bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unsteady wind‐driven ocean currents
Authors: Lighthill M. J. 
Published: February 2007

AbstractThe linear theory of unsteady wind‐driven currents in a horizontally stratified ocean is reviewed in general and applied in detail to the northern part of the Indian Ocean, for several reasons the most suitable area for comparison with observed current changes. The ocean is predicted to respond to the onset of the Southwest Monsoon principally in two modes as far as vertical distribution of current is concerned; to a somewhat lesser extent in the barotropic mode with uniform distribution, and to a somewhat greater extent in the first baroclinic mode with current distribution roughly as in Fig. 1, concentrated predominantly in the uppermost 200 m.Calculations for a zonal distribution of winds, which rather rapidly make a reversal of direction and increase of strength somewhat north of the Equator characteristic of monsoon onset, predict that the barotropic and baroclinic modes are both propagated to the west at comparable speeds of the order of 1 m s−1; the marked contrast here with other oceans (in the comparability of speeds) is given particularly detailed study. When the associated patterns of current flux reach the coast of East Africa, they become concentrated into the Somali current, which flows northward along the coast only during the Northern Hemisphere summer (after monsoon onset) but during that time is comparable in volume flow (about 5 × 107 m3 s−1) to other western boundary currents such as the Gulf Stream.Theory indicates one month (of which two‐thirds is needed for propagation of current patterns and one‐third for their concentration into a boundary current) as the characteristic time scale for formation of the Somali current, in contra‐distinction to the ‘decades’ predicted by the same type of theory for the Gulf Stream (Veronis and Stommel 1956). The flow is calculated to reach 40 per cent of a typical maximum value (observed in August) within a month of monsoon onset (May). The linear theory predicts the current as extending as far north as 6°N, but non‐linear terms are generally found in computational studies (Bryan 1963; Veronis 1966) to bring about some ‘inertial overshoot’ in concentrated boundary currents, which may explain why the current does not in fact separate until about 9°N. In the non‐equatorial oceans, however, non‐linear effects are expected to be much greater.
The influence of vertical variation of zonal wind on the response curve in atmospheric oscillations
Authors: Giwa F. B. A. 
Published: February 2007

AbstractThe Earth is treated as a flat non‐rotating plane across which tidal forces sweep from east to west. It is shown that one effect of zonal wind variation is to replace the constant quantity σ0, (iσ0 = δ/δt) by another quantity σ which varies as the zonal wind. This results in an ‘effective equivalent depth’ whose value varies with the wind.It is also shown that the effect of westerlies is to reduce the values of resonant equivalent depths while easterlies increase them. The inclusion of zonal wind gives a better value of magnification to explain the lunar tide than does the classical theory.
On the representativeness of mean ozone distributions
Authors: Pittock A. B. 
Published: February 2007

AbstractOn the basis of total ozone, Umkehr data and ozone soundings with Mast‐Brewer sondes at Aspendale, it is shown that the systematic effect of selectivity in the days on which Umkehr observations are made may be as large as 10 to 35 per cent of the annual mean content of layers 2 and 3. This selectivity effect varies with time, and is reasonably explained in terms of a correlation between ozone content in the lower stratosphere and cloudiness. Caution with regard to the use of Umkehr‐derived mean ozone distributions in climatological studies is therefore urged, and the need for further research is pointed out. The statistical limitations of mean distributions derived from ozone‐sonde flights are also discussed, with particular reference to quasi‐periodic influences.
The electrostatic forces on charged ice crystals separated by small distances in an electric field
Authors: Latham J. , Saunders C. P. R. 
Published: February 2007

AbstractMeasurements have been made, using a precision balance, of the electrostatic forces exerted on scaled‐up metallic models of cloud droplets and, particularly, ice crystals, as a function of their charges, configurations and proximity to a second model, together with the strength of the electric field E in which they were situated and the angle θ between the direction of the field and the line of centres of the models.It was found that the electrostatic forces on metallic spheres agreed closely with those calculated from the equation of Davis (1964). The forces on irregularly shaped uncharged metallic models of ice crystals were generally larger than those on spheres of equivalent volume to the crystals by a factor γ which was shown to be independent of E and θ and, in general, extremely insensitive to the separation over the range of conditions studied.The measured values of γ, together with the values of the equivalent radius Re of a crystal, deduced directly from its volume, were incorporated into a modified form of Davis' equations which should be useful in computations of the collision efficiencies of uncharged ice crystals.
Ice particles in maritime clouds near Tasmania
Authors: Mossop S. C. , Ono A. , Wishart E. R. 
Published: February 2007

AbstractAn instrumented aircraft was used to sample particles in the upper regions of small supercooled cumulus clouds in maritime air off the Tasmanian coast in May 1968. 114 clouds were studied on nine days, and it was found on average that clouds had a 50 per cent chance of containing ice particles when a summit temperature of about − 8°C was reached. Not only cloud temperature but also cloud width had a profound effect on whether ice particles were found.The cloud summit temperature at which ice particles first reached detectable concentrations in narrow clouds on a particular day was related to the ice nucleus concentration as measured in a cloud chamber, being, in general, highest on days of high ice nucleus concentration. However, in some glaciated clouds ice crystal concentrations of the order of 100 1−1 were found. These were greater by a factor of ∼ 104 than the estimated number of active ice nuclei. The process of multiplication of ice crystals may be associated with the riming of ice particles. Riming was assisted by the presence of large droplets, up to drizzle size, in these clouds. Multiplication of the number of ice crystals by a factor of 10 took place in about 8 minutes.The various stages in the glaciation process are described.
Estimates of kinetic energy over the Indian monsoon trough zone
Authors: Anjaneyulu T. S. S. 
Published: February 2007

AbstractAveraged radiosonde/rawin/pibal data for July and August have been used to study the kinetic energy budget of the troposphere over a quasi‐elliptical area containing the Indian monsoon trough.Incoming and outgoing kinetic energy fluxes have been evaluated. The computations show that the export of kinetic energy from the monsoon ellipse is about 57 × 106 Joules day−1. This export takes place in the upper troposphere, mostly above 300 mb.Production of kinetic energy occurs mainly in the upper troposphere in the southern periphery of the huge quasi‐static South Asiatic ridge in the upper troposphere.
Observations of the eddy fluxes of heat and vapour over the sea
Authors: Warner J. 
Published: February 2007

AbstractThe results are reported of 61 observations of eddy fluxes of heat and vapour at different heights above the sea surface in the trade wind régime off the eastern Australian coast at latitude 16.51°S. The flux gradients were found to be consistent with observed temporal changes in temperature and mixing ratio as the air moved over the sea. The measured fluxes were found to agree with those calculated by bulk aerodynamic methods on the assumption of a 2°C sea‐air temperature difference. The evaporation rate deduced from the vapour flux measurements is about 7 mm day −1.
The geostrophic drag coefficient and the ‘effective’ roughness length
Authors: Fiedler F. , Panofsky H. A. 
Published: February 2007

AbstractAn ‘effective’ roughness length is defined for use over heterogeneous terrain as the roughness length which homogeneous terrain would have to give the correct surface stress over a given area. A method is suggested to compute geostrophic drag coefficient, wind‐contour angle and surface heat flux, given this roughness length, latitude, geostrophic wind speed and insolation or ground‐air temperature differences.
A scheme for kinematic estimate of large‐scale vertical motion with an upper‐air network
Authors: Kung E. C. 
Published: February 2007

AbstractA scheme for kinematic estimate of the vertical p‐velocity ω is designed under the presumption that the profiles should converge to a near zero value at the top of the atmosphere without being so required when a sensitive balance between the analysis scheme and data disposition is achieved. The scheme provides a range of eight degrees of optimization in estimating the divergence through the order of polynomial representation of the wind field, the treatment of missing wind data, and the space smoothing of the divergence.The scheme is applied to synoptic wind observations from the upper‐air network over North America. The computed ω profiles and patterns of vertical motion field obtained from those profiles appear to support the proposition. It is indicated that the field of kinematic ω so computed through the depth of atmosphere will be useful in the study of large‐scale atmospheric dynamics.
The dry‐line of Northern India and its role in cumulonimbus convection
Authors: Weston K. J. 
Published: February 2007

AbstractAn interesting feature of the flow pattern over India during the premonsoon months ‐ a frontal surface separating a shallow, warm moist layer from a deeper, hot, very dry layer ‐ is studied in some detail. In particular, its role in the development of severe cumulonimbus over north‐east India is investigated. Routine observations are insufficient to resolve many of the features of this ‘dry‐line’ and a simple dynamical model is constructed which suggests an interface in the form of a step with a height (Zi*) dependent upon the pressure gradient in the moist air (A = 1/ρ ∂p/∂x), surface drag coefficient (CD) and Coriolis parameter (f), given by the expression Zi* = 4/15 A CD/f2. An extension of the model to include a frictional stress variable with height suggests a circulation within the shallow moist layer which, together with solar heating, would be likely to lead to cumulus and cumulonimbus development near the edge of the moist air; this is observed on satellite photographs.
Flooding of Venice: Phenomenology and prediction of the Adriatic storm surge
Authors: Robinson A. R. , Tomasin A. , Artegiani A. 
Published: February 2007

AbstractSince both observations and theory indicate weak dissipation, a frictionless one‐dimensional model elucidates the dynamics of the surge and is used to hindcast and forecast. Wind over the shallow northern Adriatic dominates the forcing. The relative phases of the astronomical tide, the storm tide, and the preexisting seiche determines flooding. Good real time predictions are now in progress.
A numerical study of the nocturnal atmospheric boundary layer
Authors: Delage Yves 
Published: February 2007

AbstractThe evolution of the structure of the atmospheric boundary layer during the cooling phase of the diurnal cycle is studied with the help of a one‐dimensional numerical model. The model uses a turbulent energy equation for the determination of the eddy exchange coefficients, which also involve the local value of the Monin‐Obukhov length. The surface temperature is prescribed as a function of time and the geostrophic wind is held constant. Results are presented in nondimensional form and cover a wide range of possible values for the external parameters. After several hours of cooling the inversion layer is found to reach a maximum depth, which depends strongly upon the magnitude of the geostrophic wind and, to a lesser extent, on the cooling rate of the ground surface.
The information content of remote measurements of atmospheric temperature by satellite infra‐red radiometry and optimum radiometer configurations
Authors: Peckham G. 
Published: February 2007

AbstractInfra‐red radiometry from an earth satellite is becoming an important technique for the determination of the three‐dimensional temperature structure of the atmosphere on a global scale. In this paper a quantitative expression for the information content of the data from a temperature sounding radiometer is derived. A simple model for the 15 μm CO2 absorption band is used to find radiometer configurations which give maximum information. The spectral bandwidths corresponding to these optimum configurations are considerably broader than those specified in the past for radiometers of this type. The technique of selective chopping in which the radiometer contains absorbing cells filled with CO2 is shown to make a significant increase in the information content.
A field study of the turbulent fluxes of heat, water vapour and momentum at a ‘typical’ agricultural site
Authors: Högström Ulf 
Published: February 2007

AbstractAn extensive set of measurements of turbulent fluxes of sensible heat, water vapour and momentum together with mean profiles of temperature, water vapour and wind speed at a ‘non‐ideal’ agricultural site in southern Sweden have been analysed in terms of the Monin‐Obukhov similarity theory. The fluxes of sensible heat, H, and water vapour, E, have been determined with the eddy correlation method, the accuracy of H + ELv being c. Φ 12% according to comparison with net radiation minus ground heat flux. The momentum flux has been determined from low level wind measurements, with a stability dependent ‘skin friction method’.During stationary conditions with winds from ‘undisturbed’ directions (extensive forest areas more than 3 km distant) and unstable stratification, the data for dimensionless wind and temperature gradients, Φm and ϕh, respectively, are well described by the expressions put forward by Businger et al. (1971), with von Kàrmàn's constant, k = 0.35. The corresponding dimensionless water vapour gradient, Φe, is shown also to follow similarity during these conditions (although exhibiting larger scatter than the two other plots), coinciding with Φh for strong instability but approaching Φm= 1.35 Φh, at neutrality.For stable stratification the dimensionless profiles do not follow similarity in this study, nor do cases with winds from a 700 m distant forest nor non‐stationary cases, as might be expected.A combined energy balance and gradient approach is shown to give good results not only for the ‘ideal’, unstable case but also for non‐stationary conditions and for conditions with winds from the ‘disturbed’ direction. With temperature and humidity differences measured between 0.5 and 1.14 m above ground and with Φe/Φh = 1.35 there is no systematic difference between measured and calculated fluxes, the accuracy in an individual calculated flux being better than 20%. For the stable case it is shown that the flux of sensible heat can be determined with good accuracy with the flux‐gradient method, using data from the 0.5 ‐ 1.14 m layer. The water vapour flux is obtained with good accuracy as a residual term from the energy balance equation.
The temperature structure of the Southern Hemisphere stratosphere August – October 1971
Authors: Harwood R. S. 
Published: February 2007

AbstractThe temperature field in the Southern Hemisphere stratosphere from 100 to 1mb during August to October 1971 is described using observations from the Selective Chopper Radiometer on the Nimbus IV spacecraft.Zonal and monthly mean wind fields for September and October 1971 deduced from these temperatures are presented and the behaviour of the zonal temperature waves with wavenumbers 1, 2 and 3 is discussed. The largest amplitudes of wavenumbers 1 and 2 in the horizontal coincide broadly with the maximum westerlies. The amplitudes of wavenumber 2 are generally smaller at around 20mb than above or below. The amplitudes of both waves are small north of 30°S.Wavenumber 1 exhibits little vertical coherence throughout August and September. In October, however, the slope of the wave with height is much less variable, in spite of a slow eastward movement in early October and a westward movement in late October.Wavenumber 2 travelled eastwards with a fairly uniform rate of approximately 15·5° longitude per day between 15 August and 7 October but less uniformly at other times. Changes in wave amplitude at strato‐pause levels are associated with comparable changes near the tropopause. A maximum of wavenumber 2 amplitude on 26 September 1971 is associated with falling ZPE in the lower stratosphere and rising ZPE in the higher stratosphere. The dominant contribution to the eddy available potential energy is in the lower stratosphere.In the low stratosphere there is an inverse relationship in zonal and eddy available potential energies, rises in one form being associated with falls in the other. This inverse relationship is not well marked in the high stratosphere.
Production of ice crystals by riming in slightly supercooled cumulus
Authors: Mason B. J. 
Published: February 2007

AbstractIt is shown that ice‐crystal concentrations of order 10/litre may be produced in clouds limited to the −8°C level if growing pellets of soft hail release splinters at the rates recently observed in laboratory experiments by Hallett and Mossop (1974) and provided that these splinters can continue to grow in at least three successive thermals over a period of about 1 1/2 hours.
A two‐dimensional mean circulation model for the atmosphere below 80km
Authors: Harwood R. S. , Pyle J. A. 
Published: February 2007

AbstractThe paper sets out the detailed formulation of a numerical model whose purpose is the study of the interactions of dynamics, photochemistry and radiation in the stratosphere and mesosphere. Two integrations of the model for 900 days are described in which many features of the atmosphere are reproduced but with important differences of detail.The dependent variables are zonal means of the relevant meteorological quantities, held as functions of time, latitude and height (log pressure) with a resolution of μ/19 in latitude and 0.5 in pressure scale height.Eddy fluxes of heat and matter are treated by large‐scale diffusion coefficients. This treatment is not applicable to momentum fluxes: these are currently specified from observations made mainly from the selective chopper radiometer on the Nimbus V spacecraft.Radiative coolings due to CO2and O3emission are computed from simplified expressions which are essentially cooling‐to‐space approximations with emissivities obtained by curve‐fitting against the results of more elaborate treatments. Absorption of solar radiation by ozone is obtained from tabulations of absorption against ozone amount traversed. Radiation and latent heat release in the troposphere are specified climatologically.The photochemistry in the integrations described here is the classical ozone scheme but, with a view to investigating possible stratospheric pollution problems, integrations have been performed with the inclusion of reactions involving nitrogen and hydrogen compounds. These will be described in a later paper.
The assignment of Rainfall stations into homogeneous groups: An application of principal component analysis
Authors: Dyer T. G. J. 
Published: February 2007

AbstractThe calculation of eigenvectors has been used to describe annual precipitation totals over an area of large extent. Rotation of the eigenvectors brought about further clarification of the system of recording stations. By noting the eigenvector of most importance to each station, delimitation of an area was made possible. Reduction in records, a necessary prelude to our future work on forecasting models, was obtained by discarding those stations most closely related to eigenvectors whose eigenvalue was less than 0·6.
Low‐level air flow circulation over the Arabian Sea during the summer monsoon as deduced from satellite‐tracked superpressure balloons. Part I—Balloon trajectories
Authors: Cadet Daniel , Ovarlez Henri 
Published: February 2007

AbstractDuring the northern summer of 1975, 45 superpressure constant‐level balloons were released from the Seychelles Islands (4.7°S 55.5°E) for flight at 955mb (500m), 910mb (1000m) and 860mb (1500m) within the tropical boundary layer. The balloons were located by the Random Access Measurement System (RAMS) of the Nimbus‐6 satellite. This spacecraft also operated as a data relay system and collected pressure measurements performed by transducers carried by the balloons. The mean lifetime of the balloons was about 4–5 days, some of them lasting more than 8 days. Low‐level Lagrangian air trajectories in the southwesterly flow over the Arabian Sea are presented. They show the drastic changes in the airflow direction over the southwestern Arabian Sea associated with high or low activity periods of the monsoon over the western coast of India. During the first period of the experiment, the airflow over the southwestern Arabian Sea joins the low‐level jet flowing to the east of the Somali coast. This change, due to intense convective activity near Somalia, can be associated with a break in the monsoon activity. During the second period the air joins the Bay of Bengal branch of the monsoon over the southwest coast of India. Before the end of July a complete reversal of the winds over the Seychelles Islands is observed and some balloons drift towards Madagascar. During the third period the air flow over the Arabian Sea resumes a southwesterly direction and at the beginning of August it seems to join again the Bay of Bengal branch of the monsoon.Thus this experiment shows that low‐level ballooning can be used to map air currents over vast unsurveyed areas of the oceans.
Eddy flux measurements above a pine forest
Authors: Moore C. J. 
Published: February 2007

AbstractEstimates of sensible and latent heat flux measured above a Pinus radiata forest plantation, 11km north of Mt Gambier in South Australia, by eddy‐correlation instrumentation, were found to satisfy the forest energy budget to within 20% provided the mean windspeed was greater than about 2ms−1. In lighter winds these two fluxes were severely underestimated. A study of the higher windspeed data when the forest canopy was externally dry and transpiration the only water loss, gave a Bowen ratio of 0.8 ± 0.1 during the day, with a diurnal trend similar to that for shorter vegetation types. In these conditions the hourly change in canopy heat storage was a significant component of the energy budget. When the canopy was wet from intercepted rainfall, the Bowen ratio was generally less than 0.3 and often negative. Incoming sensible heat and a cooling canopy provided energy for evaporation when the net radiation was low or negative.
Baroclinic instability in the summer mesosphere
Authors: Simmons A. J. 
Published: February 2007

AbstractBaroclinic instability is examined in idealized models of the summer circulation of the upper stratosphere and mesosphere. For all but possibly the fastest rate of thermal dissipation, results suggest the development of disturbances which have zonal wavelengths around 5000 km and which move with westerly phase speeds between 5 and 10 m−1 relative to an easterly maximum. Their periods relative to the ground are close to one day. the vertical scale of perturbation velocities is some 15 km. Temperatures exhibit a shorter vertical scale of about 5 km or less.