to indicate that significant upward movement of air through a pressure level of about 100 mb, by processes of any scale, occurs only in equatorial latitudes, but they leave uncertain the mechanism of the upward transfer. This implies that contaminants emitted into the atmosphere below this level can reach the upper stratosphere only by way of the equatorial tropopause and after passage through precipitating cloud. The minimum hemispheric exchange of mass through this level is about 1017kg per year. The mass balance of several minor atmospheric constituents, naturally or artificially introduced in the surface layers or in the high stratosphere, is shown to be consistent with this minimum mass exchange.
Dew and thermal lag: Measurements and an estimate of wetness duration on cocoa pods
Authors: Butler D. R. 
Published: February 2007

AbstractA model to estimate the duration of condensed water on the surface of cocoa pods after sunrise is modified to use readily available meteorological data. Changes in wind speed, air temperature and humidity with height and time in a cocoa plantation are presented. Pod temperature and the amount of condensation calculated from the maximum and minimum temperatures and humidity at 0900h agree well with measured values. The effects on pod wetness of changing pod size, short‐wave radiation and wind speed are investigated.
The albedo of a tropical evergreen forest
Authors: Pinker R. T. , Thompson O. E. , Eck T. F. 
Published: February 2007

AbstractThe diurnal variation of the average albedo, during 1970, over a tropical dry evergreen forest and a nearby clearing was investigated. The study is based on a most comprehensive set of solar radiation data in Southeast Asia. A strong dependence of the albedo on the zenith angle is evident. This dependence is subdued during cloudy days. The average midday albedo for the winter monsoon season is 10.6 for the forest and 13.4 for the clearing; for the summer monsoon it is 12.0 for the forest and 14.6 for the clearing. Generally, results show great uniformity. The largest standard deviations are 0.05 with a more representative value in the range 0.01–0.02.
The diagnosis of middle latitude synoptic development
Authors: Hoskins B. J. , Pedder M. A. 
Published: February 2007

AbstractThe use of diagnostics based on different forms for the forcing term in the omega equation is explored. These forms are the two‐level and continuous versions of the approximation used by Sutcliffe (1947) in his development theory, the usual dynamical meteorology version involving vorticity and thermal advection, and that involving the so‐called Q‐vectors which was introduced by Hoskins et al. (1978). The diagnostics are applied to a model baroclinic wave and to a subjectively analysed real data case. The Sutcliffe form is simplest and gives a global view of the system movement and development, but details such as active frontal regions are missed. The vorticity and thermal advection form has few advantages. It is demonstrated that the Q‐vector analysis can provide more information than the Sutcliffe form in describing details of system development, particularly with respect to (a) a vectorial view of the horizontal ageostrophic motion field, and (b) some indication of the intensity of frontal circulations. A case is presented for including Q‐vector fields in low‐ and mid‐tropospheric forecast charts.
Cluster analysis of rainfall stations of the Indian peninsula
Authors: Gadgil Sulochana , Narayana Iyengar R. 
Published: February 2007

AbstractPrincipal component analysis is applied to derive patterns of temporal variation of the rainfall at fifty‐three stations in peninsular India. The location of the stations in the coordinate space determined by the amplitudes of the two leading eigenvectors is used to delineate them into eight clusters. The clusters obtained seem to be stable with respect to variations in the grid of stations used. Stations within any cluster occur in geographically contiguous areas.
The relevance of conditional symmetric instability to the prediction of mesoscale frontal rainbands
Authors: Bennetts D. A. , Sharp J. C. 
Published: February 2007

AbstractThis paper examines the theory of Conditional Symmetric Instability (Bennetts and Hoskins 1979) and considers its relevance to meso‐scale frontal rainbands. The theoretical growth rate of the instability is evaluated from synoptic scale data obtained from a numerical forecast model and compared with observations of the horizontal structure of rainfall observed by radar. One case study is presented in detail and a further 44 cases summarized. Rainbands were observed on 80% of the occasions on which they were predicted.
Two‐dimensional convection in non‐constant shear: A model of mid‐latitude squall lines
Authors: Thorpe A. J. , Miller M. J. , Moncrieff M. W. 
Published: February 2007

AbstractNumerical simulations of two‐dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non‐constant shear. The cumulonimbus are initiated by low‐level convergence created by a finite amplitude downdraught. These experiments have constant low‐level shear and differ only in the profile of mid‐and upper‐level winds. Quasi‐steady convenction is produced if the mid‐ and upper‐level flow has small shear and the low‐level shear is large. The surface precipitation ismaximized for no intial relative relative flow aloft, if stationary, this storm (P(O)) can give prodigious locilized rainfall; P(O) is the two‐dimentisonal equivalent of the supercell. These results are placed in context with previous two‐dimensional simulations. Attention is drawn to the similiarity with previous two‐dimensional simulations. Attention is drawn to the similarity with squall lines in central and eastern U.S.A.Storm P(O) is analysed by construction of time‐averaged fields of streamfunction, vorticity, teperature, and height deviation. The smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows; an overturning updraught, a jump type updraught, a shallow downdraught, a low‐level rotor, and a boundary layer.An idealized analytical model is described by solution of the equations for steady convection. These solutions, for the remote flow, are derived from energy conversation, mass continuity and a momentum budget, and they give relationships between the non‐dimensional parameteres of the problem. It is apparent that the convection is a high Froude (or low Richardson) number flow demanding the existence of a cross‐storm pressure gradient. Inherent in this idealized model is a vortex sheet between updraught and down‐draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation. Furthermore, these results show that in two‐dimensions both non‐constant shear and a shallow downdraught are necessary to maintain steady convection.
Angular momentum transports in tropical cyclones
Authors: Holland Greg J. 
Published: February 2007

AbstractAngular momentum budget equations are developed for Eulerian and Lagrangian cylindrical coordinate systems centred on a tropical cyclone. All non‐friction terms are reduced to boundary transports and the effects of cyclone motion in the Eulerian coordinate system are isolated. A number of intensifying and weakening composite northwest Pacific cyclones are used to illustrate the physical role and relative importance of each process in the maintenance or destruction of tropical cyclones at various intensity stages.