bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind and sea disturbance in the Hebrides
Authors: Champion Donald L.
Published: July 2010

In this note an attempt is made to ascertain the effect of exposure on the disturbance of Hebridean Seas, as produced by winds from different directions and of various forces on the Beaufort Scale.

The term “sea disturbance” is taken in its broadest sense, being the actual state of the surface of the sea as experienced by the observing ships at the time of observation, whether the roughness be due to wind‐waves or swell or a combination of both these elements.

The height of waves is the apparent distance in feet from trough to crest, as estimated by eye observation by the Masters of the observing ships.

A comparison is made between the relative roughness of the Minch and the Sea of the Hebrides; and the apparent effect of the width of the channel, at right angles to the wind, on the height of waves up channel from seaward is shown from data obtained in the Sound of Sleat.
A note on the constancy of horizontal turbulent shearing stress in the lower layers of the atmosphere
Authors: Calder K. L.
Published: July 2010

It may readily be shown, from elementary arguments, that for steady fluid flow in circular tubes or between parallel plates, the shear stress in the direction of the mean motion varies linearly with the distance from the wall. This result is quite independent of the nature and origin of the fluid resistance and in particular is valid if the flow be turbulent. However, it has been proved by Ertel (1933) that in the lower layers of the atmosphere (1 ⩽ z ⩽ 30 m) the horizontal turbulent shearing stress defined by τ = η (z)∂v/∂z where η(z) is the vertical austausch coefficient and ∂v/∂z the vertical gradient of mean velocity, is to a high degree of approximation independent of the height. In view of the importance of this conclusion in atmospheric turbulence theory, and its obvious difference from the first, it has been thought worth while to examine Ertel's treatment in detail. The latter is based on the assumption of the isotropy of the coefficient of vertical turbulent momentum interchange and the final result depends on the relative smallness of the variation of wind direction with height in the surface layers. Complete neglect of this variation, however, requires a wind velocity constant with height, in which case Ertel's result would become trivial. The object of the present note is to show that the assumption of very small but plausible values for the wind direction change with height in the surface layers (of order 10‐6 radians/cm.) suffices to account for the observed wind velocity increase in the lower layers.

It may be concluded that Ertel's analysis is sound. Furthermore it appears on the basis of the theory that the mean wind direction change with height in the lower layers is too small to be observed practically.
On the conservatism of the equivalent potential and the wet‐bulb potential temperatures
Authors: Bleeker W.
Published: July 2010

It is possible to define two “equivalent” temperatures; one by consideration of an isobaric process, called isobaric equivalent temperature (Ti″), and one by consideration of dry and saturated adiabatic processes, called adiabatic equivalent temperature (Ti″). The difference (Ta″‐Ti″) equals the caloric value of an area in a thermodynamic diagram (ABCDin Fig. I).

In the same manner one can define two “wet‐bulb” temperatures; one by consideration of an isobaric process, called isobaric wet‐bulb temperature (Ti′), and one by consideration of dry and saturated adiabatic processes, called adiabatic wet‐bulb temperature (Ta′).

The conservatism of the different equivalent and wet‐bulb temperatures and their potential values is discussed and it is shown that there exists no single equivalent and wet‐bulb temperature which is conservative for all three processes: (1) dry‐adiabatic changes, (2) saturated‐adiabatic changes, and (3) evaporation of rain falling through the air. (See table page 548.)

This leads to the conclusion that the so called wet‐bulb potential temperature should be carefully handled for identification of moving air masses (Hewson 1936). The use of the wet‐bulb potential temperature may give a wrong impression of the gain of water by evaporation, and may lead to erroneous results in estimations of vertical displacements in cases where evaporation occurs.
Photo‐electric measurements of daylight under alpine conditions
Authors: Atkins W. R. G. , Rothschild Miriam
Published: July 2010

Observations have been made with vacuum sodium and with rectifier selenium photo‐electric cells, under opal flashed glass diffusing plates. The former may remain constant save when exposed to intense tropical desert heat and full sunshine for a long period. The latter are far less constant, and in time the curvature of the light‐current relation may increase; this is accompanied by a decrease in blue and green sensitivity so that the response at the long wave end of the spectrum becomes relatively greater. No serious temperature error is introduced when the current from a Ixeston selenium cell is measured with a 10 ohm galvanometer amid snowy surroundings.

Sodium cell measurements at about 0.41 μ give the reflection from the snow as being from 0.74 to 1.19 times the vertical component of mixed daylight. With a selenium cell, sensitive throughout the spectrum, observations ranged from 0.68–0.88. Calculated on the maximum values for mixed daylight the snow reflections were from 0.38–0.74 and from 0.28–0.38 respectively for the sodium and selenium cells.

Under Alpine conditions there is relatively less scattered light from the sky, consequently the sun/sky ratio is greater, in the violet, than in England or Ceylon for the same solar altitude; with the selenium cell the sun/sky ratio is even greater, with a maximum of 9.70, as against 3.55 for the violet, both determinations being made at Scheidegg (2,064 m.) with an absolutely cloudless very dark blue sky, solar altitude 48.1°.

The vertical component of daylight is higher in the violet, under Alpine conditions, than in Ceylon, for low or moderate solar altitudes, but the difference is less at higher solar altitudes. For measurements covering the whole spectrum the Alpine values are also noticeably higher. The physiological effects of Alpine sunlight are due partly to the intensity of the reflected light.
Convergence and divergence in the atmosphere
Authors: Durst C. S.
Published: July 2010

The departure of the actual wind from the geostrophic wind is defined as the agcostrophic wind. The magnitudes of the ageostrophic winds as measured from pilot ballon ascents are examined and found to be in many cases greater than can be explained by the probable errors of measurement. A method is developed of calculating the ageostrophic winds from the measurements of the geostrophic winds and of obtaining the convergence due to these ageostrophic winds.

A case is examined in detail and the convergence is calculated. It is shown that in a region where pressure was falling there was strong convergence near the surface and strong divergence at a level of 5 km.
The formation of depressions of the khamsin type
Authors: Elfandy M. G.
Published: July 2010

A further study has been made of the conditions in spring which produce khamsin conditions in Egypt. Depressions are then formed which travel from west to east to the south of, and roughly parallel to, the north African coast; and, as a rule, while the more vigorous depressions usually originate far to the west of Egypt, shallow depressions form in Egypt or slightly to the west of it. Such depressions are regarded as produced in the manner suggested by Margules—unstable conditions prevailing between intensely heated air to the south and cool air to the north, the moisture of the air playing a non‐essential part. The cold air is due to an anticyclonic distribution in the Mediterranean, while the hot air is drawn northward from the Sudanese low when it suffers large oscillations towards the north. These oscillations are in the main brought about by the travelling depressions, the current bringing the hot air being specially strong when the depressions reach the Red Sea.
Windermere basin: Rainfall, run‐off and storage
Authors: McClean W. N.
Published: July 2010

I. Characteristics of the Area and Scheme of Hydrological Stations.

1. Characteristics of the area; 2. Scheme of hydrological stations; Hydrographical Map and Diagram No. 1 showing correlation of water levels.

II. Rainfall at the Gauges and Methods of Assessing General Rainfall on the Area. 1. Method of the British Rainfall Organisation; 2. Method of “River Flow Records” Organisation; Rainfall Map and Rainfall Tables Nos. 1 and 2.

III. The Run‐off and Storage of Windermere Basin. 1. Run‐off; Table No. 3, Stage‐discharge; 2. The storages of Windermere and of the tributary areas; Table No. 4, Residual storage and lake storage.

IV. Three Examples of Analyses of the Records. 1. The seasonal relationship of Rainfall and Loss derived from the “Vickers” records of 1921, 1922 and 1925; Table No. 5, Monthly rainfall and loss; 2. Rainfall, run‐off and loss during five short periods from May 11 to August 30, 1938, each period ending with dry days; Table No. 6, Comparison of losses and an estimate of average run‐off; 3. A detailed graphical analysis of the flood period July 20 to August 13, 1938, showing the inter‐relationship of rainfall, inflow, outflow and storages throughout the period; Fig. 4, Hydrograph of inflow and outflow; Fig. 5, Running aggregates of rainfall and run‐off.

Comments.—1, Summer Losses; 2, Outflow; 3, General Rainfall; and 4, Records.
On cycles of pressure especially in the neighbourhood of symmetry points
Authors: Pollak L. W.
Published: July 2010

Schuster's criterion and the theory of probabilities have established extraordinarily few meteorological periods. The reason for the failure of periodogram analysis is that it is not applicable to damped oscillations. On the other hand, symmetry points in pressure variations appear to indicate cycles of some persistency and some short series have been analysed by Fuhrich's self‐correlating method, of which a short summary is given. The importance of Brunt's criterion for utility has been shown by applying it to the periods of the motion of the earth's pole.

Fuhrich's criterion for reality is then treated and several features are discussed—independence of the analysis interval, the representation of artificial functions and the case of equal amplitudes. Sixteen analyses of the pressure variations near symmetry points have been summarised, and it is found that a duration including two or three cycles when analysed by Fuhrich's method yields a good representation of the variations with a correlation coefficient exceeding o.8 between the observed and calculated data. The method appears capable of giving at times a forecast of the pressure for 10 to 14 days in winter in central Europe.
Further cartographic studies of drought
Authors: Baldwin‐Wiseman W. R.
Published: July 2010

After stating the need for precise drought data as the basis for the formulation of sound economic schemes of insurance of stock and crops against losses arising from drought, the author outlines methods by which all the requisite essential data can be derived from lengthy meteorological records :‐(I) In precise month‐to‐month detail, with regard to all the major droughts of a review period, by means of isodef charts showing equal percentage deficiency, and (2) in general detail for the whole review period, which is limited only by the availability of an adequate supply of reliable continuous meteorological records, by means of isnagdef charts (showing equal aggregate deficiency); these, being few in number, do not involve so much labour as the production and investigation of isodef charts for each month of the period of review.

Three typical isoagdef charts for S.E. Queensland, covering the pyear period 1886‐1935, together with sample data used in their preparation, are given in illustration of the method.

It is also pointed out that the statistical data and charts are of material value in selecting reserve agistment areas, or in deciding as to the leasehold or freehold values of pastoral and farming properties in recurrent drought areas.
Infra‐red absorption by carbon dioxide, with special reference to atmospheric radiation
Authors: Callendar G. S.
Published: July 2010

Recent additions to our knowledge of the structure of the water vapour spectrum (Elsasser 1940), and the atmospheric transmission of infra‐red radiation (Adel 1939), have tended to emphasise the importance of atmospheric radiation as a fundamental factor in meteorological processes.

Normally the greater part of this radiation comes from the large quantities of water vapour present in the air, but there are certain important regions of the atmosphere where the amount of water vapour is extremely small and where a large part of the radiation comes from the carbon dioxide always present.

It is probable that measurements of carbon dioxide absorption and radiation have been more numerous and extensive than for most other gases, but these observational data are scattered through the scientific literature of many decades and in several languages; also they are usually presented in a form which cannot be applied to atmospheric conditions and which requires much coordination and simplification before it can be used for the calculation of energy exchanges. In the following pages these measurements are reviewed and the different sets of observations are compared with the aid of a simple function which will give the absorption by any quantity of CO2 in the different wave bands.
A combined laboratory and numerical study of fully developed steady baroclinic waves in a cylindrical annulus
Authors: James I. N. , Jonas P. R. , Farnell L.
Published: July 2010

A description is given of a numerical model which has been used to simulate the steady baroclinic waves which may be observed in a fluid rotating about a vertical axis and subjected to a radial temperature gradient. the model is designed to provide accurate simulations of the observed flow without recourse to parametrization of small eddies. the model is verified by comparing the results of integrations with observed flows; many of the differences between the simulated and observed flows may be ascribed to the limited resolution of the model. the numerical model is used to provide data on the non‐linear interactions between different scales of motion present in the steady flows. It is demonstrated that the predominant non‐linear interaction, in the numerical model, involving the sidebands of the dominant wave is an interaction with the first harmonic of the dominant wave; this contrasts with an interaction with the long wave which was suggested by earlier workers. Experimental evidence is advanced to show that the sidebands may be enhanced by weak asymmetrical forcing and this sensitivity has been verified through the results the further numerical integrations.
The climate at maximum entropy production by Meridional atmospheric and oceanic heat fluxes
Authors: Grassl Hartmut
Published: July 2010

In a zonally‐average energy balance climate model (principal features as with Paltridge 1975) with the four unknowns ‐ surface temperature T, cloud amount N, total meridional heat fluxes within the ocean and the atmosphere Om+Am, and total vertical heat flux LE+CH, the maximum entropy production by meridional heat fluxes is used as a constraint to solve the system for the four unknowns in all 10 boxes of the model. Since the solution at maximum entropy production by meridional heat fluxes agrees quite well with present mean conditions, this maximum principle is used as a working hypothesis for climate sensitivity studies avoiding the use of fixed cloud amount and meridional heat fluxes. the resulting sensitivities partly agree and disagree with those of similar energy balance climate models. Disagreement is particularly high if an ice‐albedo feed‐back is included. the feed‐back is strongly reduced because of opposing effects of cloud amount in high latitudes.
A mesoscale semi‐implicit numerical model
Authors: Seaman Nelson L. , Anthes Richard A.
Published: July 2010

A three‐dimensional semi‐implicit mesoscale numerical model based on the Navier‐Stokes equations is described and tested. Numerical techniques for achieving numerical stability with long time steps are discussed. In simulating flow over mountains the model accurately reproduces the results of an explicit model. Low vertical resolution causes moderate damping of the orographically forced responses, but adjustment rates are not seriously affected. the model is stable with time steps six times those of a similar explicit model and its computational efficiency is about three times greater.

A cross‐section version is used to examine the response characteristics. With four layers in the vertical, the phase speeds of external gravity waves with wavelengths 8 Δx to 30 Δx are slowed to 50% to 85% of the analytic phase speeds, respectively. Even so, simulations with eight and sixteen layers show that the semi‐implicit model reproduces the features of simulations with the explicit model and has comparable mass and energy conservation characteristics.

Adjustment rates of the mass and momentum fields towards a steady state are studied for mountain wave and jet stream circulations. Despite the reduced gravity wave phase speeds, root‐mean‐square error calculations show very little difference between the semi‐implicit and explicit models. This is attributed to the fact that most of the adjustment is effected by relatively slow internal modes which are not greatly slowed in the semi‐implicit model. the verification that the semi‐implicit model produces adjustments between mass and momentum fields about as well as an explicit model is an important step in ensuring that the semi‐implicit technique can be successfully applied to mesoscale forecasting.
Estimating return values of environmental parameters
Authors: Carter D. J. T. , Challenor P. G.
Published: July 2010

Return values of an environmental parameter, such as wind speed or wave height, are frequently estimated from an extreme value analysis of observed annual maxima assuming that the parameter is identically distributed throughout the year. Environmental data generally have considerable within‐year variation. an indication of the error in return values resulting from this assumption is obtained by analysing monthly maxima of wave height and wind speed data. It appears that the assumption leads to an underestimation of return values.
Synoptic‐scale forcing of coastal lows: Forced double kelvin waves in the atmosphere
Authors: Bannon Peter R.
Published: July 2010

Gill (1977) has interpreted the coastal lows of southern Africa as atmospheric coastal Kelvin waves. the lows are trapped horizontally next to the steep slopes of the Great Central Plateau by Coriolis forces and vertically by a low‐level inversion. This hypothesis is tested and extended using two linear models.

A barotropic primitive‐equation analysis on an equatorial beta‐plane models the generation of these waves. an impermeable eastern boundary is included to reflect the blocking of the low‐level flow below the coastal inversion by the orography. Results of the linear analysis suggest that the formation of the coastal lows may be explained in terms of the scattering of eastward‐propagating synoptic‐scale disturbances at the meridional boundary. the boundary response is structurally similar to a Kelvin wave. At the frequencies of interest, no zonally propagating Rossby waves are excited. Further, in contrast to the case of a western boundary, the equatorial response is negligible.

A two‐layer, f‐plane model enables the dynamics of the layer of fluid below the interior inversion to be incorporated. At the period of the synoptic forcing (six days), the boundary response is a maximum along the escarpment and decays exponentially from it. the e‐folding distance is slightly less than the appropriate Rossby radius of deformation. These results, together with observations, suggest that the coastal low and its companion low over the interior may be interpreted as forced internal double Kelvin waves.

The possible application of these results to foehn (chinook) winds and lee cyclogenesis is mentioned.
An observational study of primary and secondary billows in the free atmosphere
Authors: James P. K. , Browning K. A.
Published: July 2010

A case study is presented showing the kinematic structure of a train of large‐amplitude billows associated with a strongly sheared layer of high static stability in the upper troposphere. the observations were obtained using a high‐power microwave Doppler radar with a range resolution of 30 m. A beamwidth resolution almost as good as this was achieved at the ranges of interest using a 25 m paraboloid aerial. the resulting detailed measurements revealed the kinematic structure of secondary billows of wavelength 350m growing on the back of primary billows of wavelength 4.2km. the secondary billows were regions of moderate turbulence, the outer scale of which was small compared with the radar resoluton. Streamers of cirrus ice particles were present in the region of interest and these served as tracers showing how the billows perturbed the flow over a considerable depth above and below the primary billows.
Aircraft measurements of solar and infrared radiation and the microphysics of cirrus cloud
Authors: Paltridge G. W. , Platt C. M. R.
Published: July 2010

Profiles of the upward and downward solar and infrared flux densities and of the downward beam radiance at 11 μm are reported for six cirrus cloud decks over Socorro, New Mexico. the data are used to derive empirical relations between vertical ice‐water path (obtained from simultaneously measured particlesize distributions) and solar absorptance, solar albedo, broad‐band infrared flux emittance and the 11μm beam emittance. As a guide, for ice‐water paths of about 75 gm−2 where the infrared emittances are approaching unity, the solar albedo is about 0.4, the solar absorptance is of the order of 0.15 and the geometrical thicknesses are between 1.5 and 2.5 km. Within an individual cloud there is little variation of particle size distribution with height, but the geometrically thicker clouds favour large particles. No icecrystal shape information is available, but the observed relation between albedo and emittance suggests that theoretical treatment of cirrus ice particles as ‘cylinders’ is better than treatment as ‘equivalent spheres’.
A field study of radiation fog in meppen, West Germany
Authors: Choularton T. W. , Fullarton G. , Latham J. , Mill C. S. , Smith M. H. , Stromberg I. M.
Published: July 2010

A field study of the microphysical properties of a radiation fog was conducted in Meppen, West Germany, on 17 February 1978. It is described and interpreted in terms of the prevailing meteorological conditions.

Pronounced periodic fluctuations in liquid water content (intervals ∼70s) were observed at times in the radiation fog. It is suggested that these were a result of convective motions in the form of Bénard cells. the drop size distributions were broad, containing drops of radii up to 25 μm. Calculations indicate that these larger drops cannot be produced by radiative cooling from the fog top. It is argued that these large drops may have been produced either by large supersaturation fluctuations near the fog top, resulting from downwards entrainment of warmer moister air, or by convective motions causing a fraction of the larger drops to make several excursions to the radiative cooling region near the fog top. the radiation fog was observed to clear when cloud was advected over the site. It is suggested that this was due mainly to eddy diffusion and gravitational sedimentation of drops to ground, after radiative cooling from the fog top had been severely curtailed by the cloud layer.
Estimating solar radiation income from ‘bright’ sunshine records
Authors: Revfeim K. J. A.
Published: July 2010

The potential of Campbell‐Stokes records of sunshine hours has not been exploited. Since 1924 various forms of the Angstrom equation have been used to estimate mean daily global radiation from the mean daily fraction of possible ‘bright’ sunshine. the Angstrom equation gives an equal radiation weight to all hours of sunshine and consequently the relationship is weak. As measured by the Campbell‐Stokes instrument ‘bright’ sunshine may be measured and recorded within individual hours from the hour markings on the card. Most observers routinely add up the sunshine measured for individual hours to give the daily total of sunshine hours.

Adding monthly mean fractions of ‘bright’ sunshine within each hour, weighted by the cosine of the mid‐hour zenith angle and a mid‐hour atmospheric transmission, gives standardized radiation hours which are quite precisely related to mean daily direct radiation. Making assumptions about the effects of atmospheric scattering and absorption allows calculation of diffuse radiation income as well. Thus a proper use of the information content of sunshine records can give good estimates of direct, diffuse and global radiation. These may be used in the absence of other radiation records or for the direct/diffuse partitioning of radiation as recorded by solarimeters or pyrheliometers.
Apparent absence of the quasi‐biennial oscillation in sea level pressure in the south indian and south atlantic oceans
Authors: Dyer T. G. J.
Published: July 2010

Monthly mean sea level pressure over the Indian and South Atlantic oceans can be represented adequately by a few uncorrelated pressure fields derived using principal component analysis. Apart from a major, and general, field both zonal and meridional compensatory pressure systems appear to occur over this region of the Southern Hemisphere (approximately 10°W to 60°E and 20.5°S to 40.5°S). the time series of these fields were submitted to spectral analyses, and apart from an oscillation centred at 20 months in the third component there was no evidence suggesting the existence of the quasi‐biennial oscillation in the pressure data. This result conflicts with those for rainfall over southern Africa, and sea level pressure and sea surface temperature around Australia.
Generation of coastal lows by synoptic‐scale waves
Authors: Anh Nguyen Ngoc , Gill A. E.
Published: July 2010

A model is presented in which eastward propagating synoptic waves interact with a meridional escarpment. It is shown that, under suitable conditions, trapped waves are produced at the escarpment, the dominant wave being poleward propagating. This model is intended to represent the generation of coastally trapped disturbances like those found in southern Africa.
Thermodynamic dissipation and the global climate system
Authors: Paltridge Garth W.
Published: July 2010

The principle of maximum thermodynamic dissipation (minimum entropy exchange) suggested by Paltridge with reference to the earth‐atmosphere climate system concerns selection of a particular steady state from a spectrum of possible steady states of a system whose boundary properties are functions of internal behaviour. the physical basis of such selection is suggested in terms of the system's non‐linear response to natural fluctuations. the explanation is sufficiently general that the principle presumably applies to a broad class of non‐linear (i.e. multiple steady state) systems.

With reference to the specific climate model of the earlier papers, it is pointed out that the regional or zonal ‘boxes’ of that model must be regarded as strictly zero‐dimensional; so that the earlier discussion involving a concept of upper boundary temperature was incorrect. the model is used to generate the zonalaverage climates of perpetual January and perpetual July. This leads to a determination of the seasonal change zonal‐average time constants of the climate system, which range from a minimum of about nine months at 30°N latitude to a maximum of about five years at 50°S latitude.
Further application of the theory of stochastic perturbation of deterministic systems to simple climate models
Authors: Benzi Roberto , Pandolfo Joseph P. , Sutera Alfonso
Published: July 2010

A previous paper (Sutera 1981) considered the effect of stochastic perturbation on the long‐term behaviour of a highly idealized energy‐balanced model of zero spatial dimension. It was shown that, in the presence of stochastic perturbations, transitions between different stable equilibria, or ‘climates’, of the model become possible. the expected time for a stochastically perturbed model solution to leave the attractor basin of a stable equilibrium is called the ‘exit time’. the ‘exit time’ must be considered as an important new parameter characterizing model behaviour.

In order to illustrate the methodology described in Sutera (1981) we apply these general considerations to a spatially one‐dimensional Budyko‐Sellers model. In fact, using two different heat capacity formulations, we test the sensitivity of such a model to stochastic perturbations. an interesting physical result, common to both versions of the model, is that, if the noise level is confined below a certain value, then the solution corresponding to an ‘ice‐covered earth’ will never be experienced.
Buoyancy effects on the turbulent transport processes in the lower atmosphere
Authors: Ueda Hiromasa , Mitsumoto Shigeki , Komori Satoru
Published: July 2010

Buoyancy effects on the turbulent transport processes in the atmospheric boundary layer above the surface layer have been investigated. Direct measurement of heat flux and wind and temperature profiles was made by sonic anemometers and the continuous ascending and descending operation of a kitoon, to determine the eddy diffusivity of heat and the local Richardson number. the present results, along with those of a parallel study on the stratified turbulence structure in a laboratory experiment were examined by comparison with previous results in the surface layer. Under stable conditions significantly different stability dependence in the surface layer and the layer above it is recognized; in the layer above the surface layer the eddy diffusivity of heat. KH, along with the ratio of the eddy diffusivities of heat and momentum, KH/KM, decrease remarkably with the gradient Richardson number, Ri, reaching a value of KH/KHO = 0.01 at Ri = 1 and under strongly stable conditions the ratio KH/KHO varies as (Ri)−2, while in the surface layer the ratio KH/KM remains constant or decreases slightly. This contrasting behaviour in the surface layer and the layer above is presumed due to the modification of the turbulence structure and so the turbulent transport processes by the presence of the ground, as indicated by Gibson & Launder (1978). Under unstable conditions the ground effect is not so significant that results of the present observation along with the laboratory experiment may be applied to the entire region of the atmosphere. the ratios of KH/KHO and KH/KM increase as the stratification shifts from neutral to weakly unstable conditions. the ratio KH/KM takes a peak value of about 3 at Ri ∼ −0.2 and then falls gradually with increasing instability and attains the value of unity at Ri ∼ −10.0. This fact together with the increase of Km/KMO with increasing [Ri] results in a constant value of the ratio KH/KHO equal to about 6.0.
Kolmogorov constants for structure functions in turbulent shear flows
Authors: Antonia R. A. , Chambers A. J. , Satyaprakash B. R.
Published: July 2010

Kolmogorov constants in the inertial sub‐range expressions for the second‐order velocity structure function and the one‐dimensional spectrum of the streamwise velocity fluctuation have been estimated for both laboratory turbulent free shear flows and the atmospheric surface layer. A unique relation between the spectral constant α1, and the structure function constant is expected when the Reynolds number is infinitely large. the relation is found to be inadequate in both the laboratory and the atmosphere where values of α1, obtained via the structure function are, on average, smaller by about 15% than spectral estimates of α1. For the present atmospheric data the average estimate, from the second‐order structure function data, of α1 is about 0.54 in reasonable agreement with an estimate from the skewness of the structure function. the additive constant in the r3 law is approximately zero for the laboratory data.
Radiation conditions for the lateral boundaries of limited‐area numerical models
Authors: Miller M. J. , Thorpe A. J.
Published: July 2010

Attention is focused on the use of numerical formulations of the Sommerfeld radiation condition δΦ/δt + cδΦ/δx = 0 as a lateral boundary condition. This numerical boundary condition which originally used the leap frog scheme (Orlanski 1976) is shown to be made more accurate by the use of the upstream method. In this form it is tested in a two‐dimensional model of a density current and is stable. the boundary becomes effectively transparent to incident disturbances, even under the severe test of allowing the density current head to propagate upstream and through the boundary, thus changing initial inflow to strong outflow.

An analysis is presented of various extrapolation and radiation boundary conditions, involving calculation of their accuracy for waves and more general solutions. the leading terms in the truncation error are compared, and for general disturbances some have second order accuracy, while for solutions of the wave equation, it is shown that the radiation condition is third order. It can be made fourth order, for both leapfrog and upstream differencing, by the use of an extrapolation formula to give a better numerical estimate for c. This condition derives its greater accuracy from the use of values at seven (space and time) gridpoints, in contrast to the original scheme which used four, and standard extrapolation formulae which use, at most, three points.
Radar and raingauge observations of orographic rain over south Wales
Authors: Hill F. F. , Browning K. A. , Bader M. J.
Published: July 2010

Eight detailed case studies are summarized to clarify the structure and mechanism of orographically enhanced frontal rain over hills of modest height. the observations were obtained as part of a field project in south Wales in which data from a 3‐dimensionally scanning radar were combined with autographic raingauge data. the results show that the generation of orographic rain is consistent with Bergeron's seeder‐feeder mechanism, according to which raindrops from upper‐level (seeder) clouds wash out small droplets within low‐level (feeder) clouds formed over the hills. It is demonstrated that the orographic enhancement is strongly influenced by the low‐level wind speed. the largest enhancement of rainfall occurred in association with strong winds, and also high relative humidity, below 2km. the radar showed that over 80% of the enhancement occurred in the lowest 1.5 km above the hills. It also showed that the periods of enhanced rainfall were associated with the passage of pre‐existing areas of precipitation. the precise value of the upwind rainfall rate was rather unimportant in influencing the orographic increment provided the rainfall rate upwind exceeded about 0.5mmh−1, These findings are compared with the results of theoretical calculations based upon the washout model of Bader and Roach.
The effect of cirrus of varying optical depth on the extraterrestrial net radiative flux
Authors: Platt C. M. R.
Published: July 2010

A simple model has been used to investigate the effects on the net radiation at the top of the atmosphere of a change in cirrus optical depth at various latitudes. the model employs relationships between the cloud solar albedo and the cloud infrared emittance which are based on theoretical considerations and also supported by recent observations. the model is used to predict the change in net radiant flux at the top of the atmosphere with a unit change in cloud amount and with a change in cloud emittance. Generally, tropical and mid‐latitude cirrus clouds cause a warming effect until the optical depths become large. For optical depths greater than about 12 for tropical cirrus, and about 5 for mid‐latitude cirrus, an increase in cloud will cause a cooling tendency.

The importance of specifying the correct albedo‐emittance relationships is emphasized by a comparison of the solar reflection properties of cirrus using two different theoretical models; one model envisages cirrus as composed of ice (or water) spheres and the other as composed of long ice cylinders. Recent observations tend to support the cylinder model.
Inertial capture of particles by obstacles in form of disks and stellar crystals
Authors: Prodi F. , Caporaloni M. , Santachiara G. , Tampieri F.
Published: July 2010

The process of cloud droplet capture by falling plate‐like ice crystals has been reproduced in the laboratory by impacting streams of monodisperse spherical particles (2 < R < 22 μm) onto disk‐shaped and star‐shaped fixed obstacles in the range between viscous and potential flow. the particles collected on the upwind surface of the obstacles are counted using an optical microscope. A collection efficiency is determined for the different planar shapes under the specific experimental conditions.

For the disk shape the results have been compared with those from the potential and viscous flow theories. They show that collection efficiencies computed from the potential flow theory are not representative of the actual efficiencies. Comparison with the viscous flow theory shows that in the range 0.8 < Nstk < 2 the theory fits the experimental data well. Non‐zero efficiencies have been found for Nstk lower than the theoretical cut‐off, while for Nstk < 4 the collection efficiencies are lower than theoretically predicted. This difference has been interpreted in terms of the hydrodynamic interactions between the particle and the obstacle.

For the planar shapes, the collection efficiencies regularly increase with the Stokes number and depend on the surface area distribution in the models. the values of the collection efficiencies are always higher than those of the disks of equal area.
The interaction between an internal gravity wave and the planetary boundary layer. Part I: The linear analysis
Authors: Einaudi F. , Finnigan J. J.
Published: July 2010

Using the data obtained at the Boulder Atmospheric Observatory (BAO), we have analysed a gravity wave‐turbulence event, which occurred on 18 September 1978. A 300m tower was equipped with various sensors at eight different levels and provided information on the vertical structure of the disturbance to an unprecedented degree. These data were complemented by measurements from a nearby microbarograph network which allowed us to determine the period and horizontal wavelength of the disturbance. It was the rather accurate determination of the period of the gravity wave and its near monochromaticity that made possible the utilization of the phase average operator in separating the periodic and turbulent components of the field variables. In this paper, we concentrate on describing the wave field and on comparing it with a linear model, deferring to a second paper the discussion of the effect of the periodic disturbance on the coexisting turbulence. We show that a linear model adequately describes the observed parameters (period and horizontal wavelength) and the vertical structure of the fluctuations in the temperature and horizontal and vertical velocity components.
Measurements of the flow structure around Ailsa Craig, a steep, three‐dimensional, isolated hill
Authors: Jenkins G. J. , Mason P. J. , Moores W. H. , Sykes R. I.
Published: July 2010

Observations of neutral flow around an isolated island are presented. the island has a fairly smooth shape with slopes of about 30° and a horizontal section which is roughly elliptical with axis ratio 1.5. the flow field 4 m above the surface shows a speed‐up around the sides and over the summit, with reverse flow on the lee slope. Measurements with an instrumented aircraft, of the mean flow in the wake of the island reveal a single very powerful trailing vortex, with axis close to the upstream wind direction. There are indications that the single vortex was a consequence of the asymmetry caused by the island's elliptical shape. Measurements of fluctuating quantities with a tethered balloon system show marked changes in the components of the turbulence energy in the flow around the side of the hill.
Kinematic analysis of the large‐scale mean state during phases I, II and III of GATE
Authors: Vincent Dayton G.
Published: July 2010

An analysis is presented of the large‐scale mean state kinematic properties of the wind field based on observed rawinsonde data taken over western Africa and the eastern Atlantic during Phases I, II, and III of GATE. Variables presented are wind direction and speed, zonal wind component, temporal standard deviation of the zonal wind component, vertical p‐velocity and relative vorticity. Wind direction and speed and temporal standard deviation of zonal wind were subjectively analysed at the surface, 850mb, 700mb, 500mb, 400mb, 300mb, 250mb, 200mb, 150mb and 100mb. Grid point data were extracted from analyzed charts at increments of 2° latitude and longitude and used to compute vertical motion and vorticity. Resultant analyses are examined to determine kinematic properties common to all three phases of GATE, trends in these properties from one phase to the next, and differences between properties over western Africa (land) and the eastern Atlantic (water). Features of the mean state are compared with results obtained by other investigators for such phenomena as large‐scale westward propagating wave disturbances, low‐level cyclonic vortices, satellite‐derived precipitation and cloud clusters associated with squall lines.
Mechanistic limitations to the release of latent heat during the natural and artificial glaciation of deep convective clouds
Authors: Lamb Dennis , Hallett John , Sax R. I.
Published: July 2010

The latent heat thermodynamically available in the supercooled water of deep convective clouds is released at rates governed by the glaciation mechanism, presumed here to involve primary nucleation, capture nucleation of rain by small ice particles and secondary ice production (rime‐splintering hypothesis). A simple microphysical model of the glaciation shows the importance of regenerative feed‐back on the evolution of ice when the primary nucleation and regenerative processes proceed simultaneously, leading to insensitivity to the primary ice nucleus concentration. This allows rapid glaciation and heat release to occur naturally in clouds exhibiting a broad supercooled drop size spectrum.

New observational data and model results of artificially induced glaciation are consistent with the idea that the primary microphysical role of seeding is the creation of many small ice particles which substitute for the secondary ice splinters of naturally induced glaciation. the aerodynamic capture of the splinters by the supercooled rain leads to the formation of new graupel particles and the rapid release of fusional heat, shown by calculation to dominate the heat release mechanisms. With a seeding agent acting in the contact mode the small (cloud drop) end of the spectrum is required, since Brownian scavenging of the nuclei by the few large rain drops is inefficient. the quantitative analysis of these glaciation concepts also demonstrates that realistic seeding under conditions conducive to ice multiplication could increase materially the rate of heat release and offer opportunities for artificially invigorating the dynamic structure of a cloud if glaciation is induced to occur within a relatively narrow ‘time window’ for seeding.
Water vapour absorption in the 3.5‐4.2μm atmospheric window
Authors: Barton I. J.
Published: July 2010

An analysis of Nimbus 5 Selective Chopper Radiometer data supports the measurements of Bignell (1970) and Watkins et al. (1979) which both show considerable ‘e‐type’ absorption by water vapour in the 3.5‐4.2 μm atmospheric window.
Microphysical properties of supercooled cumulus clouds in which an ice particle multiplication process operated
Authors: Mossop S. C.
Published: July 2010

Microphysical measurements made in small wintertime cumuli on five days in June 1981 are described. On all days an ice crystal multiplication process was active. the main conditions for the operation of the Hallett‐Mossop multiplication process were fulfilled—namely, the presence of both graupel particles and drops ≃ 24m̈m in diameter in the cloud zone between the ‐3 and ‐8°C levels. Shortcomings of the available theoretical models prevented any worth‐while comparisons between their predictions and the observed cloud behaviour. In these clouds, large drops (⩾300 m̈m diameter) grew by coalescence and appeared in a concentration of ≃0.1 per litre at about the same time as ice particles (graupel) of similar size. the drops reached a concentration of ≃5 per litre and then disappeared while the graupel continued to increase to concentrations of ≃10 per litre. There is evidence to indicate that the concentration of ice particles increased exponentially with time, being multiplied by a factor of 10 every 10 min between the values of 1 and 100 per litre. It is likely that the original ice nuclei activated were more numerous than the generally accepted average concentration of about 10m−3 at ‐10°C.
Initialization using laplace transforms
Authors: Lynch By Peter
Published: July 2010

The initialization of limited area models is complicated by the difficulty of determining the linear normal modes and of allowing for general boundary conditions. A new method of initialization is devised, which does not require explicit knowledge of the normal modes. the method is based on a filtering procedure which uses a modified inverse Laplace transform. the efficacy of the method is demonstrated by application to a one‐dimensional model, and the rationale for application to a general forecasting model is discussed. the method is closely related to the nonlinear normal mode method of initialization.
The calculation of stratospheric air parcel trajectories using satellite data
Authors: Austin John , Tuck A. F.
Published: July 2010

Air parcel trajectories are calculated for the mid‐stratosphere using data from the stratospheric sounding unit on board NOAA‐6. In the analysis method all the orbital data for each 24 h period are combined into a single global analysis. Three trajectory methods are used‐isobaric, isentropic and quasi‐isentropic‐and the results are compared and contrasted. For the quasi‐isentropic method a radiation model is used, via the thermodynamic equation, to imply cross‐isentrope flow at regular intervals along the trajectory. the positions of the parcels, computed using the three methods, are found in general to be in good agreement when projected on to a horizontal plane. However, the altitude varies according to the trajectory method used and changes by about 1 km along a quiescent trajectory and as much as 2 km along a disturbed trajectory, during a 10‐day period. This has important implications in the study of chemistry along parcel trajectories during disturbed periods since the temperature‐ and pressure‐dependent reactions will proceed at different rates under the different assumptions. Also, the high lapse rate in the vertical mixing ratio profile of ozone implies that the detailed photochemistry will depend critically on the height of the air parcel.

Further, potential vorticity and potential temperature are used as quasi‐conservative Lagrangian tracers, to try to determine which trajectory method is most realistic. For the quiescent period studied (June 1979 in the southern hemisphere) the isobaric and isentropic methods produced similar results throughout the ten days of the trajectory but the quasi‐isentropic method was clearly superior. A disturbed period was also studied (the February 1979 stratospheric warming), but the results from the trajectories studied were consistent with the Lagrangian conservation laws for only 6 days, at most. These results illustrate the need for caution, particularly with regard to sensitivity to initial horizontal position, in using trajectories calculated for disturbed periods.