bluuebunny/crossref_metadata_2025 huggingface dataset:
On the balance of forces and radial accelerations in hurricanes
Authors: Gray W. M.
Published: February 2007

The degree to which the gradient or cyclostrophic wind equation is applicable for hurricane winds above the surface friction layer is tested on 10 levels in four hurricanes (8 different days) in which aircraft of the National Hurricane Research Project of the United States Weather Bureau flew radial leg penetrations during the 1957–58 seasons. All 10 levels flown were between 6,000 and 16,000 ft altitude and each level had six or more radial leg penetrations except one that had five. Application of the cylindrical radial equation of motion is made for the constant‐pressure levels flown. Results show that there is lack of radial balance by a wide margin between pressure gradient, centrifugal and Coriolis forces. Evaluation of the local and advective changes of the substantial derivative only partly makes up for this lack of balance. It is therefore necessary to postulate the existence of internal radial friction, both in an instantaneous fixed‐coordinate system and in one that moves with the storm centre. This residual radial friction averages 25 to 30 per cent of the pressure‐gradient force. As a consequence, the gradient wind equation in both cyclindrical and in natural coordinates is invalid. Also, steady‐state or deepening hurricanes must have stronger pressure gradients than corresponding centrifugal and Coriolis accelerations. Comments on the possible mechanism for this internal friction are given.
Pressure oscillations and fallout downdraughts
Authors: Clarke R. H.
Published: February 2007

The generation of widespread pressure oscillations in southern Australia on 26–27 January 1960 is examined in some detail, by means of available barograms, and spectral analysis of a Melbourne Dines microbarogram. Photographs of mamma cloud taken at Adelaide give some insight into the processes at work producing both cloud form and oscillations. It is concluded that the oscillations were due to wave motions on an interface with large density contrast, at about 1,500 m altitude, and that these motions propagated approximately in the direction of vertical shear, with the velocity of the wind at about 2·5 km. Their phase and group velocities were similar, and their wavelengths in the range 10–70 km. These waves appear to have been transmitted over great distances without marked attenuation. An estimate of the energy of oscillation was compared with that which could be imparted to a horizontal interface with strong shear by the passage of downdraughts through it, and the conclusion is reached that the combination of downdraughts and shear could have provided the energy. On the other hand, there is good evidence that the waves were unstable, and could therefore have drawn their energy from that of the mean motion. Examination of other occasions on which marked pressure oscillations occurred suggested that fallout and strong shear were both necessary conditions.
Comparison of ozone variations and of its distribution with height over middle latitudes of the two hemispheres
Authors: Kulkarni R. N.
Published: February 2007

The paper contains a study of the day‐to‐day, seasonal and latitudinal distribution of ozone over the southern hemisphere in comparison with those observed in the northern hemisphere. It has been observed that there is more ozone over the middle latitudes of the southern hemisphere in summer, autumn and early winter, than in the northern hemisphere, whereas the spring maximum values are more or less the same in both hemispheres, suggesting lesser destruction of ozone from spring to autumn in the southern than in the northern hemisphere.

The distribution of ozone with height computed from umkehr observations over Aspendale by method B has been compared with that over Tateno in Japan. The results are discussed in relation to the idea of a poleward flow of air from the lower stratosphere and the neighbourhood of the equatorial tropopause in the southern hemisphere. It is concluded that the mean meridional circulation in the lower stratosphere of the southern hemisphere is weaker than, or at any rate only as vigorous as that in the northern hemisphere in spring.
The chemical composition of precipitation at cloud levels
Authors: Oddie B. C. V.
Published: February 2007

In an attempt to obtain precipitation samples free from contamination either from industrial sources or from sea spray, samples were collected by an aircraft of the Meteorological Research Flight over Southern England at heights up to 8,500 ft. Most of the samples still showed clear evidence of industrial pollution: however, five of them were collected under synoptic conditions which render pollution improbable. The amount of dissolved matter in these samples is much smaller than in the remainder, and their composition shows a close similarity with that of samples collected at ground level in regions where pollution is slight. It is considered likely that the solute has been little affected by matter derived directly from land : but it still shows characteristic differences from sea‐salt, particularly in the much smaller proportions of sodium and chlorine in comparison with all other elements. It is suggested that these differences must arise from some reaction, occurring either at the sea surface or in the atmosphere itself, but there is insufficient evidence to determine its nature.
An analysis of the origins of precipitation in Northern England, 1956–1960
Authors: Shaw Elizabeth M.
Published: February 2007

A classification of precipitation according to its occurrence in different synoptic situations is explained. The analysis of the hyetograms from seven stations in Northern England for 1956–60 is described and total amounts and proportions of rainfall in nine different categories are presented for each station.
On the formation of spongy ice
Authors: Macklin W. C. , Ryan B. F.
Published: February 2007

In supercooled water at temperatures down to‐4·5°C, ice grows in the form of flat dendritic sheets. Between‐4·5° and −5°C a transition in the manner of freezing occurs and three‐dimensional ice structures are produced. At temperatures below‐5·5°C this results in a structure which retains liquid water and so gives rise to spongy ice.
Heat transfer from hailstones
Authors: Macklin W. C.
Published: February 2007

By measuring the rate of melting of spheres and oblate spheroids of ice in an airstream, the dependence of the rate of heat transfer on shape has been determined. Applying the results to hailstones, it has been found that, in terms of the maximum dimensions of the stones, melting is more pronounced as the ratio of the minor to major axes decreases. Melting also causes the stones to become more oblate. The critical liquid‐water concentrations of spheroidal hailstones have been deduced from the experimental data and, for stones of the same maximum dimension, are dependent of the axis ratio. It is further shown that the updraught profiles required to grow spheroidal hailstones at the just‐wet condition are not much different from those required for spherical stones.
Note on the measurement of ozone in the atmosphere
Authors: Dobson G. M. B.
Published: February 2007

The absorption coefficients of ozone for ultra‐violet wavelengths which have previously been accepted as correct, do not agree with measurements made on the ozone in the atmosphere. New laboratory measurements are now reported, in which the same spectroscopic apparatus is employed as is used in the atmospheric work. The absorption coefficients so found agree well with the atmospheric values.

The possibility that there may be other gases in the atmosphere, in addition to ozone, which absorb in the ultra‐violet region is examined. Only sulphur dioxide might possibly give trouble but the amount present is too small to cause appreciable errors in the ozone measurements.
Zonal winds over the equator
Authors: Tucker G. B.
Published: February 2007

The dynamics of mean zonal flow over the Equator are described using a momentum budget. First the budget is drawn up for the troposphere, and the estimates of the mechanisms involved are shown to be consistent with the observed zonal wind/height profile. the technique is then applied to the stratosphere up to 30 km where the approximately 26‐month oscillation in zonal winds is observed. the necessity for a similar oscillation in the momentum convergence due to large‐scale horizontal eddies is deduced, and this oscillation is verified from wind observations. the vertical velocity/height profile associated with the zonal wind oscillation is derived and shown to be constant in time. the downward motion above 20 km and upward motion below is shown to be consistent with observed ozone and water vapour observations. Finally, types of synoptic systems are suggested which could be associated with the observed pattern of zonal flow and momentum convergence.
Lee wave characteristics derived from a three‐layer model
Authors: Pearce R. P. , White P. W.
Published: February 2007

It is well‐known that lee waves are usually associated with the presence of an inversion layer. A mathematical model in which the atmosphere is divided into three layers, the middle one being of high stability and the other two of much lower stability, enables criteria for the occurrence of lee waves to be calculated, the only parameters entering being Scorer's ‘l2’ for the middle and adjacent layers and the thickness of the middle layer expressed as a multiple of its height above the ground. Data from four cases in which lee waves were observed are compared with the characteristics of the model and reasonable quantitative agreement of wavelengths obtained.

The increase in wavelength and frequent disappearance of lee waves associated with convective heating of the lower layers can be deduced from the theoretical behaviour of the model as the parameters are changed to simulate the heating process.
A laboratory study of the ice nucleating properties of some mineral particulates
Authors: Roberts P. , Hallett J.
Published: February 2007

Laboratory studies using a microscope cold stage with controlled humidity environment have been carried out on the ice nucleation and preactivation properties of several naturally occurring particulate substances. For initial nucleation water saturation was necessary, but below a critical temperature a constant ice supersaturation (water subsaturation), was sufficient. The values of both temperature and supersaturation depended on the substance. In preactivation the behaviour was similar but with a higher initial and critical temperature. Typical values are : for kaolinite, initial nucleation − 10·5, − 19°C, 20 per cent; preactivation − 6, − 11·5°C, 12 per cent: montmorillonite, − 25, below − 27°C; preactivation − 4, − 13·5°C, 14 per cent. The first temperature gives one ice crystal in 104 particles; the second is critical for nucleation at water subsaturation. The low values of supersaturation required for nucleation suggest that preactivation is caused by the freezing of a supercooled, adsorbed, liquid‐like layer, rather than by the retention of ice embryos in cavities. A necessary condition for the measurement of the ice nucleating ability of particles from an air sample is that they must not be heated to a temperature above at least − 5°C or subjected to a relative humidity over ice of less than about 35 per cent before the measurement is made.
Recent spectra of atmospheric turbulence
Authors: Busch N. E. , Panofsky H. A.
Published: February 2007

Spectra of atmospheric turbulence recently measured at various heights and sites under a variety of stability conditions have been analysed and compared. The results are:

In regions over which the spectra obey −5/3 power laws, the ratio of the lateral to the longitudinal spectra shows fair agreement with the 4/3 ratio predicted by the Kolmogorov hypothesis for the inertial sub‐range. The vertical‐longitudinal ratio has a similar tendency.

Dissipation rates computed from the longitudinal spectra seem to be consistent with the hypothesis that dissipation is balanced by the total production of mechanical and convective turbulent energy, provided that the turbulence is in equilibrium. In transition from rough to smooth terrain, dissipation exceeds the other terms.

Vertical‐velocity spectra obey Monin‐Obukhov similarity theory up to a height of about 50 m. Their shapes are reasonably uniform, the major change with stability being a change of scale of the wave number axis, i.e., any characteristic nondimensional wave number is a function of z/L only. This function appears to be the same as the relation between the normalized dissipation and z/L. These results are consistent with previously measured Kolmogorov constants and with measured ratios of standard deviation of vertical velocity to friction velocity. Up to about a height of 50 m the wavelengths of the maxima of the logarithmic spectra increase linearly with height and more slowly thereafter, up to about 300 m. The spectra in stable air above 50 m suggest the existence of a buoyant sub‐range.

Longitudinal spectra do not obey similarity theory in a number of ways. The wavelengths do not scale with height, and there may be differences between sites when the spectra are plotted in similarity coordinates.

Spectra over the sea seem to have relatively more energy at low frequencies than those over land.
The dispersion of a puff of passive contaminant in the constant stress region
Authors: Chatwin P. C.
Published: February 2007

Properties of a dispersing cloud of passive contaminant released from an instantaneous source near the ground in a neutral atmosphere are investigated theoretically. The mean wind satisfies the logarithmic law, and it is assumed that the vertical turbulent transfer can be described by means of an eddy diffusivity. By using some of the results of the Lagrangian similarity theory of Batchelor, it is shown how useful results may then be obtained from the equation describing the distribution of concentration. In particular, expressions are derived for the position of the centre of mass of the cloud and for its downwind and vertical spreads as functions of the time after release. The distribution of material at a given height is also investigated. The paper concludes with a brief discussion of the results and of other applications of the type of technique presented here.
The collection efficiencies of hailstones
Authors: Macklin W. C. , Bailey I. H.
Published: February 2007

The collection efficiencies of smooth spheres and artificial hailstones have been determined experimentally. There is no significant difference between the values for the artificial hailstones and those for smooth spheres of the same cross‐sectional area. However, the results are generally lower than those predicted by the theory of Langmuir and Blodgett, particularly at low airspeeds. Using these data the critical liquid water concentrations for large natural hailstones have been calculated. These are not markedly dependent on hailstone radius and, for a cloud droplet radius of 15 μ, are approximately 3 to 5 g m−3 and 4 to 7 gm−3 at the −20 and −30°C levels respectively.
Estimations from geostrophic trajectories of horizontal diffusivity in the mid‐latitude troposphere and lower stratosphere
Authors: Murgatroyd R. J.
Published: February 2007

Zonal and meridional diffusivities Kxx and Kyy have been found at mid‐latitudes from the spreads of sets of geostrophic trajectories at levels between 700 mb and 30 mb during each season of 1965. Values have been calculated using the relationship R = e−PT cos qr for the form of the corresponding Lagrangian autocorrelograms. In addition a similar set of Eulerian data has been analysed to obtain autocorrelograms and by comparison with the trajectory data Eulerian‐Lagrangian scale relationships have been obtained.

The results show values of Kxx ranging from 0·2.106 to about 20.106 and Kyy from 0·2. 106 to about 6.106 m2 sec−1. In both cases the lowest values are found in the summer stratosphere and the highest in the spring stratosphere and in the upper troposphere in winter. Their distributions principally follow that of the wind variances. Integral time scales are mainly between 5 and 30 hours meridionally and 10 and 50 hours zonally and are greatest in the stratosphere and lowest in the mid‐troposphere. The contributions of damping and harmonic effects to these time scales are discussed. Comparison of the Lagrangian and Eulerian time scales indicates a mean value β of about 0·6 for their ratio with the meridional values smaller than the zonal values.
Some computations of meridional flow, angular momentum and energy in the atmosphere based on IGY data for latitude 30°N
Authors: Murray R. , Parker A. E. , Collison P.
Published: February 2007

Using basic data extracted from daily hemispherical cross‐sections constructed at 30°N for March, June, September and December 1958, extensive numerical calculations of mean meridional flow, angular momentum flux and energy flux (i.e. sensible heat, latent heat, potential and kinetic energy) were carried out, and the principal results are reported. Most of the computations are broadly in agreement with earlier estimates; the main differences are uncertainties concerning the energy transports.
Inviscid flows of stably stratified fluids over barriers
Authors: Pao Y.‐H.
Published: February 2007

Steady, inviscid, incompressible, two‐dimensional flows of stably stratified fluids over a barrier or barriers are examined theoretically. The density gradient anduρ1/2are assumed to be constant upstream, where ρ is the density anduis the horizontal velocity. Exact solutions of large amplitude waves valid for arbitrary Richardson numbers are obtained for barriers of finite height in a semi‐infinite domain or in a confined channel. These barriers are constructed from vortex pairs and doublets.
Relations of radiation fluxes over natural surfaces
Authors: Idso S. B. , Baker D. G. , Blad B. L.
Published: February 2007

Radiation fluxes over surfaces of bare soil and short grass sod were measured on clear days at St. Paul, Minnesota. Widely diverse types of daily cycles describing the hourly dependence of net upon net solar radiation were found. Heating coefficients depended as much upon atmospheric radiative properties as upon surface properties. Causes for these relations are proposed and tentatively verified experimentally.

The accuracy of regressions of solar on net radiation is shown to depend upon the uniform distribution of data points extending to the region of the origin. Controversies in the literature are illuminated by this analysis, both theoretically and experimentally. Two equations relating the slope of the regression of solar on net radiation to albedo are also considered. Finally, a relation between the long‐wave radiation balance and the heating coefficient proposed by Ekern (1965) is qualitatively substantiated.
Experimental studies of the effect of electric fields on the growth of cloud particles
Authors: Latham J.
Published: February 2007

Studies have been made in Yellowstone Park of the factors governing the growth of hydrometeors in natural clouds of ice crystals, droplets and supercooled droplets. In the majority of experiments an ice sphere or water drop was rotated through a droplet cloud or crystal stream and the mass MF of material collected in time γ was measured as a function of collector diameter D, crystal or droplet diameter d, impact velocity V, temperature T and, particularly, the strength of the electric field F in the vicinity of the growing particle. The approximate ranges of parameters attainable were F, 0 to 1,600 V.cm−1; T, + 20 to −15°C; V, 10 to 500 cm s−1; d, 10 to 150 microns; and D, 100 to 2,000 microns.

It was found that electric fields could exercise a marked influence upon the growth rates of ice particles exposed to ice crystals, ice spheres exposed to supercooled droplets and water drops exposed to cloud droplets at temperatures warmer than 0°C. In all cases where the measured growth in the presence of a field was significantly different from that in the absence of a field the function of the field was to accelerate the growth rate.

The aggregation of ice crystals was found to be unaffected by fields below about 500 V.cm−1 but the growth rate increased rapidly as F was increased above this value and attained about twice the field‐free value in a field of 1,500 V.cm−1. In view of the large size of the ice crystals the primary effect of the field was probably to increase the aggregation efficiency not the collision cross‐section. The most significant effect of electric forces on the growth of solid or liquid particles by the collection of droplets was to produce a rapid increase in the growth rates as F increased above a threshold value of about 1,000 V.cm−1. The growth rate at F = 1,600 V.cm−1 was typically about twice the field‐free value. The observed enhancement of the growth rate in these high fields is probably a consequence of increased collision efficiencies.

The variation of the measured growth rates of all types of particle with the parameters D, d, V and T were generally consistent with laboratory measurements of previous workers. No evidence was found for the triggering of growth by electric fields or for enhanced growth in fields of magnitudes occurring within non‐precipitating clouds.
Interhemispheric transport of air in the lower troposphere over the western Indian Ocean
Authors: Findlater J.
Published: February 2007

Equatorial cross‐sections of monthly mean meridional flow in the lower troposphere over the western Indian Ocean have been prepared for January and July. These sections have allowed new estimates to be made of the mean transport of air across the Equator in the area.
Evaporation from a papyrus swamp
Authors: Rijks D. A.
Published: February 2007

Evaporation from an old stand of papyrus was estimated by the Bowen ratio method. It was found that about 30 per cent of the net radiation reaching the top of the canopy was converted into sensible heat. The layer formed by the heads of the papyrus also seemed to act as a major resistance to turbulent exchange of water vapour from the undergrowth. Evaporation from an old stand of papyrus was estimated to be 60 ± 15 per cent of Penman estimates of evaporation from open water.
Atmospheric edge waves
Authors: Garrett C. J. R.
Published: February 2007

In an isothermal windless atmosphere Lamb's wave, the energy of which decays exponentially with height, propagates non‐dispersively with the speed of sound. In the real atmosphere the speed of sound and the wind speed vary with height, but it is known that an edge wave similar to Lamb's wave is still possible. Assuming the wind speed and variations in the speed of sound to be much less than some typical sound speed, this atmospheric edge wave is shown to have group velocity given approximately by

Where ω is the wave frequency, c̄ the mean of the sound and wind speeds weighted with the energy density of the basic Lamb wave, and D is a positive dispersion coefficient defined in terms of a simple integral of the departures of the sound and wind speeds from their weighted means. Expressions are derived for the dispersive effect of a change in the sound or wind speed at any height, and these are evaluated for a particular model atmosphere. It is shown that the effect of horizontal inhomogeneities in the atmosphere is merely to average the long wave speed and dispersion coefficient along the great circle path from source to receiver. The theory is compared with the results obtained from microbarograms of pressure pulses from large atmospheric explosions, but it is found that the paucity of atmospheric data makes it difficult to use these results to estimate winds above sounding heights on the path from source to receiver. Atmospheric edge waves are shown to be rather insensitive to the upper boundary condition in general, though the effect on microbarograms of coupling between the edge wave and waves propagating high in the atmosphere is discussed, and various decoupling mechanisms, including dissipative decoupling, are described.
Observational studies in the atmospheric boundary layer
Authors: Clarke R. H.
Published: February 2007

Winds and temperatures in the boundary layer measured during two Australian expeditions are analysed according to the similarity scheme, with the use of four stability classifications.

Under conditions of deep convection there is a minimum potential temperature and a maximum velocity component in the direction of the surface wind, at a height of about 0.12 u*/f. In the very stable cases, the temperature gradient follows rather closely a z−2 law for a considerable height range from 0.08 u*/f upwards. An expression closely fitting the mean data in stable conditions is suggested for the vertical temperature structure at all levels in the boundary layer.

Wind data processed in this way show, for all four stability classes, a rudimentary Ekman spiral. With deep convection the spiral is found to be reversed in sense, but the flow in the convecting layer is down the gradient of pressure. If the convective limit lies broadly within the Ekman layer, a spiral of the expected sense is found. The upper limit of the Ekman layer (as defined by the ‘spiral’) is found to lie at a height of 0.17 to 0.24 (increasing with stability) in units of u*/f. Stress and heat‐flux are apparently considerable above this level, with sub‐geostrophic wind, when deep convection is occurring.

Approximations to the universal distributions of stress, eddy coefficients, mixing length and rate of degradation of mean flow kinetic energy are computed for the various stabilities. The mixing length in unstable conditions increases almost as height up to a level of about 0.08 u*/f, and then decreases, but in general appears not to vanish in stable layers above the boundary layer. In the unstable boundary layer with deep convection, the eddy transfer coefficient for heat exceeds that for momentum up to 0.12 u*/f, where it becomes infinite, and is negative at higher levels. In stable conditions the transfer coefficients for a small sample of soundings were estimated to be closely similar.

The universal functions of stability, A, B and C, which enable one to compute free atmosphere wind vector and temperature, given surface conditions, have been evaluated with moderate success, although B, which essentially describes the change of wind direction with height, exhibits excessive variability. A method is suggested for computing horizontal advection in the boundary layer when this is to be ‘parameterized’ in mathematical models.

The drag coefficient, in terms of free atmosphere wind, has almost a 50‐fold range, due to stability variation only. Most of the variation occurs relatively close to neutral, so warning against too ready an assumption of neutrality in practical applications.

It is suggested that, for modelling purposes, it is preferable to adopt boundary layer formulations which are not too sensitive to departures from ideal conditions, and eddy coefficients, perhaps based on mixing lengths, may well provide the best approach currently available.
Solar radiation and solar activity
Authors: Kondratyev K. Ya. , Nikolsky G. A.
Published: February 2007

Using high‐altitude balloon soundings (1961 to 1968) and other data, it is shown that the most reliable maximum value of the solar constant is at present 1.94 cal cm−2 min−1, to an accuracy of 1 per cent. This value is observed with Wolf numbers between 80 and 100, below or above which the solar constant decreases. The maximum decrease does not exceed 2 to 2.5 per cent. The observations reveal the influence of nuclear explosions and volcanic eruptions which caused an anomalous turbidity of the upper atmospheric layers. These anomalies have been studied. The above conclusions require further confirmation using direct long‐term measurements of the solar constant outside the atmosphere.
The absorption coefficients of ozone for the Dobson spectrophotometer: A direct determination of their ratios and temperature dependence
Authors: Powell D. B. B.
Published: February 2007

The ratios of the absorption coefficients of ozone at the standard wavelength pairs for the Dobson spectrophotometer have been determined in the laboratory over a range of temperatures using the sun as light source. Temperature coefficients of absorption are calculated and compared with those derived from the results of other workers. Using – 55°G as the representative temperature of atmospheric ozone, new values are given for the absorption coefficients which differ from the currently accepted values.
Cross‐equatorial eddy momentum fluxes as evidence of tropical planetary wave sources
Authors: Dickinson R. E.
Published: February 2007

The large‐scale asymmetries in the release of latent heat in the Tropics should be an important source of planetary waves. According to planetary wave theory, such sources are accompanied by a convergence of eddy momentum flux. These planetary waves may provide eddy fluxes of momentum across the Equator from the winter to the summer hemisphere in agreement with observation.
Cospectral similarity in the atmospheric surface layer
Authors: Wyngaard J. C. , Coté O. R.
Published: February 2007

There are two asymptotic cases where the four parameters which determine surface layer turbulence structure reduce to three. In the unstable limit, which we call local free convection, the surface stress is no longer important. In the stable limit z no longer enters; we propose the name ‘local z‐less stratification’ for this state. In both cases explicit predictions result for various properties of the cospectra of stress and heat flux. Although the predictions are based on asymptotic arguments and therefore might be expected to hold only at large ∣z/L∣ values, data from the 1968 Kansas experiments show that most predictions are valid fairly close to neutral.
A study of the energetics of an upper stratospheric warming (1969‐1970)
Authors: Miller A. J. , Brown J. A. , Campana K. A.
Published: February 2007

During the winter of 1969‐1970 when a rather intense stratospheric warming of the type restricted to the upper stratosphere occurred, we were fortunate in having a considerable number of rocketsonde observations throughout the Northern Hemisphere. In addition, the Satellite Infrared Spectrometer (SIRS) on board Nimbus 3 yielded large amounts of radiation temperature data which, when combined with the above, enabled us to construct hemispheric synoptic analyses at the 10‐, 5‐, and 2‐mb levels, for seven days during the warming event.

Employing these analyses along with the daily objective analyses from 1,000‐30 mb, we computed certain of the major energy transformations for the troposphere and lower and middle stratosphere. It was found that the middle stratospheric warming event was of a direct baroclinic type, forced from below. Also, we noted that if the warming is to propagate into the lower stratosphere, it is necessary to reverse the normal eddy kinetic to eddy potential energy transfer in that region so that it operates in a direct baroclinic sense.
Studies of turbulence in the surface layer over water (Lough Neagh). III. Wave and drag properties of the sea‐surface in conditions of limited fetch
Authors: Garratt J. R.
Published: February 2007

Wave and aerodynamic properties of the sea surface at Lough Neagh, Northern Ireland, are described with mean wind speed u (at a height of 10 m) varying from 4 to 8 m s−1 and fetch F varying from 8 to 22 km.

The sea surface at Lough Neagh is characterized by wind induced waves of dominant period 2 to 4 s and a wave spectrum depending upon u and F, with a steep low frequency face (at frequency nf), sharp peak (at no) and high frequency region with ‘energy’ proportional to frequency to a variable power β in the range —4 to —5. The ‘constant’ of proportionality αg2 in the relation ϕ(n) = αg2n−β appropriate to the equilibrium range is variable between 6 and 12 (where unless stated to the contrary n in numerical expressions is in cycles s−1)‐ mean of 7·9 ‐with a mean β of —4·5, which compares to Phillips' overall mean value of αg2 of 7·2 with a mean β close to —5.

Our data, and those from other sources, suggest the following relations, valid over a range of the dimensionless fetch gF/u2 from 102 to 105,

And

The first two are found to imply σh = 1·4 n−2o.

The third relation is interpreted through identification of nf with the transition frequency separating a linear from an exponential wave growth.

Our data are consistent with the idea of Kitaigorodskii that zo (u*) depends also upon the degree of wave development σ = gσh/u*2. At Lough Neagh σ* ∼ 10–40, implying zo is closely related to u* as is found to be the case using logarithmic wind profiles.

There is evidence that

Suggested by earlier Russian work for similar values of σ*.

There is no evidence that wave power impresses itself upon the turbulence spectra of the air for values of height/wave amplitude ratio as low as 3·3:1.
Energy budgets in pine forest
Authors: Stewart J. B. , Thom A. S.
Published: February 2007

Hourly energy budgets measured in Thetford Forest, Norfolk, are analysed for seven fine days in months from May to September.

Values found for the Bowen ratio β ranging from near 1 to 4 or more, are used to show that the bulk physiological resistance rST of the forest exhibits a consistent diurnal trend, from near 1·2 s cm−1 in the forenoon (once the trees are dry) to as much as 4 s cm−1 by late afternoon ‐ consistent with independent biological measurements (Robins, personal communication). In contrast, the forest's bulk aerodynamic resistance r generally lies between 0·05 and 0·10 s cm−1. The ratio rST/r alone, of order 20:1, is shown to imply that transpiration from the forest must occur at rates much less dependent, primarily, on net radiation, Rn, than on ambient vapour pressure deficit (v.p.d.), (provided that the latter is not too small, i.e. ≮ 1 mb per 100 W m−2 of Rn, say); and also that the evaporation of intercepted rainfall from the trees must occur at about 5 times the corresponding transpiration rate under the same meteorological conditions. In addition, because lighter winds during fine weather tend to favour larger v.p.d's the observed decrease in transpiration rate with increasing wind speed is much larger than that expected from the accompanying decrease in r alone.

Other conclusions are (i) that the storage associated with a 1° C change in air temperature per hour, within the canopy, is 18 W m−2, which is not always negligible, as it is for short vegetation; and (ii) that values derived for the dimensionless excess resistance parameter, B−1, although remarkably small, 2 to 3 for u* ∼ 0·75 m s−1, are commensurate with other bulk aerodynamic resistances in the system: accordingly, the easily‐derived surface resistance parameter, rs, (Monteith 1965; Thom 1972) provides an estimate of rST for the forest within 10 per cent for all β > 0.
The evolution of droplet spectra by condensation and coalescence in cumulus clouds
Authors: Jonas P. R. , Mason B. J.
Published: February 2007

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

During July 1971, an intensive experimental programme was undertaken in south‐eastern Alberta to measure the turbulence statistics in the planetary boundary layer (PBL), using a 92‐m tower, an array of four smaller towers and an instrumented T‐33 aircraft from the National Aeronautical Establishment of the National Research Council, Ottawa.

In this first paper is reported the measurement of the translation velocity of convective plumes, determined by means of an array of towers, at a height of 3.5 m. The direction of plume motion was found to be close to that of the surface wind. The speed of plume motion was found to be close to the wind speed near the top of the surface shear zone; this result is different from previous estimates using different techniques. A dynamic model of the plume was used to show that a translation speed close to the wind speed near the top of the surface shear zone (as observed) allows plumes to exist at a lower thermal instability level than any other possible translation speed.

These results mean that Taylor's frozen field hypothesis is not applicable to plume scales since the plumes (although not the air inside them) move at a speed independent of height.
The estimation of solar radiation under cloudless skies with atmospheric dust
Authors: Collier L. R. , Lockwood J. G.
Published: February 2007

Observations of global radiation received in a small catchment in Yorkshire were analysed for clear sky conditions and an empirical relationship of the form

Q = 1380 sin θ(a + b sin θ) W m−2

Found, between incoming solar radiation Q and the solar elevation θ, where a and b are constants. The constants differ markedly from those obtained in a similar analysis of data from eastern Atlantic weather ships, suggesting that the radiation, under cloudless skies, over inland Britain, is only about 60% of that received under cloudless skies over the eastern Atlantic.
Turbulent diffusion within a wheat canopy: II. Results and interpretation
Authors: Legg B. J. , Long I. F.
Published: February 2007

The coefficient of turbulent diffusion was measured in a 1·25m tall wheat canopy using a uniform release of nitrous oxide, the energy and momentum balance methods, and the humidity profile. The nitrous oxide profile gave the most accurate values, KN in the lower two thirds of the canopy, and a regression of the energy balance estimates, KE, against KN had a slope of 1·17 ± 0·10 with a non‐significant intercept of 17cm2s−1.

The mean day time profile of KN was exponential, K(z) = K(h) exp(−γ(1‐z/h)) with γ = 3·9 when u(h) < 1·2m s−1 increasing to 5·3 when u(h) > 1·2m s−1. But analysis of KN for the height interval 0·3 to 0·8m shows the importance of thermal stability, and the results are related to the non‐dimensional stability parameter g/T(ΔT/Δz/(u(h)h2) where ΔT/Δz is the temperature gradient and u(h) is the windspeed at crop height, h.

The large scatter in the results was attributed to the heterogeneity of the crop. Also the wind profile was frequently S‐shaped defying a simple one‐dimensional analysis and causing the momentum balance to give nonsensical results. Hence it seems unlikely that one‐dimensional analysis of transfer can give values of K allowing an accurate estimate of the source and sink distributions within a dense crop canopy.
Secular changes in South African rainfall: 1880 to 1972
Authors: Tyson P. D. , Dyer T. G. J. , Mametse M. N.
Published: February 2007

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

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

New England coastal frontogenesis is investigated on the basis of individual and climatological case studies. The results suggest that differential friction plays the role of the synoptic scale geostrophic deformation in packing the isotherms together for this mesoscale boundary‐layer frontal phenomenon. An initial temperature gradient must be present for the differential friction mechanism to be effective. Geostrophic deformation is incapable of initiating coastal frontogenesis while the maximum area of observed deformation coincides with the location of the developing front.

Coastal frontogenesis is associated with a pronounced sea level cold anticyclone to the north and east of New England in all cases studied. Differential friction between the northerly inland flow and the more easterly onshore flow then sets up favourable shoreline deformation and convergence fields leading to frontogenesis in the presence of differential thermal stratification. The time scale for an order‐of‐magnitude increase in the horizontal temperature gradient appears to be one‐half to one day depending upon the contribution of differential diabatic heating.

The orientation of the New England shoreline is such as to favour frontogenesis across extreme eastern Massachusetts and Rhode Island. An axis of relatively high precipitation is noted just to the west of this favoured locale on the climatological charts, consistent with a thermally direct circulation about the front.
Note on a preliminary scheme for storm surge prediction using numerical models
Authors: Flather R. A. , Davies A. M.
Published: February 2007

The initial stages of an investigation aimed at setting up a new system for the prediction of storm surges in the North Sea are described. The proposed scheme is based on the use of dynamical finite‐difference models of the atmosphere and of the sea, the atmospheric model providing the necessary forecasts of meteorological data. These data are converted into the form required for input to the sea model, which then computes the associated storm surge.

Some preliminary results are presented and discussed and an indication given of the further development of the system.
An objective exposure correction method for average wind speeds measured at a sheltered location
Authors: Wieringa J.
Published: February 2007

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

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

The effect of radiative heat transfer on droplet growth is assessed. It is estimated that radiative cooling is the principal agent of droplet growth in radiation fog, and that supersaturations are very small – slight undersaturation may even occur – and may be relatively unimportant for droplet growth in this environment. Gravitational settling is shown to be the principal limiting factor on droplet growth in radiation fog.

It is also suggested that radiative transfer may have some relevance to the unexpectedly large numbers of 5μm radius droplets observed in cumulus clouds by Warner (1969).
The effects of air pressure and water vapour content on the propagation of positive corona streamers, and their implications to lightning initiation
Authors: Griffiths R. F. , Phelps C. T.
Published: February 2007

As a first step in the construction and testing of a theoretical model of lightning initiation, measurements have been made of the ambient electric field Eo required to support the long‐range propagation of corona streamers as a function of dry air pressure pα and the partial pressure of water vapour pw. The experiments reveal that Eo falls more rapidly with pα than would be expected on the assumption that Eä/pα = const., which has been used in previous discussions of the problem of lightning initiation. Eo was found to increase linearly with pw. It appears that Eo is considerably less than the field required to initiate corona from any type of hydrometeor excepting colliding drop pairs. Arguments based on these results are presented to show that the high fields in thunderclouds are probably restricted to regions that are small in extent compared with the dimensions of the thundercloud.