bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution to the theory of pressure variations
Authors: Petterssen Sverre
Published: February 2007

Two separate equations for the barometric tendency at a fixed point, or the height tendency of a rpessure surface are derived a from the hydrostatic equation, and (b) from the equations of motion.

The hydrostatic tendency equation, which represents a modification of the Margules—Bjerknes equations, relates the barometric tendency (or the height tendency) to the winds integrated through isobaric layers, and also to the patterns of contours and “thicknesses” of the layers. The separate contributions to the pressure variations rendered by the thermal wind, the cyclostrophic components and the horizontal divergence are identified and discussed. Methods of identifying the layer, or layers, that constitute the site of the processes and of assessing the magnitude of their contributions to the pressure variations are outlined. The reaction of the pressure distribution at sea level to the circulation aloft is discussed in some detail, particularly wit regard to the travel and development of cyclones, anticyclones, etc.

The dynamical tendency equation relates the barometric tendency to the accelerations integrate through isobaric layers. A brief discussion of this equation in relation to typical circulations is given.
Some estimates of the amount and diurnal variation of evaporation from a clayland pasture in fair spring weather
Authors: Pasquill F.
Published: February 2007

Attention is drawn to a theoretical formula for evaporation in adiabatic conditions, which has been applied generally to the case of a natural land surface by Thornthwaite and Holzman. The formula is E=pk2(q1–q2)(u2–u1)/(loge z2/z1)2 where E is the rate of evaporation, q1, q2 and u1, u2 the specific humidities and wind velocities respectively at heights z1, z2, p the air density and “k” an aerodynamic constant of magnitude 0.4.

A recent observational study described elsewhere by the writer has established the validity of the formula in adiabatic conditions and provided quantitative data on the errors which would arise on applying it in non‐adiabatic conditions. A simplified form of the equation is here employed as a justifiable approximation, in terms of near‐surface observations of the vertical distribution of wind velocity and vapour pressure, in evaluating the rates of evaporation at hourly intervals over a clayland pasture during a week of fair spring weather. These show a pronounced diurnal variation and the daily water losses evaluated therefrom lie between 1.4 and 3.6 mm. Demonstration is provided of the substantial error which could arise if for convenience the formula were to be evaluated in terms of daily mean values of the controlling factors.
The climatic fluctuation since A.D. 1850 in Europe and the Atlantic
Authors: Justin Schove D.
Published: February 2007

Trend‐curves of thirty‐year means are discussed (a) in general terms and then applied specifically to (b) temperature, (c) pressure, (d) rainfall, (e) wind, (f) temperature gradient and (g) temperature amplitude.

Correlations between the departures of the different elements suggest that we can consider the various anomalies as depending on those of pressure and wind. This is notably true of rainfall departures which can be regarded as the sum of two terms, the “area” term depending on the pressure anomaly and the “local” term depending on the vector wind anomaly. High pressure is associated not only with consistently dry years but also with cold years. Variations of wind or pressure gradient are particularly felt as changes of frequency of the prevailing wind. The southwesterly component is of course linked with the “zonal index” and the circulation of the wind systems of the earth. The increase of this component gives more maritime conditions and, except to the lee of hills or mountains, wetter weather. The recent increase explains the main differences between nineteenth and twentieth century climates but not the phases of the transition. These phases necessitate first the concept of a ring of high pressure which, by some south‐steering process, left the Arctic Circle about 1880 and reached the Tropic of Cancer about 1915. Preceding and following this ring are rings of high rainfall, low pressure and high temperature‐gradient that can be loosely regarded as frontal belts. At any one place therefore, the following sequence of five phases should occur : the first front (Frontal‐A stage), the easterly or cold period (T‐min), the pressure maximum (P‐max), the westerly period culminating in the second front (Frontal‐B stage).

In the British Isles the five phases explain the climatic fluctuations from 1875 to 1925 and much of the same sequence can be followed in Scandinavia from 1865 to 1915, Italy from 1885 to 1935 and in the United States from 1895 to 1945. Temperature data suggest that this equatorward movement with time may be of more general application, and that the preceding West European climatic fluctuations can also be interpreted as anomaly patterns which spread from the north to the south.

Pressure anomalies are normally greater over oceans than continents. The south‐steering of anomaly patterns necessitates, therefore, a backing of the prevailing wind in NW. Europe after the pressure maximum (P‐max) of about 1895. Such a change is confirmed by the wind records themselves.

An effect of persistent wind on ocean temperatures and therefore pressures might well account for the south‐steering, but there is as yet no evidence that delayed action effects of this kind occur.
The north‐east trade of the Pacific Ocean
Authors: Riehl H. , Yeh T. C. , Malkus J. S. , la Seur N. E.
Published: February 2007

First, the structure of the trade in the Pacific Ocean north‐east of the Hawaiian Islands is shown with the use of vertical cross‐sections, which extend to 3 km and include the fields of temperature, moisture, and motion. It is shown that the trade‐wind inversion cannot be a discontinuity that separates an upper dry and lower moist layer. Downward transfer of mass through the inversion takes place.

Next, the balance of heat and moisture is calculated. Although the use of several assumptions and approximate procedures is involved, a rather satisfactory result is obtained. In accordance with previous studies, the net heat export appears to be in the form of latent heat.

The concluding section first offers a hypothesis concerning the destruction of the trade inversion. This is followed by a calculation of the momentum balance and a discussion of the mechanisms that distribute moisture and momentum in the vertical.
Some characteristics of stratiform clouds over North Ireland in relation to their precipitation
Authors: Mason B. J. , Howorth B. P.
Published: February 2007

Analysis of stratiform‐cloud data from routine aircraft ascents made at Aldergrove during 1942‐4 and of ground‐station records of precipitation reveals that drizzle fell predominantly from clouds warmer than −5°C and thicker than 600 m, suggesting growth of drops by coalescence. Rain fell occasionally from clouds not extending above the −5°C level but fell mainly from clouds with tops colder than −12°C suggesting that ice crystals were mainly responsible for its release. The frequency and persistence of precipitation are analysed with respect to the temperature structure and the depth of the clouds. Some differences between the characteristics of precipitating and non‐precipitating clouds are brought out.
On the generation of charge associated with graupel formation in thunderstorms
Authors: Mason B. J.
Published: February 2007

It is argued that the generation and separation of electric charge above the 0°C level in thunderclouds are consequences of the growth and fall‐motion of graupel pellets. The results of laboratory experiments which show the acquisition of a negative charge by a growing rime deposit are used to calculate the charge liberated during the growth, in a thunderstorm cell, of ice particles by the accretion of supercooled cloud droplets. The calculations show that, in a vigorous warm cumulonimbus, it is possible for this process to generate about 1,000 C of charge within about 11 min of the activation of ice nuclei at the −10°C level, and that this volume of charge can be subsequently separated by the falling precipitation elements at a rate which can account for the production of several successive lightning flashes over a period of a few minutes.
Spectra and cross‐spectra of velocity components in the mesometeorological range
Authors: Panofsky H. A. , van der Hoven I.
Published: February 2007

Power spectra of horizontal wind components at 91 m indicate the existence of a gap near wavelengths of the order of 10 km or periods of the order of one hour.
The sampling of rain and cloud drops using hygrophotographic plates covered with various kinds of oil
Authors: Sivadjian Joseph
Published: February 2007

The preparation of a hygrophotographic plate is described, gives excellent results in the sampling of cloud droplets, when the latter have diameters between 20 and 30 μ. To avoid the shattering of larger drops (100 to 200 μ) the plate should be smeared with a layer of castor oil. The droplets of water, owing to their density being greater than that of the oil, sink to the bottom of the oily film, are immediately absorbed by the gelatine and thus are recorded.
A direct measurement of infra‐red radiation divergence to 160 mb
Authors: Suomi V. E. , Staley D. O. , Kuhn P. M.
Published: February 2007

A simple, economical balloon‐borne net radiometer is described. The net radiation is essentially obtained from the difference of fourth‐powers of the temperatures of the bottom and top radiating surfaces, and the internal conduction, which is proportional to the temperature difference between the bottom and top surfaces. The results of a measurement of net radiation to 160 mb are discussed.
The convective regime and temperature distribution above a horizontal heated surface
Authors: Croft J. F.
Published: February 2007

The convective flow and temperature distribution above a horizontal heated surface in air have been examined by optical methods. Attention has been given both to the open system and to enclosed air layers. The observations show the existence close to the surface of a mode of convection similar to the cellular convective motion previously noted in shallow enclosed layers. This motion is found to be present both in the open system and in the lower part of an enclosed layer of wide separation, i.e., large Rayleigh number.

The mean temperature profile in this region has been found for a range of surface temperatures and the results show that the logarithm of the mean absolute temperature (T) varies as the power (−1/2) of the height (Z) above the heated surface. This measured distribution has been compared with theoretical predictions in particular that of the Priestley similarity theory, which properly refers to convection above an infinite surface and in which the postulated conditions will apply more exactly in higher layers. Nevertheless the measured temperature profile in the surface region is of the form predicted by the Priestley theory with the experimental value (−1/2) in place of the theoretical (−1/3) as the power of the height (Z).
Solar radiation and the duration of sunshine in Trinidad, West Indies
Authors: Smith G. W.
Published: February 2007

Records of daily solar radiation energy extending over a period of one year have been compared with readings of sunlight duration obtained with a Campbell‐Stokes recorder. Energy records were made with a bimetallic antinograph. The regression equation obtained for the daily values in Trinidad, West Indies was R = RA (0·20 + 0·59 n/N), with a correlation coefficient of 0·91 where R = radiation actually received

RA = Angot's theoretical amounts of radiation which would reach the earth's surface in the absence of an atmosphere. These values are given by List (1951)

n = actual duration of sunlight

N = theoretical maximum duration of sunlight.
Size‐distribution of ice crystals in cumulonimbus clouds
Authors: Jones R. F.
Published: February 2007

Ice‐crystal size‐distributions have been measured in clouds associated with the intertropical convergence zone and more isolated cumulonimbus clouds in temperate zones. Mean size‐distributions fit curves ND = 1,000/D3 and ND = 1,000/D2·3 in tropical and temperate clouds respectively where ND δD is the number per m3 with diameters between D and D + δD mm. The tropical curve is a close fit throughout the measured range of D (0·05 to 4 mm) but the temperate curve is applicable in the range up to D = 2 mm only, there‐after a curve ND = 10,000/D5·4 fits the curve for D = 2 to 5 mm. In temperate clouds there is little variability with temperature except for a decrease in size of the largest particles observed as temperature decreases.

There is some evidence that the particles caught are graupel of mean density 0·6 g cm−3 and, on this assumption, variation with total ice‐crystal concentration suggests an empirical distribution law for particles with diameters 0·25 mm or greater of \documentclass{article}\pagestyle{empty}\begin{document}$ N_D = 10^{4.1} \exp [ - \frac{{2.67}}{{W^{\frac{1}{3}} }}(D - 0.25)] $\end{document} where W is the ice‐crystal content in g m−3.
A surface energy‐balance computer
Authors: House G. J. , Rider N. E. , Tugwell C. P.
Published: February 2007

A surface energy‐balance computer is described. This is fed with such information as dry‐ and wet‐bulb temperatures and temperature differences in the vertical (in the form of fine wire thermocouple outputs) and wind speed differences. The psychrometric equation is solved automatically to yield a vapour‐pressure difference and the latent‐heat term is then computed on the basis of an aerodynamic equation. The sensible‐heat term is similarly made available. The net flux of radiation and the soil‐heat flux are also recorded. A determination of each of these four fluxes is made once per minute and the values are integrated and presented on counters which are photographed at desired intervals, the smallest interval so far used being 20 min. Results indicate that for periods of an hour or more the ‘positive’ and ‘negative’ terms in the surface‐heat balance equation so obtained, agree to about 10 per cent except when the heat storage in the first two cm of soil, of which no account is taken, is obviously changing. The only complete 24 hr observational period so far covered indicates a daily balance to a fraction of a mw hr cm−2. Over approximately 80 hr observations, which were not continuous but contained about an equal number of daylight and dark hours, a balance to better than 1 per cent was obtained. A further result, which requires additional confirmation, is that the daily water loss from the centre of an extensive short‐grass area which has an ample water supply may be obtained for all practical purposes by measuring the total net radiation and assuming that all is used in the evaporative process. It becomes obvious that if hourly mean values of the profiles of temperature, humidity and wind are used to compute the evaporation then, in general, the results will be in error by up to about 20 per cent, although daily totals may be more accurate than this. The machine as it stands is not reliable for continuous operation owing to the use of a number of electro‐mechanical devices which are required to work under conditions for which they were not designed. Some improvements will be required before reliable continuous operation becomes possible.
A determinant hypothesis for the superadiabatic wind and temperature profiles
Authors: Priestley C. H. B.
Published: February 2007

The view is advanced that values of the Monin‐Obukhov coefficients, as they are obtained from field data, are products of smoothing rather than true physical constants of a steady regime intermediate between free and forced convection. This hypothesis provides a satisfactory prediction of the first coefficient and, if it is correct, reduces the dual problem of heat and momentum transfer in superadiabatic conditions to the specification of four constants : von Kármán's constant, Priestley's free convection constant, and the ratio KH/KM in neutral and in free convection conditions.

In inversion conditions it has yet to be shown whether the constancy of stress and heat flux extend very far, if at all, above the level where significant departures from the neutral profile begin. Thus the basic assumption of some common current approaches still awaits examination.
Airflow in convective storms
Authors: Browning K. A. , Ludlam F. H.
Published: February 2007

Some known properties of travelling storms are used to infer a general model of the airflow within them, in which updraught and precipitation‐maintained downdraught are fed persistently from opposite sides. Detailed radar and ground observations of a particular hailstorm are used to refine the model.
Measurements of solar ultraviolet radiation in the stratosphere
Authors: Brewer A. W. , Wilson A. W.
Published: February 2007

In order to improve the accuracy of the fundamental data required for calculations of the photo‐chemical production of ozone, the intensity of the solar ultraviolet light, λ ≈︁ 2100 Å, which penetrates to the lower stratosphere, has been measured with the sun directly overhead. The radiation was first detected at the 196 mb level where the flux was 2 × 108 photons cm−2 sec−1 and two of three ascents reached the 6 mb level where the flux was 1.2 × 1013 ph cm−2 sec−1. The results of calculations of the expected intensity at different levels are also presented and adjustments to the data used are found to be necessary in order to obtain agreement with the measurements.
The capture of airborne particles by water drops and simulated snow crystals
Authors: Starr J. R. , Mason B. J.
Published: February 2007

Collection efficiencies of falling water drops ranging from 1/10 to 1 mm in radius for spores of Lycoperdon (mean radius r = 2.25 μ), spores of black rust (r = 2.6 μ), and grains of Paper Mulberry pollen (r = 6.4 μ) have been determined. The experimental results are in fair agreement with calculations based on the assumption of potential flow around the larger drops. With both kinds of small spore the collection efficiencies reach maximum values for drops of about 400 μ radius and fall sharply for smaller drops. In this latter regime, where the potential flow solution is inappropriate and the viscous flow solution gives zero values, a sharp fall in collection efficiency is to be expected. Aggregates of two or three spores are collected slightly more efficiently than single spores, but the results show very similar trends in all cases.

Some preliminary results have been obtained on the collection of pollen grains by circular, hexagonal and star‐shaped paper discs that simulate snow crystals. The collection efficiencies, as deduced from the numbers of particles caught on their leading faces, are usually < 0.05, but the appearance of similar numbers of particles on the trailing faces suggests that particle capture in the wake of the disc is important at these Reynolds numbers of about 100.
A sunshine sensing device for long period recording
Authors: Sumner C. J.
Published: February 2007

A sunshine recording installation is described consisting of a sensing head of simple, novel design which causes a battery‐energized solenoid‐operated pen mechanism to record hours of sunshine. The equipment is capable of operating unattended for periods of six months.
Specification of sea‐level pressure from 700‐mb height
Authors: Klein W. H.
Published: February 2007

An objective method of translating a map of 700‐mb height into its accompanying chart of sea‐level pressure is derived by applying the screening regression technique to 17 years of synoptic data at 469 grid points covering the Northern Hemisphere for every other month of the year. On the average the regression equations explain almost 70 per cent of the pressure variance by means of approximately 3 heights and have a standard error of estimate of about 4 mb. The variation of these properties with geography, latitude, and month is illustrated and discussed. Valuable climatological material is also presented on the standard deviation of daily 700‐mb height and sea‐level pressure and the correlation between these variables.

The equations have been programmed for the electronic computer so that automatic, curve‐followed, and hemispheric sea‐level pressure maps can be produced in a few minutes. The programme has been applied to numerical prognostic heights prepared in the National Meteorological Center. The resulting objective forecasts of the sea‐level pressure field are illustrated and compared with predictions produced by other methods.
Absorption and emission by carbon‐dioxide in the mesosphere
Authors: Houghton J. T.
Published: February 2007

Theoretical and experimental evidence is presented which leads to a vibrational relaxation time appropriate for the v2 vibration of CO2 at 15 μ under atmospheric conditions at 210°K and standard pressure of 6·0 × 10−6sec. The effect of this on the atmospheric cooling rate near 90 km due to emission by CO2 is discussed. It is shown that absorption of solar radiation by the v3 band (at 4·3 μ) and the combination bands of CO2 (at 2·7 μ) leads to a heating rate of about 2°C (12 hr)−1 near 80 km, this being one of the largest contributions to the radiative heating rate at this altitude. The processes by which relaxation from the v3 vibration of CO2 occurs involve vibrationally excited oxygen and the v2 vibration of H2O. The magnitude of heating‐rate depends considerably, therefore, on the H2O concentration. For thermal radiative exchange by the v3 band, thermodynamic equilibrium begins to break down at 30 km; its contribution to the radiative budget of the mesosphere is consequently very small.
General and special approaches to the problem of objective analysis of meteorological variables
Authors: Kruger H. B.
Published: February 2007

A general formulation of the problem of objective analysis by computer consists of a simple equation in which the value of a meteorological variable at a given grid point is expressed in terms of three components which together include all potential ingredients. Several specialized analysis equations associated with existing schemes are obtained from the general equation, and the relevant methods of specifying weights are outlined. These methods were evaluated by performing a 500 mb height analysis using ‘perfect’ data and the same trial field with each. The best relative results were obtained when weights were determined by solving a system of linear equations involving weight parameters based on the autocovariances of observed minus trial values (residuals). A consideration of conditioning problems suggests that the choice of weight parameter should be appropriate to the manner in which the trial value at the grid point is synthesized. The implications of the investigation are that an optimum method of analysis should take into account data type, quality, distribution, predictability, prediction reliability and a statistical or empirical evaluation of the structure of the meteorological field about every grid point.
Divergence measurements from an aircraft
Authors: Axford D. N.
Published: February 2007

A comparison between the changes in wind calculated from Doppler data and from an inertial system shows that variations in Doppler winds of over five knots may be caused by small changes of heading and air speed. The accuracy of average winds over a ten minute period is thought to be better than five or six kt.

A 500 mb wind field has been measured across a 50 nm square centred on the Scilly Isles and a value for the divergence out of the square has been calculated from the wind measurements. The accuracy of this measurement is estimated to be ± 3 × 10−5 sec−1.
Air motion and precipitation growth in a wave depression
Authors: Browning K. A. , Harrold T. W.
Published: February 2007

A case study is presented to illustrate the small and medium scale air motion and precipitation patterns within a travelling wave depression. Air motion has been studied by means of isentropic and Doppler radar analyses; precipitation patterns have been studied by means of meso‐analysis of autographic rate‐of‐rainfall records and conventional 3‐dimensional radar data. The results confirm and elaborate upon earlier studies in which precipitation generation is classified according to whether it is due to large‐scale ascent alone or is modified by vertical instability. The influence of orography is also discussed.
Comparison of turbulent fluxes over water determined by profile and eddy correlation techniques
Authors: Miyake M. , Donelan M. , McBean G. , Paulson C. , Badgley F. , Leavitt E.
Published: February 2007

The turbulent fluxes of momentum and heat were determined by the eddy correlation and profile techniques for over water, fetch limited, near neutral conditions. The estimates agree well within the experimental error. The ø11 technique estimates of stress are systematically higher.
Ozone behaviour associated with the middle stratospheric circulation during the southern spring of 1967
Authors: Pittock A. B.
Published: February 2007

Large changes in the temperature and ozone content of the stratosphere at Aspendale (38 S, 145 E), Hobart (43 S, 148 E) and Macquarie Island (54 S, 160 E) are associated with the passage of planetary waves in the Antarctic polar vortex. Application of the conservation equation to an elliptical model of the polar vortex, using both ozone and potential temperature as tracers, leads to order of magnitude estimates of the vertical and horizontal motions and transports involved. Estimated vertical motions are of the order of 1 cm s−1. At the 30‐mb level there is significant horizontal advection of ozone into the vortex in the vicinity of the cold troughs and out of the vortex near the ridges, but horizontal advection of heat appears to be negligible.
A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air
Authors: Pruppacher H. R. , Beard K. V.
Published: February 2007

The internal circulation and the shape of water drops falling at terminal velocity in air of 20°C at sea level pressure, and nearly water saturated, were studied by means of a wind tunnel. Drops with an equivalent radius a0 smaller than 140 üm had within the experimental error no detectable deformation from spherical shape. Drops of sizes 140 μm ≤ a0 ≤ 500 μm were slightly deformed into an oblate spheroid. The deviation of these drops from spherical shape was found to be in fair agreement with that theoretically predicted by Imai (1950) and others. The deformation of drops of sizes 0.5 mm < a0 < 4.5 mm was found to be linearly related to the drop size. Such a linear relationship is predicted by the semi‐empirical calculations of Savic (1953).

By means of a tracer technique it was established that water drops falling at terminal velocity in air have a well developed internal circulation. The flow pattern inside a drop was found to be consistent with the flow pattern of the air around the drop and that predicted theoretically by Hadamard (1911) and by Hamielec and Johnson (1962). The surface velocity at the equator of a drop was found to be about 1/100 of the drop's terminal velocity. The experimentally determined internal velocities were compared with those predicted theoretically by McDonald (1954) from boundary layer theory and by Hadamard (1911) based on Stokes flow.
The influence of nitrogen oxides on the atmospheric ozone content
Authors: Crutzen P. J.
Published: February 2007

The probable importance of NO and NO2 in controlling the ozone concentrations and production rates in the stratosphere is pointed out. Observations on and determinations of nitric acid concentrations in the stratosphere by Murcray, Kyle, Murcray and Williams (1968) and Rhine, Tubbs and Dudley Williams (1969) support the high NO and NO2 concentrations indicated by Bates and Hays (1967).

Some processes which may lead to production of nitric acid are discussed.

The importance of O (1S), possibly produced in the ozone photolysis below 2340 Å, on the ozone photochemistry is mentioned.
Air motion and precipitation growth at a cold front
Authors: Browning K. A. , Harrold T. W.
Published: February 2007

A case study of a cold front has shown that, although appreciable ascent occurred over a deep layer, practically all precipitation growth was associated with the ascent of air which originated within the friction layer ahead of the front. Doppler radar observations showed that the ascent was accomplished in two phases; first through near‐vertical line convection to between 1 and 3 km at the surface cold front, and thence through shallow‐slope convection of the same air to between 3 and 6 km. The line convection was 2‐dimensional rather than cellular and occurred in the absence of appreciable hydrostatic instability. Horizontal convergence at low levels was very intense (10−2 s−1 averaged over 500 m vertically and horizontally), so that despite the shallowness of the line convection, the updraught attained a rising speed of 8 m s−1 which was sufficient to generate hail and thunder. The subsequent slope convection produced a period of moderate precipitation behind the surface cold front, and was associated with a pronounced transverse circulation, with strong gradients of velocity separating the weak downdraughts in (and beneath) the sloping frontal zone from the overlying updraught. The overall efficiency of precipitation production was high, 60 per cent of the water vapour flux in the rising air reaching the ground as precipitation.
Reversal of pressure gradients and wind circulation across India and the southwest monsoon
Authors: Ananthakrishnan R.
Published: February 2007

This paper describes some features of the climatology of the free atmosphere over India which are related to the onset and withdrawal of the monsoon.
Numeric calculation of turbulent diffusion
Authors: Thompson R.
Published: February 2007

A simple, flexible method involving a random number generator is given for simulating time dependent dispersion. The diffusion is simulated by letting a series of particles move with the local mean wind plus random fluctuations of this wind. This simulation method is not greatly complicated by introduction of horizontal and vertical shear, buoyancy, or anisotropic turbulence, and generally requires less computer time and storage than needed for finite difference computations of comparable accuracy over a network of fixed grid points. Solutions of particular cases compare well with known solutions.
Hysteresis effects in a differentially heated rotating fluid annulus
Authors: Cole R. J.
Published: February 2007

This paper is concerned with the motion of an annulus of fluid which is contained between two cylinders rotating about their common axis. The fluid is differentially heated in the horizontal. Examination of the stability of the wave régime flow is carried out by perturbing an averaged form of a non‐linear wave‐régime solution. This leads to a linear system describing the disturbance and is solved approximately using a truncated Fourier series. By this means theoretical stability criteria are obtained in terms of the Rossby number and the wave number. These results are compared with experimental wave change criteria and qualitative agreement is found.
Daily wind, pressure, and temperature variation up to 30 km over the tropical western Pacific
Authors: Hastenrath S.
Published: February 2007

The diurnal and semi‐diurnal variations of wind, pressure and temperature at 23 levels between 1,000 and 10 mb over eight stations in the tropical western Pacific are obtained by combining six‐hourly soundings taken at different times in April‐July 1956 and 1958. Results of all stations are combined according to local time. The prevalence of the semi‐diurnal pressure wave in the lower layers gradually yields to the first harmonic in the upper troposphere and stratosphere, as a consequence of the predominantly diurnal variation of temperature. The semi‐diurnal variation of temperature is found to increase slightly with height. Increase of the second harmonic amplitude of the u and v wind components with height is roughly proportional to the decrease of air density, with the phase remaining nearly constant, except for the lower layers.

The phase relationship between the semi‐diurnal variations of pressure, and eastward and northward directed wind components is discussed in terms of a model based on a linearized form of the equations of motion, frictionless flow, and the assumption that the oscillations are simple progressive waves.
Studies of turbulence in the surface layer over water (Lough Neagh). Part II. Production and dissipation of velocity and temperature fluctuations
Authors: Garratt J. R.
Published: February 2007

The paper is concerned with the analysis of fluctuations in vertical and longitudinal velocity components and in temperature at heights of 1.5, 4 and 12 m over a water surface (Lough Neagh, Northern Ireland) in relation to simultaneous profiles of mean wind speed and temperature to a height of 16 m. The matters at issue are (a) the evaluation of the constants in the Kolmogorov predictions on the form of the velocity component and temperature power spectra and structure functions in the inertial sub‐range, (b) the nature of the budgets of turbulent kinetic energy E and mean square temperature anomaly T̄, and (c) inferring fluxes of heat and momentum from the dissipation rates and local gradient Richardson number.

For kinetic energy, assuming a local balance between energy production and dissipation, we find the constants βu and γu in the one‐dimensional spectral density of the variance (øu(k) = βuε2/3k−5/3) and structure function (Du(γ) = γuε2/3γ2/3) relations to be 0.49 ± 0.09 and 1.61 ± 0.25 respectively, whilst that for vertical velocity βω = 0.68 ± 0.06. These results imply γu/βu = 3.25 and βω/βu = 1.38 independent of the measurement of ε. For the temperature spectrum (γT(k) = βTNε−1/3k−5/3) again assuming local balance, we find βT = 0.60 ± 0.40, i.e. a much larger relative variation.

In the light of our and other results we suggest βu = 0.50, βω = 0.67, γu = 1.6, βT = 0.8 are best estimates of the constants.

The normalized dissipation rate kξzu*−3 in relation to z/L( = ξ) is found to be broadly consistent with ξM(ξ) = (1 − 16ξ)−1/4 for ξ < 0 and ΦM(ξ) = 1 + 5ξ for ξ > 0, but is no critical test of these profile forms.

The vertical flux divergence of E appears on occasions to be significant in the energy budget but on average is small. The flux divergence of T̄2 shows even less determinate features.
The possible use of Laguerre polynomials for representing the vertical structure of numerical models of the atmosphere
Authors: Francis P. E.
Published: February 2007

The technique of expressing the vertical structure of meteorological parameters as finite sums of analytic orthogonal functions is described, and some properties of a specific set of such functions, the Laguerre polynomials, are given. The application of these polynomials to a two‐dimensional system of meteorological equations is described, and a linear analysis of the computational stability of a lateral finite difference scheme is performed. This analysis reveals a computational penalty, in that, for the example considered the necessary time‐step to ensure linear stability is an order of magnitude smaller than that needed in an equivalent multi‐level model.
A general circulation model of the atmosphere suitable for long period integrations
Authors: Corby G. A. , Gilchrist A. , Newson R. L.
Published: February 2007

The design of a general circulation model using the primitive equations in spherical form is described, including a statement of the finite difference forms used to integrate the system and explanations of the motives for unusual aspects of the finite difference scheme. The model incorporates the hydrological cycle, topography, a simple scheme for the radiative exchanges and arrangements for the simulation of deep free convection (sub grid‐scale) and for the representation of exchanges of momentum, sensible and latent heat with the underlying surface. An experiment performed with the model forms the subject of a separate paper.
The relation between temperature and humidity in the free atmosphere under conditions of stable stratification and strong thermal intermittency ‐ a case study
Authors: Warhaft Z.
Published: February 2007

Refractive index, temperature and wind profiles, to a height of 2,100 m, obtained from a tethered balloon flight are analysed in terms of static and dynamic stability on a day of an elevated temperature inversion associated with stable layering in humidity and strong intermittent temperature fluctuations. It is shown that large humidity gradients in stratified layers contribute significantly to the total density gradient and must be taken into account in the evaluation of Richardson number. Fluctuations in temperature and humidity occurred both in regions of strong positive and negative static stability. No evidence was found to suggest that the occurrence of fluctuations is associated with a critical gradient Richardson number. Cross‐correlation between humidity and temperature was found to be strongly negative across the boundaries of stratified layers and positive in strong intermittent bursts of temperature observed at the top of the temperature inversion. Spectral slopes of refractive index, temperature and humidity in the region of strong density gradients were found to be, in general, greater than the ‐5/3 slope predicted by inertial subrange theory.
The use of digital weather radar records for short‐term precipitation forecasting
Authors: Austin G. L. , Bellon A.
Published: February 2007

Weather radar may be used for forecasting the motion and development of precipitation patterns. A technique is described here which uses digital data sets and a computer pattern‐matching programme to forecast storm motion for periods between one‐half and 2 or 3 hours. The technique is able to track systems as they appear over the edge of the display by locking on to the leading edge features. Considerable attention has been given to evaluation techniques and more than 30 experiments involving seven different days of data from radars in Toronto and Montreal have been performed. It was found that although different classes of events had different forecastabilities, it was possible to obtain useful results for one hour forecasts on all the events studied.
The influence of momentum advections on a well‐mixed layer
Authors: Mahrt L.
Published: February 2007

This study examines the influence of weak horizontal advections of momentum on a well‐mixed planetary boundary layer. In the simple flow system examined, the direction and magnitude of flow modifications depend on the Rossby number, the nondimensional surface drag coefficient and the orientation of the geostrophic wind gradient field. It is found that advective modification of the boundary layer vertical motion field involves dependencies on the square of the local vorticity and dependencies on vorticity gradients. The mixed‐layer assumptions are relaxed for a special flow case to show that these results do not depend crucially on the mixed‐layer condition.
Charge separation due to water drop and cloud droplet interactions in an electric field
Authors: Jennings S. G.
Published: February 2007

Measurements were made of the electric charge acquired by drops of mean radius of about 750μm, in the presence of a vertical electric field E, the value of which could be varied from 4·5 to 27kV/m. It was found that the average charge acquired by the water drop as a consequence of the inductive process increased from 0·1fC to about 0·25fC as the electric field strength increased from 5kV/m to about 15kV/m, but there‐after decreased with increasing values of electric field.

This work suggests that the collisions between polarized rain‐drops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30kV/m; but that significantly larger fields could not be produced since all collisions in the higher fields would result in permanent coalescence.
The temperature dependence of the ozone concentration near the stratopause
Authors: Barnett J. J. , Houghton J. T. , Pyle J. A.
Published: February 2007

Using measurements from two instruments on the Nimbus 4 satellite comparisons between ozone concentration and temperature have been made at levels near 1mb during an occasion of stratospheric warming. High correlation exists between ozone concentration and temperature. Good agreement has been found with a photochemical model which incorporates ‘classical’ oxygen photochemistry together with reactions involving OH.
The nature of orographic rain at wintertime cold fronts
Authors: Browning K. A. , Pardoe C. W. , Hill F. F.
Published: February 2007

Some of the largest falls of orographic rain in the western parts of the British Isles are associated with wintertime cold fronts. This paper contains four case studies of wet cold fronts which were all characterized by south‐westerly prefrontal low‐level jets but were widely different in other respects. The distribution of rainfall in England and Wales is analysed using a network of autographic raingauges, specially augmented near the coast and over the hills of south Wales, and the orographic effects are explained using data from series of hourly rawinsonde ascents from a single station. The rain is considered in three distinct regions: pre‐frontal, the surface cold front, and post‐frontal. Behind the front orographic effects were found to be well defined but rather slight. At the surface front orographic effects were negligible, heavy rain tending to occur regardless of topography. Ahead of the front, orographic effects varied from small to very large, depending on the existence of a moist low‐level feeder cloud and seeding particles. The occurrence of heavy orographic rain ahead of the cold front is favoured by the presence of the low‐level jet, since this ensures the replenishment of a high liquid water content in the feeder cloud despite its rapid depletion by washout. Low‐level ascent, or at least the absence of descent, in the general airflow upwind of the hills is also needed if the feeder cloud is to have a high liquid water content. The required seeding particles in some cases originate from melted ice crystals grown aloft; alternatively they may be generated within the low‐level cloud itself even in the absence of the ice phase.
The field of mean vertical velocity at 200mb in south temperate latitudes as estimated from EOLE constant level balloon flights
Authors: Angell J. K.
Published: February 2007

The mean 200mb vertical‐velocity field in south temperate latitudes during 1971‐1972 has been estimated through 6200 evaluations of 24‐hour temperature changes along 46 EOLE constant level balloon flights, and use of the adiabatic method. There is a significant tendency for ascending motion to occur over the western hemisphere and descending motion over the eastern hemisphere in winter and in the mean for the year. In winter the average maximum ascending motion of more than 2mm s−1 occurs about 30 degrees longitude west of the Andes Mountains, and the maximum descending motion of 2mm s−1 occurs over Australia. It is suggested that the Andes Mountains are basically responsible for the observed longitudinal variation in 200mb vertical velocity, both because they act as a barrier to the strong westerly flow, and also because they serve to anchor the long waves and the vertical‐velocity patterns associated therewith.
Fluctuations and trends in indices of the southern hemispheric circulation
Authors: Trenberth K. E.
Published: February 2007

Indices of the southern hemisphere circulation are derived for the Australasian area using sea level pressure data. As well as considering indices of zonal and meridional flow, indices are derived based on the empirical orthogonal function analysis of Trenberth (1975). The first two patterns, P1 and P2, of this analysis can be approximately represented by only a few station values, and in this way their time series can be extended.

‘Regimes’ of weather are defined based on the short term mean behaviour of P1 and P2. These regimes are also characterized by large changes in the periodicities at which most of the variance occurs. The quasibiennial oscillation shows up as a fairly stable feature of the meridional indices and P2.

Trends in both P1 and P2 since the 1940s are related to the rising temperature trend in New Zealand. There has been a trend for less westerly especially between 25 and 45°S, some increase in westerly south of 45°S and less southwesterly or more northeasterly component to the flow across the whole of New Zealand as a result of the increased tendency for anticyclones to persist to the east of New Zealand rather than over Australia and the Tasman Sea, and their preference for higher latitude blocking.
Dynamic initialization for barotropic and multi‐level models
Authors: Temperton C.
Published: February 2007

The use of dynamic initialization is examined first for the case of a linearized barotropic model in which both the meteorological and gravity‐wave modes have non‐zero frequencies, and all variables are allowed to adjust mutually. It is shown that the gravity‐wave mode is rapidly damped, leaving the meteorological mode almost intact with appropriate values of divergence as well as balanced mass and vorticity fields. There are some problems associated with the slower rate of convergence at large scales; it is suggested how these might be overcome using spectral rather than finite‐difference methods. Mutual adjustment of the variables is shown to be generally more appropriate than forced adjustment.

The arguments are extended to a multi‐level model by diagonalizing it into its vertical normal modes. The analysis indicates that the external gravity‐wave mode should be rapidly damped by dynamic initialization, giving appropriate values of the vertically‐meaned divergence, while low‐frequency internal modes will be relatively unaffected by the initialization procedure.

A series of experiments is performed using a 5‐level hemispheric model, and the predictions of the linearized theory are confirmed. In particular it is found that the amount of computation required to reduce the amplitude of the external gravity‐wave mode to small levels is equivalent to that required for only 2–3 hours of forward integration. However, the quality of the forecast appears to be surprisingly insensitive to the presence or absence of gravity waves, and the need for such an initialization procedure is not conclusively demonstrated.
Structure and motion of tropical squall‐lines over Venezuela
Authors: Betts A. K. , Grover R. W. , Moncrieff M. W.
Published: February 2007

The characteristics of squall‐lines observed during the second Venezuelan International Meteorological and Hydrological Experiment (VIMHEX‐1972) are compared with the predictions of Moncrieff and Miller (1976). These squall‐lines are highly organized, propagate in a distinctive fashion, and effect a significant modification on both the thermodynamic and dynamic structure of the synoptic‐scale flow. The predicted propagation speeds and transport properties are similar to those observed, although some significant differences are also apparent.
Ozone trend and the stratospheric circulation over Australia
Authors: Kulkarni R. N.
Published: February 2007

Trends in total ozone for the period 1963–1974 at Australian stations Darwin, Brisbane, Aspendale and Macquarie Island have been discussed. Only Aspendale has a decreasing trend, which may be statistically significant. Trends in ozone at other places are not statistically significant.

From the trend analysis of temperature at the 100mb level, and from Umkehr analysis, it is concluded that the changes in circulation in the lower stratosphere are sufficient to explain the observed trends.