bluuebunny/crossref_metadata_2025 huggingface dataset:
A micrometeorological study of velocity profiles and surface drag in the region modified by a change in surface roughness
Authors: Bradley E. F.
Published: February 2007

This paper describes experiments in the lower atmosphere in which the wind passes from one surface to another with different roughness. Observations were made of the variation of surface stress, and of the development of velocity profiles in the region of flow modification over the downwind surface. Measurements are compared with the theories of Taylor, Elliot, and Panofsky and Townsend, and with the growth of a boundary layer on a flat plate. A large proportion of the surface stress adjustment occurs rapidly after the transition in agreement with Taylor's assumption. Velocity changes agree fairly well with the Panofsky and Townsend theory in the smooth‐rough direction, but not so well in the reverse. Growth of the modified region follows the 4/5 power law of boundary layer growth. It is concluded that the height/fetch criterion for a good micrometeorological site is about 1/200.
A shearing stress meter for micrometeorological studies
Authors: Bradley E. F.
Published: February 2007

A shearing stress meter (drag plate) for general use in micrometeorological studies is described. The mechanical principle applies to a large size range, though the instrument described specifically is of 3 ft (91 cm) diameter for installation in turf sites. The drag force is measured using strain gauges, and an absolute calibration system is built into the mechanism. The resolution of the instrument is about 0·02 dyne cm−2, and it will tolerate gusts of over 10 dyne cm−2 without damage. A detailed description is also given of the installation and operating procedure, attention to which is essential for reliable measurements.
Solar radiation on the south coast of England
Authors: Rees A. R.
Published: February 2007

Three years' data of incoming measured solar radiation at the Glasshouse Crops Research Institute are used to assess the radiation climate of the south coast. Radiation in both summer and winter is higher than at other stations in this country; this is, however, only partly attributable to the longer duration of sunshine because radiation is higher than would be expected from the longer duration of sunshine alone. A similar effect at Aberporth results from clean air, but despite the low level of pollution on the south coast, peak clear‐weather values are not abnormally high. Supplementation occurs on days that are not wholly clear; it is suggested that this is a result of reflection from orographic cloud.
A study of the effect of haze upon Umkehr measurements
Authors: Deluisi J. J.
Published: February 2007

The effect of atmospheric haze upon Umkehr observations is calculated in two ways. First, observed Umkehr curves are compared with computed Umkehr curves reconstructed from simultaneous direct soundings of the vertical ozone distribution. The difference between the two curves gives the ‘experimental’ haze effect. In the second method, Umkehr curves are computed for model atmospheres with and without haze, the difference giving a ‘theoretical’ haze effect. When the two haze‐effect curves are normalized to zero for a solar zenith angle of 60°, both exhibit the same characteristics, viz., the ‘correction’ to be subtracted from an observed (with haze) curve is negative at all solar zenith angles, the correction reaches a maximum near 81°, and there is a second small reversal near 87–88°. Application of the derived haze corrections in the Umkehr evaluation procedure results in slightly higher ozone content at and just below the main maximum and slightly lower ozone content elsewhere.
Observational studies of the general circulation of the Tropics: long term mean values
Authors: Kidson J. W. , Vincent D. G. , Newell R. E.
Published: February 2007

Data from 298 stations between 45°N and 30°S have been processed for the period July 1957 to December 1964. The mean wind and temperature fields are presented together with the momentum and heat fluxes for two three month seasons, December‐February and June‐August. The tropospheric results were obtained from objective analysis of the long term station means and the stratospheric results from latitude band means giving equal weight to data from odd and even years so that the biennial component has been virtually eliminated.

The mean temperature cross‐sections show little seasonal variation in the tropical troposphere and gradients are small. The maximum temperature is in the vicinity of 5°S during the southern summer but moves to 20°N during June‐August as a consequence of stronger heating over the continents. In the tropical stratosphere the seasonal variation is from lower temperatures in December‐February to higher temperatures in June‐August. The mean zonal wind pattern shows the tropical easterlies to be stronger and to occupy a greater range of latitudes in the upper troposphere during June‐August. The Hadley circulation obtained appears quite reasonable with the winter hemisphere cell predominating and extending over the Equator.

Although all three components of the momentum flux were evaluated for the troposphere, only the transient eddy contribution could be obtained for the stratosphere. A strong flux is observed in the upper equatorial troposphere directed into the summer hemisphere. The sensible heat‐flux in the middle troposphere is equatorward in the Tropics of both hemispheres and a small transport into the summer hemisphere is noted. This equatorward flux is countergradient in both hemispheres except during the northern summer. The mean motion transport of total energy is about an order of magnitude larger than the eddy transport at the Equator and supplies energy to the winter hemisphere.

The zonal and eddy forms of kinetic energy and available potential energy have been evaluated for the tropical troposphere together with all conversions between them except for that by transient eddies between available potential energy and kinetic energy. On the average, kinetic energy contents are about twice as large as available potential energy contents and the momentum flux conversions are larger than those involving heat fluxes. The conversion by the mean motions, however, is largest of all over the range 24°N‐24°S and leads to a rejuvenation time of some 3–5 days for the zonal kinetic energy. This conversion appears to be sufficiently large to offset the destruction in middle latitudes.

Taken together, the results presented here give a consistent pattern for the tropical circulation. The direct Hadley cell is seen as a source of both heat and momentum which are distributed by the eddy fluxes. The energy supply for the mean cell is thought to be the latent heat of condensation in its ascending branch.
Energy flux and convergence patterns in the lower and middle stratosphere during the IQSY
Authors: Newell R. E. , Richards M. E.
Published: February 2007

The vertical and horizontal fluxes of energy by large‐scale standing waves have been estimated on a monthly basis for the IQSY for the 100–10 mb region. A large upward flux into the region occurs in winter some of which passes into the atmosphere above 10 mb, where it may exceed the energy generated there by radiative processes. The meridional wave energy flux diverges from the 40°–60°N region and converges in both high and low latitudes in winter. The total energy flux convergence pattern shows that the polar night jet in the lower stratosphere in winter is a source of kinetic energy; when the jet collapses in the spring the same region turns into a strong sink and it is noted that while this was a gradual process in 1965 and occupied three months, there was a large absorption in March 1964 that dominated the energetics pattern in spring. The largest energy absorption occurs with the largest energy flux into the region, thus supporting previous suggestions that the spring warming is ultimately dependent on tropospheric events. The adiabatic approximation was used in the flux computations and the role of radiative processes in the observed events is briefly discussed.
Seasonal variation of kinetic energy in the atmosphere
Authors: Kung E. C. , Soong S.
Published: February 2007

In an attempt to broaden the observational basis of the seasonal variation of the large‐scale atmospheric circulation, Fourier analysis was applied to time series of important kinetic energy variables which were computed for a 5‐year period over the North American Continent. The variance spectra of the direct Fourier analysis are also presented.

The year‐to‐year fluctuation of the seasonal variation of the energy variables is apparent. After filtering out the year‐to‐year irregularity, clear basic features of the seasonal evolution were obtained. The kinetic energy level can be described essentially by the one‐year cycle. However, the energy generation, outflow, and dissipation show an important half‐year cycle in addition to the prominent one‐year cycle.
Surface films and the production of sea‐salt aerosol
Authors: Paterson M. P. , Spillane K. T.
Published: February 2007

The number of condensation nuclei produced by the bursting of a single bubble in sea‐water, and detectable at a few per cent supersaturation, is shown to be markedly dependent on the film pressure of naturally occurring surface‐active material adsorbed on the surface.

At low film pressures around 1 dyne cm−1 the presence of the film increases the variability of the number produced, but the number is always less than that expected for a clean water surface. With increase of film pressure the number of nuclei produced decreases markedly.

The dependence of nucleus number on the state of any surface‐adsorbed film has important consequences for the sea‐to‐air transport of organic material. This is discussed.
Modification of mean flow and turbulent energy by a change in surface roughness under conditions of neutral stability
Authors: Peterson E. W.
Published: February 2007

A theory is developed which describes the adjustment of the flow of a hydrostatically neutral fluid in the lower portion of a fully‐turbulent boundary layer, after an abrupt change in surface roughness.

The model is based on the hypothesis that the horizontal shear stress is proportional to the turbulent energy. The theory postulates that the flow is primarily governed by the dominant terms of the horizontal‐momentum, continuity, and turbulent‐energy equations. The model was solved by numerical techniques on a digital computer.

Unlike previous models there are no a priori assumptions about the distribution of velocity or stress, the behaviour of the nondimensional wind shear, mixing length, or momentum‐exchange coefficient in the transition region.

The theory, in contrast to earlier theories, suggests the distribution of turbulent energy, as well as velocity. An inflection point is predicted in the transition velocity‐profile. The nondimensional wind shear is found to differ significantly from unity in the transition region. These predictions agree with observation.
Eigenvectors for representing the 500 mb geopotential surface over the Northern Hemisphere
Authors: Craddock J. M. , Flood C. R.
Published: February 2007

A set of empirical orthogonal functions is produced which enable the large‐scale features of the 500 mb topography over the Northern Hemisphere to be represented with near optimal efficiency. The more important functions are described. Some of the properties of the coefficients of these functions which best represent the 500 mb charts for each day of the years 1965 to 1967 are summarized. The question of the number of functions required to obtain the most satisfactory representation of the 500 mb fields is discussed.
A net long‐wave radiometer
Authors: Paltridge G. W.
Published: February 2007

An ordinary net radiometer may be converted to a long‐wave instrument using black polythene as a filter to reject the short‐wave solar radiation. The polythene is formed into a spherical shell enclosing the radiometer, and the shell is spun continuously to neutralize the effect of short‐wave heating. Sample records are discussed.
Lamb waves in a nearly isothermal atmosphere
Authors: Bretherton F. P.
Published: February 2007

If the variations in sound speed c (z) and wind u (z) with height z are not too great, there is a mode of propagation of acoustic waves in the atmosphere in which the wave energy E (z) decreases exponentially with z with a scale c02/(2 – y) g (about 16 km), and the phase speed cm is given approximately by

(about 300 m s−1).
The lunar semidiurnal wind variations at Hongkong and Uppsala
Authors: Haurwitz B. , Cowley Ann D.
Published: February 2007

The lunar semidiurnal variations of the wind at anemometer level are determined from 67 years of Hongkong data and 84 years of Uppsala data. The amplitudes agree in order of magnitude with theory, but they do not show the theoretically expected increase with latitude. The tidal wind vectors turn in the direction opposite to that predicted by the theory, confirming earlier determinations at five other stations.
Some aspects of linear lee wave theory for the stratosphere
Authors: Berkshire F. H. , Warren F. W. G.
Published: February 2007

Certain theoretical features of high altitude lee waves for some simple two‐dimensional models are described. It is shown that some of these allow an intense local radiation of lee waves in a nearly vertical beam into the high stratosphere (similar to the leakage upwards of short radio waves in a familiar electromagnetic theory). Some associated quasi‐resonance phenomena are noted.
Spectra and cospectra of turbulence over water
Authors: Miyake M. , Stewart R. W. , Burling R. W.
Published: February 2007

Composite diagrams of spectra and cospectra were constructed from eight cases of velocity component and temperature measurements made over the water by an acoustic anemometer. Their universal form is discussed.
The Sheffield meteor wind experiment
Authors: Müller H. G.
Published: February 2007

An account is given of the development and application of a system for the study of high altitude winds using the radio meteor method. Three main subjects have been investigated : atmospheric tides and short term wind oscillations possibly resulting from internal atmospheric gravity waves, wind shears in the meteor zone and finally the nature of drifts obtained with the spaced receiver ionosonde technique. The Sheffield system has been steadily expanding and current developments as well as other projects linked with the Sheffield experiment are described.
Experimental measurements of the collection efficiencies of ice crystals in electric fields
Authors: Latham J. , Saunders C. P. R.
Published: February 2007

Experimental studies have been made of the aggregation of ice crystals of mean diameter about 5 μm upon an ice sphere of diameter 0.2 cm at the same temperature. The growth rate was found to be roughly independent of temperature over the range − 7°C to − 27°C and increased with electric field strength E to exceed the field‐free value by about 15 per cent, 40 per cent and 80 per cent in fields of 500, 1,000 and 1,500 V cm−1 respectively. At higher values of E the growth‐rate was reduced because of the ejection of clusters of ice crystals from the aggregate, probably under the influence of the intense electric forces. An appreciable amount of aggregation was observed at temperatures as low as − 37°C, in the presence or in the absence of electric fields.

Absolute values of collection efficiencies at a velocity of 3 m s−1 were determined at the temperatures − 7°C, − 11°C, − 17°C and − 27°C. In the absence of an electric field collection efficiencies of about 0.3 were determined at all temperatures studied. Experiments with charged ice crystals indicated that electric fields increase the growth rate by increasing the adhesion efficiency and not the collision efficiency.
A case study of frontal behaviour using a 10‐level primitive equation model
Authors: Benwell G. R. R. , Bushby F. H.
Published: February 2007

The predicted air motion and precipitation patterns obtained from a 10‐level primitive equation model of the atmosphere are presented for comparison with the observed patterns analysed by isentropic and Doppler radar techniques for the same occasion by Browning and Harrold (1969). There is considerable agreement over the scales of motion which it is possible to predict using the model though it is possible that further refinement in the handling of friction and topography and of the cloud physics can improve the predicted overall large‐scale distribution of rainfall.
Mid‐tropospheric frontogenesis
Authors: Bosart L. F.
Published: February 2007

Mid‐tropospheric frontogenesis is investigated for a case study in which special three‐hourly rawinsonde data are available. Isentropic analyses are made by objective means. Isentropic trajectories lead to the three‐dimensional description of the velocity field in space and time. Potential vorticity is used to check trajectories and to distinguish stratospheric from tropospheric air.

Miller's frontogenesis equation is applied in two and three dimensions to an intensifying mid‐tropospheric baroclinic zone. Frontogenetical and frontolytical regions arising from twisting, horizontal confluence, vertical shear of vertical velocity and ageostrophic contributions are delineated. Typical frontogenesis magnitudes are 2°C (100 km)−1 (3 hr)−1 and 2°C (km)−1 (3 hr)−1 in two and three dimensions respectively.

Previous observations of the extrusion of stratospheric air into the troposphere are confirmed.

A synoptic sequence common to many occurrences of mid‐tropospheric frontogenesis is described. A simple explanation is given of the initial development of a thermally indirect circulation accompanying the early frontogenesis. Mid‐tropospheric frontogenesis seems to accompany the extrusion of stratospheric air into the troposphere during which momentum, potential vorticity, ozone and radioactivity are transported downward and southward.
An operational linear lee wave model for arbitrary basic flow and two‐dimensional topography
Authors: Vergeiner I.
Published: February 2007

A partial survey of recent theoretical work on the flow over obstacles is presented. A model for linear, stationary mountain waves with arbitrary basic flow and two‐dimensional topography is described in detail. It contains the option of a nonlinear lower boundary condition. The wave drag is computed by three methods and the complete flow field is obtained. The sensitivity of the solutions to small changes of the upstream flow is demonstrated as a critical factor limiting the applicability of the model. The strong downslope wind storms of the Boulder area are briefly discussed in the general context of foehn phenomena. Computations indicate that resonance lee waves do not seem to be part of the mechanism of these winds.
A diagnosis of adiabatic production and destruction of kinetic energy by the meridional and zonal motions of the atmosphere
Authors: Kung E. C.
Published: February 2007

Adiabatic production and destruction of kinetic energy by the meridional and zonal motions of the atmosphere at different latitudes from 20° to 70°N were investigated with twice‐daily observed wind and geopotential data over North America during a one‐year period.

At the lower latitudes kinetic energy is produced by the meridional motion and destroyed by the zonal motion; while in the middle and higher latitudes, functions of meridional and zonal winds are reversed. Despite the general smallness of the meridional wind, the magnitude of – v δϕ/δy is comparable to that of – u δϕ/δx. As the result of the characteristic latitudinal distribution of – u δϕ/δx and – v δϕ/δ y, the resultant kinetic energy generation – V. ∇δ is maximum at the subtropical latitudes and minimum at the middle latitudes.
Clear sky radiation measurements at Lerwick
Authors: Forbes A. J. , Hamilton R. A.
Published: February 2007

Measurements of direct solar radiation in clear sky conditions a Lerwick showed that aerosol absorbs about 3 per cent of the incident radiation per unit air mass, with no appreciable diurnal variation. Systematic variations were found in the sensitivity of a Kipp solarimeter.
Momentum absorption by vegetation
Authors: Thom A. S.
Published: February 2007

Measurements were made in a wind‐tunnel of the drag on elements of a simply‐structured artificial crop, and of the wind profiles above and within the crop. Analysis demonstrates

that the drag force on an element of such an array can be calculated from the profile of the turbulent shear flow within the array, using the known (and unmodified), wind‐tunnel value of the drag coefficient of the individual element;

that the zero‐plane displacement (d) of an aerodynamically rough surface can be identified with the level of action of the drag on its elements; and

that von Kármán's constant = 0.41 ± 0.03.

The relation z0 = 0.36 (h – d) is suggested for the roughness parameter of vegetation of height h.

Calculated values of the drag force, f, on unit column of a real stand of beans in the field, using individual‐element drag coefficients (Cd) and measured wind speeds, give f = 3.5 τ0 where τ0 is the downward momentum flux derived from the shape of the wind profile above. On the evidence of conclusion (i) and the dense and complex nature of the bean canopy, the factor 3.5 is attributed to mutual sheltering of neighbouring canopy elements rather than as evidence that the Cd – values are modified by turbulent shear flow.

For the artificial crop, and for the real crop, recognition of the wind‐speed dependence of the individual‐element drag coefficients gives values of eddy viscosity, KM, almost constant in the height range h/3 < z ⩽ h and significantly larger than those found when constant drag coefficients are assumed. Constant KM within a crop canopy is consistent with the wind profile u(z)/u(h) = {1 + α(1 – z/h)}−2: an explicit expression is given for the parameter α.
The freezing of raindrops falling through strong electric fields
Authors: Smith M. H. , Griffiths R. F. , Latham J.
Published: February 2007

Supercooled water drops of radius around 2 mm and temperature ranging from 0 to −12°C were detached from a support and could be disrupted as they subsequently fell into a region of intense electric field. Photographs showed that whereas no freezing occurred if the drops were not disrupted the fraction of drops that froze increased steadily from 0 at about −5°C to around 0.6 at –10°C if they were disrupted. The passage of a spark to the drops during disruption did not affect the freezing probability. Studies were made on about 200 drops.

A series of experiments on bulk supercooled water and drops suspended from mechanical supports indicated that nucleation was initiated by means of cavitation. This conclusion was reinforced by high speed photographs showing the production and collapse of cavity bubbles when disruption occurred and indicating strongly that freezing initiated from the sites of these bubbles at the time of their collapse.
Nucleation of water drops by Brownian contact with AgI and other aerosols
Authors: Sax R. I. , Goldsmith P.
Published: February 2007

Aitken‐sized (0.01μm) particles of AgI, CuI, and ‘contaminated’ Ag2O were able to nucleate various sized water droplets in free fall (20–80μm in radius) by a direct, diffusive (Brownian) contact mechanism. The AgI aerosol was found to be the most efficient nucleator, showing a probability of 100 per cent at −16°C, 50 per cent at about −14°C, and 1 per cent at −11°C. These nucleation characteristics for AgI can be modelled from heterogeneous nucleation theory if the value of the contact parameter is assumed to be 0.70. Ag2O, passing through carrier tubing previously contaminated with iodine, was found to be only a slightly less efficient nucleating agent than AgI. CuI was found to have a nucleating efficiency corresponding to that which would theoretically be expected from an aerosol with a contact parameter of 0.55. Aerosols of the ‘pure’ oxides of silver, platinum, and chromium were unable to cause nucleation (to within detectable limits) at temperatures as low as −18°C. Auxiliary experiments indicated that the AgI aerosol had a small, but finite (10−5), nucleating efficiency at −5°C. Aitken‐sized particles of AgI did not lose their nucleating ability when captured at temperatures higher than 0°C.

It is postulated that contact nucleation by the Brownian capture of Aitken particles may be an important enough process in the atmosphere to contribute significantly to the large amounts of ice which have been observed at relatively high (−10°C) temperatures in some clouds.
Observations of lee waves by high‐power radar
Authors: Starr J. R. , Browning K. A.
Published: February 2007

A very high‐sensitivity 107 mm radar has been brought into operation for meteorological studies of airflow within the optically clear (or cloudy) atmosphere. One application of this radar has been to observe the detailed three‐dimensional structure of lee waves, using backscatter from both refractive index inhomogeneities and cirrus ‘clouds’ as means of tracing the pattern of airflow. This paper presents case studies showing how the radar has revealed the structure of lee waves downwind from the Welsh mountains. One of the case studies illustrates a steady‐state wave pattern, another illustrates an unsteady pattern with waves varying in orientation and wavelength, another illustrates a strongly damped wave pattern, and a final one illustrates two families of waves co‐existing at different altitudes. The radar method is shown to provide a direct and elegant technique for measuring lee wave properties. Although it depends on the presence of naturally occurring targets to trace the airflow pattern, such targets are found to be abundant in situations of strong lee wave activity.
A numerical model of the Adriatic for the prediction of high tides at Venice
Authors: Finizio C. , Palmieri S. , Riccucci A.
Published: February 2007

The present study deals with the application of a physical mathematical model of the Adriatic Sea to the problem of predicting the sea level variations at Venice. The equations of motion are considered. Taking into account the peculiar topography of the region, a unidimensional model of the Adriatic Sea is formulated. The conditions for the computation stability are determined; a first test of the model is carried out by computing the variation in time of some fundamental quantities like the mass and energy of the basin. Thereafter, the main effects due to the geometry of the basin are studied by using ideal ‘wind quanta’. Agreement is found between the results of the model and those obtained by means of classical hydrodynamics. Applications of the model to actual cases of sea level rise at Venice follow. Finally, on the basis of a critical analysis of the results, some considerations on the predictability of the phenomenon and on the requirements of the predicted meteorological fields are offered.
Momentum, mass and heat exchange of vegetation
Authors: Thom A. S.
Published: February 2007

Vegetation is treated as a complex surface roughness to which the transfer of mass or heat encounters greater aerodynamic resistance, γP, than the transfer of momentum, γD. The excess resistance (γP – γD) is equated to B/u*, where B−1 is the non‐dimensional bulk parameter introduced by Owen and Thomson (1963) and used by Chamberlain (1966, 1968). A general expression is obtained for B−1 in terms of the exchange characteristics of the individual elements of a vegetative canopy: this expression does not contain the surface roughness parameter Z0.

Using exchange coefficients of individual bean leaves (Thom 1968) and the bulk momentum absorption properties of a particular bean crop (Thom 1971) the relation B−1 = (constant) u*1/3 is derived. With u* in cm s−1, the constant is 1.35 for heat exchange and transpiration, 2.18 for CO2 exchange, and 1.13 for evaporation from the crop when wet. It is suggested, partly on the basis of the lack of dependence of B−1 on z0, that the same set of equations may provide a first approximation to B−1 for many types of vegetation.

Demonstrated are (i) that Monteith's (1963) method of extrapolating to zero wind speed to determine representative surface values of vapour pressure and of temperature (es and Ts) is much more rigorous if extrapolation is made to u = −B−1u* rather than to u = 0; and (ii) that the surface resistance γS, proportional to (ew(Ts) − es) (Monteith 1965) exceeds the bulk physiological, or stomatal, resistance γST of vegetation by an amount {1 − (Δ/γ).β}.B−1/u*, significant only when the Bowen ratio β is less than about 3/4(γ/Δ). (γ = 0.66 mb °C−1; Δ = dew/dT.) In particular, for B−1 = 4 and β = 0: (i) γST = 1/3 to 1/2 of γS; and (ii) use of γS with γD in the Penman equation (instead of γS, with which γD is compatible) overestimates λE by about 15 per cent.
Baroclinic instability of an idealized model of the polar night jet
Authors: McIntyre M. E.
Published: February 2007

The zonal current u(z), considered by Murray (1960, Section 4), as a model for the polar night jet in the lower stratosphere, has no shear in the model troposphere, and constant vertical shear uz in the stratosphere, u being a continuous function of z. The Richardson number is large. It is shown that this zonal current is always unstable, in the absence of dissipation, to small‐amplitude wave disturbances of essentially the same kind as those found in the theories of Charney and Eady. But, for numerical parameter values appropriate to the base of the polar night jet, predicted growth rates are small, and the disturbances have high zonal wave number (say 5 to 10) and are not very deep (several km at most).
A radiometer‐sonde for observing stratospheric emission due to water vapour in its rotational band
Authors: Brewer A. W. , Thomson K. P. B.
Published: February 2007

A balloon‐borne instrument is described which measures the downward flux from atmospheric water vapour in the 20–60 μm region. The instrument uses a thermistor bolometer as the infra‐red sensor. A special infra‐red filter composed of beryllium oxide embedded in polyethylene provides the desired optical characteristics for the instrument.

In‐flight energy calibration is carried out with two reference black bodies. The radiometer‐sonde is flown in conjunction with a conventional radiosonde, which provides atmospheric temperature, and pressure data for the ascent. Results have been obtained from 3 ascents. In the stratosphere the observed flux is consistent with the flux calculated for a water vapour mixing ratio of 2 × 10−6, and using published spectral data. The divergence of the flux corresponds to cooling at a rate of 0.4°C/day.
Direct measurement of vapour pressure and its fluctuations using fine thermocouples
Authors: Polavarapu R. J.
Published: February 2007

An instrument was developed to measure directly vapour pressure and temperature and their fluctuations compared to a moving average sampling line of 10 min. Copper‐constantan thermocouples of 75 μm in diameter are used for the measurement of fast fluctuations in dry‐ and wet‐bulb temperatures and a thermistor (100 kω at 25°C) for the measurement of mean wet‐bulb temperature. By applying the thermocouple voltages to a specially designed operational amplifier circuit, the vapour pressure is obtained as output voltage of the operational amplifier. The output voltage varies linearly with vapour pressure in the range 5‐40 mb. The values of the input and feed back resistances were theoretically determined by relating the output voltage with the Regnault's psychrometric equation. Field measurements showed that the power spectra of temperature and water vapour pressure followed −5/3 law in the frequency range 0.2 – 2.0 Hz.
The spatial variability of eddy fluxes in the constant flux layer
Authors: Dyer A. J. , Hicks B. B.
Published: February 2007

At the 1970 International Comparison of Turbulence Instruments held at Tsimlyansk, U.S.S.R., a large number of momentum and heat flux measurements were obtained simultaneously with two Fluxatrons. The data are analysed from the point of view of spatial variation of eddy fluxes, bearing in mind the limitations of the sensors, the variability of the eddy fluxes themselves, and the possibility of errors due to tilt. It is concluded that, at the Tsimlyansk site, the variation of heat and momentum fluxes both in the vertical (4 – 14 m) and the horizontal (1 – 150 m) is of the order 10 per cent or less. This result is in accord with traditional opinion, and provides a satisfactory experimental basis for the concept of a ‘constant flux layer’.
An investigation of the structure of baroclinic waves using three‐level streak photography
Authors: Douglas H. A. , Hide R. , Mason P. J.
Published: February 2007

A new technique, based on streak photography of tiny neutrally buoyant particles, for studying the three‐dimensional structure of patterns of thermal convection in a rotating fluid annulus has been devised and employed in a series of new experiments on theaxisymmetric andnon‐axisymmetric régimes offlow.Ofparticular interest in connection with the energetics of atmospheric motions and transfer processes are the experimental determinations of the depth dependence and time variations of salient features of the horizontal flow patterns of fully‐devslopedbaroclinic wavesand their theoreticalinterpretation.
The critical condition for the maintenance of turbulence in stratified flows
Authors: Arya S. P. S.
Published: February 2007

Theoretical models for predicting the critical Richardson number for the maintenance of turbulence in a stratified atmosphere are re‐examined in the light of recent observations. It is proposed that the critical condition may first arise from the failure of the maintenance of steady shear in the presence of buoyancy forces. An expression for the critical flux Richardson number is derived from the consideration of the equations of Reynolds stress and turbulent energy. This gives a range of 0.15 – 0.25 for Rfer, in agreement with the results of direct observations.
Aerial explorations of the low‐level cross‐equatorial current over eastern Africa
Authors: Findlater J.
Published: February 2007

An instrumented light aircraft has been used to investigate the low‐level cross‐equatorial current over eastern Africa. Using Doppler radar wind‐finding equipment the core of the current has been located and explored on four separate days, and the main features of wind, temperature, cloud and moisture content distribution have been determined. Mean fields of horizontal and vertical shear have been derived, and patterns of divergence and vertical motion around the core of the current have been deduced.
A simple climatological model of the dynamics and energetics of the nocturnal circulation at Lake Victoria
Authors: Fraedrich K.
Published: February 2007

The local atmospheric night‐time circulation at Lake Victoria (East Africa) is simulated by a simple model which is cylindrically symmetric. It consists of an upper layer (linearized, steady state, hydrostatic, incompressible, saturated over the lake) above a surface boundary layer (constant flux layer, log + lin profile). Analytical solutions are derived for the dynamical, energetical, and hydrological parameters. They mainly depend on the surface temperature difference between land and lake, which is the driving mechanism of the motion, and the choice of representative mesoscale transport coefficients Km, Kh. The results are compared with the climatological features of the nocturnal circulation.
The propagation and transfer properties of steady convective overturning in shear
Authors: Moncrieff M. W. , Green J. S. A.
Published: February 2007

A conservative quantity is found as an integral of a component of the vorticity equation and used to formulate a non‐linear theory of steady, two‐dimensional convection in shear. The steering‐level and propagation speed are determined in terms of a Richardson number and a density‐scaling parameter. Case studies indicate a favourable agreement between theory and observation, especially where the Richardson number is of order unity. The parcel theory of convection is extended and the importance of the horizontal pressure gradient as a control on the updraught intensity is discussed quantitatively. Heat and momentum transfer laws are obtained in terms of the mean flow parameters, and define a non‐Fickian transfer.
Turbulent transfer mechanisms in the atmospheric surface layer
Authors: McBean G. A. , Miyake M.
Published: February 2007

The objective of this study was to investigate the turbulent transfer mechanism near the surface. ‘Direct’ measurements of the turbulent fluxes of momentum, heat, and moisture were made in the atmospheric surface layer 2 m above a grass surface at Ladner, Canada.

The spectral correlation coefficients were considered to be a measure of the transfer efficiency as a function of scale size. For momentum transfer the efficiency decreased at all scales as instability increased. It is postulated that this was due to greater amounts of momentum being transferred in bursts of short duration, thus making the spectral correlation coefficient, averaged over sufficient time, smaller.

The Ladner results for heat transfer showed that its transfer efficiency increased at all scales when instability increased. The ratio of the transfer efficiency of heat to that of momentum was greater than 1 for most scales, even for near neutral stratifications, and increased to between 2 and 3 for more unstable conditions.

The efficiency of moisture transfer was usually smaller than that for heat transfer and was found to depend on the correlation between moisture fluctuations and those of temperature.
The generation of available potential energy by sensible heating in Southern Ocean cyclones
Authors: Bullock B. R. , Johnson D. R.
Published: February 2007

Estimates of the generation of available potential energy by sensible heating in the boundary layer for two extratropical cyclones in the Southern Ocean are presented. Boundary layer frictional dissipation is also estimated to contrast the relative importance of the storm's energy source by diabatic process with its sink by frictional effects. In the storm area of 2,000 km radial extent, representative average generation estimates by the sensible heating and frictional dissipation are 0.5 and 2.1 W m−2, respectively, for the late developing stage. In the occluding stage, the generation increased to 0.9 W m−2 and the frictional dissipation increased to 6.2 W m−2. The generation to frictional dissipation ratio of 1:3 and 1:7 for the two stages indicate that the in situ diabatic source of storm available potential energy is significant in the cyclogenetic stage but that its importance decreases as the storm decays.

Because of the paucity of data in the Southern Ocean a simplified model to estimate the sensible heat flux is developed in this study. The model estimates the upward flux through the sea‐air interface for the synoptic scale from analyses of the depth of the adiabatic boundary layer, the surface pressure and the sea surface temperature.
Observations on certain features to be seen in a photograph of haloes taken by Dr. Emil Schulthess in Antarctica
Authors: Tricker R. A. R.
Published: February 2007

A more complete theory than has been available before of the Lowitz arc and its associated upward pointing companion, is given. The theory of the supralateral arc to the halo of 46° is also given and it is shown that, at least in the case of the halo photographed, the suggestion put forward by Hastings (1920a) about the nature of the halo of 46° is untenable. It follows that his explanation of the arcs of contact to this halo have also to be revised. Alternative explanations are put forward.
Spectral characteristics of surface‐layer turbulence
Authors: Kaimal J. C. , Wyngaard J. C. , Izumi Y. , Coté O. R.
Published: February 2007

The behaviour of spectra and cospectra of turbulence in the surface layer is described within the framework of similarity theory using wind and temperature fluctuation data obtained in the 1968 AFCRL Kansas experiments. With appropriate normalization, the spectra and cospectra are each reduced to a family of curves which spread out according to z/L at low frequencies but converge to a single universal curve in the inertial subrange. The paper compares these results with data obtained by other investigators over both land and water.

Spectral constants for velocity and temperature are determined and the variability in the recent estimates of the constants is discussed. The high‐frequency behaviour is consistent with local isotropy. In the inertial subrange, where the spectra fall as n−5/3, the cospectra fall faster: uω and ωθ as n−7/3, and uθ, on the average, as n−5/2. The 4/3 ratio between the transverse and longitudinal spectral levels is observed at wavelengths of the order of the height above ground under unstable conditions and at wavelengths of the order of L/10 under stable conditions. This lower isotropic limit is shown to be governed by the combined effects of shear and buoyancy on small‐scale eddies.
Diurnal wind variations in Antarctica
Authors: Hisdal V.
Published: February 2007

For the three Antarctic ice shelf stations considered (Norway Station, Maudheim, and Halley Bay) it is shown that from spring to autumn a systematic diurnal variation of the mean vector wind at the surface exists. Different factors that may be responsible for this variation are discussed. The results seem to agree well with the assumption that in areas far from the ice front (the seaward edge of the ice shelf) the main cause is the larger net gain of momentum in the lowest layers during the middle of the day, while closer to the ice front there is an additional effect of the varying contrast between the air temperature over the sea and over the ice shelf.
Wind profiles and change of terrain roughness at Risø
Authors: Panofsky H. A. , Petersen E. L.
Published: February 2007

The Risø 125 m tower is situated on a narrow peninsula, surrounded by bays of varying width. The resulting surface roughness changes are clearly reflected by ‘kinks’ in the measured wind profiles, whose characteristics depend on the wind direction. The height of the lowest kink for water‐to‐land trajectories is in good agreement with theory.

The roughness lengths computed for the immediate surrounding of the tower vary with wind direction in a manner consistent with terrain features. However, the roughness lengths of the water estimated from the profiles are unrealistically small.

The mean profiles obtained when the trajectory passes over relatively homogeneous terrain are represented quite well by wind profile expressions that are usually applied only in the surface layer.
On the variance spectra and spatial coherences of equatorial winds
Authors: Parker D. E.
Published: February 2007

The variance spectra of daily zonal and meridional winds in the troposphere and lower stratosphere over Gan (00°41′S, 73°09′E) were investigated. The total zonal variance considerably exceeded the total meridional variance at all the levels studied except the surface. In the upper troposphere the total zonal variance had a marked peak caused almost entirely by effects with periodicities greater than 10 days. The variance due to 4‐ to 5‐day meridional effects usually had a maximum slightly below the tropopause. However, at all the levels investigated this variance fluctuated considerably with time although without showing any long‐term regularities. Some specific 4‐day meridional motions at 150 mb over the equatorial regions between Gan and East Africa appeared to progress westward with a zonal wavelength of between 10,000 and 12,000 km.

The vertical coherence of daily tropospheric winds over Gan was found to be weak on a scale of several km. Correlation coefficients between daily tropospheric winds over Gan and corresponding winds over Port Victoria (04°37′S, 55°27′E) were found to be small except for part of the upper troposphere.
Spectra of the temperature and humidity fluctuations in the marine boundary layer
Authors: Warner J.
Published: February 2007

The results are given of the analysis of temperature and humidity fluctuations observed from an aircraft in 61 runs at heights of 30–550 m above the open sea in conditions of active convection in the south‐east Trades. The dimensionless temperature fluctuations varied with ( − z/L)−1/3 for scale heights from about 0·2 to 2 but thereafter showed little change with height. The spectra obeyed the −5/3 power law for dimensionless frequencies in excess of about 0·3. The variance of virtual potential temperature showed a maximum at a lower dimensionless frequency than the variance of vertical air velocity observed during the same series of observations.
The use of Nimbus 4 radiance and radio‐sonde data in the construction of stratospheric contour charts
Authors: Aanensen C. J. M.
Published: February 2007

The construction of 10, 3 and 1 mb contour charts using thicknesses derived from Nimbus 4 selective chopper radiometer (SCR) measurements is described. Examples of such charts during the 1972 stratospheric warming period are given. Heights and deduced gradient winds obtained from these charts were compared with radio‐sonde and rocket observations. At 10 mb the average heights using satellite measurements exceeded those from radio‐sondes by 5 dam in a ‘quiet’ period and by 14 dam in the warming period, the greatest difference occurring in the area of warming. Rocket data showed the average height difference increased upwards to some 40 dam at 1 mb. Consideration of derived gradient winds supported the impression that the shape of contours is better than the spacing. Though there is evidence of increased error on the occasion of major warmings it is concluded that the method described produces realistic charts.
A note on the relationship between large scale energy functions and characteristics of climate
Authors: Smith R. F. T.
Published: February 2007

A study has been made of large‐scale energy functions using 500 mb height and 500–1,000 mb thickness data for 1954–1956 and associated synoptic charts in order to consider further the relationship between blocking anticyclones and eddy kinetic energy (K′) as proposed by Everson and Davies (1970). For the winter of 1955–1956, K′ displayed much larger amplitude variations with a longer period than those for the winter 1954–1955. The difference in weather was also quite marked, the 55–56 winter being dominated by blocking anticyclones whilst the 54–55 winter was comparatively mild. The onset of large‐scale blocking activity generally coincided with minima of K′ as anticipated.

It was further found that a minimum of K′ coupled with a relatively low value of zonal kinetic energy (K̄) and a significant land‐sea temperature contrast was generally followed by European blocking, whereas a minimum of K′ in other circumstances was not.