bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rainfall evaporation in thunderstorm downdraughts
Authors: Kamburova Petia L. , Ludlam F. H. 
Published: February 2007

AbstractIt is explained that in air descending at speeds of some m sec−1 raindrop evaporation must proceed at a large subsaturation. Under some simplifying steady‐state assumptions, the vertical temperature profiles in thunderstorm downdraughts of a range of speeds are estimated, and it is shown that the most favourable conditions for the production of strong draughts are a small raindrop size, and, especially, an intense rainfall rate and a general lapse‐rate close to the dry adiabatic. The two latter conditions are often associated in severe storm situations, and the downdraught then arrives near the ground with a rather low relative humidity, and a temperature little lower than found generally at the same level.
On the role of mean meridional motions in the biennial wind oscillation
Authors: Wallace J. M. 
Published: February 2007

AbstractDetailed time‐height sections and meridional cross‐sections of zonal wind are presented for the zonally averaged conditions between 32°N and 20°S. The patterns which appear in the sections vary slowly and systematically with latitude and time. The biennial wind oscillation is evident in the sections, but since 1963, the two year periodicity, as such, has vanished and the wind fluctuations, though still similar in form to the previous ones, have become much less predictable. The sections suggest that the lower edges of westerly regimes propagate downwards more rapidly than those of easterly regimes.The momentum budget of the region is then examined, term by term, and it is concluded that a mean downward motion is necessary over the Equator to account for the downward propagation of the wind regimes there. It is suggested that the enhanced vertical motion during the descent of westerly regimes at the Equator might account for the observed downward propagation at sub‐tropical latitudes. The heat budget is then examined with respect to the vertical motions suggested from momentum considerations. It is found that a heat sink in the equatorial stratosphere would be required to support the vertical motion field. It is shown that enhanced downward motion during the descent of westerly regimes (which the zonal wind data suggest) is necessary to keep the temperature field in geostrophic equilibrium with the wind field.
Temperature and vertical velocity fluctuations in strong convection
Authors: Myrup L. O. 
Published: February 2007

AbstractAn experimental study of the structure of thermal convection in the lower atmosphere is presented. The measurements were undertaken with the primary purpose of comparing the statistics of convective motion occurring in the lower atmosphere under conditions of light winds and strong surface heating with the laboratory heated plate results of Townsend and also with the predictions of the similarity theory of free convection. Temperature and vertical velocity fluctuations were measured above a desert dry lake bed in Southern California using a light aircraft as an instrument platform. Modern data acquisition methods were used which allowed high speed data sampling and rapid computer processing of several million data points. Negative Richardson numbers at 1·5 m of the order of 2 or more were typical of the midday hours. The temperature traces obtained during horizontal aircraft traverses had the typical intermittent structure previously noted both in the atmosphere and in the laboratory by other investigators. Individual warm pulses often had an asymmetric appearance in that the upwind edge tended to be the warmest. This was noted to hold even for the lightest wind conditions included in these data (1 ms−1 at 4 m). Although the observed intermittency of the temperature field agreed qualitatively with Townsend's description of the laboratory case, the variation with height of the r.m.s. temperature and vertical velocity fluctuations agreed with the predictions of the similarity theory of free convection. It is concluded that the light wind case in the atmosphere differs considerably from the laboratory case with no mean motion. Since winds appreciably lighter than those occurring during this study are quite rare for lapse conditions in the atmosphere, it is suggested that there may always be a fundamental difference between atmospheric measurements and those made for the classical heated plate experiments. These data are also used to construct a preliminary kinetic energy budget for various heights above the lake bed. The results indicate that the flux divergence of turbulent kinetic energy is a large term in the budget under the conditions of these measurements.
Temperature persistence at Bombay during the South‐West Monsoon
Authors: Sarker R. P. , Mhaiskar P. R. 
Published: February 2007

AbstractIn this note three‐day mean temperature values observed at Colaba (Bombay) during the years 1871 to 1960 have been examined by means of contingency tables for evidence of any pattern of persistence during the South‐West Monsoon. It appears that the tendency for the existing temperature character to persist from one triad to the next at least is strong during the entire monsoon, being strongest in the month of August, when it may persist over a period of 4 triads or so.
An improved Millipore filter technique for measuring the concentrations of freezing nuclei in the atmosphere
Authors: Stevenson Catherine M. 
Published: February 2007

AbstractA technique to measure the concentration of freezing nuclei in the atmosphere is described. It is a development of the Millipore filter method described by Bigg, Mossop and Heffernan (1961), from which many of the difficulties experienced by them and other workers in the field have been eliminated.The main advantages which this technique has over others using Millipore filters are as follows:

the ability to work at relatively low and controlled supersaturations;
the ability to activate large numbers of nuclei on the filter without the crystals interfering;
the finding of a linear relationship between the number of nuclei detected and the volume sampled, except in very dusty conditions;
an improved reproducibility.
Some extensions and applications of the new random model for molecular band transmission
Authors: Rodgers C. D. 
Published: February 2007

AbstractThe general line shape transmission is derived for the new random model described by Malkmus (1967) for the representation of molecular band transmission. The model is applied to two absorbing paths in series, where an expression is found which is simpler than the corresponding expression for the Goody random model. The new model is also used to give an empirical fit to the ozone transmission measurements of Walshaw (1957).
The effect of vertical line averaging on the spectra of temperature and heat‐flux
Authors: Kaimal J. C. 
Published: February 2007

AbstractThe paper describes an attempt to evaluate the effects of vertical line averaging on temperature statistics by using simultaneous measurements from sensors of different lengths. Results show that the transfer function for vertical line averaging derived by Gurvich for the vertical velocity component applies also to temperature spectra. Heat‐flux, when computed with vertical velocity measurements from a sonic anemometer, is relatively insensitive to line averaging (at least up to 80 cm at 9 m height). But the coherence between the line average and its mid‐point value shows consistent behaviour only for short line lengths of the order of 20 cm. With longer lengths the coherence is likely to vary from one run to another depending on mean wind speed.
Measurements of atmospheric infra‐red emission with a balloon‐borne multifilter radiometer
Authors: Pick D. R. , Houghton J. T. 
Published: February 2007

AbstractA radiometer sonde has been constructed to observe radiation from the atmosphere above the radiometer in the spectral region 5–7 μ with a spectral resolution of about 0·3 μ. The results from a flight of the instrument at night up to a height of 25 km are presented. Emission from water‐vapour indicates a dry stratosphere with a mass mixing ratio of about 3 × 10−6. An energy flux originating above 25 km amounting to about 2 μW cm−2 has been observed near 5·7 μ. Various possible sources for this additional radiation are discussed.
Some average wave lengths on short‐crested seas
Authors: Scott J. R. 
Published: February 2007

AbstractTwelve average sea spectra are truncated at 1·6 rad s−1 and fitted with tails in which energy density varies inversely with the fifth power of frequency. By use of a spread parameter measured in typical rough weather these spectra are converted into symmetrical two‐dimensional wave number equivalents, which are, inter alia, numerically integrated along normals to the dominant wave direction, yielding the wave number spectra of instantaneous wave profiles along that direction. These spectra provide unbiassed estimates of average wave lengths, while the originals provide similar estimates of average periods. Zero‐crossing averages are shown to be preferable to those measured from crest‐to‐crest.It is found that, for the estimation of average zero‐crossing wave lengths, the original frequency tail can be replaced by one in which the density varies inversely with frequency raised to the power of 5·5, and that the fourth moments of the main (truncated) spectra require reduction by about a quarter, to allow for the effect of spreading. These findings also appear to be applicable in individual situations where the dominant direction is well defined.The variations of zero‐crossing periods and wave lengths with wave height are studied for two locations.
The temperature profile near the ground on calm clear nights
Authors: Oke T. R. 
Published: February 2007

AbstractAn observational study of the temperature profile over grass, snow and bare soil surfaces in strong stability is presented. It was found that in nearly calm, clear conditions the minimum temperature occurred 1 to 50 cm above the surface. The height and intensity of the minimum is strongly correlated with wind speed, surface roughness and stability. A discussion of existing hypotheses suggests that the most likely explanation for the phenomenon should involve both turbulence and infra‐red flux divergence.
Richardson number limited shear zones in the free atmosphere
Authors: Browning K. A. , Harrold T. W. , Starr J. R. 
Published: February 2007

AbstractTwo case studies are presented of the detailed structure of frontal zones with strong vertical shear. Temperature structure has been obtained from sequential radiosonde ascents. Wind structure, including the fields of horizontal divergence and deformation, has been obtained on scales of 1 to 10 km by means of Doppler radar techniques. The results are consistent with the frontal zones being at least partly controlled by shearing instability, in so far as there was a balance between a wind field tending to diminish the Richardson number (Ri) and shearing instability tending to impose a lower limit to Ri. One of the main factors tending to diminish Ri was stretching deformation in a direction normal to the local shear vector. A typical rate of decrease of Ri which this would have produced in the absence of shearing instability was 10−4 s−1. The Richardson number itself within the frontal zones was mainly between 0.2 and 0.4 when averaged vertically over 200 m and horizontally over circles of diameter 10 km; however, Ri diminished to about half of these values locally on horizontal scales of about 1 km. As a result shearing instability is thought to have led to turbulent breakdown in only isolated patches rather than in a sustained fashion over the entire depth of the frontal zones.
An observation of gravity waves in shear flow in the lower stratosphere
Authors: Axford D. N. 
Published: February 2007

AbstractDuring a routine instrumentation flight check in the lower stratosphere periodic variations of temperature and winds were observed. It is deduced that these variations are gravity waves which appear to be associated with a narrow frontal zone separating regions with different potential temperatures. Vertical and horizontal wind changes of ± 1 m s−1 and potential temperature variations of up to ± 2°C are measured with a wavelength of 2.3 km. The breakdown of waves such as these may be associated with observations of clear air turbulence in the stratosphere along shear layers separating weak flows of different origin.
On the influence of synoptic development on the production of high level turbulence
Authors: Roach W. T. 
Published: February 2007

AbstractThis paper considers free shear layer turbulence in the atmosphere (clear air turbulence) as a mechanism for relieving the formation of discontinuities of wind and temperature in the vertical plane by shearing and stretching deformation.An expression for the rate of change of the logarithm of the gradient Richardson number following the air motion is derived and the assumption is made that turbulence counteracts the dynamical processes which are reducing the Richardson number, maintaining it at a limiting value. The rate of working required to do this is equated to the turbulent energy dissipation rate and in the model used is given by Φ (ΔV)2/24 (where the logarithmic rate of reduction of Ri which would take place in the absence of turbulence, and ΔV is the velocity difference across the turbulent layer).Two preliminary tests of the theory as a forecasting tool using the Bushby‐Timpson 10‐level numerical model show that the dynamical processes changing Ri are largest in areas where clear air turbulence might be expected from synoptic experience.
Buildings in the wind
Authors: Owen P. R. 
Published: February 2007

AbstractSome of the problems arising from the flow of the wind about buildings are selectively illustrated in terms of the aerodynamics of vortex shedding and the interaction between a bluff body and turbulence in the approaching stream. Examples chosen draw attention to the spanwise incoherence of vortex shedding from a rigid body and vortex‐capture by an oscillating body, the effects of geometrical taper and shear in the undisturbed stream and the pecularities exhibited by the wakes behind porous windbreaks. Galloping oscillations of cables together with the large amplitude motions that can be engaged in by stranded electrical conductors are also briefly mentioned.As a preliminary to discussing the effect of turbulence on the flow past a body, as well as the distortion of the turbulence produced by the body, observations are offered on the relation between the known properties of the micro‐spectrum of atmospheric turbulence and wind tunnel measurements made in turbulent boundary layers. An interpretation of the latter in terms of the ‘inactive’ component of the unsteady motion near a surface, contributed by eddies in the outer parts of the boundary layer, suggests that further meteorological data, so frequently demanded by architects and aerodynamicists, may fail to add systematic information about the behaviour of the u‐component of the turbulent velocity other than is already available.Modern techniques of wind tunnel testing, which attempt to represent mean and turbulent properties of the wind, are described and cautionary remarks are made about the prospect for significant further refinement.
Drag coefficients of water droplets decelerating in air
Authors: Ogden T. L. , Jayaweera K. O. L. F. 
Published: February 2007

AbstractThe relation of drag coefficient to Reynolds number for decelerating water droplets was tested by releasing into a 50 m s−1 airstream droplets up to 230 μm in diameter. After travelling for 1.83 m in the airstream, the droplets passed through a small hole into still air, and the distances they subsequently travelled could be predicted fairly well by assuming that the effective drag coefficients were about 20 per cent below the steady‐velocity values.
The structure and intensity of turbulence in air over the sea
Authors: Warner J. 
Published: February 2007

AbstractMeasurements of atmospheric turbulence have been made from an aircraft at heights in excess of 30 m over the open sea in convective situations. They are related to height, wind speed, heat flux and stability. The variation of the r.m.s. vertical velocity with height is examined for two different scaling systems. From calculations of the power spectra a length scale is derived for the vertical velocity fluctuations which is found to increase slowly with height.
Non‐Boussinesq effects and further development in a model of upper tropospheric frontogenesis
Authors: Hoskins B. J. 
Published: February 2007

AbstractIn previous papers, upper tropospheric frontogenesis has been exhibited in a model in which a horizontal deformation field acts on a temperature distribution in a Boussinesq two fluid system. The basic approximation made is that the flow along the incipient front is geostrophic. This approximation allows the reduction of the problem to that of solving a non‐linear second order partial differential equation. Here this equation is solved by a slightly different technique. Non‐Boussinesq effects are included and are shown to produce a strengthening of the upper‐tropospheric front and its associated jet stream. Further deformation is allowed and the development of a more realistic front described.
The shedding of accreted water during hailstone growth
Authors: Carras J. N. , MacKlin W. C. 
Published: February 2007

AbstractIcing tunnel experiments have shown that loss of accreted water occurs in both the dry and wet growth régimes at ambient temperatures above about −12°C. The loss in the dry growth régime is probably due to splashing while that in the wet growth régime is undoubtedly due to shedding of water from the liquid layer which covers the surface of the accreting object. The latter can affect appreciably the growth rates of hail stones. These data, together with calculations of the collection efficiency, have shown that the structure of the hailstone analysed by Macklin, Merlivat and Stevenson (1970) is consistent with growth in an adiabatic updraught.
Precipitation characteristics during the Venezuela rainy season
Authors: Riehl H. , Cruz L. , Mata M. , Muster C. 
Published: February 2007

AbstractAn extensive program of observations designed to determine the structure of tropical mesoscale rain areas over land and their relation to synoptic envelopes was carried out during the rainy season of 1969 (June to September) in eastern Venezuela.The frequency distribution of precipitation in the area seen by radar (radius 100 km), as given by the average of 30 stations, was highly skewed: 14 per cent of the days in the experiment delivered half of the precipitation; 80 per cent could be attributed to rain episodes related to mobile synoptic systems. On the hourly basis, 0·45 per cent of all hours (or 10 hours) produced half of the precipitation.Daily precipitation in the radar circle was not correlated with radar echo height but markedly with echo area. Heavy rainfall occurs when a few very large clouds appear.A cloud distribution in terms of area and rain productiveness was determined for rainy and for dry days. Rain productivity increases with cloud area; however, since the number of clouds also decreases as their size increases, water yield to the ground is almost independent of cloud scale. No clear difference in the 200 mb flow could be found between cloud ensemble.On rainy days the temperature is lower and the specific humidity higher than on dry days confirming that cold‐core precipitation takes place also over Venezuela. A mean ascending velocity appears to exist in and out of clouds in the convection cores, but could not be found prior to onset of afternoon convection.
Baroclinic instability at the winter stratopause
Authors: Simmons A. J. 
Published: February 2007

AbstractBaroclinic instability is examined in an idealized model of the winter stratopause. The upper stratosphere is more stably stratified than the lower mesosphere, and instability can occur when the zonal flow has westerly shear., Using representative parameter values, a maximum doubling time of 2 days is found for a disturbance with zonal wavelength 4000 km and vertical scale 10 km, moving with a velocity within 2ms−1 of that of the zonal wind at the stratopause. Newtonian cooling reduces growth‐rates by some 80% of the damping rate, and becomes important for relaxation times of less than 7 days.
Crystal size in accreted ice
Authors: Rye P. J. , Macklin W. C. 
Published: February 2007

AbstractStudies have been made of the crystallographic orientation of 100μm‐radius supercooled droplets frozen on ice substrates whose c‐axis orientations varied from 0 to 90° to the surface normal. For a given droplet temperature and substrate orientation, there is a critical substrate temperature below which a frozen droplet has a high ( > 0·8) probability of having an orientation which differs from that of the substrate. Above this critical substrate temperature there is a small ( < 0·2) residual probability of reorientation which is dependent on the droplet temperature and substrate orientation but independent of the substrate temperature.The lengths and maximum widths of ice crystals in accreted ice deposits have also been determined. In the dry growth regime there is a general decrease in the mean length from ∼ 8 to 0·25mm, and in the mean maximum width from ∼ 1 to 0·2mm, as the ambient temperature decreases from − 5 to − 30°C. At ambient temperatures above − 15°C there is no dependence of the crystal dimensions on the temperature of the deposit. At ambient temperatures below this value, the crystal dimensions vary with deposit temperature in a manner consistent with the individual droplet studies. Consequently, measurements of the crystal dimensions in hailstone layers may give useful indications of their growth conditions.
The effects of vertical wind shear on the evolution of convective clouds
Authors: Pastushkov R. S. 
Published: February 2007

AbstractThe effects of ambient wind shear Uo on the evolution of an isolated three‐dimensional convective cloud are studied. Sixteen cases are considered which differ from one another both in the value of U′0 in the initial value of the energy of atmospheric instability per unit height of the unstable layer, E0. It is found that convective clouds may be grouped into two types, ‘weak’ and ‘strong’: if E0/H < 0−65 × 102cm s−2 then convection is ‘weak’; if E0 0−65 × 10−2cm s−2 then convection is ‘strong’. For ‘weak’ convective clouds there is a critical value of shear, U′0cr |U′0| < U′0crthere is an inhibiting effect on the development of convection; and for |U′0| U′0 its evolution is completely suppressed. The essential new result is that ‘strong’ convective clouds are intensified under the effect of U′0. In this case there is a resonance value of shear, U′0res at which the degree of the intensification of convection has a maximum (30–40%).
Budget studies of heat flux profiles in the convective boundary layer over land
Authors: Cattle H. , Weston K. J. 
Published: February 2007

AbstractObservations of the convective boundary layer over southern England using an instrumented light aircraft and radio‐sondes enable its structure and development to be described for two periods of active, shallow convection. Budgeting is used to deduce the sensible heat flux as a function of height, showing a downward flux in the upper part of the boundary layer associated with entrainment of warmer air from above. For the two occasions studied results indicate that the entrained sensible heat flux is about 0·3 of the sensible heat flux at the ground. For one of the occasions a moisture budget was possible yielding a value of the mean latent heat flux at the ground.