bluuebunny/crossref_metadata_2025 huggingface dataset:
Point‐discharge currents and the earth's electric field
Authors: Hutchinson W. C. A.
Published: February 2007

An account is given of measurements of the current flowing to earth through a point set up at a height of 12 m, together with the electric field near the ground. Point‐discharge current of either sign may be represented approximately as increasing with the square of the field, as found by Whipple and Scrase. In the light of recent work on corona discharges between a point and a plane in air at atmospheric pressure it is suggested that for high fields the point‐discharge current will vary directly as the field. Irregularities in the curves relating averages of discharge current and field are attributed to space charge arising from local point discharge at or near the raised apparatus used for measuring the field. An advancement of field changes ahead of the corresponding point‐current changes is considered to be an example of the reversal, by space charges, of the sign of field between the level of a raised point and the ground, described by Lutz.
Note on eddy diffusion in the atmosphere between one and two kilometres
Authors: Charnock H.
Published: February 2007

Information on eddy diffusion in the atmosphere at heights between one and two kilometres has been obtained from an analysis of observations made on pairs of smoke puffs by using a camera obscura.

The results are compared with a prediction of the Kolmogoroff similarity hypotheses.
The heat economy of a rimed cylinder
Authors: Ludlam F. H.
Published: February 2007

A method is described for calculating the surface temperature of a slender cylinder which is moved through a supercooled cloud and becomes covered with rime ice. When the surface temperature reaches 0°C the ice formation proceeds at the maximum possible rate; the associated liquid‐water content of the cloud is calculated and found to be usually less than the maximum theoretical value inside a deep cumulus cloud. The rotating‐cylinder technique of determining water content and drop‐size distribution cannot therefore be used without consideration of the heat economy, and may otherwise lead to large underestimates of water concentration in severe icing conditions.
A statistical model for water‐vapour absorption
Authors: Goody R. M.
Published: February 2007

A statistical model of a water‐vapour absorption band is discussed, and comparison with computations made by Cowling shows that it provides a very accurate account of the average transmission over narrow frequency bands. The model can be used to compute the atmospheric transmission by water vapour under conditions of meteorological importance which were not treated by Cowling.
The evaporation of raindrops
Authors: Best A. C.
Published: February 2007

The evaporation of a single drop of water as it falls through an atmosphere in which the lapse rate is 6·5°C/km and the surface temperature either 15°C or 41°C is examined. By making certain justified assumptions, it is shown that the change in surface area of a large drop (i.e., with radius exceeding 0·15 mm) as it falls from height z1 to z2 is proportional to (1 — f)1·13 exp (— lz) where 100 f is the relative humidity and l is a constant. Values are given for the constant of proportionality and for l. If the drop has a radius less than 0·15 mm the change in volume of the drop is proportional to (1 — f)1·062 exp (— lz).

These results are then used to assess the effect of evaporation on the size and size distribution of raindrops falling through a constant atmosphere. It is shown that if the size distribution of raindrops at some initial height is given by 1 — F = exp [ — (2a/b)n] where F is the fraction of liquid water comprised by drops with radius less than a, and b and n are constants, then evaporation will lead to a change in the values of b and n but will not affect the general validity of the formula. As the rain falls through the non‐saturated air the distributive index n tends to a value between 3·5 and 4·0 whether it was greater or less than such a value initially. If the initial value of n is less than 3·0 the scale diameter b increases as a result of evaporation. If the initial value of n exceeds about 3·5 the scale diameter decreases. The effect of evaporation upon the radar response from falling rain is also examined.

In the last part of the paper the effect of the evaporation of rain into air which is initially unsaturated is considered. It is shown that the air temperature tends to a steady value and the relative humidity to 100 per cent. The excess of temperature above the steady‐state value and the deficit of relative humidity below 100 per cent decrease exponentially to zero with time. The depression of the steady‐state temperature below the initial temperature is a function only of the initial temperature and relative humidity and a table is given showing the value of the steady‐state temperature for nine different sets of initial conditions. The rate at which the final state is approached depends however only upon the rate of rainfall and a formula is derived for this dependence.
Evening waves
Authors: Roper R. D.
Published: February 2007

In the evening after a sunny day glider pilots soaring over hills often find increasing lift which carries them to heights they have been unable to attain all day. An example of this is described and an explanation in terms of lee waves is offered.

In an appendix by R. S. Scorer this explanation is shown to accord with theory.
Some further aspects of night cooling under clear skies
Authors: Saunders W. E.
Published: February 2007

The nature and cause of the evening temperature discontinuity near the ground is discussed, evidence being given that this is a result of the commencement of dew formation. Regression equations for forecasting the temperature of discontinuity are given. Methods of forecasting the subsequent cooling are discussed, and a detailed procedure given for Northolt. The relation between screen and grass minimum temperatures is briefly discussed.
A note on an intertropical discontinuity
Authors: Scott J. R.
Published: February 2007

The existence of a line or zone in which air flow has zero vorticity is inferred from the equation of motion. This zone is called the Intertropical Discontinuity. The detection, development and movement of this zone are discussed. It is shown how knowledge of its location and properties might be of value to forecasting near the equator.
On the theory of large‐scale disturbances in a two‐dimensional baroclinic equivalent of the atmosphere
Authors: Thompson P. D.
Published: February 2007

The equations of non‐viscous, adiabatic flow have been reformulated to apply to a two‐dimensional equivalent of a three‐dimensional baroclinic fluid. The state of this ‘equivalent‐baroclinic’ fluid is to be identified with conditions at a definable ‘level of equivalence’ in the true atmosphere. The two equations of equivalent‐baroclinic flow, in which neither vertical motions nor vertical dependence enter explicitly, involve only two dependent variables ‐ the temperature and height of an isobaric surface. Since those equations form a closed system, they constitute a mathematically complete theory of the development and movement of large‐scale disturbances at the level of equivalence. The stability criterion for a special type of flow, previously studied by Fjörtoft and others, has been derived from the theory and compared with Fjörtoft's earlier results. This comparison shows that the stability characteristics of three‐dimensional baroclinic flow are reproduced in two‐dimensional equivalent‐baroclinic flow, and, accordingly, that the present theory allows for the development of disturbances once they are initiated. An iterative scheme, based on successive calculations of the temperature and height tendencies, has been proposed for solving the general non‐linear equations of equivalent‐baroclinic flow. This method provides the basis for a new technique of numerical weather prediction.
Theory of airflow over mountains: II ‐ The flow over a ridge
Authors: Scorer R. S.
Published: February 2007

Three kinds of flow over unlevel ground are defined according to their scale ‐ aerodynamic, barostromatic, and geostrophic flow ‐ and it is seen that the practical difficulties in the way of obtaining the correct value of the relevant non‐dimensional numbers in model experiments are almost prohibitive.

The flow over a ridge with varying degrees of static stability is calculated, and the vertical displacement is seen to depend very much on the details of the airstream. When the flow is oblique to the ridge the air is permanently displaced sideways from its original path; and if the original airstream contains shear, shear in almost any direction may appear over a ridge. This may be displayed in billow‐cloud formations.

Diurnal variations in the length of lee waves are due to the development and disappearance of an adiabatic layer at the ground. The flow is calculated in a particular case and the temperatures recorded by radiosonde balloons are shown to contain spurious inversions as the balloon passes through the waves.

The disappearance of the adiabatic layer at the ground makes orographic effects a maximum around sunset on sunny days; and the appearance of a statically neutral layer in middle levels, for instance by condensation, renders steady laminar flow impossible.
Rainfall at Bidston, 1867–1951
Authors: Reynolds G.
Published: February 2007

The 85 years (1867–1951) of rainfall record at the Liverpool Observatory and Tidal Institute, Bidston, are the longest uninterrupted series in NW. Cheshire. Their salient features are:

(i) The mean annual rainfall in the calendar year is 28–68 in. with one exceptionally wet year, 1872, when 45.66 in. were recorded.

(ii) The mean of the seasonal year is 28.74 in. In this case, although the standard deviation is larger than with the calendar year, the driest and wettest years are not so extreme.

(iii) October, although it has been getting drier, is the wettest month, and April is the driest. The characteristics of the other months are scrutinized and compared following the computation of mean daily rainfall figures.

(iv) The probability of a month being the wettest in any year is directly proportional to the cube of its mean rainfall.

(v) The probability of a month being the driest in any year is inversely proportional to its mean rainfall.

(vi) Spring is the driest season and autumn the wettest, summer having significantly more rain than winter.

(vii) No significant correlation exists between one season's rainfall and any subsequent season's fall.

(viii) There have been very few occasions of heavy rainfall, the maximum recorded in 24 hr being just over 2 in., and only three noteworthy falls. This is due to Bidston's geographical position, as it misses the most violent instability storms and is partially in the rain‐shadow of the Welsh mountains, which protect it from the heaviest depression rains.

(ix) On the average there is an absolute drought once every 15 months and it is of 19 days' duration. Only two droughts have lasted longer than 26 days.

(x) Frequency curve graduation of annual and seasonal rainfall proved disappointing, as few absolute conclusions relating to extreme values could be drawn from the figures owing to the large probable errors involved, with what, in a statistical sense, is a relatively short period of observations, only 85 years. Deductions based on such computed curves are, however, the best method of estimating rainfall probabilities.
A comparison between observed and geostrophic winds in low latitudes
Authors: Jordan Charles L.
Published: February 2007

Low‐latitude wind and pressure data are used to determine the mean departure of the actual wind speed from the geostrophic speed. The computed departure becomes progressively greater equatorward of 30°N and attains a magnitude of about 10 m/sec at 10°N.
On the physics of dusty atmospheres
Authors: El‐Fandy M. G.
Published: February 2007

Measurements of particle size and concentration of atmospheric dust have been made at Alexandria in various degrees of turbidity. Except for ‘dust haze,’ reasonable agreement is obtained between the measurements and Koschmieder's equation for visibility in terms of optical attenuation. In ‘duststorms’ the required attenuation implies a scatter coefficient per particle 8/3 times the cross‐sectional area of the particles, while in occasions of ‘dust’ the scatter coefficient implied per particle is 4 times the cross‐sectional area of the particles. The results are as follows:

Dusty atmosphere
Visibility (m)
Average concentration (cm−3)
Average particle diameter (μ)
90% of particles have diameter ≤ (μ)
Scatter coefficient per particle/cross‐sectional area of particles

Dust haze
5,000–6,000
200
0.5
1.3

Dust
2,000–2,500
330
1.3
2.0
4

Duststorm
750–1,000
550
2.0
3.5
8/3
A further study of the upper westerlies; the structure of the wind field in the eastern North Atlantic and western Europe in January 1950
Authors: Johnson D. H.
Published: February 2007

(a) A study of 62 vertical cross‐sections through the middle‐latitude wind fields of January 1950 confirms previous conclusions regarding the broad structure of the upper westerlies.

(b) A mean January section from Greenland to the Mediterranean contains a wind maximum of 60 kt at a height of 9 km, 61°N. Examination of mean winter‐flow patterns for the North Atlantic shows the mean south‐westerly jet stream to be a normal seasonal feature.

(c) Comment is made on two features which require further study : high‐speed currents in the Arctic stratosphere and low‐latitude jet streams.
A note on the classification of annual rainfall‐distribution types
Authors: Gregory S.
Published: February 2007

This is an attempt to introduce into earlier methods of classifying rainfall‐distribution patterns the factor of intensity, by means of three intensity grades ‐ exceptionally wet, normal and exceptionally dry. Several significant distributional features are commented upon, and an attempt is made to correlate these distributions with the frequency of ‘weather types.’
Computation of tendencies and vertical motion with a two‐parameter model of the atmosphere
Authors: Bushby F. H. , Hinds Mavis K.
Published: February 2007

The system of partial differential equations given by Sawyer and Bushby (1953) for the rates of change of the 1,000‐500‐mb thickness and the 500‐mb contour height have been solved on an electronic computing machine for three synoptic situations and the fields of vertical motion were also computed. The results, described in this paper, show reasonable agreement with actuality. The implied 1,000‐mb height tendencies also agree quite well with those actually observed.
A note on the use of the stereographic map projection in dynamical meteorology
Authors: Ellison T. H.
Published: February 2007

The equations of motion in curvilinear coordinates, in which the curvature of the earth is taken into account, are shown to be quite simple when the coordinate system is a particular one, closely related to the stereographic map projection. As an illustration of the use of these coordinates, derivations are given of the vorticity equation and of Ertel's Theorem.
A simple mechanism to improve the sensitivity of a Dines anemograph
Authors: Trollund A. E.
Published: February 2007

The motion of the brass rod which connects the float to the recording pen of the Dines anemograph is controlled by three ball bearings instead of the usual collar. The sensitivity of the instrument to small changes in wind speed and the reproducibility of the zero line have been much improved by this change.
Radiation and lag errors of the Meteorological Office radiosonde and the diurnal variation of upper‐air temperature
Authors: Scrase F. J.
Published: February 2007

Radiation errors of the Meteorological Office radiosonde have been obtained from calculation of the rates of absorption of radiation and of heat loss by forced convection. the effect of the heating of the radiation shield on the temperture of the air reaching the thermometer element becomes very large at high levels. The errors due to direct solar radiation and to radiation reflected and emitted from below an ascending sonde have been calculated for different solar altitudes and for heights up to 30 km.

At solar altitudes between 40° and 60° the errors amount to about 1°C, 2°5°C and 9°C at 5, 15 and 25 km respectively. Observed differences in readings from ascending and rapidly descending sondes indicated that the error at 25 km was withing about 7 per cent of the calculated value.

Lag coefficients have been derived from the heat‐transfer coefficients and the calculated value for ground level is in good agreement with laboratory measurements.

The errors of the radiosonde can account for the whole of the observed differences between day and night observtion up to 15 km. Above that height, however, the differences are appreciably greater than the errors and suggest that the daily range of temperature variation over the British Isles in spring and autumn is about 1.5°C at 20 km and about 3°C at 25 km.
The concentration, size distribution and production rate of large salt nuclei over the oceans
Authors: Moore D. J. , Mason B. J.
Published: February 2007

The sampling and measurment of large condensation nuclei (equivalent salt contents greater than 2 × 10−14g) on board of Weather Ships in the N. Atlantic, 200 mi from land, reveal the existence of two distinct types of size spectra. It seems that the nuclei which predominate when waves are breaking (Type I distribution) are the residues of spray droplets, but that those which occur with wind speeds of less than 7 m sec−1 have a (Type II) distribution which closely resembles that of continental aerosol. In winds of up to 15 m sec−1 the measured concentrations of large salt nuclei rarely exceeded 10/cm3.

From the measured concentration and size distribution of Type I nuclei, it is deduced that in winds of 15 m sec−1 the rate of production at the sea surface of salt nuclei with mass greater than 10−13g is about 40 cm−2 sec−1; very similar values have been obtained from laboratory experiments in a wind‐wave tunnel. The corresponding rate for nuclei with m >2 × 10−14g would be about 100 cm−2 sec−1.

Laboratory studies show that the bursting of air bubbles of diameters between 0.3 mm and 4 mm at the surface of sea water produces small numbers of rather large drops (diameters 50‐500μ), the majority of which would fall back quickly into the sea. The large salt nuclei found in the atmosphere are probably the residues of smaller drops produced by disintegration of the bubble caps.
The tilt of a 12‐hourly atmospheric tidal wave
Authors: Thrane P.
Published: February 2007

Forced oscillations of 12‐hr period, stationary relative to the sun, are considered in a model atmosphere enclosed in a canal coincident with the earth's equator. Two‐dimensional, inviscid motion is assumed. The study is based on equations of perturbation containing linear terms and second‐order product terms. The oscillations are excited thermally and gravitationally. In the general case such waves have a variation of phase with height, a ‘tilt’, and this is necessary in order that a vertical transport of energy may take place. In non‐tilting waves no tidal energy can be supplied to the model atmosphere. An adiabatic wave can have no tilt. The method of perturbation is applicable to the tilting waves only for a limited time interval.
Microclimatological profiles in grass cover in relation to biological problems
Authors: Waterhouse F. L.
Published: February 2007

Selected climatic profiles, as measured by adapted meteorological techniques in the Angus area, were found in general to conform with work done elsewhere either in grass or corn fields. Seasonal and diurnal differences in air‐temperature stratification were related to height, density and mode of growth of crop, and solar altitude. The presence of a matted basal layer of dead grass in wild grassland, or the co‐existence of a clover crop in hay and silage fields, was noted to be important in maintaining a cool, humid atmosphere next to the ground. Such a zone was favourable to insects when arid conditions obtained at higher levels. In the upper regions where more edible grass leaves extend, wind was shown to be a most significant factor. This was due to the sudden reduction of wind speed within the crop. A steep gradient of wind speed, from zero to 90 or 100 cm/sec, might thus commonly be expected in the region some 40 cm to 15 cm below the upper surface of the stand under a variety of wind and grass conditions. Such a gradient could make available to an insect so situated a considerable range of body temperatures and states of water loss during periods of insolation. Field experiments, however, suggested that convective cooling often extended beyond the depth at which radiation intensity fell off greatly, since, in grass, insect body‐temperatures were frequently close to that of the surrounding air. The latter, however, was usually markedly different to that noted in a Stevenson screen. Wind conditions were also noted to be significant biologically wherever experimental procedure required the enclosure of grassland or the proximity of wind‐shielding hedges or walls. The ensuing alteration of microclimate particularly as regards air temperature might seriously upset the original purpose of such experiments, a fact noted by workers investigating other crops. Whilst figures quoted might provide a guide to the order of magnitude of some of the microclimatic phenomena encountered in the Angus area due regard should be paid to the lack of uniformity in most grass stands and the sometimes rapid variability of weather conditions.
A three‐front model for synoptic analyses
Authors: Penner C. M.
Published: February 2007

A model for synoptic frontal analyses derived from frontal‐contour‐chart studies is described. Three frontal systems named the polar front, the maritime arctic front and the continental arctic front are necessary to portray adequately the thermal‐frontal structure of the atmosphere. In‐phase wave development on at least two of the frontal systems occurs during major cylogenesis. The three‐front (or four‐air‐mass) cyclone is verified by aerological analyses while the classical occlusion model is not usually observed.
The atmosphere between 85 and 105 km studied by means of radio‐echoes from meteor trails
Authors: Browne I. C.
Published: February 2007

Meteors falling into the earth's atmosphere produce, by a process which was described briefly, a trail of ionised air. By studying the reflection of radio waves from these trails (‘meteor echoes’) the atmosphere at heights near 95 km can be sampled several hundred times per hour throughout the day, simply and at low cost. The paper summarized results obtained by many workers at Jodrell Bank since 1946 (see references).

The intensities and heights of appearance of meteor echoes lead directly to estimates of air density (about 3 × 10−9 g/cm3 at 95 km) and of scale height (about 6·5 km at 95 km), while the durations of meteor echoes afford a means of measuring the atmospheric diffusion coefficient. The measurements were compared briefly with independent estimates.

By a special technique, movements of meteor trails of the order of 1 m are detected, and hence winds measured at heights of the order of 95 km. Although ‘winds’ obtained by ionospheric methods may represent travelling disturbances, the ‘meteor’ winds are true mass movements of the air. It is found that there is usually a prevailing wind of the order of 10 m/sec, upon which is superimposed a semi‐diurnal variation which may have an amplitude of 30 m/sec. The phase and amplitude of the semi‐diurnal component show seasonal changes. The winds increase with height, the shear having a value of about 2 × 10−3 sec−1, a value comparable with that found in the troposphere, although there is no change in wind direction with increasing height. There is no detectable vertical component of wind.
Upper winds from geomagnetic observations
Authors: McIntosh D. H.
Published: February 2007

The belief that it may be possible to interpret geomagnetic observations in terms of upper atmospheric winds is based on the theory proposed by Balfour Stewart in 1882 to account for the observed daily magnetic variations. Balfour Stewart's suggestion was that the upper atmosphere is highly conducting and that this conducting air in its daily horizontal tidal movement across the vertical component of the earth's field induces by dynamo action a varying electric current whose magnetic field is observed at the ground as the magnetic daily variation. The theory of the magnetic solar daily variation, and of a corresponding lunar effect, was developed by Schuster and later by Chapman. All the problems of the theory have not been resolved but its essential correctness has received support in three ways which have led to its general acceptance : the experimental discovery of the ionosphere; characteristics of the magnetic effect which accompanies a large solar flare; and the discovery by a rocket ascent in 1949 of a discontinuity of the geomagnetic field at about 100 km due to the concentration of an electric current there.

The atmospheric dynamo theory of the magnetic daily variations implies that any steady wind in the upper atmosphere must also be reflected in the magnetic records, and during the past ten years Wulf has examined this possibility, with limited success. Recently Vestine, proceeding on the assumption that all currents causing magnetic disturbances are located within the high atmosphere, has derived wind systems compatible with the annual variation of magnetic disturbance and with the features shown by a particular magnetic storm. Although the validity of Vestine's basic assumption is in considerable doubt, his contribution remains an important one and points the way to future progress. The prospect of obtaining actual measurements of the ionospheric winds by means of the newly developed radarsonde, combined with the regular ionospheric measurements now available, make it probable that important progress with this problem will be made in the next few years.
Noctilucent clouds
Authors: Paton J.
Published: February 2007

Brilliant displays of the rare noctilucent clouds have recently been seen from central Scotland, and their height, position and speed have been determined from parallactic photographs. Observations of these clouds provide information concerning the physical state of the upper atmosphere at the height of about 80 km at which they invariably occur. Besides yielding direct measurements of wind, they indicate the existence of a temperature minimum at 80 km. Wind speeds of the order of 50 m/sec have been measured; Störmer has recorded speeds of more than 100 m/sec, and Jesse of about 300 m/sec. On every occasion when the clouds have been observed from Scotland, this movement has been from the east‐north‐east. But, since they are made visible by the sunlight scattered by the material of which they are composed, they are observed only on nights when the sun remains close below the horizon — that is, during the summer months in middle latitudes. Presumably they may be present at other times and in other latitudes, but they will not remain sunlit long enough to be observed. Their nature is still in doubt, though their tendency to appear at times of comet and meteor occurrences strongly supports the belief that they consist of meteoric dust. E. G. Bowen has recently pointed out that they appear either on or very near the dates of the daylight meteor streams discovered at Jodrell Bank, but Scottish observations show no such tendency. On one occasion, a portion of the clouds was observed to change colour from vivid blue to white, suggesting growth of the cloud particles by condensation. When opportunity offers, the new spectrograph at St. Andrews will be employed to investigate such changes in the spectrum. Finally, slides were shown illustrating a remarkably sudden change from their characteristically stable structure to quite chaotic shapes that occurred in the early morning of 25 July 1950. Noctilucent clouds have been observed on twenty‐two nights since 1939; but this was the only occasion when turbulence was seen. It may be significant that it was also the only occasion when aurora occurred simultaneously with the noctilucent clouds.
The frequency distribution of the annual maximum (or minimum) values of meteorological elements
Authors: Jenkinson A. F.
Published: February 2007

It is shown that the probability P that the annual maximum value of a meteorological element is less than a given value x can be expressed as exp
equation image
where a and k are constants such that ak is positive.

The parameters a and k can be evaluated from data of annual maximum values for a given period of years. Hence we derive the average highest and lowest in sets of T annual maxima, and also the maximum value to be expected once in T years.
Theory of non‐horizontal adiabatic flow in the atmosphere
Authors: Scorer R. S.
Published: February 2007

The equation of continuity takes the formwhen there are appreciable vertical displacements (see Section 1 for list of symbols). The stream function, Φ, for two‐dimensional steady motion satisfies an equation which for vertical displacements of less than about a kilometre reduces to the formwhereG1andG2are functions of Φ determined by the profile of the air current entering the region under study. This is probably the best form for numerical solution.

Bernoulli's equation shows that (gz+q2– τ) is constant along a streamline in steady adiabatic flow.

The perturbation equations which have already been widely used are derived as a special case. Except in this case the solution for three‐dimensional flow is very much more difficult to obtain than that for two‐dimensional flow.

The lateral stretching of vortex lines in flow over unlevel ground reduces or increases the surface wind according as the wind increases or decreases with height. This process may be used to explain the location of blow‐downs in forests on hillsides.

The generation of shear in non‐horizontal motion can occur at already existing discontinuities of temperature (or velocity). If the motion is unstable so that turbulence is generated, other things being equal the more stable (statically) the temperature inversion the more likely it is to produce turbulence in mountain waves.
Short periods of unseasonal warmth or cold in daily mean maximum temperatures at Bidston
Authors: Reynolds G.
Published: February 2007

Daily means of maximum temperature at Bidston over the 54 years 1900–53 have been examined and in them short periods of unseasonal warmth or cold have been found. Efforts to demonstrate the statistical significance of the anomalies met with difficulties which are outlined, but the results are tabulated and briefly compared with those of previous workers in this field.
Medium‐scale turbulence in the trade winds
Authors: Charnock H. , Francis J. R. D. , Sheppard P. A.
Published: February 2007

Double‐theodolite observations of pilot balloons were made in trade‐wind air at Anegada (18°45′N, 64°20′W), a small, low‐lying island in the British Virgin Islands, in Spring 1953. Ascents were made at 5 to 15 min intervals over working days of 7 to 8 hr duration on 15 days extending over a total period of 27 days. They provided values of the component air velocities u, v, w, in orthogonal co‐ordinate directions x, y, z respectively (x, y axes fixed in horizontal plane, z vertical), over 50 m intervals of height (20‐sec intervals of time) up to about 1·5 km.

Fluctuations in the motion at heights up to 1·5 km and of time‐scale varying from about a minute to several days are analysed and discussed. The work is a pioneer study over most of this spectrum and has the special interest of dealing with a field of flow in which the directions of the mean surface wind and the thermal wind are opposed (there was a maximum in the profile of mean wind speed at a height of a few hundred metres) and in which cumulus convection is almost always present.

Fluctuations from the mean flow were analysed using averaging periods increasing from about 3 hr up to the whole 27‐day period. For none of these averaging periods was there equipartition of eddying energy in the three velocity components; w′2 was one to two orders of magnitude lower than u′2 and v′2, the difference being greater the longer the averaging period.

The covariances u′v′, u′w′, v′w′ were also evaluated for motions at various heights and for the various averaging periods. u′v′ increased with averaging period and changed sign with height: it appeared that horizontal momentum was being transferred to the north by the larger‐scale motions, a smaller amount being transferred to the south by smaller‐scale motions. u′w′ and v′w′ were in general less than u′v′ and generally varied less systematically with averaging period. Values computed from the smaller components of the motion sampled were in fair agreement with shearing stresses computed by the method of geostrophic departure (using profiles of mean wind and the observed pressure field). The direction of the resultant of u′w′ and v′w′ agreed surprisingly closely with the direction of the vertical shear vector of the mean wind velocity, the implied coefficient of eddy viscosity for the spectral range sampled being about 105 cm2 sec−1 over the whole range of height.
The relation between standard deviation of contour height and standard vector deviation of wind
Authors: Jenkinson A. F.
Published: February 2007

A formula is derived, believed to be valid for all places outside the tropics and at all levels between the top of the friction layer and about 300 mb, expressing standard vector deviation of wind as a constant multiplied by the product of the standard deviation of contour height and the cosecant of latitude.

The formula may be written σ = 0.064 s cosec where a is the standard vector deviation of wind in kt, s is the standard deviation of contour height in ft and ϕ is the latitude.

A similar relationship is derived for levels between 300 mb and 100 mb. We may write σ = κw cosec ϕ where κ has the same value at all places but decreases uniformly with height from 0.064 at 300 mb to 0.033 at 100 mb.

World seasonal maps of the standard vector deviation of wind immediately above the friction layer have been prepared from corresponding maps of the standard deviation of surface pressure; and seasonal maps of standard vector deviation of wind at 500 mb over part of the North Atlantic were prepared from maps of standard deviation of contour height computed directly from daily values.
Short‐period variations in the atmospheric electric potential gradient
Authors: Whitlock W. S. , Chalmers J. Alan
Published: February 2007

Measurements made with 2 field mills, 100 m apart, along the direction of the surface wind, have been used to obtain information about the charges responsible for variations in the potential gradient over periods of the order of minutes. In general these variations are caused by the horizontal motion of wind‐home space charge contained within the first few hundred metres of atmosphere. In fair weather, there are effects probably caused by locomotive steam, and others perhaps to be associated with convection cells. In overcast weather there is evidence for concentrations of negative charge in the base of the thicker portions of the cloud. In showers, the main result is that the pattern of the potential gradient is very much affected by space charges from point discharge.
On the heat balance and maintenance of circulation in the trades
Authors: Riehl H. , Malkus Joanne S.
Published: February 2007

The heat balance is calculated for the Pacific north‐east trade during summer and it is shown that the trade exports sensible as well as latent heat. The sensible‐heat gain is related to the surface pressure distribution; it is found that the low‐level circulation in the region considered is self‐driving.
A theoretical estimate of the collection efficiencies of small droplets
Authors: Pearcey T. , Hill G. W.
Published: February 2007

The effective collision cross‐sections between pairs of small water droplets, falling freely through air under the influence of gravity, have been computed on the assumption of hydrodynamical effects alone being important. It has been assumed that each droplet tends to fall freely at its terminal velocity with respect to the surrounding medium, which also moves under the influence of the motion of a neighbouring droplet. By the use of previously computed fields of flow of a viscous medium around a uniformly translated sphere, the trajectories of motion of one droplet with respect to another were computed for a range of droplets having radii between 4 μ and 200 μ.

It is found that the collision cross‐sections increase to values considerably greater than the corresponding geometrical cross‐section as the droplets approach equality of size. As the difference in size increases, the collision cross‐section decreases to values close to the geometrical cross‐section, and finally decreases to zero. For any one particular size of the collecting droplet there is a minimum size of collected droplet below which no collection is possible. This size decreases with increasing size of the larger droplet greater than 10 μ in radius. For droplets smaller than 10 μ in radius, collision can occur only between droplets of nearly equal size. The results could account for coalescence becoming an important factor in the rapid formation of raindrops for droplets of radii greater than 10 μ.
Barometric tendency and weather at Changi, Singapore
Authors: Sharp F. A.
Published: February 2007

Barometric tendencies at Changi are ‘corrected’ for the diurnal effect and then examined in relation to the occurrence of rain in the following period. It is shown that the three‐hourly corrected tendencies are of no value in forecasting rain.
The relation between an umkehr curve and the vertical distribution of atmospheric ozone
Authors: Walton G. F.
Published: February 2007

An expression is derived for the intensity‐ratio for two wavelengths in the ultra‐violet of primary scattered sunlight received from the zenith at the base of a plane‐stratified atmosphere. The logarithm of the intensity‐ratio is expanded in a series which reveals the nature of the relation between it and the vertical distribution of atmospheric ozone. The information on the vertical distribution given by zenith observations when the sun is high in the sky is discussed.
Instruments for micro‐meteorology
Authors: Long I. F.
Published: February 2007

Several instruments suitable for long‐term recording of temperature, humidity and wind gradients among growing crops have been constructed. Practical details are given of the use of thermistors and miniature nickel resistance thermometers as wet‐ and dry‐bulb psychrometers, and of the use of these units for direct recording of both dew point and dew‐point gradient. Modifications of the sensitive cup anemometer, appropriate circuits and details of a ‘hot‐bulb’ anemometer using a resistance thermometer, are described.
Harmonic analysis of the mean northern‐hemisphere wind field for the year 1950
Authors: Saltzman Barry , Peixoto Josép.
Published: February 2007

Harmonic analyses of the mean northern‐hemisphere wind field for the year 1950 along latitudes 30°, 45° and 60° are presented. The seasonal variations of these spectra are investigated and the relative contributions of the various scales of mean eddies to the meridional transport of angular momentum are calculated.
Variation with height of rainfall below the melting level
Authors: Harper W. G.
Published: February 2007

3‐cm radar signal intensity measurements, made at a range of heights up to 6,000 ft on three days with widespread moderate rain, suggest that there was considerable uniformity of drop‐size distribution and of rainfall rate with height once melting of snowflakes was complete and terminal velocity was achieved, and that in these warm‐front type situations no significant growth of precipitation was taking place below the melting layer.
The measurement of gustiness in the first few thousand feet of the atmosphere
Authors: Jones J. I. P. , Butler H. E.
Published: February 2007

A description is given of instruments which have been designed and used to measure gustiness, in the form of inclination and total speed of the wind, from a position on the cable of a captive balloon. A lightweight wind vane with automatic compensation for tethering cable angle, and a sensitive vane airmeter are used as sensing heads. The data, with reference signals, are relayed by electric cable to ground level and recorded on multi‐channel recorders. Both instruments have good response to wind fluctuations with periods down to one second.

A brief account is given of some observations made at Cardington, Beds., and some examples are presented of records made at 1,000, 2,000 and 3,000 ft in contrasting meteorological conditions.
A numerical study of the wavelength and amplitude of lee waves
Authors: Wallington C. E. , Portnall Janet
Published: February 2007

Wavelengths and variation of wave amplitude with height are computed for 19 airstreams in which lee waves have been observed. Comparison between the computed and observed wavelengths suggests that the tropospheric flow is sufficiently independent of conditions in the stratosphere to allow reasonable latitude in making a boundary assumption at some high level.
Vanishing potential temperature gradients in strong convection
Authors: Webb E. K.
Published: February 2007

Temperature profiles recorded up to 30 m show an unexpected feature in conditions of free convection with light wind. Above the strong lapse near the ground, there is a transition to zero potential temperature gradient. The height of the transition level falls as the wind strength decreases, becoming less than 8 m when the negative Richardson number at 1·5 m is greater than 0·4. From reported observations over the sea it seems that the feature is present there also.
The movement of precipitation belts as observed by radar
Authors: Harper W. G. , Beimers J. G. D.
Published: February 2007

The movement of 51 belts of precipitation of cold‐front type over south‐east England has been measured from radar records and compared with upper winds at each 50‐mb level from 950 to 500 mb. The mean speed of the belts is found to be in close agreement with the mean wind component across the belts at the 700‐mb level, with a correlation in excess of 0·9. Even at 650 and 750 mb the correlation is significantly lower, while at 950 mb it is only 0·6. The same pattern of correlations and of wind components was found in 31 belts associated with occlusion situations, and no significant variation in correlation level was found despite subdivision of the material on the basis of the height ranges of the observed echoes.

A simple forecasting rule is suggested, that ‘belts of precipitation of cold‐front type move with a speed equal to the component of the 700‐mb wind across them’.
On the characterization of tropical rainstorms in relation to runoff and percolation
Authors: Hutchinson Sir Joseph , Manning H. L. , Farbrother H. G.
Published: February 2007

The statistical characterization of tropical rainstorms is considered. Linear relationships are demonstrated between log duration and rate, and between log amount and rate.

The fate of rainfall when it reaches the ground is then considered, and it is shown that from the linear regression of amount of rain and rate, together with runoff data, percolation rates can be estimated. The consistency of estimates of percolation rate is demonstrated from data from Namulonge, Uganda, and from the Ozark Highlands in Arkansas.
A numerical study of the topographical factor in lee‐wave amplitudes
Authors: Wallington C. E.
Published: February 2007

A numerical study of the effect of mountain shape on two‐dimensional lee‐wave flow shows that asymmetrical ridges are slightly more favourable than symmetrical profiles for the formation of lee waves, especially for short wavelengths. A technique is suggested for determining the lee wavelength when only part of the lee‐wave flow is observable.
The emissivity of the earth's surface
Authors: Houghton J. T.
Published: February 2007

Some measurements from aircraft of the emissivity of the earth's surface are described. They show that for the type of surface studied, the earth's surface is radiating as a black‐body at a temperature somewhere between screen air temperature and grass or sea‐surface temperature.
Temperature variations at Resolute, Northwest Territories
Authors: Longley Richmond W.
Published: February 2007

From a study of temperature data at Resolute, Northwest Territories, it is shown that in the Arctic regions the time of minimum temperature occurs near the end of February or in early March. This delay, relative to the corresponding time in temperate latitudes, is a result of the lack of incoming radiation during the polar night. Because of fog off open water in late July, the maximum temperature occurs during the second week of July.
World temperatures during the Pleistocene
Authors: Simpson George C.
Published: February 2007

In previous papers it has been shown that the glacial and pluvial periods of the Pleistocene can be explained qualitatively on the assumption that during this period there were three oscillations of solar radiation. Accepting this assumption the present day zonal temperatures ‐ mean temperatures along a circle of latitude ‐ are considered and the physics of the relationship between changes in solar radiation and the consequent changes in the zonal temperatures are discussed. By a graphical method of trial and error a family of curves relating the zonal temperatures of all latitudes with the oscillations of the solar radiation is prepared and discussed. These results are tabulated and used to plot curves showing the variations of the zonal temperatures of five latitudes between the Equator and the North Pole during a complete cycle of solar radiation and applied to the glacial and interglacial periods.

The difference between the actual temperatures of any place and the zonal temperature of the latitude on which it is situated ‐ the so‐called temperature anomaly ‐ is then discussed and two diagrams are prepared showing the local temperatures at places in the British Isles and North America during the last cycle of solar radiation embracing the period from the beginning of the Mindel‐Riss interglacial to the present day. The geological evidence for the temperatures thus derived is briefly discussed.
Deposition of iodine‐131 in Northern England in October 1957
Authors: Chamberlain A. C.
Published: February 2007

Iodine‐131 and other radio‐elements were emitted from the stack of the Pile No. 1 at Windscale, Cumberland, during the night of 10‐11 October 1957. The detailed distribution of the activity deposited on the ground was determined as far south as Preston and Leeds. The deposition of the radio‐iodine is attributed mainly to diffusion to the grass, but washout by rain and precipitation from some nearby cooling towers may have increased the rate of fallout in some areas.
An Irish weather diary of 1711‐1725
Authors: Dixon F. E.
Published: February 2007

The oldest extant weather diary for Ireland is critically examined and the results presented in a series of tables. Some comparisons are made with modern data.
Estimation of surface stress and heat flux from profile data
Authors: Priestley C. H. B.
Published: February 2007

The problem of estimating shearing stress from the wind profile in the lowest layers is discussed from the operational viewpoint. It is concluded that wind‐profile data alone may never in practice be sufficient, even though a universal profile with the stress as a separable parameter may be established by future research. On the other hand the determination of both stress and heat flux, with adequate accuracy, may be possible from single values of temperature gradient and wind gradient observed simultaneously. A difficulty common to all indirect methods lies in interpreting the sampling variations.