Showing papers in "Tellus A in 1955"

Available Potential Energy and the Maintenance of the General Circulation

Abstract: The available potential energy of the atmosphere may be defined as the difference between the total potential energy and the minimum total potential energy which could result from any adiabatic redistribution of mass. It vanishes if the density stratification is horizontal and statically stable everywhere, and is positive otherwise. It is measured approximately by a weighted vertical average of the horizontal variance of temperature. In magnitude it is generally about ten times the total kinetic energy, but less than one per cent of the total potential energy. Under adiabatic flow the sum of the available potential energy and the kinetic energy is conserved, but large increases in available potential energy are usually accompanied by increases in kinetic energy, and therefore involve nonadiabatic effects. Available potential energy may be partitioned into zonal and eddy energy by an analysis of variance of the temperature field. The zonal form may be converted into the eddy form by an eddy-transport of sensible heat toward colder latitudes, while each form may be converted into the corresponding form of kinetic energy. The general circulation is characterized by a conversion of zonal available potential energy, which is generated by low-latitude heating and high-latitude cooling, to eddy available potential energy, to eddy kinetic energy, to zonal kinetic energy. DOI: 10.1111/j.2153-3490.1955.tb01148.x

Some Aspects of the Flow of Stratified Fluids

Abstract: The investigations of Parts I and II are extended to include experiments and theoretical considerations relating to the behavior of fluid systems with continuous gradients of density. The general equation of steady-state motion derived in Part I is integrated to yield the flow of a stratified fluid over an obstacle of finite dimensions. The results indicate a more or less complicated laminar wave motion for obstacles of maximum height below a certain value. Larger barriers cause an overdevelopment of the waves to a point where closed circulations and negative horizontal velocities appear. It is shown that this is accompanied by locally unstable distributions of density and eventual turbulence. If the height of the barrier is further increased, the velocity increases indefinitely in some parts of the field, becoming infinite for an obstacle of a certain size. No steady-state solution exists for larger barriers. The two critical values of the obstacle height depend primarily on the Froude number: If this number exceeds 1/π the solution exists and is stable for all obstacles; for small Froude numbers the barrier must be small if the solution is to exist or be stable. If the obstacle is small enough to permit laminar or moderately turbulent motion, the accompanying experiments verify all important features of the theory with remarkable fidelity. Larger obstacles cause considerable turbulence and blocking effects which propagate upstream, causing alternate maxima (jets) and minima of horizontal velocity in the vertical. DOI: 10.1111/j.2153-3490.1955.tb01171.x

The Use of the Primitive Equations of Motion in Numerical Prediction

Abstract: An obstacle to the use of the primitive hydrodynamical equations for numerical prediction is that the initial wind and pressure fields determined by conventional means give rise to spurious large-amplitude inertio-gravitational oscillations which obscure the meteorologically significant large-scale motions. It is shown how this difficulty may be overcome by the use of a relationship between wind and pressure which enables one to determine these fields in such a manner that the noise motions do not arise. The method is illustrated by a numerically computed example. The wind-pressure relationship is in a sense a generalization of the geostrophic approximation and may be used where the latter approximation is inapplicable, either to determine initial conditions or to derive a set of filtering equations for numerical prediction analogous to the quasi-geostrophic equations. DOI: 10.1111/j.2153-3490.1955.tb01138.x

Some Aspects of the Flow of Stratified Fluids: 111. Continuous Density Gradients

Abstract: The investigations of Parts I and II are extended to include experiments and theoretical considerations relating to the behavior of fluid systems with continuous gradients of density. The general e...

Numerical Weather Map Analysis

Abstract: A method to analyze upper air charts numerically is presented. The analysis is expressed by the height values of the pressure surface in gridpoints. The computed height in a gridpoint is obtained as a weighted mean of height values derived from the surrounding height and wind observations, the forecast height in the point and the corresponding normal height. Nine 500 mb maps are analyzed with the aid of the Swedish computor BESK, six of these consecutive. The size of the grid was 32 × 41 points. The analyses have been compared with two independent conventional analyses. The mean values of the root mean square of the differences between the numerical and the conventional analyses were 26 m and 24 m respectively and 26 m between the two conventional ones. The root mean square of the differences between the observed and analyzed heights was 22 m in the mean. This is roughly what should be expected judging from the existing knowledge about observation errors. Three barotropic forecasts have been computed from the numerical analyses. They are compared with the corresponding numerical forecasts from conventionally analyzed maps. It was not possible to find any significant difference between the goodness of the forecasts based on the numerical analyses and the conventional analyses. DOI: 10.1111/j.2153-3490.1955.tb01170.x

Studies on the General Development of Motion in a Two‐Dimensional, Ideal Fluid

Abstract: The purpose of this paper is to discuss qualitatively certain kinds of asymptotic motion in a two-dimensional, ideal fluid by help of methods of statistical mechanics. It is stressed that the final development of such a fluid cannot be adequately described by use of the ordinary equations of motion, but that a “coarse grain” representation should be used. In this representation, the development is characterized by the forming of a single, large vortex accompanied by a certain non-viscous dissipation. The final equilibrium is probably reached almost explosively after a finite time. Some experiments which are carried out seem to support this result. In the earlier stages of development we may expect to have some kind of a quasi-equilibrium motion. It is attempted to find conditions under which such a motion can exist, by studies of a point-vortex model. DOI: 10.1111/j.2153-3490.1955.tb01147.x

Results of Detailed Synoptic Studies of Squall Lines

Abstract: A system of synoptic analysis on a mesometeorological scale has been developed through the combined use of space and time sections applied to all regular and special stations in an area 500 by 900 mi. in the Central United States. Two periods of development of large thunderstorm areas are analyzed. In both of these periods tornadoes occurred. The synoptic model of a squall line in this scale involves three principal features of the pressure field—the pressure surge, the thunderstorm high and the wake depression. Another feature, called the tornado cyclone, accompanies tornado funnels. Divergence values of 10 to 60 · 10 −5 sec −1 over areas of 100 to 10,000 sq. mi. are measured. The mesosynoptic disturbances greatly influence the situation as viewed on the regular synoptic scale, which is about 10 times the meso-scale, and make conventional analysis hopelessly difficult. DOI: 10.1111/j.2153-3490.1955.tb01181.x

The Water Content of Cumuliform Cloud

Abstract: Measurements have been made of liquid water content throughout many cumuliform clouds. The amount of water present at any level was always less than the adiabatic value, and the ratio of these two quantities decreased with height above cloud base. This ratio was found to be independent of the horizontal extent of the cloud except in the case of very small clouds. The transition between clear air and dense cloud was frequently abrupt. DOI: 10.1111/j.2153-3490.1955.tb01183.x

Hydraulic Jump in a Fluid System of Two Layers

Abstract: The number of conjugate states for the flow of a fluid system of two layers is investigated by means of the momentum principle. The uniqueness of the conjugate state is proved for the cases in which the modified Froude number for either layer is predominantly large. Specific experimental results for three special cases demonstrate the uniqueness of the state downstream from the hydraulic jump, and show that, for a first approximation, the simple analysis provides a means for determining the downstream depths, with smaller errors for lower jumps. DOI: 10.1111/j.2153-3490.1955.tb01172.x

Numerical Forecasting with the Barotropic Model

Abstract: The experiments with numerical forecasting using the barotropic model have been continued and a number of 24, 48 and 72 hour forecasts are presented. The initial data for these forecasts covered an area of about 9,000 by 12,000 km. The results indicate that the boundary influences have been reduced to be unimportant in the centre of the area in the 24-hour forecasts but they may still cause errors in the 72-hour forecasts. In view of the approximations made very good 72-hour forecasts have been obtained in some cases. The most successful one gave a correlation of 0.87 and a relative error of the forecast height changes of 0.58. Most of these extended forecasts should be of definite value in forecasting the weather. Large errors are, however, still obtained in some cases. The neglection of baroclinic process is one of the reasons for these errors but it is quite obvious that the largest errors are of a different nature. Experiments are at present conducted to find the sources of these errors. One line of this research is a general re-analysis of the assumptions made in deriving the barotropic model which is presented in the latter part of this paper. A number of improvements are suggested for further tests. DOI: 10.1111/j.2153-3490.1955.tb01139.x

A Theoretical and Experimental Study of Cellular Convection in Rotating Fluids

Abstract: The stabilizing and cell-shape changing influence of a basic rotation upon thermally produced cellular circulations are developed in a first order, perturbation theory. The theoretical possibility of a special “overstable” oscillating mode in certain fluids under the influence of rotation is recognized. In this preliminary report, the theory obtained for ordinary convection is compared to results obtained in laboratory experiments with rotating cylinders of water, and the existence of the overstable oscillating mode is demonstrated experimentally. Several possible applications of the theoretical results to atmospheric convection are developed by means of numerical examples, including models that are consistent with the observed association of deep convection with cyclonic relative vorticity and the distribution of clouds in regularly spaced clear and cloudy areas. DOI: 10.1111/j.2153-3490.1955.tb01137.x

Air Borne Salts and the Chemical Composition of River Waters

Abstract: The yearly discharge of chloride by rivers in Scandinavia and in the eastern USA is shown on two charts. The isochlor pattern strongly indicates the marine origin of chloride. From the composition of river, lake and ground water compared to rain water it is inferred that the salt in these are to a very great extent air borne. DOI: 10.1111/j.2153-3490.1955.tb01158.x

The Acidity of Scandinavian Precipitation

Abstract: Data on the pH of the total monthly precipitation at stations of a Swedish network for sampling and chemical analysis of precipitation and atmospheric aerosols during the year July 1953—June 1954 are presented and discussed, together with the pH data from the first two months of operation of a larger pan-Scandinavian net. It is found that well-defined regions of acidity and alkalinity relative to the pH of water in equilibrium with atmospheric carbon dioxide exist, and that these regions persist to such an extent that the monthly deviations from the pattern of the annual mean pH at each station are relatively small. The mean pH of the entire network shows a distinct annual cycle, with greatest acidity in winter and greatest alkalinity in late spring. Coastal stations unaffected by local pollution show persistently high acidity, while inland northern stations show equally persistent alkalinity. Some possible reasons for the observed distributions are considered. DOI: 10.1111/j.2153-3490.1955.tb01159.x

On the Electric Field Theory of Magnetic Storms and Aurorae

Abstract: The electric field theory is discussed and further developed. The basic assumption of the theory is that the sun emits beams of rarified ionized gas which are electrically polarized. The electric field of the beam produces a discharge of Malmfors-Block's type around the earth. At the same time the electric field produces a variation in the Cosmic Ray intensity. The theoretical treatment starts by an analysis of the motion of charged particles in the equatorial plane of the earth under the action of the electric field. This phenomenon is supposed to be of basic importance. The motion produces space charge in certain regions. This charge is supposed to leave the equatorial plane along the magnetic lines of force. These two basic assumptions, which are supported by the model experiments, lead to a theory which gives a fairly good picture of magnetic storms and aurorae. In the earlier presentation of the theory the inertia of the beam was neglected. The theory gave a description of the main phase of a storm. The motion in the equatorial plane produces a clockwise ring current at about 7 earth-radii from which a discharge to the auroral zones takes place. In the present paper also the inertia of the beam is taken into account. The result is that a second ring current is produced, which flows anti-clockwise at about 30 earth-radii. This current which seems to account for the initial phase of a storm, should be associated with an “ inner auroral zone ” with a polar distance of 5°—10°. The importance of observing aurorae and magnetic disturbances in this region is stressed. DOI: 10.1111/j.2153-3490.1955.tb01140.x

Current Data on the Chemical Composition of Air and Precipitation

Abstract: Last spring an informal conference on atmospheric chemistry, initiated by Prof. C. G. Rossby, was held at the Meteorological Institute of the University of Stockholm and a note on this conference was published in Tellus (ERIKSSON, 1954). Among other things a new network of collecting stations for precipitation and air samples was discussed; this network was to extend over the whole of Scandinavia and Britain. DOI: 10.1111/j.2153-3490.1955.tb01146.x

The Equatorial Undercurrent in the Light of the Vorticity Equation

Abstract: The Equatorial Undercurrent, recently observed in the central Pacific Ocean by Cromwell, Montgomery, and Stroup, is a narrow eastward current occupying the lower part of the surface layer at the equator. In the present study the Undercurrent, treated as a permanent feature of the oceanic circulation, is found to be consistent with the conservation of absolute cyclonic vorticity in the equatorward flow comprising one segment of the meridional circulation. The continental barriers permit the formation of the longitudinal pressure-gradient component essential for the existence of the Undercurrent. DOI: 10.1111/j.2153-3490.1955.tb01189.x

On the Chemical Climate and its Variation with the Atmospheric Circulation Pattern

Abstract: A study of the chemical composition of monthly precipitation samples from a number of stations in Sweden brings out the existence of significant variations in the relative proportions of chlorides and sodium depending upon the general character of the prevailing circulation. In maritime westerly flows the weight ratio of chloride to sodium decreases eastward to values which lie far below the value characteristic of sea water. In precipitation falling from arctic or polar continental air masses the chloride component is almost completely absent. The highest amounts of chlorides relative to sodium are observed in precipitation from warm and most air masses reaching Sweden from the south or southeast. Significant variations are observed also in the yearly means of the sodium and sulphur deposits depending upon the dominance of maritime or continental air currents. A sketch map of the “average” chloride concentration in European precipitation prepared from miscellaneous older data lends support to the results of the analysis of the monthly data. The separation of the chemical components indicated by this study would seem to be of considerable geochemical interest since it would permit different maritime salts to be deposited in widely separated parts of the continents. It is not inconceivable that a detailed study of the association between different circulation patterns and the corresponding chemical climates might permit us to draw inferences concerning variations in the atmospheric circulation during post-glacial times, e.g. from the data on the chemical stratification in raised bogs now becoming available through the investigations by Mattson and Koutler-Andersson . DOI: 10.1111/j.2153-3490.1955.tb01145.x

Physical Aspects of Rapid Cyclogenesis in the Gulf of Alaska

Abstract: The Gulf of Alaska is often the site of rapid development of large-scale cyclonic activity which can have profound effects on the long-wave pattern over North America in a matter of 24 to 48 hours. During much of the year such cyclogenesis takes place in the presence of a large heat source associated with rapid modification of cold Arctic air masses moving from Alaska out over the warmer sea surface of the Gulf. In order to get some insight into the mechanism of cyclogenesis under these special conditions a case of intense development occurring early in February 1950 has been studied, mainly in terms of the vorticity equation. The effects of barotropic redistribution of vorticity seem to account for much of the development. However, it is found that there exist pronounced fields of divergence and vertical motion, which particularly at the time of most rapid development reflect the influence of heat sources on the circulation. DOI: 10.1111/j.2153-3490.1955.tb01186.x

Tests of the Salt-Nuclei Hypothesis of Rain Formation

Abstract: Atmospheric chlorides in sea-salt nuclei and the chlorides dissolved in shower rainwaters were recently measured in Hawaii. A comparison of these measurements reveals the remarkable fact that the weight of chloride present in a certain number of nuclei in a cubic meter of clear air tends to be equal to the weight of chloride dissolved in an equal number of raindrops in a cubic meter of rainy air. This result is explained as an indication that the raindrops grow on the salt nuclei in some manner which prevents a marked change in the distribution of these nuclei during the drop-growth process. The data presented add new evidence in further support of the salt-nuclei raindrop hypothesis previously proposed by the first author (Woodcock, 1952). DOI: 10.1111/j.2153-3490.1955.tb01182.x

Artificial Snowfall from Mountain Clouds

Abstract: A tentative theory of provoking snowfall from simple orographic clouds is composed, using simplifying assumptions, and it is shown reasonable to suppose that winter snowfall on Central Swedish mountains might be substantially increased by skillful seeding of supercooled mountain clouds. DOI: 10.1111/j.2153-3490.1955.tb01164.x

The Production of Condensation Nuclei by Crystallizing Salt Particles

Abstract: Experiments were conducted to examine the possibility of condensation nuclei being produced by salt droplets when the environmental humidity was lowered sufficiently for crystallization to take place It was found that condensation nuclei were in fact produced when salt particles crystallized, each salt particle producing at least several hundred nuclei It is suggested that these nuclei consisted of minute salt crystals, with mass in the range 10 −18 to 10 −14 g, released from the main mass of salt during crystallization DOI: 101111/j2153-34901955tb01184x

Routine Forecasting with the Barotropic Model

Abstract: Since 1 December 1954 the Royal Swedish Air Force Weather Service has been conducting a series of test forecasts of the 500-mb topography under operational conditions. Forecasts for 24, 48 and 72 hours have been prepared on a routine basis, using the barotropic model and the digital computer BESK. The tests to date have covered the periods 1-16 December 1954, 17 January-25 February 1955 and from 12 April 1955 to the time of writing. It was originally planned to issue 42 sets of three forecasts during the first two periods, but some forecasts failed due to minor breakdowns of the computer (see tables). DOI: 10.1111/j.2153-3490.1955.tb01162.x

Model Experiments on Aurorae and Magnetic Storms

Abstract: Model experiments on Alfven's electric field theory of aurorae and magnetic storms have been performed. The transformation laws from nature to model are considered. It is concluded, that a proper scaling down of every detail in nature is not possible. Only the most significant features are scaled down properly. It is shown, that a mechanism like Alfven's proposed auroral mechanism is very likely to be present in the model. In particular the conception seems to be experimentally confirmed, that space charge accumulated in the discharge region rather than destroy the whole pattern of motion, discharges along the magnetic field lines. DOI: 10.1111/j.2153-3490.1955.tb01141.x

Microdetermination of CO2 in the Air, with Current Data for Scandinavia

Abstract: Krogh and Brandt Rehbergs method for estimation of CO 2 in atmospheric air has been investigated and modified. The method is used for continous investigation of the CO 2 content of the air in Scandinavia. A permanent net of sampling stations has been established, 6 in Sweden, 4 in Finland, 3 in Norway and 2 in Denmark. The samples are taken three times each month. A simple method of taking air samples is described. Current data for November, December 1954 and January 1955 are published. DOI: 10.1111/j.2153-3490.1955.tb01160.x

The Particulate Matter in the Sea as Determined by Means of the Tyndall Meter

Abstract: The Tyndall scattering has been studied for different material occurring in the sea, such as minerogenic matter, calcareous matter, and some marine organisms. It is shown that the scattering is proportional to the total surface of the particles provided that they are larger than 2 μ. This relationship is practically independent of the concentration. The size distribution of particles in marine waters is discussed with a view to estimate the amount of matter removable by sedimentation. DOI: 10.1111/j.2153-3490.1955.tb01155.x

On the Use of Space-Smoothing in Physical Weather Forecasting

Abstract: In section 1–2 a certain space-smoothing operation is defined and its usefulness in solving elliptic equations is demonstrated in the case of a Poisson equation. It leads to solutions in a closed form which possess the numerical simplicity of the ordinary iteration methods, but is converging more rapidly. The reverse operation of unsmoothing is also defined as far as it can be done, and it is mentioned that the combined processes of smoothing and unsmoothing are convenient tools for obtaining a spectral analysis of horizontal scalar fields, and also to remove systematical errors which are made when derivatives are taken as finite differences. In sections 3–6 the application of smoothing is shown in the barotropic forecasting problem. At first a general theorem is proved concerning trajectories of two-dimensional non-divergent flow. It states that if the streamfunction ψ 1 of such a flow can be decomposed into two components ψ 2 , α of which α is individually conserved in the ψ 1 -motion, then the displacements of the fluid particles up to any time can be found by at first displacing in the stationary flow α t=o = const and then adding from the resulting positions the displacements in the flow with the streamfunction ψ 2 . The theorem is first applied to barotropic flow. In this case the first stationary field to displace in is the deviation between the actual and smoothed flow, while the second field to displace in is the smoothed flow. The space-smoothing is next applied to an equation expressing the individual conservation of a quantity s in a two-dimensional non-divergent flow. The Reynolds term belonging to the smoothed equation is studied and found to depend essentially upon the deformation properties of the velocity field. The role of deformation for the net spectral flow of energy in the s -field is studied. The smoothing is in particular applied to the vorticity equation to show how this possibly can be utilized in the integration problem. In sections 7–11 the baroclinic case is considered. In sections 7–8 is shown the fundamental role of deformation for the interchange of potential and kinetic energy. It is found that in the advective model there is direct proportionality between the change in total kinetic energy and total thermal wind energy, and also a direct proportionality between the change in kinetic energy for the vertically mean motion and the thermal wind energy. In section 9 is discussed the possible importance of non-linear interference for the understanding of the creation and local distribution of disturbances in the atmosphere. The integration problem is discussed in sections 10–12. At first an extension of the barotropic displacement rule is given for the vertically mean motion. The trajectory problem for levels other than the mean level is touched in section 12, and a simple non-advective model discussed shortly in section 11. DOI: 10.1111/j.2153-3490.1955.tb01185.x

Distribution of Radioactivity in Pelagic Clays

Abstract: An attempt is made to study the localization of radioelements in different mineral phases of pelagic clay sediments. The results so far obtained indicate that the ionium supported radium is redistributed by diffusion through the interstitial solution and that the authigenic zeolite phillipsite plays an important role as a scavenger of radioelements within the deposit. The mechanism of transfer of radioelements from the ocean to pelagic deposits is discussed, and points of uncertainty in the interpretation of the distribution of gross beta-activity are indicated. DOI: 10.1111/j.2153-3490.1955.tb01156.x

The Spectrum of Large-scale Turbulent Transfer of Momentum and Heat

Abstract: A method for obtaining the spectrum of turbulent transfer of a fluid property is presented based on cross-correlations and Fourier transforms. An application to large-scale eddy transfers of momentum and heat at 850 mb over the southeastern part of the United States shows that most of the transfers may be attributed to disturbances of periods from 0 to 10 days, the most important transfers occurring in the neighborhood of 4 days. Some implications of these results on the problem of the general circulation are discussed. DOI: 10.1111/j.2153-3490.1955.tb01150.x

Upper Air Temperatures over an Antarctic Station: A preliminary note by

Abstract: Typical features of antarctic upper air temperature distributions are demonstrated by means of average values and selected ascents. A great seasonal change in the height of the tropopause is pointed out. Attention is drawn to the remarkable agreement between observed stratospheric temperatures in winter and Dobson's estimated values. The causes for the heating of the stratosphere in late winter and spring are discussed. The difference between the tropospheric temperatures in summer between Arctic and Antarctic is assumed to be due to the different value of the surface albedo. Rough estimates indicate that the absorption in the 9.7 μ band by ozone is of great significance to the observed stratospheric temperature contrast between the two polar regions in winter. DOI: 10.1111/j.2153-3490.1955.tb01142.x