bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of horizontal convergence in precipitation using a Doppler radar ‐ a case study
Authors: Harrold T. W. 
Published: February 2007

AbstractA method of measuring convergence in precipitation using a Doppler radar is described. A case study illustrates the results obtainable. The presence of a ‘wind front’ (sloping shear zone), which could not be related to any feature on the synoptic scale, was revealed (Fig. 6). Layers of convergence and divergence, particularly in association with a frontal inversion, were identified (Fig. 7). Convergence below the front was largely compensated by a pronounced divergence (D ∼ 50 × 10−5 sec−1) immediately above the front. The computed vertical velocities (Fig. 9) showed ascent of the order of 10−2 mb sec−1 during the rain.Although measurements were made over an area of less than 300 km2, the evidence suggests that the variations of convergence were not purely local, but were a consequence of an organized dynamical system on a scale comparable with other features of fronts.
Lidar: A new atmospheric probe
Authors: Collis R. T. H. 
Published: February 2007

AbstractPulsed‐light techniques of probing the atmosphere have been greatly extended by employing lasers as energy sources in instruments called ‘lidars.’ Because of the nature of laser energy and the manner in which it is used in current and proposed systems, lidar is best discussed in terms of radar. Apart from the basic capabilities of lidar for detecting backscattering from atmospheric constituents, possibilities exist for more sophisticated techniques based on the wave nature of the energy. The basic capabilities of lidar, however, make it possible to observe the atmosphere with previously unknown resolution and sensitivity. Apart from providing new information about clouds, lidar has shown that the concentration of the particulate matter content of clear air is highly variable and that such variations can indicate the structure and motion of the clear atmosphere. These capabilities have applications in atmospheric and meteorological research and various operational activities.
An experimental study of wind‐generated waves on a water current
Authors: Francis J. R. D. , Dudgeon C. R. 
Published: February 2007

AbstractIn a laboratory wind tunnel, air was circulated above water which itself was moved by a pump. The resultant waves were measured photographically at fetches less than 7·3 m, and crudely averaged. With opposing water currents, both wave heights and wave lengths were larger than those produced with the same relative wind speed but with no water current: with an assisting water current, wave heights and lengths were both smaller. The waves were of the same steepness ratio for all wind speeds, and were breaking.
Mean meridional circulations in the Northern Hemisphere lower stratosphere during 1964 and 1965
Authors: Vincent D. G. 
Published: February 2007

AbstractZonally‐averaged mean monthly circulations in the meridional plane, which have been forced from momentum and heat sources, are presented for the 100–50 mb, 50–30 mb and 30–10 mb pressure layers, between 25°N latitude and 80°N latitude, during 1964 and 1965. The zonal momentum and continuity equations, written in spherical coordinates, are combined, using an iteration process, to compute mean meridional and vertical motions.Fixed boundary values are required for the vertical component at 10 mb where the downward vertical integration starts and for both components at 22·5°N and 82·5°N latitudes. These values are computed from the initial guess fields, which are based on approximate thermodynamic balance for the vertical component and a momentum balance for the meridional component. The effects of these boundary conditions on the interior motions are discussed.The results of the computed velocity components show a reasonable and consistent pattern, both in time and space. In winter months, motions are much more intense than in summer months and the flow patterns are characterized by cell‐like structures, having upward motions over the pole and downward motions over middle latitudes. It appears as though the lower stratospheric motions over mid‐latitudes are an extension of the tropospheric indirect mean cell. There is a poleward shift in the motions as winter progresses into spring and an equatorward shift as autumn progresses into winter. In summer, the motions are small and not too well organized.In the January and July 1964 momentum budgets, it is shown that a near balance exists between the Coriolis torque and the convergence of eddy momentum flux, which gives an approximate expression for calculating mean meridional velocities. In the January 1964 heat budget, at middle latitudes, a near balance is shown between adiabatic subsidence and heat sources due to radiation and eddy heat‐flux convergence. This balance implies an approximate solution for mean vertical motions. However, this approximation does not appear to be valid near the latitudinal boundaries during January or in certain regions during July.
The coreless winter at Scott Base, Antarctica
Authors: Thompson D. C. 
Published: February 2007

AbstractThe temporary early‐winter reversal of the downward trend in monthly mean surface air temperatures, which has been noted for other stations in the Ross Sea – South Pole region, is a particularly marked and persistent feature at Scott Base. An examination of temperature records shows that this reversal in the trend is probably due to a more frequent destruction of the low‐level surface inversion in these months, rather than a temporary increase in the level of warm air advection into the region.
The polar low as a baroclinic disturbance
Authors: Harrold T. W. , Browning K. A. 
Published: February 2007

AbstractThis paper describes the three dimensional airflow and precipitation within small ‘polar’ depressions which sometimes cross Britain during northerly outbreaks and which in winter can be responsible for heavy snowfalls. The data used in the study consist of Doppler and conventional radar information, together with routine synoptic data and sequential radiosonde ascents from the radar station. Three dimensional airflow was derived from the radiosonde data assuming that wet bulb potential temperature was conserved. Horizontal and vertical air velocities were also derived from the Doppler radar measurements.Previous knowledge of polar lows is meagre; they are generally thought to be shallow features resulting from enhanced convection within cold air flowing over a warm sea. However, the well‐developed polar low which is the main subject of this paper is shown to have been an essentially baroclinic disturbance. Although enhanced small‐scale convection occurred in one sector, the main area of widespread precipitation associated with the polar low was produced not by small‐scale convective overturning but rather by slantwise convection within a narrow tongue of air ascending steadily at about 10 cm s−1.The speed of travel and short wavelength (900 km) of the polar low in this study are consistent with its having formed in a region of enhanced baroclinicity within the polar air below 850 mb rather than in the major baroclinic zone bounding the polar air mass. Considerable low‐level baroclinicity within the polar air is also shown to have been present during the formation of other intense polar lows.
A theoretical study of cup and vane anemometers ‐ Part II
Authors: Ramachandran S. 
Published: February 2007

AbstractThe differential equation for cup and vane anemometers, developed earlier (Ramachandran 1969) is checked by comparing the computed overestimations of mean values in sinusoidally fluctuating winds with the experimental results of Deacon (1951). The equation predicts an overestimation of low frequency components in winds containing more than one sinusoidal component.Results from direct measurements are compared with those obtained from compensated data, using an approximate compensation technique.The logarithmic power spectra obtained from compensated data show peaked shapes arising out of the removal of the nonlinear overestimation of response at the low frequencies.
Eigenvector representations of Northern Hemispheric fields
Authors: Craddock J. M. , Flintoff Susan 
Published: February 2007

AbstractThe best eigenvector representations of Northern Hemispheric fields of the height of the 1,000 mb surface and the 1,000‐500 mb thickness are compared with those previously found for the 500 mb surface. It is shown that the use of the first 50 eigenvectors of the 500 mb fields, for all three types of field, produces a representation which is only marginally inferior to that obtainable by using three different sets of eigenvectors.
Generalizations of the Richardson criterion for the onset of atmospheric turbulence
Authors: Hines C. O. 
Published: February 2007

AbstractThe energetics of air‐parcel interchange are examined for the case in which the atmospheric potential temperature θ and background wind U are continuous but otherwise arbitrarily varying in space, and in which the direction of U is free from constraint. Interchange along a single s‐axis, inclined at angle α to the vertical, is shown to be energetically feasible if

where g is the gravitational acceleration. This condition, which is in general far less stringent than that imposed by the standard Richardson criterion, is suggested as a condition portending the onset of anisotropic turbulence. An isotropic interchange throughout a sphere is shown to be energetically feasible if

where the z co‐ordinate of the Cartesian x, y, z system is directed upward. This condition, which is in general somewhat less stringent than that imposed by the elementary Richardson criterion, may well portend the occurrence of isotropic turbulence. An outer time scale for the turbulence is estimated in each case, and its relevance to the occurrence of turbulence is discussed for the case when the background parameters of the system change with time.
Ice crystal concentrations in cumulus and stratocumulus clouds
Authors: Mossop S. C. , Cottis R. E. , Bartlett B. M. 
Published: February 2007

AbstractConcentrations of ice crystals of the order of 100 l−1 were found in some of the cumulus clouds sampled on four different days over or near the Australian mainland. These concentrations were 102 to 104 times higher than those of the ice nuclei present. The clouds had summit temperatures no colder than −13°C.Penetrations of shallow stratocumulus clouds with similar top temperatures showed that ice particle enhancement was much less important in these clouds, a factor of 10 being the upper limit.This difference in glaciation behaviour is considered in the light of differences in measured drop spectra, the stratocumuli having much narrower drop size distributions than the cumuli.Of all the suggested mechanisms by which the number of ice crystals could be enhanced, the evidence presented here favours the production of secondary ice crystals when ice particles grow by riming.
Electric field recovery after lightning as the response of the conducting atmosphere to a field change
Authors: Illingworth A. J. 
Published: February 2007

AbstractComputations are presented to show that the rearrangement of space charge existing in the fair weather conductivity profile of the atmosphere can explain the observed rapid recovery of electric field after a lightning flash without invoking a core of high conductivity within the cloud or charge at the cloud boundary. An exponential conductivity profile accurately accounts for the first second of observed recoveries at the ground, predicting increasingly rapid recoveries at greater distances. The whole of the rapid recoveries observed above clouds is also explained, but the suggestion that recoveries become even more rapid at higher altitudes remains to be verified by observation.The conductivity near the ground is less than that given by the exponential profile, and if the model is restricted to include only the clear air above the cloud, the complete recovery curve at all distances on the ground is explained, while recoveries above the cloud are unaffected. The slight but significant deviations from the exponential form of distant recoveries observed on the ground are also accurately forecast.The simple Coulomb field of a regenerated charge within the cloud cannot result in more rapid recoveries after distant discharges than after close ones.
Aerosol and solar radiation in Britain
Authors: Unsworth M. H. , Monteith J. L. 
Published: February 2007

AbstractThe irradiance of the solar beam was measured on cloudless days at Sutton Bonington in the English Midlands and at sites in north‐west Scotland. Total and diffuse fluxes were also measured on some days. An attenuation coefficient for aerosol τa was defined by

relating the measured flux at normal incidence S(τa) to the flux calculated for a dust‐free atmosphere when the air mass number is m. Changes of τa from day to day were related to changes of air mass origin; local sources of aerosol were relatively unimportant. In maritime air, τa ranged from 0.05 to 0.15, and in continental air, from 0.1 to 0.5. In a tropical maritime air mass, τa decreased from 0.13 at sea level to 0.07 at 1,340 m.The fraction of (ultra‐violet + visible) to total radiation was (0.54 – 0.28 τa) and the ratio of diffuse to total radiation (m < 2) was (0.1 + 0.7 τa). The ratio of total scattering to absorption by aerosol decreased from 4 at m = 1.1 to 0.5 at m = 2.Mean monthly values of τa at four Meteorological Office stations were calculated from records of solar radiation and hours of sunshine and corresponding values of total and diffuse flux were tabulated for ‘isolated’, ‘rural’ and ‘urban’ sites.
A synoptic climatology of satellite observed cloud vortices over the Southern Hemisphere
Authors: Streten N. A. , Troup A. J. 
Published: February 2007

AbstractA classification scheme for satellite observed cloud vortices is used to assess some general features of the behaviour of Southern Hemisphere depressions. From coincident conventional observations the mean variation of surface pressure and upper level geopotential anomaly near the centre of, and in west‐east cross‐section through an extratropical vortex is determined in relation to its age. Data are obtained on the geographical variation of occurrence of vortex type, duration, and frequency of change between development stages. The percentage of vortices developing without a pre‐existing cloud band is found to be greater at higher latitudes but, in general, over 50 per cent of developments occur in this way.Persistent maxima of early vortex development are found in the western South Atlantic and in the central South Pacific, both regions extending into lower latitudes than elsewhere in the hemisphere. Two less prominent maxima are located in the central Indian Ocean, and south of Australia. Generalized vortex track and speed data are obtained, and several areas of high frequency of termination of depression track are observed at high latitudes near the Antarctic coast.In total, the observations tend to point to a circulation pattern having a high frequency of major long wave troughs east of the Andes, and in the central Pacific, with a further frequent trough more variable in space and time being located between the central Indian Ocean and the longitude of the Great Australian Bight.
Geostrophic drag and heat transfer relations for the atmospheric boundary layer
Authors: Arya S. P. S. 
Published: February 2007

AbstractThe empirical determinations of the similarity functions of geostrophic drag and heat transfer relations by Zilitinkevich and Chalikov (1968) and by Clarke (1970a, b) indicate large disparities between their results, raising serious doubts on the universality of these relations. Some reasons for these large differences are investigated by reanalysing the available data from the two sites (O'Neill in Nebraska, U.S.A., and Hay in New South Wales, Australia) in the same format, using the best available flux‐profile relations and reasonable criteria for the selection of suitable runs. Although there is still considerable (but, much less than in previous studies) scatter of data points, when plotted in the similarity framework, we find no significant differences in the results of two sites. Thus a large part of the above noted disparities must have been spurious, probably caused by different ways of determining surface fluxes and of defining external variables by the previous investigators.Our empirical results are compared with those obtained from recent theoretical models for both stable and unstable boundary layers. Having fitted some third degree polynomials through the same, nomograms are obtained for geostrophic drag and heat transfer coefficients and also for the surface cross‐isobaric angle as functions of dimensionless parameters defined in terms of easily measured ‘external’ variables. These show expected trends with stability.
Comparison of evaporation measurements using different methods
Authors: Grant D. R. 
Published: February 2007

AbstractDuring the 1971 growing season continuous measurements were made (with some breaks in the record due to instrumental faults) of the evaporation from barley using five methods:

Bowen ratio method;
aerodynamic method;
use of the energy balance equation and the aerodynamic heat flux to obtain evaporation as the residue (for convenience called the energy balance method);
a weighing lysimeter; and
a neutron moisture meter.
In this paper some estimates are made of the error expected from each method and the results of the measurements are presented. It is shown that the energy balance method is almost as good as the Bowen ratio method and has the advantage of not requiring humidity measurements.
Variation of the sea surface drag coefficient with wind speed
Authors: Smith S. D. , Banke E. G. 
Published: February 2007

AbstractEddy correlation measurements of wind turbulence obtained at a sand spit on Sable Island, Nova Scotia, in winds ranging from gentle breeze to strong gale force agree with other recent measurements over water. There is a significant increase in the drag coefficient with wind speed which is well described by the equation of Charnock (1955). The heat transfer coefficient is slightly lower than the drag coefficient.
Forecasting of vertical temperature profiles in the atmosphere during nocturnal radiation inversions from air temperature trend at screen height
Authors: Anfossi D. , Bacci P. , Longhetto A. 
Published: February 2007

AbstractA theoretical model for vertical distribution of air temperature in lower layers during night‐time calm periods has been developed by modifying some boundary conditions of the classical Brunt's model, on the ground of a more realistic behaviour of low atmosphere.The model allows the vertical temperature profile to be deduced from screen data records and it fits with experimental data collected from a meteorological tower better than the classical model.Radiative heat exchange is assumed to play the principal role, with diffusion thermal coefficient constant with height and time; previous work has shown that such an assumption holds true in the Po Valley air flow, when sky is cloudless and winds are light.
Wind profile relationships from the ‘wangara’ experiment
Authors: Hicks B. B. 
Published: February 2007

AbstractFrom over 1000 half‐hour observations of near‐surface wind profiles at Hay, NSW, more than 500 high quality sets of data are selected. In unstable conditions, these closely confirm previous analyses and suggest near equality between z/L and Ri. The data are well described by either the KEYPS relationship (Panofsky) or that of Businger: ϕM = (1–16z/L)−1/4. In stable conditions, a log‐linear formulation (ϕM = 1+az/L) is found to give an adequate description of the wind profile up to z/L ≃ 0.5, with some evidence for a slight variation in α between the values 4.0 at neutral and about 6 when z/L ≃ 0.2. The average value of α between these limits is found to be 5.0±0.2.In conditions of very high stablity, a linear profile (du/dz = cu*/(kL)) is suggested above the height z ≃ 10L. In the transition region between the log‐linear and linear profile regimes, the log‐linear formulation appears to tend towards a purely logarithmic law as stability increases. There is no evidence for any sudden change in behaviour, nor is there any suggestion that a purely logarithmic relationship is ever attained as an average situation. The value of c in the purely linear relationship is found to be between 0.4 and 0.9. The data also indicate that in extremely stable conditions (L ≃ 50cm) the dimensionless gradients of heat and of momentum may differ by about a factor of two, with ϕH being the larger.The roughness length of the site used is found to be 1.2±0.1 mm, considerably less than the values appropriate to earlier experiments performed in the same general area. There is some evidence for an increase in z0 with decreasing wind speed (reaching about 3 mm when the wind at 1 m is about 1 ms−1), in accord with Deacon's hypothesis concerning the form drag of roughness elements. From the point of view of applying a low‐level drag coefficient in order to estimate friction velocities, the errors arising from the change in roughness length are sometimes comparable to those resulting from stability effects.Not surprisingly, the data show that in slightly stable conditions dewfall was low, whereas in extremely stable situations dewfall accounted for most of the heat loss from the air.The data used here form part of a much larger body of information obtained during 1967 and known as the ‘Wangara’ experiment.
Spatial and temporal variations of the Southern Oscillation
Authors: Trenberth K. E. 
Published: February 2007

AbstractThe Southern Oscillation is an important mode of operation of the atmosphere. Several indices of the Southern Oscillation have been recognized, but for many purposes an index that gives a continuous, homogeneous time series is required. Phase differences between various areas complicate the definition of a simple index but weighted values of seasonal surface pressure at Darwin and Tahiti seem suitable for reference purposes. Time series of short period correlation coefficients prove useful for revealing temporal variations in the character and amplitude of the Southern Oscillation and reveal times when it is not very prominent. Lag relationships are determined and used to indicate some aspects of the circulation near times of phase reversal of the oscillation.Spectral analysis showed most variance to be in the range of 2 to 10 year periodicities, and cross spectral calculations further indicated that only for the 2–10 year range, and mainly for the 3–6 year range, of periodicities is there large‐scale coherence and out‐of‐phase relationships between stations in the South Pacific and Darwin. This defines the time scale of the Southern Oscillation.The Southern Oscillation is not confined to tropical and subtropical latitudes but is clearly linked to mid‐latitude systems and long waves in the westerlies. East‐west circulations coupling the South Pacific Convergence Zone and the South Pacific high also appear to play an important role in the Southern Oscillation.