bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy budgets in pine forest
Authors: Stewart J. B. , Thom A. S. 
Published: February 2007

AbstractHourly energy budgets measured in Thetford Forest, Norfolk, are analysed for seven fine days in months from May to September.Values found for the Bowen ratio β ranging from near 1 to 4 or more, are used to show that the bulk physiological resistance rST of the forest exhibits a consistent diurnal trend, from near 1·2 s cm−1 in the forenoon (once the trees are dry) to as much as 4 s cm−1 by late afternoon ‐ consistent with independent biological measurements (Robins, personal communication). In contrast, the forest's bulk aerodynamic resistance r generally lies between 0·05 and 0·10 s cm−1. The ratio rST/r alone, of order 20:1, is shown to imply that transpiration from the forest must occur at rates much less dependent, primarily, on net radiation, Rn, than on ambient vapour pressure deficit (v.p.d.), (provided that the latter is not too small, i.e. ≮ 1 mb per 100 W m−2 of Rn, say); and also that the evaporation of intercepted rainfall from the trees must occur at about 5 times the corresponding transpiration rate under the same meteorological conditions. In addition, because lighter winds during fine weather tend to favour larger v.p.d's the observed decrease in transpiration rate with increasing wind speed is much larger than that expected from the accompanying decrease in r alone.Other conclusions are (i) that the storage associated with a 1° C change in air temperature per hour, within the canopy, is 18 W m−2, which is not always negligible, as it is for short vegetation; and (ii) that values derived for the dimensionless excess resistance parameter, B−1, although remarkably small, 2 to 3 for u* ∼ 0·75 m s−1, are commensurate with other bulk aerodynamic resistances in the system: accordingly, the easily‐derived surface resistance parameter, rs, (Monteith 1965; Thom 1972) provides an estimate of rST for the forest within 10 per cent for all β > 0.
The evolution of droplet spectra by condensation and coalescence in cumulus clouds
Authors: Jonas P. R. , Mason B. J. 
Published: February 2007

AbstractThe paper describes calculations of the development of droplet‐size spectra in cumulus clouds under the combined effects of condensation and coalescence. It is demonstrated that the concentration of condensation nuclei is a more important factor in controlling the onset of precipitation than is the updraught, at least for small clouds. It is shown that condensation can indirectly affect the growth rate of droplets larger than 25 μm radius by enhancing the growth of the smaller droplets which are then captured more efficiently by the larger ones. The overall result is to produce more rapid distortion of the droplet spectrum and more rapid growth of the largest drops than would occur by condensation and coalescence acting separately to produce an apparent barrier to the growth of droplets between 20 μm and 30 μm in radius. The onset of precipitation in continental clouds containing a high nucleus concentration depends rather critically on the values used for the collection efficiencies of droplets of radius < 40 μm and may be considerably accelerated if the collection efficiencies are increased by small‐scale atmospheric turbulence.
The translation velocity of convective plumes
Authors: Davison Douglas S. 
Published: February 2007

AbstractDuring July 1971, an intensive experimental programme was undertaken in south‐eastern Alberta to measure the turbulence statistics in the planetary boundary layer (PBL), using a 92‐m tower, an array of four smaller towers and an instrumented T‐33 aircraft from the National Aeronautical Establishment of the National Research Council, Ottawa.In this first paper is reported the measurement of the translation velocity of convective plumes, determined by means of an array of towers, at a height of 3.5 m. The direction of plume motion was found to be close to that of the surface wind. The speed of plume motion was found to be close to the wind speed near the top of the surface shear zone; this result is different from previous estimates using different techniques. A dynamic model of the plume was used to show that a translation speed close to the wind speed near the top of the surface shear zone (as observed) allows plumes to exist at a lower thermal instability level than any other possible translation speed.These results mean that Taylor's frozen field hypothesis is not applicable to plume scales since the plumes (although not the air inside them) move at a speed independent of height.
The estimation of solar radiation under cloudless skies with atmospheric dust
Authors: Collier L. R. , Lockwood J. G. 
Published: February 2007

AbstractObservations of global radiation received in a small catchment in Yorkshire were analysed for clear sky conditions and an empirical relationship of the formQ = 1380 sin θ(a + b sin θ) W m−2Found, between incoming solar radiation Q and the solar elevation θ, where a and b are constants. The constants differ markedly from those obtained in a similar analysis of data from eastern Atlantic weather ships, suggesting that the radiation, under cloudless skies, over inland Britain, is only about 60% of that received under cloudless skies over the eastern Atlantic.
Turbulent diffusion within a wheat canopy: II. Results and interpretation
Authors: Legg B. J. , Long I. F. 
Published: February 2007

AbstractThe coefficient of turbulent diffusion was measured in a 1·25m tall wheat canopy using a uniform release of nitrous oxide, the energy and momentum balance methods, and the humidity profile. The nitrous oxide profile gave the most accurate values, KN in the lower two thirds of the canopy, and a regression of the energy balance estimates, KE, against KN had a slope of 1·17 ± 0·10 with a non‐significant intercept of 17cm2s−1.The mean day time profile of KN was exponential, K(z) = K(h) exp(−γ(1‐z/h)) with γ = 3·9 when u(h) < 1·2m s−1 increasing to 5·3 when u(h) > 1·2m s−1. But analysis of KN for the height interval 0·3 to 0·8m shows the importance of thermal stability, and the results are related to the non‐dimensional stability parameter g/T(ΔT/Δz/(u(h)h2) where ΔT/Δz is the temperature gradient and u(h) is the windspeed at crop height, h.The large scatter in the results was attributed to the heterogeneity of the crop. Also the wind profile was frequently S‐shaped defying a simple one‐dimensional analysis and causing the momentum balance to give nonsensical results. Hence it seems unlikely that one‐dimensional analysis of transfer can give values of K allowing an accurate estimate of the source and sink distributions within a dense crop canopy.
Secular changes in South African rainfall: 1880 to 1972
Authors: Tyson P. D. , Dyer T. G. J. , Mametse M. N. 
Published: February 2007

AbstractAnalysis of time series for 157 stations with records covering the period 1910–1972 and for fewer stations with records extending back to 1880 suggests that the commonly held view that South Africa, as a whole, is undergoing progressive desiccation must be questioned. Instead the data suggest the specific regional occurrence of weak (but nonetheless readily discernible) oscillations of 16–20 and 10–12 years, the ubiquity of 3–4 year fluctuations and the spatially distinctive occurrence of a quasi‐biennial oscillation.
Penetrative convection in the absence of mean shear
Authors: Farmer David M. 
Published: February 2007

AbstractThis paper reports the first large‐scale observations of a developing mixed layer in which only convection can be causing the deepening. The convection arises from solar heating of water beneath lake ice. Since the water is below its temperature of maximum density, heating due to the absorption of radiation passing through the ice results in a mixed layer which increases in thickness with time. Observations taken with an electronic bathythermograph and by recording thermistor chains have permitted the estimation of that fraction of kinetic energy made available by the gravitational instability, which is converted into potential energy by entrainment of stable fluid as the convecting layer advances. Twelve independent estimates vary from 0.003 to 0.113 with an average value of 0.036. This result qualitatively agrees with the laboratory work of Deardorff, Willis and Lilly (1969) who found that only a small fraction (about 0.015) was recovered in this way. However, relatively little penetration can have a significant effect on mixed layer growth; the results obtained in the present study correspond to a mixed layer thickness 17% greater than that predicted for zero penetration in the case of a linear initial density profile.
New England coastal frontogenesis
Authors: Bosart Lance F. 
Published: February 2007

AbstractNew England coastal frontogenesis is investigated on the basis of individual and climatological case studies. The results suggest that differential friction plays the role of the synoptic scale geostrophic deformation in packing the isotherms together for this mesoscale boundary‐layer frontal phenomenon. An initial temperature gradient must be present for the differential friction mechanism to be effective. Geostrophic deformation is incapable of initiating coastal frontogenesis while the maximum area of observed deformation coincides with the location of the developing front.Coastal frontogenesis is associated with a pronounced sea level cold anticyclone to the north and east of New England in all cases studied. Differential friction between the northerly inland flow and the more easterly onshore flow then sets up favourable shoreline deformation and convergence fields leading to frontogenesis in the presence of differential thermal stratification. The time scale for an order‐of‐magnitude increase in the horizontal temperature gradient appears to be one‐half to one day depending upon the contribution of differential diabatic heating.The orientation of the New England shoreline is such as to favour frontogenesis across extreme eastern Massachusetts and Rhode Island. An axis of relatively high precipitation is noted just to the west of this favoured locale on the climatological charts, consistent with a thermally direct circulation about the front.
Note on a preliminary scheme for storm surge prediction using numerical models
Authors: Flather R. A. , Davies A. M. 
Published: February 2007

AbstractThe initial stages of an investigation aimed at setting up a new system for the prediction of storm surges in the North Sea are described. The proposed scheme is based on the use of dynamical finite‐difference models of the atmosphere and of the sea, the atmospheric model providing the necessary forecasts of meteorological data. These data are converted into the form required for input to the sea model, which then computes the associated storm surge.Some preliminary results are presented and discussed and an indication given of the further development of the system.
An objective exposure correction method for average wind speeds measured at a sheltered location
Authors: Wieringa J. 
Published: February 2007

AbstractThe representativity of station wind measurements can be increased by elimination of sheltering effects caused by small‐scale obstacles. It is shown how correction factors for this purpose can be obtained for each wind azimuth sector from analog wind records of the station itself, by extracting maximum gust speeds during periods with strong wind. The transformation is achieved using a gust factor model (Wieringa 1973) which relates the ratio of maximum and average wind speed to measuring height, surrounding roughness and gust wavelength. The concept of ‘effective height’ is criticized. It is indicated how the actual duration of the recorded maximum gusts can be obtained from station instrumentation response specifications, and it is shown that this duration exceeds 10 seconds for the usual combination of cup anemometer and galvanometric recorder. A trial climatological application shows how omission of exposure correction may lead to exaggeration of mesoscale horizontal wind gradients.
On some quasi‐periodic oscillations observed during a field investigation of radiation fog
Authors: Roach W. T. 
Published: February 2007

AbstractQuasi‐periodic oscillations of period 10–15min, observed in net flux of long‐wave radiation, surface temperature and wind during the development of a radiation fog on 7 December 1971, were found to have a significant phase relationship which persisted for about three hours. An interpretation of this phenomenon is suggested in terms of the evidence given by Roach, Brown, Caughey, Garland and Readings (1976) and Brown and Roach (1976) that the development of radiation fog is controlled by a (fluctuating) balance between radiative cooling and turbulent diffusion.
On the effect of radiative exchange on the growth by condensation of a cloud or fog droplet
Authors: Roach W. T. 
Published: February 2007

AbstractThe effect of radiative heat transfer on droplet growth is assessed. It is estimated that radiative cooling is the principal agent of droplet growth in radiation fog, and that supersaturations are very small – slight undersaturation may even occur – and may be relatively unimportant for droplet growth in this environment. Gravitational settling is shown to be the principal limiting factor on droplet growth in radiation fog.It is also suggested that radiative transfer may have some relevance to the unexpectedly large numbers of 5μm radius droplets observed in cumulus clouds by Warner (1969).
The effects of air pressure and water vapour content on the propagation of positive corona streamers, and their implications to lightning initiation
Authors: Griffiths R. F. , Phelps C. T. 
Published: February 2007

AbstractAs a first step in the construction and testing of a theoretical model of lightning initiation, measurements have been made of the ambient electric field Eo required to support the long‐range propagation of corona streamers as a function of dry air pressure pα and the partial pressure of water vapour pw. The experiments reveal that Eo falls more rapidly with pα than would be expected on the assumption that Eä/pα = const., which has been used in previous discussions of the problem of lightning initiation. Eo was found to increase linearly with pw. It appears that Eo is considerably less than the field required to initiate corona from any type of hydrometeor excepting colliding drop pairs. Arguments based on these results are presented to show that the high fields in thunderclouds are probably restricted to regions that are small in extent compared with the dimensions of the thundercloud.
Lidar observations of the stratospheric aerosol: California, October 1972 to March 1974
Authors: Russell P. B. , Viezee W. , Hake R. D. , Collis R. T. H. 
Published: February 2007

AbstractThirty night‐time observations of the stratospheric aerosol were made between October 1972 and March 1974, using a ground‐based ruby lidar (laser radar) at Menlo Park, California (37.5°N 122.2°W). Vertical profiles of scattering ratio and particulate backscattering coefficient were obtained by reference to a level of assumed negligible particulate backscattering.The observation period preceded the major stratospheric penetration of the Fuego volcanic eruption and was evidently one of minimal volcanic influence. Nevertheless, there was appreciable variation among observations, including significant vertical movement of the scattering ratio peak near the time of the 1973 stratospheric warming. Maximum scattering ratios ranged between 1.08 and 1.19, indicating a decline in particulate backscattering by approximately an order of magnitude since the maximum observed shortly after the 1963 eruption of the Agung volcano. This decline in backscattering is shown to agree with the overall trend in twilight scattering and particle data, from balloons, during the same period. On a single night, sequential observations with ruby (694 nm) and dye (589 nm) laser transmitters were made, showing significant scattering‐ratio differences, due primarily to the wavelength dependence of molecular backscattering.An optical model, consistent with a number of stratospheric measurements made in the early 1970s by a variety of techniques, is used to convert the lidar‐measured backscattering values to other quantities. In this manner, good agreement is demonstrated between particle mass values inferred from lidar and aircraft filter measurements made on the same date. Values for turbidity and particulate optical thickness are similarly derived from the lidar data, giving values considerably smaller than those measured by search‐light in 1964–1965. To assist in radiative transfer calculations for the nonvolcanic period, a table of these optical thickness values is provided. Between 10 and 30 km, the lidar‐derived nonvolcanic particulate optical thicknesses are 0.005 and 0.004 for wavelengths of 550 and 700 nm, respectively.
Differentiation of diastereomeric conduramine derivatives under electron ionization and chemical ionization mass spectral conditions
Authors: Ramanjaneyulu G. S. , Prabhakar S. , Bhaskar G. , Vairamani M. , Yadav J. S. , Murty V. S. R. , Soujanya Y. , Sastry G. Narahari 
Published: February 2007

AbstractDiastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)‐6‐(N‐carbomethoxyamino) 1,2‐O‐isopropylidenecyclohex‐4‐ene‐1,2,3‐triol (1 and 2) and their O‐acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high‐resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H]+ ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra. Copyright © 2007 John Wiley & Sons, Ltd.
Effects of habitat restoration on the macroinvertebrate fauna in a foreland along the river waal, the main distributary in the Rhine delta
Authors: Bij De Vaate Abraham , Klink Alexander G. , Greijdanus‐Klaas Marianne , Jans Luc H. , Oosterbaan Johan , Kok Frank 
Published: February 2007

AbstractRiver engineering in the Rhine delta and water pollution have been major threats for the ecological functioning of the river in The Netherlands. To mitigate effects of river engineering, secondary channel construction in the forelands along the existing distributaries is considered to be an important measure for river restoration. These areas are the remnants of the former Rhine floodplain and the only area where habitat restoration is possible due to the river functions assigned. Secondary channel construction in the area called ‘Gamerensche Waarden’ was taken as an example to show effects of habitat restoration on the macroinvertebrate fauna. Totally 322 macroinvertebrate taxa were found during the monitoring period. During the first 3 years species richness in the area increased rapidly due to colonization processes in the channels following habitat development. After that period total number of taxa found in the channels stabilized at around 170. A clear positive relationship was demonstrated between habitat quality and species richness. Furthermore, the density of exotic species in the secondary channels was less than in the groyne fields of the main channel. The relatively low number of taxa in polluted habitats could be explained by the presence of the PCB 28 congener. Copyright © 2007 John Wiley & Sons, Ltd.
Water quality response to a pulsed‐flow event on the Mokelumne river, California
Authors: Henson Solomon S. , Ahearn Dylan S. , Dahlgren Randy A. , Nieuwenhuyse Erwin Van , Tate Kenneth W. , Fleenor William E. 
Published: February 2007

AbstractControlled water releases from reservoirs (i.e. artificial floods) are used as a management technique to remove fine sediments and detrital materials from spawning gravels, mobilize gravel bars and clear encroaching brush from stream banks. The effects of a managed release event on water quality were investigated on the lower Mokelumne River in the western Sierra Nevada, California. The managed release was characterized by an increase in flow over a 4‐day period (from 11 to 57 m3 s−1). Automatic pump samplers were used to collect samples for water quality from 0.7, 16.4, 37.4 and 54.4 km below Camanche Dam. These sampling sites provided water quality data for three distinct stream reaches: a gravel and sand‐textured substrate reach (0.7–16.4 km), a reach characterized by lentic conditions associated with a small reservoir (16.4–37.4 km), and fine sand and silt‐textured substrate reach (37.4–54.4 km). Water samples were analysed for total suspended solids (TSS), total nitrogen, ammonium (NH4‐N), nitrate (NO3‐N), total phosphorus, soluble reactive phosphorus (SRP), dissolved organic carbon (DOC), foecal coliforms and E. coli. Chemographs for all constituents exhibited spikes in concentration with each increase in streamflow for the rising limb. Fluxes of TSS, total P and total N released from the 0.7 to 16.4 km reach were 322, 0.32 and 0.70 Mg, respectively. The small reservoir acted as a sink for particulate materials retaining about 50% of TSS, 48% of total P and 43% of total N. However, the reservoir acted as a source of dissolved nutrients (NO3‐N = 0.28 Mg and SRP = 0.055 Mg). The stream reach below the reservoir (37.4 to 54.4 km) was a source of particulate materials, dissolved nutrients and bacteria, possibly due to agricultural and urban inputs. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of flow variability modification and hydraulics on invertebrate communities in the great fish river (Eastern Cape province, South Africa), with particular reference to critical hydraulic thresholds limiting larval densities of Simulium chutteri lewis (Diptera, Simuliidae)
Authors: Rivers‐Moore N. A. , De Moor F. C. , Morris C. , O'Keeffe J. 
Published: February 2007

AbstractFlow patterns in the Great Fish River in the Eastern Cape province of South Africa have changed from being seasonal, with predictable no‐flow periods during winter, to perennial following the completion of an inter‐basin transfer scheme in 1977 to provide a regular supply of irrigation water. Simulium chutteri (Diptera: Simuliidae) consequently became a problem species of pestilential proportions, due to increased flow volumes and current velocities favouring this species. In this study, aquatic invertebrates were sampled from the stones‐in‐current biotope with a range of current velocities at three sites on the Great Fish River, with a particular focus on pool/rapid areas favouring S. chutteri. The main aim of this paper was to determine whether critical hydraulic thresholds, including current velocity, could be derived for this species. Knowledge of the hydraulic preferences of S. chutteri is a prerequisite for any integrated control programme which combines larvicidal control with flow manipulation. S. chutteri was found to favour the rapids biotope with current velocities in excess of 90 cms−1, with preferences for higher current velocities increasing with life cycle stage. Additional hydraulic variables, at the scale measured in this study, did not correlate with larval densities. There is potential for more effective long‐term control of problem populations of larval blackfly in the Great Fish River through further research on the potential for using constructed in‐stream vanes to reduce current velocities in rapids of the river at critical periods of the year (July–October), based on flow duration/current velocity relationships. Copyright © 2007 John Wiley & Sons, Ltd.