bluuebunny/crossref_metadata_2025 huggingface dataset:
A global analysis of the variability of the quasi‐biennial oscillation
Authors: Dartt D. G. , Belmont A. D.
Published: February 2007

Monthly‐mean zonal wind data from approximately 200 rawin stations have been filtered to remove the annual and shorter period variations. Data from 1950–1964 for levels from 700 to 7 mb were analysed. The primary variation is the quasi‐biennial oscillation of the equatorial stratosphere and its extension to higher latitudes. There is much greater variability with longitude and time of the weak quasi‐biennial oscillation at higher latitudes than observed in the equatorial stratosphere. However, as the vertical and meridional phase progression patterns of the oscillations in both troposphere and stratosphere are systematic, these properties are probably real. The main fluctuations can frequently be traced from the surface to at least 35 km except in the middle latitudes of the Northern Hemisphere where the stratospheric variations often do not appear related to those of the troposphere. The most organized phase progressions with latitude are the apparent opposite ones observed in the stratosphere and troposphere of the Northern Hemisphere. Prior to 1960, well‐defined poleward progression is observed in the troposphere (300 mb), while weaker Equatorward progression is evident in the stratosphere (30 mb). In 1961 the pattern reverses, with poleward progression at 30 mb and Equatorward progression at 300 mb. In the tropical stratosphere during the years 1960–1961, the quasi‐biennial oscillation was characterized by unusually low amplitude, short‐period fluctuations.
Recent developments in long‐range forecasting in the Meteorological Office
Authors: Murray R.
Published: February 2007

Six years ago at the end of November we issued the first monthly forecast to the British public. At that time the forecasts were based on an Analogue Selection procedure and a so‐called Physical Discussion. In principle these two inter‐related approaches still form the basis of the present operational method, but considerable changes have taken place and these are reflected in a modest improvement in the accuracy of the monthly forecasts.

This overall improvement arises from three main sources. In the first place, we have steadily extended and improved our store of readily available, processed data. Many people have of course been responsible for the essential data‐processing side of our work, which is still continuing, but I must mention J. M. Craddock and M. H. Freeman for laying good foundations in the early days. In the second place, we have carried out numerous synoptic and empirical studies. All of these have given useful background information and some understanding of the nature of large‐scale circulation and weather anomalies. Many of our investigations have been aimed at providing statistically based aids for the prediction of UK weather. We have increased the scope and range of our studies which are not confined to the monthly time scale. In particular a good deal of work has been done on the seasonal time‐scale, and in the past year or two we have carried out experimental forecasts, originally for winter and summer but now for every season. In the third place we have gained a lot of experience of the particular problems as a result of both research and operational forecasting. I would like to touch upon a few points in elaboration of these remarks.
Reflection coefficient of natural vegetation, crops and urban surfaces in Nigeria
Authors: Oguntoyinbo J. S.
Published: February 2007

Reflection coefficients measured over a wide variety of natural and agricultural vegetation surfaces in Nigeria (lat. 4° 40′ to 13° 30′N) were between 0.057 to 0.251; and were inversely related to the vegetation height. Considerable seasonal differences were found with unexpected low values of reflectivity during the harmattan haze in the dry season. Possible reasons for these seasonal differences are discussed. The weighted mean annual reflection coefficient for Nigeria was calculated to be 0.178. This value was consistent with the relationship between surface reflection coefficient and latitude found from similar results from six other locations in the Northern Hemisphere. Urban coefficients were found to be lower than those for rural settlements or temperate zone urban centres.
The detection of ice clouds from remote measurements of their emission in the far infra‐red
Authors: Houghton J. T. , Hunt G. E.
Published: February 2007

It is demonstrated that a pair of wavelengths can be chosen in the far infra‐red such that the absorbing properties of water‐vapour are the same at the two wavelengths while the scattering and absorbing properties of ice particles are different. The results of calculations show that emission from the atmosphere as observed by a satellite radiometer at the two wavelengths will be sensitive to the presence of cirrus cloud. From such measurements of emission near 50μ and 120 μ in wavelength, an indication of the thickness of the cloud can be obtained. Supporting measurements near 2.6 μ will also supply information regarding the particle size in the cloud.
Ozone profiles and ozone fluxes in the atmospheric surface layer
Authors: Galbally I. E.
Published: February 2007

Some new measurements of the ozone flux by the profile method have been made and these are compared with others in the literature. A treatment of ozone transfer to the surface is given which takes account of the resistances offered by the fully turbulent air layers and by the surface roughness layer. It is found that the ozone flux is proportional to the ozone concentration at the Earth's surface and, for the surfaces considered, the ozone destruction coefficient has an approximate value of 1 cm s−1.
Absorption coefficients of ozone for use in the determination of atmospheric ozone
Authors: Walshaw C. D. , Dobson G. M. B. , MacGarry B. M. F.
Published: February 2007

Laboratory measurements at low temperatures of the ozone absorption coefficient differences required in the standard spectroscopic measurement of atmospheric ozone are described. The measurements were made with a Dobson spectrophotometer and a quartz‐iodine source. The results at the standard wavelength pairs are

The effective temperature was – 42°C (± 2°C).

These results are compared with those of other workers.

The error in measured total ozone amount caused by changes in stratospheric temperatures is discussed. Maximum errors of about 4 per cent seem possible in spring warmings, the apparent ozone amount being too low.
Lagrangian‐Eulerian time‐scale ratios estimated from constant volume balloon flights past a tall tower
Authors: Angell J. K. , Pack D. H. , Hoegker W. H. , Delver N.
Published: February 2007

The ratio of Lagrangian and Eulerian time scales of motion in the planetary boundary layer is estimated from radar observations of 35 constant volume balloons (tetroons) flown past the 460 m high BREN tower at the Nevada Test Site. On the average, the peak energies of the Eulerian and tetroon vertical velocity spectra occur at periods near 6 and 18 minutes, yielding a mean Lagrangian‐Eulerian scale ratio, β, of about three, β increases with increase in wind speed, decreases with increase in r.m.s. vertical velocity, and is inversely related to vertical turbulence intensity, with β ranging from 4.5 at a turbulence intensity of 0.05 to 2.5 at turbulence intensities exceeding 0.3.
The importance of instrumental tilt on measurements of atmospheric turbulence
Authors: Rayment R. , Readings C. J.
Published: February 2007

This note discusses the equations that govern the dependence of observed turbulence characteristics on instrumental tilt and then considers the magnitudes of the effects within the constant stress layer.
The first year of the selective chopper radiometer on Nimbus 4
Authors: Barnett J. J. , Cross M. J. , Harwood R. S. , Houghton J. T. , Morgan C. G. , Peckham G. E. , Rodgers C. D. , Smith S. D. , Williamson E. J.
Published: February 2007

The selective chopper radiometer, an instrument for the remote measurement of atmospheric temperature from the surface to about 50 km altitude, was launched on the Nimbus‐4 satellite in April 1970. The performance of the instrument during its first year of operation is described. Good data have been received throughout this period. Various mean atmospheric cross‐sections, temperature profiles and thickness maps are presented as examples of the data which are available from the instrument.
The measurement of mesoscale vertical motions in the atmosphere
Authors: Hardman M. E. , James D. G. , Goldsmith P.
Published: February 2007

A technique is described for determining the three‐dimensional field of vertical air motion in the vicinity of mobile fronts. Radar reflectors are dropped from an aircraft at a height of 5 km and followed by high precision tracking radars. By making assumptions regarding the movement and conservativeness of the frontal system it has been possible to use this technique to obtain horizontal winds over a volume approximately 150 × 100 × 4 km depth with a typical drop separation of 30 km. Using the equation of continuity, vertical velocities have been calculated with an uncertainty of ± 1 ‐ 2 cm s−1. In a warm front investigated on 19 January 1969, close agreement was obtained between the rainfall observed at the surface and that computed from the vertical velocities assuming saturation of the rising air.
Coalescence in a turbulent cloud
Authors: Woods J. D. , Drake J. C. , Goldsmith P.
Published: February 2007

The results of two experiments show that the collision efficiency of small droplets is significantly increased when the interacting drops fall through a laminar shear flow of about 10 s−1. The structure of microturbulence in clouds is considered and it is shown that shears of this magnitude are likely to occur only within a narrow spectral band. This peak in the shear spectrum occurs at a scale that is much larger than the interaction distance of cloud droplets having radii of about 20 γm. Hence it is a good approximation to describe droplet collisions in a turbulent cloud as though they occurred in a steady laminar shear flow. It is argued that this enhanced droplet coalescence in turbulent clouds may account for the observed development of large cloud droplets (radii < 30γm) in cumulus clouds at rates greater than can be explained by condensation and the efficiency of still‐air coalescence.
Terminal velocities of ice crystals
Authors: Jayaweera K. O. L. F. , Ryan B. F.
Published: February 2007

The terminal velocities of small plate‐like and columnar ice crystals have been measured experimentally. Good agreement was found between theory and experiment.
The influence of tropical east Pacific Ocean temperatures on the atmosphere
Authors: Rowntree P. R.
Published: February 2007

A version of the nine‐level hemispheric model of the atmosphere developed at the Geophysical Fluid Dynamics Laboratory has been used to test Bjerknes' hypothesis that fluctuations of ocean temperatures in the tropical east Pacific are responsible for major variations in the position and intensity of the Aleutian surface low. The results of four 30‐day integrations, two with warm and two with cool tropical east Pacific (maximum differences 3.5°C) are analysed, and verified against observational data.

The ocean variations had important effects on the model atmosphere, both tropical and extra‐tropical. The warmed ocean heated the air above and induced a surface low near the sea temperature maximum; associated low‐level convergence and ascent gave increased tropical rainfall over the central and east Pacific with decreases over the west Pacific and parts of South America. The related upper flow changes generated a subtropical jet maximum with persistent troughing to the north over the mid‐latitude east Pacific. The Aleutian low was shifted east and deepened, confirming Bjerknes' hypothesis. There was strong similarity between the mid‐latitude flow over the Pacific in the warm cases despite major differences between the two cases with cool tropical east Pacific.

The importance both of tropical surface conditions and of extra‐tropical influences on the model Tropics is indicated and an interaction mechanism proposed. The early development of differences between the experiments suggests that it is important to use correct tropical sea temperatures for short‐range numerical prediction in the Tropics. However, mid‐latitude effects were not significant till a week after the onset of deep tropical convection.
An investigation into meso‐scale precipitation distributions in a warm sector depression
Authors: Atkinson B. W. , Smithson P. A.
Published: February 2007

After reviewing previous work on the subject, a case study is presented to illustrate and to explain the different spatial scales of rainfall distribution associated with a warm sector depression. Autographic rain gauge records for England and Wales are used to determine short period (13 min) rainfall patterns throughout the passage of the depression. From these data, large meso‐ (200 km) and small mesoscale (50 km) rain areas are distinguished in the warm front and warm sector. In the warm front, the small mesoscale rain areas are an expression of similar‐sized precipitation systems, which, as they move parallel to the surface front, trace out the large mesoscale rain areas. Mesoscale rainfall pulses are found in the warm sector, but their origin remains obscure.
Charge separation due to riming in an electric field
Authors: Aufdermaur A. N. , Johnson D. A.
Published: February 2007

Ice pellets were grown by accretion of supercooled drops, 20–100 μm diameter, at temperatures between −5 and −15°C in a small wind tunnel at an air speed of about 10 ms−1. An electric field of about 50–150 kV m−1 could be applied at the surface of the pellet. The pellet, and induction rings upstream and downstream of the pellet, were connected to electrometers and analysing circuits of sufficient sensitivity and speed to measure, correlate and display individual charging events. Charged particles entering the apparatus could be excluded from analysis by the upstream induction ring. The downstream ring was used to identify charged particles originating at the pellet. Significant charge separation occurred only in the presence of an electric field, and was consistent with charging by electrical induction. Charges between 2 and 30 fC (1 fC = 10−15 Coulomb = 3.10−6 e.s.u.), depending on drop size, were observed at a rate of about one to ten events per 1,000 accreted drops. Evidence suggesting that these charging events are the result of some drops colliding with the pellet at grazing incidence is described. This process seems adequate to account for the generation of charge in thunderclouds.
A case study of a high level Canberra flight on 11 September 1968
Authors: Axford D. N.
Published: February 2007

A case study is presented of a high level flight by the MRF Canberra showing most of the characteristic features of intermittent clear air turbulence, gravity waves and smooth flight. Winds and temperatures obtained from two 500 km runs across a sharp upper trough are used to calculate energy spectra and cross‐spectra over a range of wavelengths from 250 m to 100 km. The spectra show clearly the important contribution of the gravity waves in the range 1 km to 10 km, and the negligible contribution of the total high frequency energy in the case of intermittent slight clear air turbulence.
The measurement of surface pressure from a satellite
Authors: Smith S. D. , Colles M. J. , Peckham G.
Published: February 2007

The surface pressure can be determined from a measurement of the atmospheric transmission in a spectral region near an absorption band. The feasibility of achieving such measurements for a satellite‐borne instrument is discussed.
Humidity and temperature microstructure near the ground
Authors: Martin H. C.
Published: February 2007

Day‐time records of the microstructure of humidity and temperature at 2 and 4 m are analysed. Supporting data include the temperature and wind gradients, the net radiation, the sensible heat flux, and a derived value for the latent heat flux.

The two variables are remarkably similar and share the following properties: The characteristic scale of turbulence increases with height and decreases with increasing instability beyond near‐neutral conditions. The logarithmic spectra follow a −5/3 slope for wave numbers greater than 0.15 m−1. In this range, the spectral estimates increase with increases in the appropriate flux (sensible or latent heat flux for temperature or humidity spectra), and decrease with height.

The humidity variance contains large‐scale components which are of lesser importance in the temperature variance. This difference in the two variables has tentatively been attributed to properties of the site.
The spectral density technique for the determination of eddy fluxes
Authors: Hicks B. B. , Dyer A. J.
Published: February 2007

The determination of turbulent fluxes from measurements of spectral densities of velocity, temperature and humidity is discussed as a technique applicable to the open ocean. A preliminary investigation over land using specially designed equipment measuring spectral densities of wind and temperature at a single frequency indicates that present understanding of the Kolmogorov and flux/gradient relationships is adequate for the purpose. Although humidity spectra are included in the treatment, no measurements of them were made. Values of the effective Kolmogorov constants for velocity and temperature are found to be 0.54 ± 0.03 and 0.71 ± 0.04 respectively, in good agreement with other recent determinations.

The principles of application of the technique at sea are discussed. The method assumes that the divergences of the eddy energy fluxes can be neglected. Whilst the present results appear to support this assumption, there is a need for further examination of this aspect.
Time spectra and cross‐spectra of kinetic energy in the planetary boundary layer
Authors: Hess G. D. , Clarke R. H.
Published: February 2007

Temporal spectra and cross‐spectra of the three turbulent wind components for meso‐synoptic scales at 250 m vertical intervals in the planetary boundary layer are presented. The data were derived from hourly simultaneous balloon ascents from a 5‐point grid at Hay, New South Wales, Australia (lat. 34 ½S), during the Wangara expedition. The spectra indicate a meso‐scale gap for u (eastward component of wind) and v (northward component). The computed w‐spectra suggest that no marked gap is present. For periods less than 1 day the u‐ and v‐spectra, with a correction applied for high frequency noise, fall off approximately as n−2·6, where n is the frequency, and this result appears to be invariant with height within and just above the planetary boundary layer. The corrected w‐spectra exhibit n−1 dependency in this frequency range. The uv, uw, and vw cospectra also show only small contributions on the meso‐scale (periods less than a day) compared to the synoptic scale, indicating that meso‐scale motions may not have to be explicitly modelled in atmospheric general circulation models. An inertial peak is found for u and v but the w‐spectra show a diurnal peak. The phase angles showed that u and v were in approximate quadrature at the inertial frequency, demonstrating the existence of the inertial cycle. Tests for horizontally two‐dimensional isotropy indicated that the turbulence did not obey this simplification.
The Leipzig wind profile and the boundary layer wind‐stress relationship
Authors: Carson D. J. , Smith F. B.
Published: February 2007

Swinbank's recent claim that Mildner's so‐called Leipzig wind profile data for the atmospheric boundary layer support the hypothesis that the shearing stress vector and the wind vector are parallel, is critically examined and compared with the conflicting classical hypothesis that stress and velocity shear are parallel as previously applied by Lettau. The geostrophic wind direction, known only imprecisely from Mildner's measurements, is allowed to vary in order to produce best‐fit profiles consistent with each hypothesis and generally accepted ‘boundary’ conditions. The degree of fit (theory to measurements) is roughly ten times better in the classical case than in Swinbank's case, the former showing a r.m.s. angular difference between the stress and shear vectors in the lowest 800 m of only 2°.
Non‐precipitating cumulus convection and its parameterization
Authors: Betts A. K.
Published: February 2007

This paper discusses the thermodynamic transports of heat, liquid water and (briefly) water vapour by non‐precipitating cumulus convection. It is shown that because of the irreversible mixing between cloud and environment, there is a downward transport of enthalphy in the cumulus layer. A lapse‐rate adjustment model relates stratification to the life‐cycle of a model cloud parcel. A sub‐cloud layer model specifies the lower boundary of the lapse‐rate model, and the convective transports through cloud‐base. Budget equations together with the lapse‐rate model, and its time dependent boundary conditions, predict the time development of the cumulus layer, and show the dependence on large‐scale mean vertical motion, cloud‐base variations, and the surface sensible heat flux.
On the summer hemisphere Hadley cell
Authors: Schulman L. L.
Published: February 2007

In the extreme seasons the winter hemisphere Hadley cell dominates the entire zonally averaged mean meridional circulation by extending well into the summer hemisphere, and the summer hemisphere Hadley cell practically disappears. The hypothesis that this apparent disappearance is due to the process of zonal averaging, and that a summer hemisphere Hadley cell does exist when the averaging is restricted to the longitudes not occupied by the Asiatic monsoon, is tested. Using data for 1957–1964 covering the months June‐August, it is found that the summer hemisphere Hadley cell was indeed present over the longitudes 160°E‐0–30°E, or two thirds of the Tropics. It is argued that some of the most interesting features of the meridional circulation and their associated transport processes are obscured by the zonal averaging process.
The laminated structure of the ozone in the atmosphere
Authors: Dobson G. M. B.
Published: February 2007

Ozonesonde ascents have shown that frequently the vertical distribution of the ozone in the stratosphere is very complicated with strong maxima and minima. Such a complicated distribution was not expected. In an attempt to find the cause of this highly laminated structure of the ozone, the variations in the intensity of the lamination with both season and latitude have been studied. It is found that a highly laminated structure is most frequent in spring and in the higher latitudes. It is also shown that well marked minima in the vertical distribution of the ozone are found at a height of about 15 km. The frequency of occurrence of these minima is also greatest in spring and in the higher latitudes. It is suggested that the ozone‐weak air in these minima has entered the stratosphere at the sub‐tropical tropopause break and has been carried polewards. A region of minimum ozone is also sometimes found at heights of around 23 km but less frequently than at 15 km. These high level minima are only found in late summer or autumn and in very high latitudes.
A simple theory of certain heliacal and anthelic halo arcs. The long hexagonal ice prism as a kaleidoscope
Authors: Tricker R. A. R.
Published: February 2007

G. H. Liljequist and J. R. Blake have both recorded anthelic halo arcs on several occasions in Antarctica, with the sun at comparatively low elevations, which exclude on some occasions, and almost exclude on others, the mechanism put forward by Alfred Wegener to account for such arcs. A particularly complete display reported by J. R. Blake enables these arcs to be identified with those predicted by a very simple theory giver in the following paper, to which are added some remarks about the formation of an anthelion.
Momentum, heat and water vapour transfer to and from natural and artificial surfaces
Authors: Garratt J. R. , Hicks B. B.
Published: February 2007

Recent atmospheric and wind tunnel data on the heat, mass and momentum transfer above natural and artificial surfaces indicate a general increase in the quantity kB−1 (= In(zo/zp), where zp is the roughness length appropriate to the quantity p) between aerodynamically smooth and fully rough flow. Below a roughness Reynolds number, u*zo/v, of about 100, kB−1 appears to be a single valued function of u*zo/v, closely approximated by the assumption of a molecular sub‐layer for heat and water vapour fluxes. Beyond u*zo/v = 100, there is no unique value of kB−1, but rather the observations suggest that the behaviour falls into either of two categories. For surfaces comprised of arrays of widely spaced solid roughness elements, kB−1 continues to increase (with some evidence for a plateau being reached by about u*zo/v = 1,000, when kB−1 ≃ 10), whilst for surfaces comprised of randomly distributed fibrous roughness elements, kB−1 gradually decreases with increasing roughness Reynolds number beyond about 100.
A note on the spectra of wind velocity components in the surface layer
Authors: Shárán V. Kr. , Wickerts Sture
Published: February 2007

Results of our recent investigation of spectral measurements of wind velocity in the surface layer are analysed in light of the hypothesis proposed by Kaimal et al. (1972). It is confirmed that in the inertial subrange the spectra for all the three components and varying stability converge to a −2/3 line at the high frequency end. At the low frequency end the spectra cluster together in random fashion in a certain bandwidth and do not show any ordered arrangement with z/L.
Central England temperatures: Monthly means 1659 to 1973
Authors: Manley Gordon
Published: February 2007

An up‐to‐date Table is provided of the monthly and seasonal means representative of the air over central England from 1659 onward, incorporating some minor revisions and extensions of the earlier Table (Manley 1953 and 1959). Comments on its construction, and on the prospect of further extension backward in time, are added.
The effect of volcanic eruptions on global turbidity, and an attempt to detect long‐term trends due to man
Authors: Dyer A. J.
Published: February 2007

Following a brief discussion of early radiation measurements and the interpretation of the effects of volcanic eruptions in the light of current knowledge of the stratosphere, recent radiation data from USSR, Japan, USA and Australia are examined. Whilst the effects of the Agung eruption are clearly seen on a global scale, the analysis yields no convincing evidence for a recent world‐wide increase in atmospheric turbidity. The need for extreme measurement accuracy is emphasized in the context of long‐term atmospheric monitoring.
Multi‐level measurements of turbulence over the sea during the passage of a frontal zone
Authors: Bryant G. W. , Browning K. A.
Published: February 2007

A Doppler radar technique originally proposed by Lhermitte (1968) has been used to measure the horizontal components of turbulence simultaneously at closely spaced height intervals from an altitude of 80m to 2500m. The observable range of turbulence scales was between about 200m and 5000m. Observations were made over the sea, with the radar situated on the Isles of Scilly, to minimize the effects of in‐homogeneities in terrain.

The measurements reported in this paper were made during the passage of a warm frontal zone with strong surface winds; they show the change with height in the structure of turbulence simultaneously in both the planetary boundary layer and a free shear zone situated some way above it. Below 600m, in the planetary boundary layer, the two horizontal components of turbulence were rather similar in intensity, the total variance of horizontal velocity in the observed spectral range decreasing from 1·7m2s−2 at 80m to less than 0·1m2s−2 at 700m. For much of the observed spectral range the turbulence spectra were of the form kS(k) α k−n, with n decreasing from 1·2 below 300m to 0·7 at 700m. The lapse rate was slightly less than dry adiabatic in the planetary boundary layer with broken cloud above 300m, consistent with slight stability below 300m and some instability above. The decrease in the value of n is thought to have been due to the decrease of stability with height. The spectral scale λm increased with height reaching a value of 1·6km at 900m. Above the boundary layer for most of the time there was a placid layer several hundred metres deep and this was surmounted by a free shear layer in which the variance of velocity increased again to typically 0·5m2s−2. In the free shear layer the horizontal components of turbulence resolved parallel and perpendicular to the local shear vector were rather similar in intensity at scales less than 500m but were markedly unequal at scales between 500m and 2km. This is consistent with the occurrence of Kelvin‐Helmholtz billows with a wavelength of 1 to 2km.

The Doppler radar measurements also enabled the vertical flux of horizontal momentum to be calculated. The quantity −u′w′ was found to decrease from about 0·2m2s−2 in the planetary boundary layer to about 0·01m2s−2 in the placid layer, before increasing again to about 0·1m2s−2 in the free shear layer. The energy dissipation rate ϵ was estimated from the turbulence spectra in those cases where the spectral slope n was not greatly different from 2/3. Values of ϵ decreased from 10cm2s−3 at 400m to 2cm2s−3 in the placid layer, before increasing to a second maximum of about 20cm2s−3 in the free shear zone. The rate of mechanical production of turbulence was calculated from the Doppler radar measurements of momentum flux and shear and it was found to vary with height in a rather similar manner to ϵ.
The simulation of particle motion in the atmosphere by a numerical random‐walk model
Authors: Hall C. D.
Published: February 2007

Of all the models of turbulent motion that are based on a random‐walk technique, the simplest are ones which simulate individual particle trajectories. The accuracies of two such models are assessed by applying them to low‐level diffusion in the atmosphere. It is found that one based on a Markov‐Chain principle predicts particle concentrations over short and medium ranges which are consistent with observation. Calculations are extended to include dispersion in unstable conditions, and by postulating the dependence of several important turbulence parameters on z/L, it is possible to derive a physically realistic model.
An attempt to predict the anomalies in the monthly mean sea level pressure field a month ahead
Authors: Colgate M. G.
Published: February 2007

This article investigates an eigenvector technique for predicting monthly surface pressure anomalies over a network of grid points covering most of the Northern Hemisphere from the previous months' surface pressure anomalies. Eigenvector analyses on archival monthly surface pressure anomalies enabled the anomalies to be represented by natural components whose coefficients were used as predictors in linear regression models for estimating the next month's surface pressure anomaly at each of the grid points.

The results show that most of the predictive value was provided by about the first ten natural components accounting for the highest proportion of monthly surface pressure variance. They gave weak, but significant, predictions even after allowing for long period climatic trends, and for persistence of surface pressure anomalies from one month to the next.

Further investigation was carried out to discover the nature of the relationships, and these results are also presented.
A spectral barotropic model in horizontal empirical orthogonal functions
Authors: Rinne Juhani , Karhila Vesa
Published: February 2007

A limited area barotropic vorticity equation model is integrated using a representation in terms of 57 horizontal empirical orthogonal functions. No boundary conditions are applied; the inflow and outflow of weather systems are absolutely free. The length of the time step in a normal centred scheme can be as much as 10 hours. With a time step of 6 hours, the model was integrated up to ten days without any smoothing, and the energy and enstrophy terms still had reasonable values. The skill of the forecasts is at least as good as, probably better than, comparison finite difference forecasts.

The present climatological functions were transformed to make them closer to two‐dimensional harmonics. About half of the new functions resembled two dimensional harmonics; their wave lengths were about 3000–5000km.
Vertical wind shear measurements in the lower stratosphere
Authors: Cadet D.
Published: February 2007

During two flight series of superpressure constant‐level balloons conducted in the lower stratosphere by the Laboratoire de Météorologie Dynamique, the vertical wind shear vector over 100 metres has been measured. It has been found from a record of almost two months that the r.m.s. wind shear is about 1·5 × 10−2s−1. The shear can reach 5 × 10−2s−1 in association with a breakdown of the stably stratified flow. From the records of wind shear vectors over 100 metres, 15 wind shear hodographs have been drawn which in turn have been divided in two groups. In the first group, the shear vector keeps a constant direction with time and in the second one it rotates anticlockwise with a 7 to 8·5 hour period suggesting the existence of gravity‐inertia waves in the flow. The modulus of the wind shear oscillates with a similar period but this feature is found whichever the group to which the hodograph belongs.
Turbulent fluctuations in convective conditions
Authors: Caughey S. J. , Readings C. J.
Published: February 2007

The dependences of the standard deviations of temperature (σr), total horizontal and vertical velocities (σuH and σw respectively) on local parameters are investigated in the atmospheric boundary layer. Useful expressions are obtained that enable rough estimates of σw and σT to be made in the bulk of the boundary layer.
The use of a multipoint filter as a dissipative mechanism in a numerical model of the general circulation of the atmosphere
Authors: Francis P. E.
Published: February 2007

A multipoint filter for use as a dissipative mechanism in a numerical model is formulated, and some of its properties discussed. The results of three numerical experiments are compared, of which one employs a non‐linear diffusion term, another has the filter applied in the zonal direction only, and the third employs the filter in both zonal and meridional directions. The simulated climatology of the filtered experiments is seen to be significantly better in some respects than that of the experiment using a diffusion term.
A monthly analysis of the global wind stress and the ocean transports predicted from a numerical model
Authors: Bye J. A. T. , Noye B. J. , Sag T. W.
Published: February 2007

The monthly wind stress fields over the oceans have been calculated from marine climatic data incorporating the effect of thermal stability. The resulting angular momentum balance due to frictional torques indicates that the drag coefficients used in the study are essentially correct. A half‐yearly oscillation of zonal wind stress in high temperate latitudes in the southern hemisphere is clearly evident. The curl of the wind stress computed from the wind stress data has been used as the driving for a numerical model of the transports of a homogeneous flat‐bottomed world ocean. The variations of the ocean transports obtained are comparable with the rather sparse data except in the case of the Circumpolar Current and the Gulf Stream.
Mesoscale wind spectra
Authors: Lyons T. J.
Published: February 2007

Spectral analysis of hourly wind records obtained at Adelaide, South Australia, illustrate a shift of the major sources of kinetic energy from the locally induced diurnal oscillation in summer to synoptic variations in winter. The physical significance of the summer oscillation is also shown to be location dependent.
Electric field growth in thunderclouds
Authors: Winn William P. , Byerley L. G.
Published: February 2007

We have constructed a balloon‐borne instrument for measuring the magnitude of the horizontal component of the electric field in thunderclouds. It consists of two hollow, copper spheres 15cm in diameter held 2cm apart. The spheres spin about an axis that can be described as the perpendicular bisector of the line segment between the centres of the spheres. The sinusoidally‐varying charge that is induced on the spheres by an electric field is amplified and telemetered to ground. The amplifier and telemetry transmitters are located inside one of the spheres. The spheres also serve as the telemetry antenna. The time behaviour of the electric field in the cloud is substantially different than that at the ground. The effects of corona discharge from the ground and of the finite conductivity of the air outside the cloud seem to be negligible in the presence of the intense field near a region of charge inside a cloud. Measurements of electric field intensities inside a cloud just before and after a lightning flash when combined with measurements at the ground can be used to obtain an approximate value for the total quantity of charge in a region of cloud just before it is partially discharged by lightning. In two cases the charge just before lightning was estimated to be −120C and −160C. During a brief interval in one of our flights the electric field at the balloon reflected the time behaviour of the electric field in the cloud; the electric field increased linearly with time between lightning flashes.
The role of eddies in atmospheric water vapour transport
Authors: Wu Mao‐Fou
Published: February 2007

It is demonstrated by applying a theory developed by Starr that the mean meridional circulations cannot transport atmospheric water vapour across surfaces of constant mean values of water vapour mixing ratio, and that the work of transferring the moisture from zonal regions of surplus to those of deficit must therefore be accomplished by eddy components of motion.
Evaporation and advection II: evaporation downwind of a boundary separating regions having different surface resistances and available energies
Authors: McNaughton K. G.
Published: February 2007

Using the model and methods developed in Part I of this study, it is shown that steady‐state evaporation, downwind of a sharp boundary separating uniform regions with constant but different surface resistances and available energies, can be written as

where ϕx is a dimensionless ‘exchange function’ that decreases from unity to zero as distance increases downwind of the boundary. The symbols have their conventional meanings and the primes signify upwind values. The form of ϕx depends on the profiles of wind speed and effective diffusivity, and on the downwind surface resistance and temperature via the parameter γrs/(s+γ).

Empirical expressions for ϕx are obtained from a known solution of the atmospheric diffusion equations assuming power law forms of the wind speed and effective diffusivity profiles and from a simple model assuming perfect vertical mixing and constant wind speed beneath an impermeable inversion base. These may give some indication of the form and magnitude of ϕx at small and at large distances respectively.
Determination of surface stress from vertical‐velocity spectra
Authors: Moravek D. , Panofsky H. A. , Weber A.
Published: February 2007

Many recent measurements of vertical‐velocity spectra in the atmospheric boundary layer are combined in order to derive the dependence of the maximum of the logarithmic spectrum, normalized by surface stress, on stability. An empirical equation is suggested which fits the observations and has the proper limiting form for free convection. It is suggested that this equation can be used to derive surface stresses from relatively simple measurements of the most energetic part of the spectrum, and from a stability parameter.
Airflow and hail growth in supercell storms and some implications for hail suppression
Authors: Browning K. A. , Foote G. B.
Published: February 2007

Multiple radar and aircraft observations of a damaging supercell hailstorm in northeastern Colorado are synthesized to show that the airflow and hail growth conformed in many respects to earlier models derived by the lead author. Some features that before had to be inferred indirectly are now substantiated and elaborated upon by direct observation. As a result of our increased confidence in certain aspects of the model we have been able to draw implications regarding the feasibility of suppressing hail by different means.

The observations indicate that an important stage in the growth of large hail is the entry of hailstone embryos into the edge of an intense updraught. These embryos are grown near the storm's right flank and get carried around the forward flank under the influence of a strong environmental airstream which divides at the stagnation point and flows around on either side of the main updraught. The main updraught itself is characterized by a weak‐echo vault and the embryos grow into large hail as they follow a simple up‐and‐down trajectory over it.

The vault takes on added significance in that it is a symptom of inefficiency in the conversion of cloud water to precipitation. Paradoxically it is this very inefficiency that encourages the growth of large hail by minimizing the effects of competition for the available supercooled droplets. Those recirculating embryos that find their way to the edge of the vault via the embryo curtain are seen to compete unfairly by being the first to encounter the undepleted cloud water in the vault. It is difficult to suppress their growth artificially because seeding in the main updraught at economical rates produces particles that rise above the hail growth region before they can have any significant influence on the available water.

The existence of a large vault implies that the flow field is so restricting the number of embryos re‐entering the main updraught that they may be sweeping up only a small proportion of the overall cloud water. Thus there is a danger that, if a mode of seeding were used which caused additional embryos to re‐enter the updraught along with the re‐entering natural embryos, this would lead to the production of additional large hailstones. Hence, at least for some storms, doubt is cast on the credibility of the competing embryo hypothesis for hail suppression, according to which the generation of additional embryos by seeding is supposed to promote competition for a restricted amount of cloud water to the extent that none can grow large.
Tropical forcing of atmospheric motions in a numerical model
Authors: Rowntree P. R.
Published: February 2007

The effects of tropical forcing on the atmosphere have been isolated in two general‐circulation models – one hemispheric, one global – by eliminating other zonally asymmetric forcing such as mountains and extratropical ocean/land thermal contrasts. Tropical surface temperatures were found to force upper tropospheric geopotentials in the tropics and geopotentials throughout the troposphere in middle and high latitudes with little scale dependence up to about wavenumber 5. In the hemispheric experiment the tropical forcing generated Rossby–Haurwitz waves similar to tesseral harmonics with 3 or 5 nodes between the poles; the associated phase agreement between tropical forcing and the tropical and extratropical response was also a dominant feature of the global experiment despite the more complicated structure of the forcing field. Some aspects of the results are explicable by wave propagation theory including a strong dependence on wavenumber of the geopotential response in the tropical lower troposphere.
The approximation of particulate scattering coefficients in the determination of total ozone
Authors: Basher R. E.
Published: February 2007

For the purpose of total ozone measurement, the atmosphere's particulate scattering spectrum in the 305 to 340 nm interval is approximated by a parabolic function. The inclusion of this function in the usual total ozone equations gives rise to expressions which allow the experimental determination of the “true” total ozone as well as the otherwise unknown expansion coefficients of the function.

The theory can be both illustrated and tested by the graphical methods which are described. The parabolic model is found to be very well supported by an experimental data sample. Of note is the finding that this sample's double wavelength‐pair total ozone values differ from the true total ozone value by as much as 0.024 atm‐cm. Some implications of the theory are discussed.
Interpretation of 8–13μm measurements of sea‐surface temperature
Authors: Cogan James L.
Published: February 2007

The difference between the true sea‐surface temperature and that inferred from satellite measurements of infrared radiances when viewing vertically through a cloud‐free atmosphere may be estimated to a useful accuracy for the 8–13μm radiometers of Defense Meteorological Satellite Program satellites. A simple parametric formula is developed that gives the difference to within ±0.6 K of that computed by a numerical method of solving the equation of radiative transfer. A comparison with data suggests that accuracies ⩽1.3K may be achieved relative to the actual value. Further work is necessary to confirm this accuracy because of an apparent discrepancy in the satellite data.
The flux‐angle distribution of momentum as determined from propeller anemometer measurements
Authors: Weiss A. , Allen L. H.
Published: February 2007

Flux‐angle distributions of momentum derived from measurements of a UVW propeller anemometer were compared with results from a three‐component sonic anemometer and were found similar. Under unstable and near neutral conditions, momentum fluxes were negative both at small angles of attack for updraughts and at large angles of attack for downdraughts. At other angles of attack, the momentum flux‐angle distribution was always positive. A flux‐angle distribution algorithm is presented which shows the relative contribution made by each angle of attack of the flow to the total flux.
Thermally driven vortices: A numerical study with application to dust‐devil dynamics
Authors: Smith R. K. , Leslie L. M.
Published: February 2007

This paper describes a series of numerical experiments designed to explore the close interplay between the rotational, the pressure gradient, and the buoyancy, force fields in concentrated vortex flows driven thermally by heating from below. The calculations are motivated by a desire to understand the dynamics of dust‐devils and to provide a theoretical framework in terms of which both past and future observations of these vortices may be interpreted.

In the model, a vortex is generated along the vertical axis of a cylindrical region of fluid bounded by a rigid (no‐slip) lower boundary, and a sidewall consisting of a rigid, impermeable upper portion and a rotating, porous, lower portion through which fluid at ambient temperature enters the cylinder and acquires rotation. The flow is driven by maintaining a circular portion of the lower boundary at a fixed temperature above ambient and fluid is allowed to enter or leave the cylinder normally through the upper boundary. For a cylinder of given size, the flow behaviour depends on the magnitudes of two nondimensional parameters which characterize the strength of the thermal forcing and of the imposed rotation. According to the sizes of these, flows with axial downflow on part or all of the axis of rotation are possible and, in some cases, a closed cell of reversed flow is possible. In each case it is possible to give a complete description of the force field balance which combines to produce the particular flow pattern.

The calculations go a long way to providing an understanding of the main features of dust‐devils as observed in a careful and detailed study by Sinclair and corroborate well with the experimental results of Fitzgarrald in relation to laboratory vortices. In particular, we show how rotationally induced axial pressure gradients can supplement buoyancy forces in accelerating the vertical flow in dust‐devils as appears necessary to explain the large vertical accelerations observed near the ground in these vortices.