bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical corona from ice hydrometeors
Authors: Griffiths R. F. , Latham J. 
Published: February 2007

AbstractIn contradiction to earlier work it has been found that substantial corona currents can be initiated from ice surfaces over a wide range of conditions. Measurements have been made of the critical fields required to initiate corona from ice particles a few millimetres in length suspended in a uniform electric field. The variables included size, shape, purity, orientation and the surface features of the particles, their initial charge, pressure and temperature. Currents of about 0.1 μA at onset were obtained and the details of the forms of discharge and associated currents were determined as a function of applied field. A particularly interesting finding was that substantial corona currents were obtained only at temperatures higher than −18°C. A semi‐quantitative explanation of these results is given in terms of the surface conductivity of ice. The characteristics of the streamers observed have been related to the Dawson‐Winn model as extended by Phelps. In view of these new results it is suggested that the role of corona from ice hydrometeors in a thunderstorm is of much greater importance than has previously been realized, particularly in connection with the initiation of lightning and the enhancement of ionic conductivity; the onset fields for corona emission from ice in the central regions of thunderclouds are probably in the range 400 to 500 kV/m.
Transmission function for infrared radiative transfer in an inhomogeneous atmosphere
Authors: Kuriyan Jacob G. , Shippony Zvi , Mitra Subir K. , Wurtele M. G. 
Published: February 2007

AbstractCalculations of the transmission of infrared radiation through the atmosphere must take into account inhomogeneities in the path due to variations of temperature, pressure and absorbing matter. For ozone absorption the method due to Curtis and Godson does not seem to yield results that are sufficiently precise. In this paper an improved approximation is developed that yields an analytic expression for the transmission function and this is compared with the exact results obtained from the Goody random model.
A case study of the measurement of snowfall by radar: An assessment of accuracy
Authors: Collier C. G. , Larke P. R. 
Published: February 2007

AbstractRadar measurements during a period of snowfall in a region of variable terrain are described. The accuracy of estimates of areal snow depth, using a calibrated radar, is shown to be similar to that achieved for areal rainfall using the same technique. This detailed case study supports similar conclusions made by other workers, who used more cases but fewer validating measurements. It is also shown that provided the variations in terrain height are not very large, compensation for the effects of melting over low terrain can be made in deriving the snow depth field by using two independent snow depth calibration measurements ‐ one representative of upland areas, and the other of lowland areas.
Persistence and orographic modulation of mesoscale precipitation areas in a potentially unstable warm sector
Authors: Hill F. F. , Browning K. A. 
Published: February 2007

AbstractIn this paper we use data from radars and raingauges in England, Wales and southern Ireland to study the motion and changes in intensity of mesoscale precipitation areas (MPAs) some tens of kilometres across as they traversed two regions of high land and an intervening stretch of sea. The MPAs studied were associated with an area of middle‐level potential instability within a windy and moist wintertime warm sector, a situation known to produce major orographic effects. Despite the very large modulation of the rainfall intensity by orography, it was found that most of the MPAs could be tracked for 6h over a distance of 600 km, all the way from the west coast of Ireland to southern England. The implications of this are discussed with regard to the use of radar and satellite data in short‐period forecasting.
Effects of coronae on electric fields beneath thunderstorms
Authors: Standler Ronald B. , Winn William P. 
Published: February 2007

AbstractIntense electric fields beneath thunderstorms produce electrical discharges (coronae) at the tips of trees, bushes and other sharp objects attached to the surface of the earth. We find typical corona current densities of about 1 nA m−2 in an 8 kV m−1 field at the ground. The ions released into the air limit the magnitude of the field at the ground to about 10kV m−1. Our measurements beneath thunderstorms with a balloon‐borne electric field meter show that the magnitude of the field a hundred metres above the ground is several times larger than at the ground; in one case the field 300 metres above ground was 6 times that at the ground. The substantial thickness of the space charge layer and the speed with which it vanishes when the electric field strength declines imply that the charge carriers have substantial velocities (0.4m s−1) either because their mobilities are high or because they are carried by air motions.Coronae also influence the time behaviour of the electric field at the ground. The field at the ground often changes very rapidly after a lightning flash. The rate of change decreases as the field approaches the value it had prior to the flash. In contrast, the field a hundred metres above the ground, which is often above most of the influence of space charge produced by coronae, increases more uniformly (linearly) during the time interval between lightning flashes. This behaviour is similar to that of the field farther aloft in the interior of the cloud. Our numerical simulations of the shapes of recovery curves indicate that the corona current density is more accurately described by a cubic function than by a quadratic function of the electric field strength at the ground.Despite strong influences of coronae, three properties of the field at the ground accurately reflect what happens above the space charge layer. First, the rapid changes in electric field during a lightning flash are not usually affected by corona space charge. Second, when the field at the ground is nearly constant it usually has the same polarity as the field above the space charge layer. And third, when the field strength at the ground is nearly zero, and when certain other conditions are met, the time rate of change of the field at the ground is the same as that above the space charge layer.
A Lagrangian statistical analysis of diffusion from a ground‐level source in a turbulent boundary layer
Authors: Hunt J. C. R. , Weber A. H. 
Published: February 2007

AbstractA Lagrangian statistical analysis is proposed for the motions of a single particle and the growth of a small cloud released from the ground in a turbulent boundary layer, essentially by considering the fluctuating as well as the mean vertical Lagrangian velocity, by noting that its integral time scale is much smaller than the travel time of a particle from the source and by estimating (quite conventionally) the Lagrangian statistics in terms of the measured Eulerian statistics of atmospheric surface layer turbulence, in neutrally stable conditions.Comparing the results with a 1968 analysis by P. C. Chatwin based on a diffusion equation, the same value is obtained for the dispersion of the vertical displacement of a particle as a function of its mean travel time; however, a small but physically significant difference is predicted for the growth of a cloud released at ground level.The validated diffusion equation is then used to relate the concentration of a cloud to that of a continuous plume. It is shown that the index, s, used in the exponential formula exp(–Azs) to describe observations of the concentration in a plume, varies slowly with distance downwind of a source. Diffusion measurements in the atmospheric boundary layer and in wind tunnels are shown by the theory to be consistent with turbulence measurements. The theory suggests the kind of further turbulence and diffusion measurements that ought to be made.
Turbulent transfer of sulphur dioxide to a wheat crop
Authors: Fowler D. , Unsworth M. H. 
Published: February 2007

AbstractFluxes of sulphur dioxide to wheat were measured over two growing seasons. The deposition velocity, vg, depended primarily on affinities of surfaces for SO2 and varied from less than 0.1 to about 1.5cms−1. Stomata were an important sink, and diurnal changes in stomatal resistance accounted for most of the variation in vg when leaves were green and dry. When leaves were wet with dew, vg was generally large, irrespective of the physiological state of vegetation. A resistance analogue of transfer to the canopy agrees well with published work and is used to estimate seasonal uptake of SO2 by the crop, showing that 30% of the sulphur content of the crop at harvest was probably supplied by absorption of SO2 through stomata.
Shade‐ring corrections for pyranometer measurements of diffuse solar radiation from cloudless skies
Authors: Steven M. D. , Unsworth M. H. 
Published: February 2007

AbstractWhen a shade ring is used to shield a pyranometer from direct solar radiation, a correction to the measured diffuse radiation is necessary to account for diffuse radiation intercepted by the ring. A general analysis is developed to relate shade‐ring corrections to the radiance distribution of diffuse radiation. The corrections are split into two components: a geometric component based on an isotropic sky and varying with shade‐ring dimensions; and an anisotropy component, relatively independent of ring dimensions. Shade‐ring corrections are calculated using mean distributions of the radiance of cloudless skies. Tables and figures are given for calculating these corrections as functions of latitude, ring dimensions and time of year. Comparisons with published measurements at a variety of sites reveal generally good agreement with calculations. Some of the discrepancies may be due to differences in aerosol scattering.
Long‐term budget of zonal momentum in the free atmosphere over Europe in winter
Authors: Holopainen Eero 
Published: February 2007

AbstractTwo sets of aerological data are used to study the time‐averaged budget of the zonal momentum in the free atmosphere over Europe in winter. In many respects the budget appears to be different from that reported by Holopainen et al. (1980) for North America.Over Europe the coriolis force associated with the southward‐directed ageostrophic meridional flow tends to decrease the westerly momentum. A compensating effect is caused by horizontal momentum flux convergence which takes place in the zonal as well as in the meridional plane and is due mainly to transient flow systems (large‐scale turbulence).The residual term in the momentum budget indicates that over Europe the sub grid‐scale processes on the average cause a small accelerating effect on the large‐scale zonal flow in the upper troposphere. The residual force over the mountainous region of Europe (5 °E ‐ 30 °E, 45 °N ‐ 50 °N) is a decelerating one in agreement with the results for the corresponding area of North America.
Measurements of the mean, solar‐fixed temperature and cloud structure of the middle atmosphere of Venus
Authors: Schofield J. T. , Taylor F. W. 
Published: February 2007

AbstractData from the orbiter infrared radiometer (OIR) of the Pioneer Venus mission have allowed the global structure of the middle atmosphere of Venus to be studied in detail for the first time. Between 4 December 1978 and 14 February 1979 this instrument made over 300 000 soundings in ten spectral channels, covering most of the northern and some of the southern hemisphere in the altitude range 65–100 km (100–0·01 mb). Preliminary analyses indicate that mean atmospheric structure in this region is strongly dependent on latitude and local time of day, although day‐to‐day variations are seen. This paper presents the mean temperature field and cloud top structure retrieved from the data of five OIR channels averaged in a solar‐fixed coordinate system. The retrieval scheme and the derivation of the weighting functions that characterize the vertical response of each channel are also described.The middle atmosphere can be divided into two distinct regions separated by a low‐latitude temperature minimum of less than 170K at 95km in the retrieved zonal‐mean temperature field. Below 95km, day‐night temperature contrasts are small but above 70km pole‐equator contrasts are positive reaching a maximum of 20–25 K at 85km. Fourier analysis shows that within 45° of the equator the longitudinal variation of temperature is dominated by wavenumber‐2 tidal structure with a phase that moves eastwards with increasing altitude. Above 95km, the pole‐equator temperature gradient is reversed, day‐night contrasts become appreciable and wavenumber‐1 longitudinal structure dominates. At equatorial latitudes mean cloud optical depth at 11·5 μn is unity at 100mb (66·5 km), and the cloud top has a scale height of 0·85 times the atmospheric value. The cloud top falls slowly with increasing latitude and has a wavenumber‐1 longitudinal dependence of £20mb (£1 km), with the highest cloud found just before the evening terminator. Retrievals are insensitive to cloud structure in the polar regions, but it is clear that the cool collar that surrounds the warm polar region is not a high‐cloud feature. It is in fact a deep temperature inversion in which temperatures can be more than 30 K less than equatorial values at the same level.
Air motion and precipitation growth in a major snowstorm
Authors: Browning K. A. 
Published: February 2007

AbstractA mesoscale analysis of the snowstorm of 8–9 January 1982 has been carried out using data from the U.K. weather radar network, the geostationary satellite Meteosat and other more conventional sources. More than 60cm of snow accumulated over S.E. Wales and neighbouring parts of England in association with an intense frontal zone. Much of the snow occurred during a period when synoptic forcing and orographic modulation were essentially steady. The depth of cloud and moist air was not great in the region of heavy snowfall in south Wales, but an orographically enhanced circulation on the mesoscale nevertheless led to efficient growth of precipitation through the seeder‐feeder mechanism. The seeder cloud was generated within a shallow current of air which ascended above the front and which originated from low levels, probably mostly from the boundary layer, on the warm side of the front. Precipitation was initiated within this current repeatedly along a well‐defined and remarkably stationary line just upwind of the south Wales coast. As the rising current travelled inland towards the E.N.E., convective generating cells embedded in it produced precipitation particles which fell into the underlying cold easterly flow. Considerable growth occurred as these particles descended through orographically enhanced feeder cloud, much of the growth occurring in the lowest kilometre or so.
The effect of Gaussian particle‐pair distribution functions in the statistical theory of concentration fluctuations in homogeneous turbulence
Authors: Sawford B. L. 
Published: February 2007

AbstractThe consequences for the theory of concentration fluctuations of different proposals by L. F. Richardson and G. K. Batchelor about the rate of separation of pairs of marked particles (giving rise to non‐Gaussian and Gaussian particle separation probability density functions respectively) are explored via two Lagrangian Monte Carlo models.The models are applied to an instantaneous one‐dimensional cloud source (which is approximately equivalent to a continuous line source) and in many respects give similar results for concentration fluctuations. The crucial difference is that whereas the non‐Gaussian model predicts, in agreement with observation, that at large time the fluctuations remain the same order of magnitude as the mean field (the ratio depending only on the source size), the Gaussian model incorrectly predicts that fluctuations ultimately vanish compared with the mean field.The reason for the failure of the Gaussian model is explored by partitioning the total fluctuations into contributions due to the variation of the distribution of material within the cloud (i.e. in coordinates relative to the centre‐of‐mass) and due to motions of the cloud as a whole (meandering). It is shown that at large time the Gaussian model accounts only for the meandering contribution to fluctuations, and by smoothing out all internal structure of the doud eliminates relative fluctuations.
A model of the feeder–seeder mechanism of orographic rain including stratification and wind‐drift effects
Authors: Carruthers D. J. , Choularton T. W. 
Published: February 2007

AbstractOrographic enhancement of rain via the ‘feeder‐seeder’ mechanism has been calculated using a stratified airflow model. The effect of wind drift on precipitation has been included. Comparisons have been made using potential flow models both in two and in three dimensions and in the model of M. J. Bader and W. T. Roach.For high windspeeds (≥ 15ms−1), when large enhancements occur, the potential flow treatment is sufficient. Inclusion of stratification does not significantly affect the total washout, although in the case of long hills (half‐length ≥ 10km) the precipitation maximum is moved upwind. For long hills the results are also in close agreement with the model of Bader and Roach. Over shorter hills both wind drift and non‐hydrostatic effects are important. Wind drift decreases both maximum and total enhancements. The Bader and Roach airflow formulation is inaccurate since it overestimates streamline displacements over the hill. Three‐dimensional effects are small except over short steep hills.
A weather radar correction procedure for real‐time estimation of surface rainfall
Authors: Collier C. G. , Larke P. R. , May B. R. 
Published: February 2007

AbstractSeveral sources of error have been identified in measuring rainfall by radar. In this paper we discuss these sources of error as they affect the calibration of a radar system using raingauge data. Present calibration techniques are considered, and the need for procedures based upon a knowledge of the structure of precipitation systems is noted. Finally, a new procedure is described, and its performance assessed for a number of cases of frontal and convective rainfall.
On sympathetic fluctuations of cloud water content and cloud top height in anticyclonic stratocumulus
Authors: Roach W. T. 
Published: February 2007

AbstractEvidence is produced which suggests that sympathetic fluctuations in cloud top height and total cloud water content observed during two case studies of nocturnal anticyclonic stratocumulus at Cardington (52°06′N, 0°24′W) may be due to vertical adiabatic displacements of the cloud layer as a whole, perhaps forced by local topography. Simultaneous observations from more than one site will be needed to test this tentative hypothesis, and these are defined.
The evolution of planetary‐scale 200 mb divergent flow during the FGGE year
Authors: Lorenc A. C. 
Published: February 2007

AbstractA descriptive study of the large‐scale horizontally divergent wind field during the FGGE year is presented, using empirical orthogonal functions (EOFs) of the 200 mb velocity potential. The mean flow and annual cycle are shown to be realistically related to climatological features. These and large‐scale patterns represented by the EOFs are consistent with very similar patterns of opposite sign seen at 850 mb.The main result of this work is the clear description of an eastward propagating wave in the 200 mb divergences with zonal wavenumber 1 and period 30–50 days. This mode has been deduced in other studies, and related to variability in the Asian summer monsoon. These results show it to exist throughout the FGGE year, and imply that a relationship exists between the planetary‐scale eastward propagating mode and smaller‐scale divergence bands apparently propagating northward over the monsoon region.
Convective and boundary layer parametrizations in a diagnostic model of atmospheric fronts
Authors: Thorpe A. J. , Nash C. A. 
Published: February 2007

AbstractNumerical integrations of initial value problems and observations have shown that along‐front geostrophy is a good approximation in frontal regions, even in the presence of strong frontogenetic forcing. Consequently the cross‐frontal circulation equation described by A. Eliassen in 1961 is a powerful diagnostic tool. Extra terms have been added to represent parametrized convective and boundary layer physics. The inclusion of cumulus heating modelled on that used in CISK theories produces bands of ascent whose scale decreases as the heating amplitude increases. For realistic cold fronts bands are produced just ahead of and behind the surface temperature contrast depending on the type of frontogenetic forcing.The application of this convective parametrization to finite amplitude circulations about a front is rather different from previous uses in theories of CISK. The solution method makes it simple to examine a much larger class of representations, hence providing a fresh appraisal of the parametrizations.The integrated frontogenetic tendency is calculated in the frame of reference moving with the front for the various cases considered. This allows discussion of the notion of a steady state front and indicates the crucial role of convective and boundary layer processes.
On the stability of forced non‐zonal flows
Authors: Andrews David G. 
Published: February 2007

AbstractAttention is drawn to the fact that the stability of forced, zonally asymmetric atmospheric flows depends not only on the flow configuration but also on the nature of the forcing. This fundamental point is illustrated by consideration of topographically induced flows in a barotropic non‐divergent model. It is shown that a steady barotropic basic flow which is not a free solution of the equations of motion can be forced in this model by any one of an infinite number of topographic configurations. Since the topography also influences the disturbances to the basic flow, the stability of this flow depends crucially on which topography is present.Other mechanisms which may contribute to the forcing of atmospheric climatological mean states (such as diabatic effects and the time‐averaged effects of transient eddies) are also mentioned, together with the implications of the present study for numerical investigations of the instabilities of such states.
Radiation budget components and their parametrization in JASIN
Authors: Lind Richard J. , Katsaros Kristina B. , Gube Marianne 
Published: February 2007

AbstractComponents of the radiation balance over the sea surface were measured from RV Meteor and MV Endurer during July, August and September in the eastern North Atlantic (59°N 12°W) during the 1978 Joint Air Sea Interaction (JASIN) Experiment. Each component was modelled using routine hourly surface weather observations and compared to measurements. These models were used to estimate radiation components for RV John Murray and HMS Hecla. Daily net radiation at the surface ranged from 50 to 190 Wm−2 during JASIN. Standard deviations of daily mean net radiation averaged 45 Wm−2 for phase I of JASIN (23 July through 8 August), and 23 Wm−2 for phase II (22 August through 3 September). Shortwave irradiance estimates made with an empirical formula due to F. E. Lumb, using solar zenith angle and cloud amount and type, gave results to within 10 Wm−2 for most 5‐day periods, confirming results of other investigators. Shortwave exitance calculations, based upon smoothed observations of albedo by R. E. Payne, were made using both measured and model‐derived shortwave transmittances. Our results showed high correlation between model results and measurements. A recent model of longwave irradiance by two of the authors, RJL and KBK, gave results to within 10 Wm−2 when compared to daily mean measurements. The accuracy of these models, over periods of a few days, was found to approach what is obtainable with direct measurements.