bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass, heat and momentum exchange between stands of plants and their atmospheric environment
Authors: Cowan I. R. 
Published: February 2007

AbstractA model of mass and momentum transfer in the air layer occupied by a stand of plants is presented which takes account of the differing mechanisms of mass exchange and momentum dissipation near to the leaf surfaces. An analysis of momentum transfer leads to expressions for the vertical transport coefficient and windspeed in terms of the mean drag coefficient of the leaves, the drag coefficient of the stand as a whole and the area of leaf per unit volume of space. These expressions are used in the solution of the equations describing mass transfer with constant concentration of mass at the leaf surface. The effect of a chemical or physical resistance to transfer at the leaf surface is examined. The resistance to mass exchange between the stand and the atmosphere above is compared with that for momentum exchange. The transfer of water vapour in the stand is considered, the boundary conditions at the leaf surfaces being linked with those for sensible heat transfer. It is shown that, when leaf resistance to transpiration is negligible, the vapour and heat‐fluxes are readily obtained from simple mass transfer theory and a knowledge of the distribution of radiation in the stand. The formal relations are extended to allow for finite leaf resistance. Computed profiles of the fluxes, temperature and humidity in a plant stand of assumed characteristics with defined boundary conditions are presented and compared with published observations. The interrelationship between leaf resistance, transpiration and leaf temperature is discussed. An expression for the total evaporation from a stand is derived and contrasted with a relation based on the analysis of Penman and Schofield (1951) and Monteith (1965).
Recent measurements of cospectra for heat‐flux and stress
Authors: Panofsky H. A. , Mares E. 
Published: February 2007

AbstractRecent measurements of cospectra for stress at different sites show no significant difference when plotted in similarity coordinates, but vary with stability only. Further, there is no significant difference between heat‐flux and stress cospectra when plotted in such coordinates.Cumulative cospectra derived from the recent data agree well with much earlier results compiled by Deacon.
The circulation driven by ring convection in a rotating system
Authors: Turner J. S. 
Published: February 2007

AbstractA recent survey of hurricane dynamics has suggested an investigation of the motions which could be driven entirely by convection in the eye wall. A laboratory experiment based on this idea has been performed in a rotating tank of water, with convection in a ring produced using air bubbles. A steady circulation having many features of the mean hurricane circulation can be maintained by this means.
Observational characteristics of atmospheric fluctuations with a time scale of a month
Authors: Sawyer J. S. 
Published: February 2007

AbstractThe time series of 500 mb heights and 1,000‐500 mb thickness at a network of points over the Northern Hemisphere are filtered in a way which extracts those disturbances with periods in the range 15 to 60 days. Such disturbances are shown to have a maximum amplitude in latitudes 60 to 70 degrees north and be strongly influenced geographically. They are closely linked to the phenomenon of blocking.
The collision efficiency of small drops
Authors: Hocking L. M. , Jonas P. R. 
Published: February 2007

AbstractThe forces and couples on a pair of spheres rotating and translating in a viscous fluid have been obtained by Davis (1969) and O'Neill and Majumdar (1970) from accurate solutions of the Stokes equations. These forces and couples have been used to calculate the collision efficiencies of pairs of small cloud droplets. The results show that the collision efficiencies are finite for all the pairs of droplets considered, in contrast with the results of Hocking (1959) who predicted that for droplets of radius less than 19 μm the collision efficiencies were zero. The collision efficiencies of droplets of radius less than 20 μm is shown to vary considerably with the critical minimum gap between the droplets below which collision is assumed always to occur. The approximations involved are discussed and the effects of electric fields or charges on the drops are shown to be negligible in the early stages of cloud droplet growth.
Results of a comparison between Umkehr and ozone‐sonde data
Authors: Kulkarni R. N. , Pittock A. B. 
Published: February 2007

AbstractResults of an intercomparison of 26 pairs of vertical distributions of ozone obtained at Aspendale (38°S) using the Umkehr technique and Mast‐Brewer ozone‐sondes on the same days are presented. Correlation coefficients between the integrated ozone amounts found by the two methods for Umkehr layers 2, 3 and 4 are found to be between 0.82 and 0.88, while the correlations for layers 1 and 5 are 0.47 and 0.37 respectively. On the average the Umkehr method indicates substantially more ozone in layers 1 and 2 than do the ozone‐sondes, but slightly less in layer 4. The Umkehr method thus tends to smooth out the vertical distribution of ozone relative to that observed by the ozone‐sondes. Results of comparisons at different times and places suggest a variation in the response of the Umkehr method relative to sonde methods.
Scale length in atmospheric turbulence as measured from an aircraft
Authors: Taylor R. J. , Warner J. , Bacon N. E. 
Published: February 2007

AbstractScale lengths, defined in four different ways, have been derived from previously reported spectra and autocorrelations of vertical air velocity component measured from an aircraft at heights between 10 and 1,310 m. Below about 200 m the scale length increases with height more slowly than linearly and it does not seem possible to attribute this result to stability effects. At higher levels, no systematic height dependence can be shown. The results offer some support for the suggestion that the scale length is greater in lapse conditions than otherwise.
Simultaneous airborne measurements of cloud condensation nuclei and sodium‐containing particles over the ocean
Authors: Hobbs P. V. 
Published: February 2007

AbstractSimultaneous airborne measurements have been made over the Pacific Ocean of the concentrations of cloud condensation nuclei (CCN) active at 0.5 per cent supersaturation and the concentrations and size‐spectra of sodium‐containing particles (SCP) over a wide range of sizes. The concentrations of SCP decreased sharply with increasing height above the ocean and it is likely that most of them originated from the ocean. However, even at altitudes as low as 50 ft above the surface of the ocean, and over surf, the measured concentrations of SCP were only a few per cent of the concentrations of CCN at G.5 per cent supersaturation. Also the average concentrations of CCN did not change significantly with altitude up to at least 10,000 ft. These observations indicate that sea‐salt particles were not the major source of the CCN.It is suggested that the production of sulphates in cloud droplets, followed by the release of these particles when the droplets evaporate, is an important mechanism for increasing the efficiency of CCN in the air.
Charge separation during splashing of large drops on ice
Authors: Shewchuk S. R. , Iribarne J. V. 
Published: February 2007

AbstractAn investigation was performed on the electrification associated with splashing of water drops at 0°C on ice coated rotating spheres. The influence of different parameters was studied: roughness of the surface, drop size, collision speed (up to 30 m s−1), liquid composition, including pH, and ice temperature (down to ‐ 20°C). It is shown that the sign of the charge acquired by the ice, usually negative for low temperatures and dilute solutions, becomes positive for temperatures close to 0°C, for large concentrations of electrolyte and for solutions containing ammonium ion. The electrification increases with drop size and with the violence of the impact, while it is strongly reduced by the concentration of hydrogen ion in acid solutions. Flash photographs at high speeds show the splashing process to be similar to that at room temperature on other solid surfaces.The results are discussed in the light of a theory previously developed for splashing at room temperature and of the selective incorporation of ions into the ice. Some speculation is done on the relative importance of the process in clouds.
On an observation of turbulent waves on the tropopause surface
Authors: Axford D. N. 
Published: February 2007

AbstractAn analysis of aircraft measurements at a well defined tropopause inversion is presented. It is found that there is turbulence on the inversion which is closely correlated to some form of wave activity.The observations show that any aircraft flying at the level of a strong inversion may expect sudden changes in both temperature and horizontal and vertical wind due to wave motions on the interface, and that these changes can amount to the full temperature excursion through the surface (in this case 10°C); and the full shear (in this case 7 ms−1) in a horizontal distance of about 1 km.
A wind tunnel investigation of freezing of small water drops falling at terminal velocity in air
Authors: Pitter R. L. , Pruppacher H. R. 
Published: February 2007

AbstractA method utilizing a vertical wind tunnel is described, by which supercooled water drops and ice particles can be stably suspended at temperatures between 0 and −30°C. Using this method, we studied: (i) the freezing temperature of water drops of various purity and volume, (ii) the freezing temperature of drops nucleated by contact with dry clay particles and the freezing temperature of drops nucleated by clay particles which were suspended in them, (iii) the crystallographic characteristics of frozen drops, and (iv) the free fall motion of supercooled drops and frozen drops freely suspended in air. The first study showed that the median freezing temperature of a population of equal size water drops is a linear function of the logarithm of the drop volume, in agreement with the law found by Bigg for water drops in oil. The second study showed that the temperature at which a drop froze when nucleated by contact with dry clay particles was over 10°C warmer than the temperature at which a drop of the same size froze when nucleated by clay particles suspended within the drop. The third study showed that frozen drops, recovered from the wind tunnel airstream and investigated under a polarization microscope, were single crystalline or polycrystalline depending on the drop volume, the temperature of freezing, and the heat dissipative capability of the medium surrounding the drop. The lowest temperature for single crystalline freezing is significantly colder for drops which freeze while completely surrounded by air than for drops which freeze on contact with an ice crystal. The fourth study showed that a supercooled drop falls with a constant velocity and no horizontal movement, while a frozen drop often spins and tumbles, and falls along a helical path with a terminal velocity which is 6 to 7 per cent smaller than that of the supercooled drop before it froze. This means the life time of a cloud particle lengthens as a result of freezing.
Translation speed of convective plumes in the atmospheric surface layer
Authors: Kaimal J. C. 
Published: February 2007

AbstractExperiments conducted over a flat uniform ploughed field indicate that the small convective plumes commonly observed in the surface layer travel as an entity with horizontal speeds proportional to the friction velocity, u. This proportionality, in turn, implies a direct relationship between the inferred height of the plume base and roughness length. For these experiments, the height of the plume base averaged 1.2 m.
On the low‐level wind structure in the Atlantic trade
Authors: Brümmer B. , Augstein E. , Riehl H. 
Published: February 2007

AbstractFrom ship‐borne radiosonde and radar wind observations during the Atlantic Trade Wind Experiment 1969 (ATEX) the relation between actual and geostrophic wind in the subcloud layer is determined. The frictional force and the divergence of vertical transport of momentum between the sea surface and 500‐m height are computed by the ageostrophic method.Along the surface wind direction, balance between pressure gradient and frictional force is closely established. Perpendicular to the surface wind the expected balance of pressure gradient and Coriolis force is not obtained but a substantial frictional force results from this component.The boundary condition that the stress vanishes at the lowest wind maximum leads to an underestimation of surface stress by about 35 per cent. It is suggested that convective transport of momentum must take place in the subcloud layer.
The ionic conductivity of electrified clouds
Authors: Griffiths R. F. , Latham J. , Myers V. 
Published: February 2007

AbstractCalculations have been made, on the basis of the ionic balance equations derived by Phillips (1967), of the electrical conductivity of clouds in the presence, and in the absence, of secondary ion production resulting from corona.In weakly electrified clouds ‐ no corona ‐ the immobilization of ions on cloud droplets resulting from diffusional capture results in a reduced ionic concentration and conductivity. The normalized conductivity λ the ratio of the in‐cloud value to the clear‐air value at the same altitude Z was calculated for three different cloud types (cumulus congestus, strato‐cumulus and fog) as a function of Z, liquid water content L, droplet charge Q and field strength E. λ was found to be very sensitive to variations in L and E, but only slightly affected by changes in Z, Q and the manner in which the charge is distributed over the size‐spectrum. For example, when E = O λ possessed the values 0.034 and 0.17 in a cumulus congestus cloud for L = 0.5 gm/m3 and 0.1 gm/m3 respectively, whereas when E = 90 kV/m λ was 1.5 times; 10−3 and 7.6 times; 10−3 respectively for the same two values of L.The experimental measurements of corona onset fields and currents from ice hydrometeors, Ec and ic respectively, made by Griffiths and Latham (1974) were used to calculate the normalized conductivity within strongly electrified clouds. Corona from ice provides a copious supply of positive and negative ions which causes λ to increase from between 10−3 and 10−4 to greater than 1 when Ec is achieved. The value of λ once corona is initiated depends on L and the concentration of corona sites, J. In this situation altitude Z plays an important role because Ec decreases quite rapidly with decreasing pressure. For example, with a typical distribution of temperature and pressure within a thundercloud, corona will be initiated from hailstones at Ec = 720 kV/m if Z = 2.5 km (0° C) and 540 kV/m at 5.5 km (‐18° C); the corresponding values of Ec for snowflakes are 540 and 390 kV/m respectively. At 2.5 km is slightly higher than and lower than 10 respectively, as L is increased from 1 to 5 gm/m3 with J = 1 m−3.It is concluded that the introduction of an ionic leakage current into calculations of field growth within thunderclouds is unnecessary, and that the distribution of electric field is crucial in determining whether corona, once initiated, will trigger lightning or merely increase the ionic conductivity.
A case study of the structure and energetics of an inversion
Authors: Rayment R. , Readings C. J. 
Published: February 2007

AbstractUsing data obtained from a probe mounted on the flying cable of a tethered kite balloon, this paper presents a fairly comprehensive description of the structure of a ‘hummocky’ subsidence inversion and the associated air motions, including the formation and breakdown of billows at the crests of the hummocks. Below the inversion, the transfer of warm air downwards was detected and the rate at which this occurred estimated using the model proposed by Readings et al. (1973). This estimate is shown to be in good agreement with that derived from some radio‐sonde ascents. The fluxes of potential heat downwards at the inversion and upwards at the ground are estimated and their ratio is shown to be about 0.25.
A numerical investigation of polar lows
Authors: Duncan C. N. 
Published: February 2007

AbstractA quasi‐geostrophic numerical model is employed to find normal mode solutions for unstable disturbances with low static stability near the earth's surface. Three occasions on which polar lows developed are analysed to provide the necessary data for the model. The normal mode solutions which are obtained are, therefore, those which have the highest growth rates under conditions in which polar‐air depressions have developed. Since the model is two‐dimensional, being a cross‐section through the mean flow, the perturbation amplitude and energy conversion rates of the growing disturbances in this plane are described for each case. It is shown that horizontal variations in static stability are an important factor in the forecasting problem and some criteria for polar‐low development are suggested.
A new parameterization of deep convection for use in the 10‐level model
Authors: Hayes F. R. , Jonas P. R. 
Published: February 2007

AbstractA convection parameterization scheme recently incorporated into the Meteorological Office 10‐level model is described. A one‐dimensional cloud model incorporating entrainment and detrainment, together with a simple representation of cloud microphysics, is used to provide heat and moisture fluxes for the predictive equations of the parameterization. Results of the scheme in operational use are presented.
Empirical orthogonal analysis of atlantic ocean surface temperatures
Authors: Weare Bryan C. , Newell R. E. 
Published: February 2007

AbstractAn empirical orthogonal function analysis has been performed on monthly mean sea surface temperature observations in the Atlantic Ocean between 70°N and 30°S for the years 1949–69. This method derives the most important ‘modes’ of variation, defined as those functions which explain the largest total variance in the data field. Such modes are calculated for two sets of temperature deviations in which the annual cycle is both included and excluded. For the seasonal case, only four functions explain more than 90% of the total variance, whereas in the nonseasonal case, ten functions explain less than 50% of the total. the most important seasonal mode indicates lower minimum temperatures in winter in the later years of study. the dominant nonseasonal function shows a cooling trend starting in early 1951. Nonseasonal functions of the tropical region alone suggest large variations, having a characteristic period of a few months.
Climatology of the vertical distribution of ozone over Aspendale (38°S 145°)
Authors: Pittock A. B. 
Published: February 2007

AbstractData from the first eight years (1965–73) of an ozone sounding programme at Aspendale, Victoria, have been analysed. the mean annual cycle is compared with that derived from similar data from the northern hemisphere. Close agreement is found at similar latitudes in the two hemispheres for the stratosphere at and below the primary ozone maximum, whereas in the free troposphere there is a much smaller seasonal variation in the southern than in the northern hemisphere. There appears to be a marginally higher ozone concentration around the 10 mb region in the northern as compared with the southern summer.The variance about the overall mean vertical distribution has been partitioned between various time scales. the seasonal contribution dominates the variance around the level of the primary ozone maximum, with substantial contributions also in the stratosphere at lower altitudes. the synoptic and other shorter timescale variance (including instrumental ‘noise’) is low above the 50 mb level, where ozone and pressure sensors are least reliable, but it exceeds the seasonal contribution below 70 mb. This suggests that the maximum contribution of the shorter timescales to the variance around the 100 mb level is largely synoptic in character.Significant linear trends in the data are discussed briefly. No evidence for quasi‐biennial or 10 to 11 year solar cycle periodicities is found but significant correlations between ozone variations and the position of the subtropical surface high pressure belt (Pittock's L index) are shown to occur in the stratosphere at and below the level of 50 mb.
The rime‐splintering hypothesis of cumulus glaciation examined using a field‐of‐flow cloud model
Authors: Koenig L. Randall , Murray Francis W. 
Published: February 2007

AbstractA mathematical experiment was conducted to test the hypothesis that the occurrence of unexpectedly large concentrations of ice particles in certain clouds is caused by the production of small ice particles (‘splinters’) during the riming of mother ice particles. the experiment used an axially symmetric two‐dimensional field‐of‐flow model incorporating parameterized liquid and ice microphysics. the behaviour of clouds, growing with either wide or narrow initial droplet size distributions, with and without splintering, was simulated. Splintering criteria were based on recent laboratory data.The rapidity of liquid to ice conversion was found to be a strong, direct function of the prior presence of large liquid drops. the dynamical properties of the clouds influenced both splinter production and also the over‐all glaciating characteristics regardless of the presence or absence of an ‘ice multiplication’ mechanism. Cloud condensate at levels having strong updraughts and vigorous growth was more slowly converted to ice than condensate in regions of dissipating cloud. the simulations permitting ice generation by splintering more closely duplicated pertinent observations in nature than those without splinter production. Unexpectedly, the characteristics of the liquid phase exerted substantial influence on the dynamics of the simulated clouds.
The electrical structure of an inversion
Authors: Chisnell R. F. , Latham J. , Ryder P. , Stromberg I. M. 
Published: February 2007

AbstractMeasurements were made, using an instrumented aircraft, of the vertical electric field strength, E, and the ionic conductivity, λ, of the atmosphere in the vicinity of a temperature inversion. It was found—moving downwards through the inversion — that the reduction in λ associated with ionic immobilization upon aerosol particles occurred over an appreciably shorter vertical distance than the accompanying increase in E. the ionic current density was not preserved over the region of changing E. These observations suggested that some of the space‐charge created in the region of conductivity gradient was being transported downwards by eddy diffusion. A theoretical model of this process was constructed, based on the principle of current continuity. Excellent agreement between the particularly simple field structure measured on one flight and the theoretical structure existed if the characteristic diffusion length was about 60 m. This corresponds to an eddy diffusion coefficient, K, of about 3.0 m2s−1.It is suggested that in some circumstances, the simultaneous measurement of E and λ affords a quantitative technique for the determination of K.