bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculations of the ascent of a saturated buoyant parcel with mixing
Authors: Mason B. J. , Emig R.
Published: February 2007

Numerical computations are made to show how the vertical velocity, temperature, humidity‐mixing ratio and liquid‐water content of a cloudy parcel will vary with height and time as it ascends from the condensation level, rises through, and mixes with, the surrounding environment whose temperature and humidity distributions are specified. The rate at which the parcel is diluted by mixing is formulated in two different ways which lead to essentially the same conclusions. This treatment does not attempt a detailed description of the mixing processes but arrives at rather critical values for a single parameter used to represent the rate of mixing. If this is sufficiently large to prevent the vertical motion undergoing large oscillations (such as are experienced by a closed parcel), the first‐formed cloud is small ‐ usually only a few hundred metres deep over land and perhaps less than 100 m deep over the oceans. This implies that large clouds must evolve by successive thermals rising through air which has been warmed and moistened by their predecessors. Computations are made to demonstrate this stage‐by‐stage growth. The formation and growth of the first visible cloud appears to depend rather critically upon the excess temperature and velocity with which the thermal reaches the condensation level. These conclusions, and also the computed vertical profiles of temperature, updraught speed and liquid‐water in these small clouds, appear to be consistent with observations.
A simplified theory of the generation of sea breezes
Authors: Pearce R. P.
Published: February 2007

The equations of heating and motion are averaged vertically, assuming vertical distributions of velocity and temperature. A non‐linear partial differential equation of hyperbolic type is found to be satisfied by the surface velocity of the sea breeze. Numerical solutions are given for varying heating rates and for a superposed off‐shore wind. The method of integration of the equations leads to a spurious stable oscillation in the solutions and this is shown to be associated with the finite difference method used. Using dimensional analysis, a criterion for the prediction of the occurrence of sea breezes is suggested.
A smoke‐trail technique for measuring wind
Authors: Cooke T. H.
Published: February 2007

In the firing of low‐acceleration sounding rockets a knowledge of low‐altitude wind velocities before and during firing is necessary. Existing meteorological methods are inadequate, and the smoke‐trail technique here reported has been developed to augment these. The technique consists of visual or photographic analysis of the movement of a column of smoke and can be used to obtain the wind structure to heights up to about 1,500 ft.

The present method of laying the smoke‐trail is by small solid‐fuel rockets, and suggestions are made for other methods which would reduce the cost of laying each trail. Possible uses of the smoke‐trail technique are considered.
Determination of stress from wind and temperature measurements
Authors: Panofsky H. A.
Published: February 2007

An integrated form of the diabatic wind profile based on similarity theory is used to estimate surface stress from measured winds and temperatures. It is shown that excellent estimates of stress can be made, given the roughness length, an estimate of the Richardson number and an accurate wind at one level. The theory can further be applied to estimate the roughness length from relatively few observations of wind and temperature not necessarily under neutral conditions.

Suggestions by Taylor and Deacon for the determination of surface stress from autocovariance functions are tested on O'Neill observations. The results show that fair stress estimates can be made if instrumental response is taken into account.
The growth of large hail within a steady updraught
Authors: Browning K. A.
Published: February 2007

An analysis of the large‐scale organization of the Wokingham storm (Browning 1962b) shows that one of its constituent cells was particularly large and persistent. Throughout a 30‐min period, when it was most intense and producing the largest hail, this ‘Supercell’ exhibited a fairly steady structure which has been used to derive a model of the associated airflow (Browning and Ludlam 1962). In Part I of the present paper this model is given a quantitative basis. As a first approximation it is assumed that the airflow was two‐dimensional, but since the resulting model fails to account for the observed durations at the ground of hail and heavy rain it is modified to take into account a substantial convergent inflow towards the updraught from the right flank and towards the downdraught from the left flank. By applying and extending the analysis of hailstone growth within steady updraughts presented by Browning, Ludlam and Macklin (1963) and by relating it to the model of the airflow, it has been possible in Part II of this paper to account for the growth and the observed distribution of hail within the Wokingham storm. Two of the largest hailstones recovered are considered in detail because their structure can be explained only in terms of rather specific airflow characteristics. Their growth is shown to be consistent with the assumed vertical airspeeds within the updraught. Consideration of their growth‐times along with the distribution of hail at the ground suggests the presence within the updraught of horizontal components of motion relative to the storm of about 7 m sec−1 both towards its rear and towards its left flank. Finally, the existence is inferred of an abundant source of hailstone embryos owing to hailstones of all sizes re‐entering the foot of the updraught at levels above 4 km.
Bi‐annual variation of atmospheric ozone over the tropics
Authors: Ramanathan K. R.
Published: February 2007

It is shown that there is a bi‐annual variation of atmospheric ozone over equatorial, subtropical and lower middle latitude stations, a year of high ozone being followed by one of low ozone. A high ozone year in the sub‐tropics and lower middle latitudes corresponds to a year of low ozone near the equator. A possible connexion of this with the bi‐annual variation of zonal winds in the stratosphere of low latitudes is indicated.
The exponential wind profile
Authors: Swinbank W. C.
Published: February 2007

From a definition and a hypothesis the form of the wind profile in the turbulent boundary layer when the air is thermally stratified is derived as magnified image.

This solution is expected to be applicable in all stabilities and to all heights below which the shearing stress and the vertical heat flux remain constant.

A critical examination of the experimental procedure necessary to test the validity of this, or of any, formulation for the steady‐state wind profile leads to a specification which the observational site and the weather conditions should meet.

The results of a series of experiments are presented and analysed. These comprise measurements of wind speed and temperature at a number of levels up to 16 metres, supplemented by observations of net radiation, heat flux into the air and into the ground, and shearing stress. the analysis affords good verification of the form proposed for the wind profile.

A variety of evidence is adduced to show that buoyancy modifies the transfer of heat more strongly than that of momentum, and that the discrimination increases with height above the surface.
Wind and temperature profiles near the ground in stable stratification
Authors: McVehil G. E.
Published: February 2007

Observed wind and temperature profiles from O'Neill, Nebraska and Antarctica are analysed to determine their characteristics in inversion conditions. Analyses of the similarity between wind and temperature profiles are presented. These show that the profiles are generally similar when the Richardson number is small. However, there is strong evidence in the Antarctic data for a departure from similarity and a decrease in the ratio of eddy conductivity to eddy viscosity for Richardson numbers greater than 0·08.

It is shown that the log‐linear wind profile fits the observations well for Richardson numbers less than about 0·14. the constant in the log‐linear equation is found to have a value of approximately seven in stable air, implying a critical gradient Richardson number of 1/7.

From the log‐linear theory, heat flux and surface stress can be calculated given winds at two levels and the surface roughness. Predicted values are compared with observations. the agreement is good in the case of surface stress and fair for heat flux.
The equatorial tropospheric wind regime
Authors: Tucker G. B.
Published: February 2007

Wind observations in the troposphere above seven stations in the vicinity of the Equator have been analysed for the years 1961 and 1962. Strong mean meridional circulations emerge as features of the tropospheric wind regime. Easterly winds occur throughout most of the troposphere, but at times during the northern hemisphere winter a net westerly wind appears to exist in the upper troposphere. There is a strong momentum flux towards the summer hemisphere; the greatest contribution to this comes from the standing eddy flux which is due largely to strong monsoon influences on the flow patterns at 200 mb and above in the Indian Ocean‐West Pacific sector.
The flux‐gradient relation for turbulent heat transfer in the lower atmosphere
Authors: Dyer A. J.
Published: February 2007

Data obtained during February and December 1962 at a carefully‐chosen micrometeorological site at Kerang in Northern Victoria are used to examine the flux‐gradient relation for sensible heat transfer. The analysis is carried out for 70 half‐hour runs specially selected for steady state lapse conditions to determine the variation with the stability parameter, z/L, of the Monin‐Obukhov ‘universal function,’ øH.

In the range 0.02 < |z/L| < 0.6 it is found that the value of the index ϵ in øH α |z/L|ϵ is − 0.33 ± 0.02 in excellent agreement with the ‘free convection’ regime of Priestley and the −4/3 power form of the temperature profile. The corresponding value of H* is 1.32 ± 0.06.

For |z/L| > 1, ϵ is found to be −0.38 ± 0.10 in contrast to Townsend's suggestion of −1 for this region based on laboratory evidence. Regression analysis for the region |z/L| > 0.2 yields a value of ϵ of −0.50 ± 0.02. The suggestion is offered that the motions observed by Townsend may occur in the atmosphere but as transient phenomena in which the applicability of the conventional similarity principles is to be questioned.

The formula H = 24Δθ3/2 based on Priestley's regime with sensible heat H in mw cm−‐2, and potential temperature difference Δθ between 1 and 4 metres in ° provides a practical basis for the evaluation of the heat flux from profile measurements.
The effect of wind shear and vertical diffusion on horizontal dispersion
Authors: Tyldesley J. B. , Wallington C. E.
Published: February 2007

Features of analytical solutions of atmospheric diffusion equations show that the effect of wind shear and vertical diffusion on horizontal dispersion is important at great distances. Methods of using an analogue or a digital computer to solve the equations for all but very short distances are described. Computations indicate that the wind shear effect is probably dominant over a wide range, and these indications are confirmed by reference to broad and specific deductions from experimental data.
Some aspects of convection as measured from aircraft
Authors: Grant D. R.
Published: February 2007

Temperature and humidity fluctuations obtained from a fast‐responding thermometer and radio refractometer in convective conditions over a flat surface have been studied. Warm, moist ascending patches of air emerging from a layer of mechanical turbulence near the surface were observed up to about 600 m. The excess temperature of these patches decreased rapidly with height. Between 1,000 m and cloud base (1,300 m) there was evidence of warm dry air descending from above cloud base. This could make a significant contribution to the warming in the convective layer.
Estimating the longitudinal wind spectrum near the ground
Authors: Berman S.
Published: February 2007

A graphical procedure for estimating the spectrum of the longitudinal wind component from height, mean wind speed, roughness length, and stability data is presented, based on observed spectra at many locations.

Using non‐dimensional coordinates following Monin, the amplitude of the spectrum peak in neutral stability shows no systematic variation with height, while the corresponding dimensionless frequency varies with height to the 0.75 power. At relatively high frequencies, spectra observed in unstable conditions are indistinguishable from those in neutral stratification. At lower frequencies the ratio of the spectrum in highly unstable conditions to that in the neutral case approaches 3 : 1 at low heights and decreases to less than one in stable air.
Estimation of insolation for West Africa
Authors: Davies J. A.
Published: February 2007

Coefficients are determined for regressions of insolation upon sunshine using data from six West African stations. The analysis, using total, station and monthly data groupings, indicates high correlation (r = 0.86 to 0.99) for monthly groupings. A pronounced annual cycle and range in the coefficients (a = −0.12 to 0.26, b = 0.50 to 0.99), are explained in terms of variations in cloud cover and atmospheric turbidity. A turbidity index ‘t,’ has values similar to those obtained in East Africa.
Vertical profiles of total precipitation in shower situations
Authors: Hamilton P. M.
Published: February 2007

Vertical profiles of the total precipitation in the area scanned by a radar have been obtained for the first time. Profiles in shower situations show that precipitation commonly accumulates at an upper level. In the more severe storms the accumulations persist for an hour or more, descending slowly during this time. There is evidence that the storms dissipate quickly with a marked increase in severity as the accumulation reaches the melting level.

Observations have shown that the height at which the accumulation forms steadily increases with the available energy of convection. Theoretical work by East (1957) and Kessler (1961) predicts an accumulation at a height that increases with the updraught speed. A combination of these two approaches has led to relations among the three quantities: energy of convection, updraught speed and height of accumulation. The value of these relations in the analysis of convective storms is demonstrated by using them to interpret the behaviour of a particular severe storm.
The vertical distribution of atmospheric ozone and possible transport mechanisms in the stratosphere of the Southern Hemisphere
Authors: Kulkarni R. N.
Published: February 2007

An analysis of the small‐scale fluctuations in the vertical distribution of ozone calculated from Umkehr observations at Brisbane (27°.5S, 153°.0E) and Aspendale (38°.0S, 145°.1E) shows that these fluctuations extend up to about 30 km in late summer and early autumn and only up to about 24 km in late winter and early spring. Ozone content in the troposphere and lower stratosphere increases with increasing total ozone.

Mean meridional distributions of ozone with height have been constructed for the Southern Hemisphere for summer and spring and the results are discussed in relation to the idea of meridional poleward and downward flow of air from the upper part of the tropical troposphere and lower stratosphere. It appears that the changes in the spring amounts of ozone from year to year take place essentially in the 24 to 36 km layer in the middle latitudes of the Southern Hemisphere. Also, above about 25 km, the ozone amount is smaller at 65°S with greater amounts on either side of it. To explain this a transport mechanism above 25 km, consistent with isentropes above that level, is suggested.
Some aspects of the theory of fronts and frontal analysis
Authors: Kirk T. H.
Published: February 2007

Fronts are considered as aspects of development and it is shown that their characteristics can be deduced without recourse to the traditional concept of air masses. The approach interprets the current practice of synoptic analysis in terms of dynamical theory and, as a corollary, affords the possibility of utilising automatic computational methods for the objective depiction of frontal zones and their associated weather.
Vertical diffusion of aerosols over a city
Authors: McCormick R. A. , Kurfis K. R.
Published: February 2007

Vertical exchange coefficients for aerosol material, KA, were determined from measurements of atmospheric turbidity at λ = 0.5 μ following the motion of air flowing over Cincinnati, Ohio. Values of the coefficient for sensible heat, KH, were also obtained at the same time in some instances. Most of the values of KA were in the range 0.1 × 105 to 10 × 105 cm2 sec−1 with a marked seasonal variation of the average values. No significant variation of KA with height (100 to 600 m) was found.
Charge transfer between rigid spheres separated in an electric field
Authors: Latham J. , Freisen R. B. , Mystrom R. E.
Published: February 2007

Measurements have been made of the maximum separation X at which charge is transferred by means of a discharge process between two rigid spheres of radii r and R located in a uniform external electric field E. The experimental relationships between X, E, r and R are in good agreement with the calculations of Davis (1964). It was observed that for small separations charge transfer occurs even in the presence of weak external fields because the local field between the near surfaces of the spheres is greater than the external field strength by an amount that increases rapidly as their separation decreases.
The use of emissivity in atmospheric radiation calculations
Authors: Rodgers C. D.
Published: February 2007

The use of emissivity for calculating atmospheric radiation fluxes due to water vapour is investigated with a view to finding the most accurate way of using the approximation. It is shown that with care it is possible to adjust the emissivity so that errors in fluxes of less than 0·05 mW cm−2 are incurred, when compared with calculations using more accurate methods. This can be attained with the aid of a least squares fit of emissivity on calculated flux. ‘Laboratory’ type emissivities give errors of up to 1·3 mW cm−2.
The generation of shear flow in a wind tunnel
Authors: Lloyd A.
Published: February 2007

A method of generating a shear flow in a wind tunnel is described. A grid of flat plates with added turbulence generators is used in conjunction with an artificially roughened floor. The velocity profile and turbulence profile produced by the grid are matched to the floor roughness so that a virtually non‐developing flow is achieved.
Determination of turbulent fluxes of heat and momentum from the wind profile
Authors: Klug W.
Published: February 2007

A method suggested earlier by the author to determine turbulent fluxes of heat and momentum from a measured wind profile is tested by using Swinbank's observational data.
Some evidence for inertial oscillations along transosonde trajectories
Authors: Angell J. K.
Published: February 2007

Spectral and cross‐spectral analyses applied to ageostrophic winds derived from transosonde trajectories provide some evidence for the existence of inertial oscillations in the atmosphere, with the evidence considerably stronger in the stratosphere than in the troposphere.
Characteristics of billow clouds and their relation to clear‐air turbulence
Authors: Ludlam F. H.
Published: February 2007

Existing theory of the stability of a stably stratified fluid containing a strong vertical shear suggests that unstable waves may develop when the curvature of the velocity profile changes sign and the Richardson number is somewhere less than 1/4. Some observations are described which show the properties of atmospheric billow clouds formed in travelling amplifying waves (transverse to the shear vector), on occasions when these conditions appear to be met. Static instability seems to arise in parts of the wave‐pattern where layers are inverted, and to cause a convective overturning, which may halt the wave development. The most pronounced waves occur in the upper troposphere in association with jet streams, in layers of strong wind shear which are usually dry. They probably only rarely produce clouds, and may more frequently be responsible for the clear‐air turbulence encountered by aircraft. The associated relative air velocities occur over a range of scales: up to about 1 km in the convective regions, and up to the several km associated with the billow wave‐lengths, with magnitudes of up to 10 m sec−1 or more.
An experimental investigation of the selective ion‐capture theory of cloud electrification
Authors: Abbas M. A. , Latham J.
Published: February 2007

Measurements made of the charges acquired by water drops and smooth ice spheres suspended in electric fields and exposed to streams of positive ions only, negative ions only, and ions of both signs present in equal and unequal concentrations were found to be in excellent quantitative agreement with the equations of Whipple and Chalmers. Electrical masking was probably responsible for the slightly increased charging obtained when the experiments were repeated with ice spheres of irregular surface structure. The charges acquired by drops falling through ion streams in electric fields are explicable in terms of the Wilson process.
Cross‐pollination between fields of sugar beet
Authors: Chamberlain A. C.
Published: February 2007

Theoretical and experimental data on the travel and deposition of small particles in the atmosphere are used to calculate the cross‐pollination between neighbouring plots of sugar beet grown for seed.

If two 20 acre plots are situated at a distance apart of 1,000 m the number of pollen grains falling on one plot which come from the other is about 4 × 10−3 of the number which come from the plot itself. The effect of varying the size and separation of the plots is calculated, and a very approximate estimate of the contribution from background sources of pollen is given.

The calculations are made for average meteorological conditions. In moderately unstable conditions the proportion of cross‐pollination between plots is likely to be reduced by about 25 per cent.
Glacier resurgence at the Atlantic/sub‐Boreal transition
Authors: Mercer J. H.
Published: February 2007

Some mountain glaciers in both the Northern and Southern Hemispheres advanced in late Atlantic and early sub‐Boreal time, between about 5,200 and 4,600 radiocarbon years ago, and several in the Southern Hemisphere reached their greatest post‐glacial extents. This suggests that the cool phase was as severe as at the start of the sub‐Atlantic (ca. 2,800 radiocarbon years ago), but many botanists believe that the fluctuation was weak. Much botanical evidence indicates that the cool phase was followed by renewed warmth and divided the Hypsithermal Interval into two parts of unequal length.
Horizontal and vertical air motion and precipitation growth, within a shower
Authors: Browning K. A. , Harrold T. W. , Whyman A. J. , Beimers J. G. D.
Published: February 2007

Two Doppler radars have been used to measure simultaneously the vertical and horizontal velocity components within an isolated air mass shower. Precipitation growth was found to be restricted to a small region of gently rising air within which the vertical and horizontal air velocities relative to the shower rarely exceeded 1 m sec−1. Ice crystals within the updraught were balanced by it; graupel particles developed during descent through it. The growth rate of the graupel was consistent with a cloud liquid water content about half the adiabatic value. As in many showers studied using Doppler radar, the updraught was restricted to the upper parts of the shower. The descent of the graupel beneath the updraught was associated with weak downdraughts and a local increase in the horizontal winds relative to the shower.
Global spread of volcanic dust from the Bali eruption of 1963
Authors: Dyer A. J. , Hicks B. B.
Published: February 2007

The global spread of volcanic dust from the Mt. Agung eruption of 17 March 1963 is assessed on the basis of the decrement of direct solar radiation. The initial injection at 8°S lodged an equatorial reservoir in the stratosphere at a height of 22–23 km. Most of the dust remained in the Southern Hemisphere, but a significant fraction entered the lower Northern Hemisphere stratosphere. Seasonal effects appeared in both hemispheres, the apparent dust amounts showing a ‘winter’ maximum of constant amplitude in any one season with a poleward progression of 40 cm sec−1 between 30° and 90° latitude. At 15°N, seasonal effects were also evident but significantly out of phase with the sequence at higher latitudes, suggesting a hand‐over in the horizontal transport process at 20°–30° latitude.

Whilst the ‘winter’ maxima in the Northern Hemisphere were almost identical in amplitude for 1963 and 1964, the Southern Hemisphere data showed a significant reduction in dust amount over these years. The latter effect can be shown to imply an updraught in the lowest 2 km of the equatorial stratosphere of about 0·02 cm sec−1. By continuity, the poleward outflow from this circulation would be consistent with the observed rate of poleward progression. It is speculated that the seasonal effects could arise from an annual oscillation of the axis of this meridional circulation.

Attempts to relate the observations by a diffusion model are less convincing, but in the absence of more direct information, no firm conclusion can be drawn. The paucity of suitable radiation data for equatorial regions severely limits the extent to which inferences can be made.
Seasonal and year‐to‐year ozone variations from soundings over South‐Eastern Australia
Authors: Pittock A. B.
Published: February 2007

Seasonal mean vertical distributions of ozone obtained with Mast‐Brewer electrochemical ozone sondes are presented for Aspendale (38°S, 145°E) from winter 1965 through winter 1967. They reveal a winter‐spring maximum at the 30 to 40 mb level and a marked seasonal variation in the 100 to 350 mb region. Transient and standing eddy transport of ozone is found to be important at some levels, while vertical motion plays a significant role. The zonally averaged mean meridional transport could at most be comparable with the transient eddy term in some seasons. Year to year variations between corresponding seasons are found to be large and significant in all seasons. Large variations in the ozone content of different altitude layers occur in opposite senses, and apparently systematic patterns of change with altitude and time are found for Aspendale and also for Boulder, Colorado (40°N, 105°W). These could be related to the quasi‐biennial oscillation of other atmospheric properties. The data are not considered sufficient to establish representative climatological means.
Similarity theory and geostrophic adjustment
Authors: Gill A. E.
Published: February 2007

The length and velocity scales appropriate to geostrophic adjustment are discussed for both neutral and lapse conditions. Similarity arguments based on these scales lead to (i) an improved derivation of the relation between geostrophic and surface winds for the neutral case and (ii) the result that, in lapse conditions, the Coriolis force does not affect the relation between geostrophic and surface winds to the first order. Nevertheless a region of weak geostrophic adjustment may be defined. The case of inversion conditions is also discussed.
On the earth's core ‐ mantle interface
Authors: Hide R.
Published: February 2007

Recent work on the magnetohydrodynamics of the liquid core of the Earth and on the interaction between core motions and the overlying solid mantle has yielded a number of novel results. A new type of magneto‐hydrodynamic wave has been discovered through an attempt to explain the geomagnetic secular variation; the nature of the horizontal stresses at the core‐mantle interface that are implied by the ‘decade’ fluctuations in the length of the day has been elucidated; and evidence pointing to a previously unsuspected correlation between the Earth's gravitational and magnetic fields has been found. Global‐scale undulations in level of the core‐mantle interface that are so shallow (a kilometre or so) as to be unresolvable by contemporary seismological techniques are strongly implied by some of these results.
The temperature fluctuations in stable stratification
Authors: Okamoto M. , Webb E. K.
Published: February 2007

The intensity and spectrum of temperature fluctuations recorded at a height of 2 m over flat grassland in stable conditions are examined. Thr results show a demarcation between two distinct régimes, ‘ turbulent ’ for Ri less than a critical value of about 0.2 and ‘ quiet ’ for larger Ri.

The magnitude of the temperature fluctuations, scaled relative to z δz, is comparatively large in the turbulent régime, decreases as Ri increases towards the critical value, and remains small in the quiet régime. The temperature, while always of a typically turbulent character in the turbulent régime, is of variable behaviour in the quiet régime ‐ intermittently quiescent with occasional isolated smooth pulses (usually negative), or wave‐like with assorted frequencies, or turbulent.

In the turbulent régime, the spectrum approximates to the − 5/3 power form for normalized frequencies nz/U greater than 0.6. In the quiet régime, the form of the spectrum varies unpredictably from one occasion to another.
Non‐linear baroclinic instability of a continuous zonal flow
Authors: Drazin P. G.
Published: February 2007

In this theoretical paper, Eady's linear model of baroclinic instability of a zonal basic flow of an inviscid non‐conducting Boussinesq fluid in quasi‐geostrophic motion is extended by consideration of non‐linearity. The method of normal mode cascade is used to find the non‐linear development of a slightly unstable linear disturbance. Amplitude vacillations are found, similar to some observed in experiments on a differentially‐heated rotating annulus. Interactions of the zonal flow and non‐linear waves are described analytically and related to instability of the westerlies in mid‐latitudes.
Dynamics of disturbances on the Intertropical Convergence Zone
Authors: Bates J. R.
Published: February 2007

The dynamics of disturbances on a theoretically derived Intertropical Convergence Zone (ITCZ) are studied.

Radiative cooling over a hemisphere is parameterized by a Newtonian cooling law, relative to a radiative equilibrium temperature which decreases from Equator to Pole. Release of latent heat of condensation in the Tropics is treated as a function of convergence in the planetary boundary layer.

The zonally symmetric field of motion which evolves in response to these sources of energy shows a concentrated region of rising motion near, but not at, the Equator. The associated low‐level wind field possesses a strong cyclonic shear.

Asymmetric perturbations periodic in longitude are introduced by means of truncated Fourier series. The wavelengths are chosen to correspond to maximum instability in the ITCZ, and as such are too small to permit baroclinic instability in middle latitudes. In this way, the stability of the low latitude flow is examined while excluding middle latitude perturbations.

The low‐level wind field in the vicinity of the ITCZ is found to be barotropically unstable, the wavelength of maximum growth rate being about 2,000 km. The corresponding e‐folding time is found to be of the order of two days, depending on the frictional and heating coefficients.

The perturbations are allowed to grow to finite amplitude. In the initial stages of growth, the Reynolds stresses supply most of the perturbation energy. At the mature stage, the energy is provided mainly by direct conversion of condensationally produced eddy available potential energy. Further growth is then limited by frictional dissipation of kinetic energy.

The mean flow is in turn influenced by the disturbance through the mechanisms of Reynolds stresses, eddy conduction and the modification of the mean flow condensational heating through boundary‐layer pumping. The influence is seen on the mean temperature and zonal wind fields, and may extent to latitudes poleward of where the perturbation amplitude in situ has decreased to zero.

A framework is thus provided for viewing tropical disturbances as an integral component of the general circulation of the atmosphere.
The effect of wind shear on a puff
Authors: Richards J. M.
Published: February 2007

This paper corrects Hall's work in the light of more complete experiments which have established that a thermal is merely a special case of a buoyant puff. The general theory, presented here, applies to any isolated buoyant or non‐buoyant puff in shearing surroundings of uniform potential density.

This theory is then applied to the case of constant mass deficit and constant wind shear, and solutions are obtained in the form of algebraic equations and simple definite integrals. When these solutions are evaluated numerically, using experimentally determined constants, it is found that the ratio of the coefficients of vertical transport of momentum and heat attributable to the puff lies in the range 0.27 σ to 0.7 σ approximately, where σ is the (small) proportion of the area of the horizontal plane through any height which is occupied by puffs. Also, realistic variation of the angle of spread of puffs is found to produce a very considerable effect on the depth of the convective layer. Only narrow puffs rise far.
Atmospheric frontogenesis models: Some solutions
Authors: Hoskins B. J.
Published: February 2007

In this paper are presented some solutions of analytic models in which large‐scale velocity fields act on initially large‐scale distributions of temperature. Phenomena very similar to atmospheric fronts both surface and upper tropospheric are described. At the surface front there is a tendency to form discontinuities in velocity and temperature in a finite time. The upper tropospheric front and its jet stream are associated with the descent of a tongue of stratospheric air. The main assumption underlying the models is the justifiable one of geostrophic balance across but not along the front.
The effect of variable target reflectivity on weather radar measurements
Authors: Rogers R. R.
Published: February 2007

Weather radar signals fluctuate because of relative motions among the scatterers; these fluctuations must be accounted for in quantitative reflectivity measurements. The standard theory of weather signal fluctuations assumes targets of fixed reflectivity. In actual measurements, signals from a volume in space and over a short period of time are combined to yield an overall reflectivity measurement. Within this measurement region the reflectivity may not be constant, in which case the standard‐fluctuation theory will not strictly apply.

It is shown that the theory can readily be extended to include reflectivity variations. Models of the reflectivity structure are introduced to assess the effects of these variations on reflectivity measurements. If the measurement is made by averaging the signal and applying the standard theory, it will tend to underestimate the actual target reflectivity whenever variations are present except for the special case of a radar with a quadratic receiver response. If reflectivity is measured by selecting the maximum intensity level from a sample of size N and applying standard theory, it will tend to overestimate the actual target reflectivity when variations are present. The variance of the measurement is increased by reflectivity variations, whether averaging or peak‐detecting is employed. These effects are expected to introduce only small errors (less than 5 dB) in all but extreme cases of reflectivity variations, but such errors can be significant in applications of radar to problems in hydrology or communications, where high accuracy of measurements is required.
Parameterized processes in the surface boundary layer of an atmospheric circulation model
Authors: Delsol F. , Miyakoda K. , Clarke R. H.
Published: February 2007

A general circulation model is modified successively by adding five new features in the lower boundary layer; namely, (i) a different roughness parameter over land and sea, (ii) a Monin‐Obukhov type treatment of the turbulent transfer process in the constant‐flux layer, (iii) a Richardson number dependent parameterization for Ekman layer process, (iv) a diurnal variation of insolation, and (v) heat conduction into the soil. To assess the effect of each, the experiments are repeated by gradually increasing the complexity of the model. The circulation model has relatively low horizontal grid resolution and 9 vertical levels, and it is applied to a winter case for 14 day predictions. The results indicate that the sophistication of the boundary layer physics does not produce a particularly large effect on the synoptic scale prediction until about 7 days. Its effect may become large after 10 days. One noteworthy result is that the effect of the diurnal variation of insolation is not great for the free atmosphere but an influence is effectively transferred in the vertical, if the Richardson number dependent parameterization for the Ekman layer process is incorporated. The entire study is a preliminary test, the purpose of which is to determine the relative magnitude of each effect. A detailed comparison with observed data was not attempted.
Structure of the atmosphere in the vicinity of large‐amplitude Kelvin‐Helmholtz billows
Authors: Browning K. A.
Published: February 2007

Data are presented for 17 separate occurrences of Kelvin‐Helmholtz billows in the upper troposphere for which the crest‐to‐trough amplitude exceeded 200 m. The billows were detected in clear air by means of high‐power radar. The associated mesoscale patterns of static stability, vertical wind shear, and Richardson number have been derived from sequences of hourly radiosondes tracked by precision radar. Every occurrence of billows was found to be closely associated with well‐defined, local, wind‐shear maxima. In some cases the shear was as strong as 9 m s−1 per 200 m. The minimum value of the Richardson number when evaluated over layers 200 m deep was usually found to be in the range 0.15–0.3.
Raindrop interactions and rainfall rates within clouds
Authors: Brazier‐Smith P. R. , Jennings S. G. , Latham J.
Published: February 2007

Experiments showed that when a pair of water drops of raindrop dimensions collide and separate in air at their relative terminal velocities satellite drops are generally produced. Although the numbers and sizes of satellites resulting from individual interactions are highly variable a typical event produces about 3 satellites each having a volume of 0.04 ViVj/(Vi + Vj), where Vi and Vj are the volumes of the parent drops.

A full stochastic treatment is presented of the development of rainfall in a volume within a cloud where water is being released by condensation at a constant rate J. The production of satellites and an experimentally verified expression for the coalescence efficiency ε are incorporated into these calculations. Computations are made of the variation with time of the cloud water content, C, the rainwater content, L, the radar reflectivity, Z, the rainfall rate, P, and the drop‐size distribution. The calculations show that the crucial parameter in governing the intensity and duration of rainfall is J, and that the microphysical processes are of secondary importance; C, L and P are all insensitive to ε and the production of satellite drops. The influence upon rainfall development of the break‐up of large raindrops on attaining their maximum size within a cloud is found to be even less than that of the satellites.

The drop size distribution after several minutes of growth is insensitive to the initial spectrum but is markedly dependent upon ε and the production of satellites, which tend eventually to produce a bimodal spectrum. The radar reflectivity increases very rapidly with time (typically by about an order of magnitude every 2 1/2 minutes) and depends quite strongly on ε, but is unaffected by the production of satellites.
Observation of Kelvin‐Helmholtz billows and their mesoscale environment by radar, instrumented aircraft, and a dense radiosonde network
Authors: Hardy K. R. , Reed R. J. , Mather G. K.
Published: February 2007

On 19 February 1970, a T‐33 jet aircraft, equipped with fast‐response meteorological instruments, obtained measurements of a wave structure and clear air turbulence. The clear air structure was simultaneously detected with a sensitive 10·7 cm wavelength radar at Wallops Island, Virginia. From a special network of radiosonde stations with separations of about 100 km, the detailed mesoscale synoptic conditions associated with the clear air structures were determined. The turbulence and wave structure occurred between heights of 2 and 3 km within an upper level frontal zone which had advanced well ahead of the surface cold front. The wave pattern consisted of two‐dimensional Kelvin‐Helmholtz billows. The billow velocity was close to the mean wind velocity of the sheared layer, and the Richardson number for the layer was about 0·15 which is consistent with the criterion for instability based on theoretical and wind tunnel results. The most intense turbulence occurred where the billows were rolling up or breaking.
The wave patterns produced by a moving body in a compressible, density‐stratified fluid
Authors: Rarity B. S. H. , Hide R.
Published: February 2007

The two‐dimensional wave field generated by a steadily moving source in a stratified compressible medium is determined. The dispersive character of the waves gives rise to wave crests of an asymmetrical form, present in some parts of the plane and forbidden in others. It is shown how the location, direction of motion and the length scale of the source can be estimated from the observed wave field, acknowledging that such information will usually be fragmentary.
Global meridional interactions in stratosphere and troposphere
Authors: Pittock A. B.
Published: February 2007

Significant correlations have been found between year to year mean latitudes of the surface high pressure belt, L, over eastern Australia and atmospheric parameters such as total ozone, winds and temperatures at various levels in the troposphere and stratosphere, and rainfall. In those years when, in late winter and spring, the high pressure belt lies nearer to the Equator it appears that the Hadley circulation and poleward transport processes in the lower stratosphere and upper troposphere in middle latitudes are stronger. This is probably also associated with the earlier breakdown of the winter stratospheric polar vortex.

Evidence is presented to support the view that L is determined to a good approximation by the criterion for baroclinic instability which was derived by Phillips and Smagorinsky and applied to climatology by Flohn and Henning. Thus variations in L are related to variations in the driving force of the Hadley circulation, which in turn may well be related to variations in sea surface temperature. This encourages the view that an empirical and theoretical basis for long‐range seasonal forecasts of temperate zone climate may be in prospect. The results should lead to a greater understanding of the nature of global climatic change.
Hurricane Agnes — an event shaped by large‐scale air‐sea systems generated during antecedent months
Authors: Namias J.
Published: February 2007

An attempt is made to show that the life history of hurricane Agnes was determined by the antecedent slow evolution of the general circulation on a time scale of months. A self‐aggravating complex of midtropospheric anomalies is described and quantified ‐ this complex predisposing the eastern seaboard to the aberrant path assumed by Agnes and providing deep moisture‐laden air masses from a very warm western Atlantic. The stable configuration of the centres of action is partly attributed to ocean‐atmosphere interactions.
Vertical velocities and vertical eddy fluxes derived from serial soundings at one station
Authors: Tucker G. B.
Published: February 2007

Detailed 3‐hourly soundings of the atmosphere from 0–30 km for one month (September/October 1967) over Laverton, Victoria (38°S) are analysed to obtain vertical velocities using the heat balance method. Results are assessed to be reliable from the point of view of error estimates, synoptic compatibility and statistical features for the whole month. The tendency for a reversal of vertical velocity between low and high troposphere occurs, with occasional very strong downward velocities (∼ 30 cm s−1) at the tropopause level. Convergence of vertical eddy flux of both momentum and sensible heat is shown to occur near the levels of maximum poleward eddy transport with magnitudes equivalent to 1 · 5°K/day and 3 m s−1/day. Similar computations based on routinely available upper‐air soundings at standard pressure levels at 12‐hourly intervals are shown to give quite different (spurious) results. As a supplementary result, strong horizontal eddy transports are revealed in the middle stratosphere.
Meso‐scale circulations and rainfall patterns in an occluding depression
Authors: Atkinson B. W. , Smithson P. A.
Published: February 2007

Synoptic and meso‐scale precipitation and airflow patterns in the occluding depression which passed over England and Wales on 8‐9 March 1967 are analysed. Large‐scale circulations are illustrated in terms of airflow relative to the synoptic system within the framework of surfaces of constant wet‐bulb potential temperature (θw). Meso‐scale precipitation and airflow configurations are inferred from a sequence of over 120 large‐scale maps of 13‐min precipitation amounts. There was no obvious ‘conveyor belt’ in the occluding depression, but the upward relative flow coincided closely with large rain areas of the warm front and the depression centre. Subsidence at the cold front and within the warm sector inhibited precipitation growth in those parts of the depression.

Large (200 times; 50 km) and small (50 times; 50 km) meso‐scale rain areas were found in the depression. The latter resulted from clusters of generator cells, which formed in an area where potential instability was released by large‐scale upward motion. The clusters moved with the winds at about 550 mb. The large meso‐scale rain area lay at a small angle to the surface warm front and lasted for about three hours. Its size, location, and orientation were due to the movements of three small meso‐scale systems within the relative flow at their generator level. The location and intensity of a small meso‐scale rain area on the eastern flanks of the Pennines, together with the associated rainshadow to the west of the upland, were analysed with the aid of a modified lee‐wave equation. Other small meso‐scale precipitation areas were due to airflow over sub‐synoptic deformations in the θw surfaces. All types fit into a two‐tier scaling of meso‐scale circulations in frontal zones.