bluuebunny/crossref_metadata_2025_split huggingface dataset:
Troughs in the Upper Westerlies and cyclonic developments in the Nile Valley
Authors: El‐Fandy M. G. 
Published: February 2007

AbstractIn the Middle East Area (M.E.) troughs in the upper westerlies are found, generally, at levels over 2 km above M.S.L. intruding into low latitudes as far south as the Northern Sudan (lat. 20° N.). These troughs usually travel eastwards, but tend to trail over the NW. of the Abyssinian Plateau. They also frequently remain stationary for about three days (on the average) over the SE. Mediterranean, owing to the effect of the plateau of Asia Minor.At the southern limits of these troughs, centres of convergence are usually set up within the westerlies, which have thus extended (at upper levels) into low latitudes, between lat. 22° N. and lat. 15° N. For the purpose of studying them the stream‐line map has been found the most satisfactory; the usual pressure map is of little assistance.As a rule a cyclone (say of type “A”) tends to form at a centre of convergence, and travels towards the NE., NNE., or even N.; the northward movement of the cyclones being due to the tendency for them to move towards the “centres” of the quasi‐stationary troughs over the SE. Mediterranean. Cyclones may eventually appear on the surface synoptic charts as shallow areas of low pressure.Another set (say of type “B”) of upper‐air cyclones, which move south‐westwards, tends to form farther south by the setting up of wave‐like perturbations in the usual E.–NE. upper current of the atmosphere of the Central Sudan. These perturbations appear at the time of re‐establishment of the E.–NE. current over the N. Sudan with the northward retreat of the westerlies, extend into low latitudes, and generally, when an upper‐air cyclone of type “A” has reached the M.E., another cyclone of type “B” develops over the East‐Central Sudan.The analysis has some value in forecasting upper winds on the Cairo—Khartoum air‐route and the local weather associated with these cyclones, and also in studying the general circulation in these latitudes, more especially the characteristic features of these cyclones.
The upper‐level flow‐structure near typhoons
Authors: Thompson B. W. 
Published: February 2007

AbstractFrom flow charts drawn at the Royal Obsrvatory, Hong Kong, it appears that typhoons commonly develop at airflow discontinuities with Easterlies to the north and Westerlies to the south. Others probably develop within a single airflow, notably N. Pacific Trades, and perhaps N. Indian Westerlies. Typical streamlines in the neighbourhood of typhoons in different localities are presented, and the development and relations of the associated flows are discussed.
The apparent diurnal temperature variation in the lower stratosphere
Authors: Kay R. H. 
Published: February 2007

AbstractTwo years of upper‐air data from the four daily radiosonde ascents from five stations in the British Isles are analysed for the pressure levels 150 mb, 100 mb and 80 mb ‐ some 14,000 ascents in all.The apparent diurnal temperature changes are discussed and the need is shown for further experimental evidence concerning the reality of the measured high‐level daylight temperatures. The observed daylight heating is too great to be caused by the absorption of radiation and must either be dynamical in origin or due to radiation error of the thermometer element in the radiosonde. From 1948, the times of ascent are suitable for computing the nocturnal cooling throughout the year, independent of radiation error. The temperature falls during the night by about 0.05°C hr−1 at these levels, the sort of change to be expected if radiative processes predominate.The apparent rate of change of temperature closely following sunrise and just preceding sunset is about ten times more rapid than the nocturnal cooling.It is concluded that the amplitude and rate of the apparent variations of temperature measured in daylight ascents should be treated with reserve until further experimental evidence as to their reality is available.
An essay on the general circulation of the atmosphere over South‐East Asia and the West Pacific
Authors: Thompson B. W. 
Published: February 2007

AbstractThe major airflows between the surface and 10,000 ft are studied for the area between Japan and the equator and longitudes 100°E. to 150°E., and a description is given of upper‐level influences which have not been apparent hitherto since only surface analyses were prepared before World War II. Convergence zones between airflows near the equator take the place of the fronts of high latitudes.The traditional theory of the intertropical front of summer is inapplicable to the region and a new concept, developed from observations, is described of an impermanent intertropical convergence zone formed by the occurrence of localized clockwise eddies in equatorial regions which bring southern hemisphere air across the equator and into contact with that to the north. If considered in relation to the West Pacific the traditional intertropical front of India is shown to be in reality part of the West Pacific polar front.
Dynamical aspects of some simple frontal models
Authors: Sawyer J. S. 
Published: February 2007

AbstractThe dynamics of the motion at an idealized frontal surface are considered theoretically. For this purpose the front is treated as a simple discontinuity of density, but it is assumed that horizontal and vertical gradients of temperature and wind may exist within the air masses. It is shown that at a front of this character between two non‐homogeneous air masses there must be a discontinuity of vertical velocity at the frontal surface, i.e., there must be up‐sliding or down‐sliding. The discontinuity in vertical velocity is related to the gradients of wind in the two air masses and is shown to be of a similar magnitude (or only slightly smaller) than the vertical velocities believed to occur in frontal regions.
Structure of the upper westerlies; a study of the wind field in the eastern Atlantic and western Europe in September 1950
Authors: Murray R. , Johnson D. H. 
Published: February 2007

AbstractOn the basis of 60 cross‐sections over western Europe and the northeast Atlantic, two for each day of September 1950, it is concluded that:Daily charts are given showing the jet axes and intensities at 300 mb superimposed on the surface analysis.
The westerlies always contain one or more wind maxima in the upper troposphere with structure broadly similar to that described by other writers on jet streams but with much variety of intensity and velocity profile.
The mean horizontal wind shear on the warm side of the jet stream is about two‐thirds of that on the cold side where it averages 20 kt/100 mi and may exceed 100 kt/100 mi.
The geostrophic relation gives a broadly correct representation of the true winds.
There is a broad connexion between fronts and jet streams, but the relationship is often less simple than that suggested in published work hitherto. Divided jets, distinct double jets and other complexities arise.
Precipitation growth in stratiform clouds
Authors: Wexler R. 
Published: February 2007

AbstractThe radar observations along the vertical of precipitation in stratiform clouds are compared with the theoretical growth rates of ice crystals in such clouds. The analysis indicates that no liquid water exists in these clouds at levels above about −5°C. The variation of signal strength from the −3°C level through the ‘bright band’ and the drop‐size distribution in the rain measured at the ground can be satisfied by reasonable assumptions concerning the coalescence of ice crystals.
Observations of the westerlies over the sea
Authors: Sheppard P. A. , Charnock H. , Francis J. R. D. 
Published: February 2007

AbstractObservations of wind speed and direction at 50 m intervals of height in the first few hundred metres have been made over the NE. Atlantic during 10 winter days of westerly winds. The following results were obtained:
The vertical gradient of wind speed is of the same order at all levels and there is no identifiable transition from a layer of frictional influence to a layer of friction‐free wind.
The wind speed at 300 m was on the average 21 per cent greater than the surface wind, though in 24 per cent of cases the latter was greater than the former. The mean change of direction in the same interval of height was 3·6° veer but the spread was much greater than the mean. On over 30 per cent of cases the wind at 300 m was backed on the surface wind and the speed at the upper level was then only 5 per cent greater than the surface speed.
The vector variation of wind velocity with height in the layer 200–500 m is accountable as thermal wind.
Turbulence of scale greater than about 10 min is of order 10 per cent of the mean motion and increases on average with height.
The mean inclination of the surface wind to the isobar is not more than 1° or 2° and is more likely to be towards high pressure than low.
It is inferred that the classical conception of the frictional boundary layer in a barotropic atmosphere has little validity in the atmosphere over the sea. In particular the shearing stress in the first few hundred metres of the westerlies probably varies only slightly with height and may increase if the thermal wind is strong. Measurement of surface drag by the method of frictional geostrophic departure is hardly possible in the baroclinic westerlies.
Precipitation streaks as a cause of radar upper bands
Authors: Browne I. C. 
Published: February 2007

AbstractSeveral workers have reported enhanced radar echoes, from regions well above the freezing level, in layer‐type rain clouds. Usually, there is a decrease with time in the height of these ‘upper bands,’ as Bowen has called such enhanced echoes. This paper describes an investigation into upper bands which has been made at Cambridge, using a 3‐cm radar with a vertically directed beam.The mean downward velocity of upper bands at a height 9,000 ft above the freezing level is found to be about 20 ft/sec, the velocity generally decreasing systematically with time. Such velocities are much greater than the rate of fall of the ice particles which are shown to be responsible for the upper‐band echoes, which, it is suggested, are produced by precipitation streaks in a region of vertical wind shear. A simple theory is worked out which gives the apparent rate of fall of an upper band in terms of vertical wind shear, the horizontal wind speed near the cloud top, and the terminal velocity of the ice particles forming the precipitation streak. Measured values of the fall speed of upper bands agree reasonably well with those predicted by this theory.A previous theory of upper bands (Bowen 1951) is shown to be untenable, though it is possible that the upper bands observed by Bowen in Australia have a different origin from those observed at Cambridge. It is proposed to make further observations to settle this question.
A record of the micro‐structure of a cold front
Authors: Samuel D. R. 
Published: February 2007

AbstractA record is presented showing the fine structure of wind speed, azimuth and inclination, temperature and water‐vapour pressure taken over a five‐minute period within which a cold frontal passage occurred. A particular advantage of the method of recording, using rapid‐response instruments, is the graphic illustration provided of the extreme sharpness of the front. The transition zone, estimated to be 70 m in horizontal extent, passed in 8 sec, during which time the temperature fell 5°C and the water‐vapour pressure increased by 2 mb.The record, together with two others taken shortly before and after, has been analysed and the results, including the mean vertical velocities, the vertical eddy fluxes of heat, water vapour and momentum, and the K values for heat are presented. Direct evidence is submitted of the vertical eddy transfer of heat, water vapour and momentum through the transition zone.
Note on the reflection of diffuse daylight from still water
Authors: Middleton W. E. Knowles 
Published: February 2007

AbstractThe luminous reflectance of still water for the light from an overcast sky is found to be less than the commonly accepted value (R = 0·066), because such skies are brighter at the zenith than at the horizon. For a sky three times as bright at the zenith as at the horizon, the value R = 0·051 is computed.
Rainfall over Egypt
Authors: Soliman K. H. 
Published: February 2007

AbstractThe problem of rainfall over Egypt has been investigated.The distribution of annual amounts of rainfall is given and remarkable variations along the Mediterranean coast are discussed.Winter is the season of rain in the north of Egypt, but in the south (Upper Egypt), two main seasons are found, namely, May and October.The diurnal variation of rain of two coastal stations and one inland station is given and discussed.Warm‐front rain practically does not occur, and cold‐front rain forms only a small proportion of the total amount and occasions of rain. Most rainfall is found to be non‐frontal and associated with upper cold troughs (or lows) which seem to play an important role, not only in Egypt, but all over the Eastern Mediterranean.Rainy situations in each season are discussed. It is found that, in winter, rain is generally associated with Mediterranean depressions, but when these depressions are not associated with upper cold troughs, they move quickly with very little precipitation. In the spring and autumn, however, rain is usually associated with small desert lows with cold upper lows or troughs.
The onset of turbulence in an elevated layer near sunrise
Authors: Wanta R. C. 
Published: February 2007

AbstractAbrupt changes at heights 46 m and 125 m above the ground from smooth flow, or flow in which damped eddies occur, to a flow characterized by continuing gustiness are investigated in terms of a critical Richardson number. Such transitions at Upton, N.Y. during the period October‐November 1950 are identified from continuous records of the wind direction. Account is taken of the time for the transition to propagate across the layer. Fourteen transitions during the period studied, all near sunrise, indicate that the (layer) critical number for eddies with periods somewhat less than one minute lies within the range from 1/3 to 1/2. It is suggested that the method used may be applicable to other eddy sizes.
Airborne measurements of the concentration of natural and artificial freezing nuclei
Authors: Smith E. J. , Heffernan K. J. 
Published: February 2007

AbstractAn aircraft‐mounted instrument for measuring the concentration of freezing nuclei in the free atmosphere is described. It has been calibrated and its limitations investigated.Preliminary observations, in flight, of natural freezing nuclei were made. The temperature at which a given concentration of ice crystals formed on natural nuclei varied markedly from day to day, and increased with altitude.Measurements in flight of the concentration of freezing nuclei in silver‐iodide smoke, released from a ground generator, are described. The nucleating properties of small particles produced by a hydrogen burner deteriorated very rapidly, while larger particles produced by a kerosene burner were more durable.
A note on the two‐dimensional equation of diffusion in the atmosphere
Authors: Davies D. R. 
Published: February 2007

AbstractIn this paper the shearing advection term, suggested recently by H. Lettau, is introduced into the well‐known two‐dimensional equation formulated by Sutton and Calder in their treatment of turbulent diffusion, and a solution of the ensuing equation is obtained subject to the conditions prescribed by the problem of diffusion from an infinite continuous line source, situated at ground level and orientated in a direction normal to that of the mean wind velocity. The predicted values of cloud height and peak concentration at a distance of 100 m downwind of the source, when compared with previous theoretical values and available experimental results in neutral stability conditions, show that no significant change in theoretical values is obtained by the introduction of Lettau's term, and the order of magnitude of the deviation from the Calder prediction produced by this term is found to be the same at all distances downwind of the source. The shearing advection term may consequently be ignored in the conditions investigated.
Wind stress on a water surface
Authors: Francis J. R. D. 
Published: February 2007

AbstractValues for the shear stress τ0 of the wind on a water surface, found in seven later experiments, are compared with the data of Francis (1951). Four sets of the new data show that the stress coefficient C = τ0/ϱu2 is not constant, but that it increases somewhat with windspeed u (ϱ = air density). Three sets merely show a large experimental scatter of C, and do not support any consistent law of drag. A theory is also discussed that τ0 is mainly caused by the drag of the small ripples, and not by the drag of the big waves.
THE AIRFLOW OVER MOUNTAINS. A review of the state of current knowledge
Authors: Corby G. A. 
Published: February 2007

AbstractA brief survey is first given of the observational evidence regarding special airflow effects in the neighbourhood of mountains, as provided by the visual evidence of clouds, the experiences of glider pilots and effects noted by the pilots of powered aircraft. This serves to indicate the phenomena requiring explanation. The review of theoretical studies is confined mainly to the work of Queney and Scorer. Both these authors apply the perturbation method to laminar, isentropic and inviscid flow over an ideal ridge. Queney deals with a uniform airstream (constant velocity and constant stability) and derives streamlines showing wave motions, both vertical and horizontal. Queney's waves are dependent partly on the stability and partly on geostrophic forces, and the order of the wavelength is several hundred km. Scorer, in his treatment, deals with smaller‐scale phenomena, so enabling geostrophic forces to be neglected, and provides for variations of stability and wind shear in the vertical. He finds that realistic wave effects, of the type observed in nature are predicted by the theory provided the variation of stability and wind shear with height is in accord with certain criteria. Past experimental work with models in wind tunnels is briefly considered in the light of what can be deduced from theoretical treatments regarding the conditions for dynamical similarity. More recent work by Long, using a tank containing several layers of immiscible liquid to simulate a density gradient is referred to briefly; this technique appears to have promise. A comprehensive field study by Forchtgott, who wed teams of gliders, is summarized. From his observations, Forchtgott has built up a theory of the flow patterns which occur in the lee of mountains. The main value of Forchtgott's work lies in the practical support it provides for some of the results deduced by perturbation theory and in throwing light on the nature of non‐laminar flow patterns which cannot be dealt with by existing theoretical treatments. In a concluding section, aviation applications of existing knowledge on this subject are referred to briefly. The criteria have some practical value for forecasting purposes.
The microwave properties of precipitation particles
Authors: Gunn K. L. S. , East T. W. R. 
Published: February 2007

AbstractThe theory of scattering and attenuation by rain, snow and cloud is reviewed and theoretical results are presented in the form of equations, tables and graphs, so that the radar response to meteorological particles can be calculated at six wavelengths (10, 5.7, 3.2, 1.8, 1.24 and 0.9 cm) and various temperatures. Particular emphasis is placed on developments since Ryde's comprehensive paper in 1946. Published experimental results are compared with the theory.All results computed from the theory are contained in Tables 4 and 5. The attenuation by water vapour and oxygen is given in an Appendix.
Annual rainfall areas of southern England
Authors: Gregory S. 
Published: February 2007

AbstractThis paper attempts to define areas throughout which the fluctuation of annual rainfall is relatively uniform. A general pattern is defined on the basis of graphs of ten‐year running means, and a more detailed pattern is presented from a consideration of individual yearly values of exceptionally high and exceptionally low rainfall. A comparison of the results obtained by these two methods is then made to enable the relative validity of the several areas defined to be assessed.
The development of lightning discharges
Authors: Pierce E. T. 
Published: February 2007

AbstractThe interpretation of experimental observations, described in a preceding paper, of the electrostatic field‐changes due to lightning flashes, is considered. It is found that almost all the recorded field‐changes can be most simply explained in terms of leaders carrying negative charge and originating in the lower part of a thundercloud. Those that reach the ground are succeeded by return strokes. It is considered that both leaders and return strokes consist of a central core surrounded by an envelope of corona; this corona concept, originally advanced by Bruce, leads to a coherent picture of the phenomena observed.
Radar evidence for aggregation and orientation of melting snowflakes
Authors: Mason B. J. 
Published: February 2007

AbstractMeasured values of the relative intensities of the echoes received from the melting zone, the snow above, and the rain beneath suggest that, in general, each snowflake in the melting zone coagulates with one or more (on average, two) others of much the same mass to form horizontally‐oriented aggregates which scatter as oblate water spheroids of mean diameter/axis ratio 4.
Wind stress on a water surface
Authors: Charnock H. 
Published: February 2007

AbstractThe vertical distribution of horizontal mean wind in the lowest 8 metres over a reservoir (1·6 km × 1 km) has been measured using sensitive anemometers freely exposed from a fixed mast in water 16 m deep, the fetch being more than 1 km. The resulting profiles are closely logarithmic, the small differences being systematic and possibly due to the thermal instability which existed when the measurements were made.The usual law for wind profiles in neutral stability is

where u is the wind speed at height z, k is von Kármán's constant, log z (0) the intercept on the log z axis, and u* the so‐called friction velocity defined by τ0 = pu, τ0 being the surface drag and rH the density of the air.To characterize the profiles u*/k, their slope, was plotted in relation to z (0), their intercept; this allowed a direct comparison with other profiles, in particular those recently measured in a laboratory channel by Sibul. The agreement was better than expected and indicated that z (0) was comparatively independent of fetch and stability but was largely determined by u*. The relation between u* and z (0) agreed roughly with the simplest non‐dimensional relation between them, gz (0)/u = constant, so that one is led to a generalized wind profile for flow over a water surface

which specifies the drag, given the wind at one known height. An approximate value of the constant is 12·5.This expression can be compared with earlier work. The better wind‐profile observations show rough agreement; the experimental scatter is necessarily large since a water surface is aerodynamically much smoother than most land surfaces, precision anemometry in difficult circumstances being required to provide sufficiently precise values. Oceanographic measurements of the tilt of water surfaces are in fair agreement at high wind speeds but at low wind speeds the data are conflicting. The early results which imply that the drag‐coefficient (u/u2) increases with decreasing wind speed in light winds are thought to be in error; some support for this belief comes from recent estimates of drag using a modified ageostrophic technique, which agree roughly among themselves and with the general expression.