bluuebunny/crossref_metadata_2025_split huggingface dataset:
The dynamics of stratospheric warmings generated by a general circulation model of the troposphere and stratosphere
Authors: O'Neill A. 
Published: February 2007

AbstractA feature of integrations with a general circulation model of the troposphere and stratosphere was that events were spontaneously produced closely resembling stratospheric sudden warmings. One example is examined in detail by means of momentum, heat and energy budget calculations, after a description of its main synoptic developments. Brief reference is made to two other model‐simulated warmings. It is argued that Matsuno's simplest idealization of stratospheric sudden warmings does not provide an adequate description of these events. The appearance of equatorward eddy momentum fluxes was found to have played a central role in their evolution. A mechanism is proposed by means of which such a flux reversal might occur in the stratosphere. The model warmings were apparently instigated by planetary‐scale changes in the troposphere, rather than by internal hydrodynamic instability.
On the entropy balance of the earth‐atmosphere system
Authors: Nicolis By G. , Nicolis C. 
Published: February 2007

AbstractThe entropy balance associated with a Budyko‐Sellers climatic model is developed. It is shown that different regimes, associated with decreasing, as well as increasing values of entropy production (which measures the rate of dissipation in the system) in the course of time are possible. This immediately poses the problem of stability of steady states of the climatic system. An explicit criterion of climatic stability is thus derived, which is expressed in terms of thermodynamic quantities related to excess entropy production. The results are illustrated on simple cases involving diffusive energy transport. A comparison with Paltridge's minimum entropy exchange principle is also attempted.
A model of the quasi‐biennial oscillation on an equatorial beta‐plane
Authors: Plumb R. Alan , Bell Robert C. 
Published: February 2007

AbstractAn equatorial beta‐plane model of equatorial wave‐mean flow interaction in the lower stratosphere is described. Kelvin and mixed Rossby‐gravity waves generated by a specified forcing on the lower boundary radiate upward through the model domain where they are subject to thermal and mechanical dissipation. The wave‐mean flow feedback problem is solved on the assumption that changes in the zonal mean state occur slowly enough for the wave field to be steady, locally in time.A quasi‐biennial oscillation develops in the model with a period of about 1000 days. A novel feature of this model is the incorporation of latitudinal structure and of thermal and meridional wind components of the oscillation. The influence of the meridional circulation on the structure of the zonal wind oscillation is discussed in some detail.
A Simple Model for the Synoptic Analysis of Cold Fronts
Authors: Browning K. A. , Monk G. A. 
Published: February 2007

AbstractA split cold front model, with an over‐running upper front (or humidity front) ahead of a surface front (or humidity front), is shown to provide a useful representation of the principal characteristics of many katafronts. The use of such a model leads to more consistent analyses, especially of cloud and rain, than are achieved using unmodified classical concepts.
Units For Column Amounts of Ozone and Other Atmospheric Gases
Authors: Basher Reid E. 
Published: February 2007

AbstractThis paper points out the unsatisfactory character of the units for expressing column amounts of atmospheric ozone (i.e., total ozone), it examines a number of alternative units suitable for column amounts of not only ozone but any gas in any planetary atmosphere, and it argues the case for using the SI derived unit of mole per square metre.
A data assimilation experiment and the global circulation during the FGGE special observing periods
Authors: Lyne W. H. , Swinbank R. , Birch N. T. 
Published: February 2007

AbstractDuring the two Special Observing Periods of the First GARP Global Experiment (FGGE) a data assimilation experiment was conducted at the UK Meteorological Office. Throughout the period of the experiment observational data were assimilated dynamically into a numerical forecast model at the four main synoptic hours of each day.In the first part of the paper, the method of data assimilation is briefly described. Following that, a description is given of the zonally averaged atmospheric circulation, as diagnosed from our analyses. The results of this study are in generally good agreement with those found by previous workers.
Profile relationships in the superadiabatic surface layer
Authors: Webb E. K. 
Published: February 2007

AbstractBy analyses of profile data for the superadiabatic surface layer from the Johns Hopkins group (U.S.A.) in 1953 and from Swinbank and co‐workers (Australia) in 1962–64, mean profile forms which give a close representation of the data are adopted.For the profiles of U, θ, and r the gradients initially pass from z−1 dependence through a smooth transition at z/|L| ⋍ 0.03 towards z−4/3 dependence. The corresponding ‘1m4/3’ form adopted is broadly similar to the O'KEYPS, Businger‐Dyer, and BWIB (Kansas) U profiles, but its change of gradient with increasing instability is a little more rapid than for these three. This form is maintained, with KH/KM remaining constant, up to z/|L| ⋍ 0.27.For larger z/|L|, KH/KM increases, |∂θ/|z and |∂r/∂z| falling relatively more rapidly and ∂U/∂ relaively less rapidly. Intermittent near‐vanishing of |∂θ/∂z| is observed over intervals of a few minutes. Approaching z/|L| values around 1 (the data limit) the profiles, while not tightly defined by the data, are suitably represented by a continuing z−4/3 dependence with KH /Km nearly twice its near‐neutral value.The analyses and results are independent of the von Kármán constants ku kθ and kr (a possible dependence on the ratio kθ/ku in relation to the stability parameter being avoided by use of a modified from of Obukhov's lenght). The do not provide values of these three constants and the adopted forms remain unaffected by any future assignment of these values.
A variational theorem for circulation integrals applied to inviscid symmetric flows with variable stability and shear
Authors: Emanuel Kerry A. 
Published: February 2007

AbstractConditional symmetric instability has recently been proposed as an explanation for rain and cloud bands which are imbedded in larger regions of precipitation associated with extratropical cyclones (Bennetts and Hoskins 1979). In their paper, Bennetts and Hoskins discuss the use of a circulation integral for calculating growth rates of the instability. The purpose of this note is to demonstrate that the growth rates so calculated will be exact eigenvalues of the associated linear perturbation equations provided that these growth rates are maximized with respect to the path of integration. A simple application is presented and compared with results of a numerical experiment using the Bennetts and Hoskins model. The circulation integral method appears to be a simple way of assessing the potential for conditional symmetric instability in the atmosphere.
Aircraft observations of marine stratocumulus during JASIN
Authors: Slingo A. , Nicholls S. , Schmetz J. 
Published: February 2007

AbstractObservations of marine stratocumulus obtained by three research aircraft during the JASIN experiment are presented. Detailed measurements were made of the thermodynamic, cloud physics and radiation fields. These showed an essentially well‐mixed boundary layer with cloud liquid water contents close to their adiabatic values. The mean drop radius increased steadily towards cloud top, where evidence of inhomogeneous mixing was found. Both the longwave and shortwave radiative components of the cloud layer energy budget were measured. Good agreement was obtained between the observations and several radiation schemes and in particular the measured cloud shortwave absorption was close to the theoretical values. At midday, the net longwave cooling of the cloud layer was found to be approximately compensated by the shortwave warming, although the regions of net warming and cooling were separated vertically, thereby promoting convection within the cloud. The wider implications of these results to studies of stratiform cloud are discussed.
An internal symmetric computational instability
Authors: Hollingsworth A. , Kållberg P. , Renner V. , Burridge D. M. 
Published: February 2007

AbstractA rapidly growing instability in energy‐enstrophy conserving finite difference forms of the primitive equations is described. The instability is unusual in that it is purely internal. It arises because the linearized forms of the equations do not conserve momentum. The modifications necessary to control the instability are discussed.
Simulation of the atmospheric response to soil moisture anomalies over Europe
Authors: Rowntree P. R. , Bolton J. A. 
Published: February 2007

AbstractPositive and negative anomalies in the initial soil moisture over central Europe were introduced in turn into integrations of a global model of the July atmosphere. The results show that by modifying the partitioning of the turbulent fluxes such anomalies can have major effects on the modelled rainfall, humidity and temperature during the following 50 days over the anomaly area and that the anomalies can propagate into adjacent land areas. Similar results were obtained with a lower‐resolution version of the model.The effects on rainfall were already important on day 3 of the integration over the anomaly area and on day 6 over parts of Scandinavia outside the anomaly area.The experiment was repeated with a version of the model in which the prevailing flow over Europe was less weak with increased moist westerly flow from the Atlantic. In this case the dry anomaly persisted for only about 20 days before it became too weak to affect the evaporation significantly.
Laboratory studies of the charging of soft‐hail during ice crystal interactions
Authors: Jayaratne E. R. , Saunders C. P. R. , Hallett J. 
Published: February 2007

AbstractA laboratory investigation of electric charge transfer during the impact of vapour‐grown ice crystals and supercooled water droplets upon a simulated soft‐hailstone target has shown that the magnitude of the charge transferred to the riming surface when crystals separate from it is a function of temperature, crystal dimension, relative velocity, liquid water content, and impurity content of the water droplets and hence the impurity content of the riming target. The sign of the charge transfer depends on temperature, liquid water content and droplet and rime impurity content.In the absence of crystals, no charge transfer was detected during riming. In the absence of supercooled water droplets, crystals impacting at 10ms1 on an evaporating rime target produced a small negative charge on the rime of less than − 0.25fC per separating crystal. When the target surface grew by vapour diffusion it gained a small positive charge during such interactions. Much larger charges and completely different charge transfer behaviour was noted during riming. The target became positively charged at high liquid water contents and temperatures above a critical value, but negatively charged at lower temperatures or with lower liquid water contents. The critical sign reversal temperature at a liquid water content of 1 gm−3 was about − 20°C. At − 10°C with a liquid water content of 2gm−3, a 125 μm crystal impacting at 3ms−1 charged the target by +101C upon separation. The charge transfer increased sharply with impact speed and crystal size. Warming the positively charging rime to cause it to evaporate failed to reverse the sign of the charge transfer. Experiments with impurities showed that the sign reversal temperature increased if the droplets contained contaminants at concentrations found in cloud water.It is suggested that there are two distinct charge transfer processes during crystal interactions with an ice target, the dominant one requiring the presence of supercooled water droplets. Careful control and knowledge of the microphysical properties of the clouds used in these experimental simulations has permitted an examination of charge transfer under many of the conditions used in previous studies. The results provide an understanding of the differences and a reconciliation between some of the previously disparate findings in terms of the two distinct charge transfer regimes.
The effects of horizontal diffusion on baroclinic development in a spectral model
Authors: Macvean M. K. 
Published: February 2007

AbstractLinear and non‐linear effects on baroclinic development of linear horizontal diffusion of the form K▽2q, where q is an integer and k, in general, a constant, are investigated using a spectral model and a climatological wintertime northern hemisphere basic state.An eigenvalue approach shows the greatest linear sensitivity to the diffusion to be in the high zonal wavenumbers (m > 12) which, in the absence of diffusion or with the more scale‐selective formulations (large q), are more unstable than the intermediate wavenumbers (m = 7–9). The ▽4 diffusion with a decay time scale of 6 h on the shortest retained scale, which has traditionally been used in our model, is shown to affect significantly the linear stability of almost all wavenumbers, whereas the more scale‐selective formulations have only a very small effect on m < 12.Without dissipation, integrations exhibit grossly physically unrealistic features after about nine days even with very high resolution, indicating the crucial role played by dissipation in non‐linear baroclinic development. Non‐linear integrations with dissipation show great sensitivity to the formulation used. Typically about three times more energy is converted from potential to kinetic with a ▽6 than with a ▽4 diffusion having a similar decay time scale on the smallest retained spatial scale. It appears that as the dissipation time scale on the large spatial scales is increased while retaining sufficiently short time scales near the truncation limit to prevent the accumulation of energy there, so the amount of potential to kinetic energy conversion approaches a limiting value equal to about five times the energy conversion with the ▽4 diffusion. In the limiting case the amount of energy lost to dissipation is equivalent to about 45% of that converted from potential to kinetic energy, again emphasizing the crucial role played by dissipation.It is found that if the decay time scale on the short spatial scales is too long then the integrations exhibit large truncation dependency. This provides a criterion for judging the suitability of a particular choice of dissipation, which might have quite general applicability.
Spectral representation of the vertical structure of turbulence in the convective boundary layer
Authors: Berkowicz R. , Prahm L. P. 
Published: February 2007

AbstractA model is presented of the vertical structure of turbulence in the convective boundary layer. The model is based on representation of the fluctuating velocity components by trigonometric orthogonal functions. The vertical velocity component is represented by a sine and the horizontal by a cosine expansion. The sine representation of the w component ensures that w = 0 at z = 0. The expansion coefficients are uncorrelated if the sine functions are eigenfunctions of the vertical correlation function.A simple form, based on the inertial sub‐range, is adapted for the energy spectrum.Constant parameters of the model are evaluated from the surface layer measurements of the wind velocity variances, and it is shown that the model agrees with the measured vertical structure of variances through the whole boundary layer.
Some simple analytical solutions to the problem of forced equatorial long waves
Authors: Heckley W. A. , Gill A. E. 
Published: February 2007

AbstractThis paper describes some simple time‐dependent analytical solutions to the problem of a sudden ‘switch‐on’ of heating localized about the equator. The equations used are the shallow water equations on the β plane under the ‘long wave approximation’. It is shown that, with a reasonable amount of dissipation, it can take several days for a steady state response to be established. In the early stages, the circulation differs considerably from that of the steady state. The long time scale for the adjustment process has implications in numerical weather prediction since it implies that if the initial data are not in balance with the model's forcing, it may take several days for a balance to be established, by which time the quasi‐stationary tropical flow may have been irrevocably changed.
On stochastic perturbation of simple blocking models
Authors: Benzi Roberto , Hansen Anthony R. , Sutera Alfonso 
Published: February 2007

AbstractIn this paper we discuss some problems connected with the stochastic dynamics generated by the effect of small random perturbations acting on prototype equations governing large‐scale flows. We focus on the features of the process which occur when the main instability is the result of orographic forcing on simple barotropic motion. In particular, we study a three‐mode truncation of barotropic flow over topography when a stochastic white forcing acts on the system. We found analytical estimates of the exit times from the attraction domains of the steady solutions of the model. The exit times were found to range widely as a function of the zonal forcing.In addition, we included a representation of the large‐scale forcing in terms of a red process. We found that as a function of the variance of the perturbing process and the model's parameters, the bimodal nature of the barotropic model can be obscured.
Towards the monitoring and prediction of north‐east Brazil droughts
Authors: Hastenrath Stefan , Wu Ming‐Chin , Chu Pao‐Shin 
Published: February 2007

AbstractThe purpose of this study is to develop a method of forecasting the March‐April and March‐September rainfall in northern north‐east Brazil. Earlier diagnostic research has documented that the droughts of northern north‐east Brazil are heralded by identifiable departures in the quasi‐permanent circulation systems in the tropical Atlantic sector.Dynamically plausible predictor candidates are selected on the basis of the aforementioned diagnostic results and simple correlation. These include sea surface temperature, pressure and wind in key areas of the tropical Atlantic, pre‐season rainfall in north‐east Brazil and northern South America, and an index of the Southern Oscillation. Candidates for the period 1921–30 plus 1946–56 are entered into a stepwise multiple regression scheme. This yields regression equations for each of the months October through February preceding the March/April peak of the rainy season. For January, these explain about 65% of the rainfall variance.The regression equations are then used to produce forecasts for each of the years 1958 through 1972, in terms of a seasonal rainfall index for the northern Nordeste as a whole. The forecasts account for 41–62% of the variance of observed rainfall, with which they are thus highly correlated. Unusually abrupt seasonal evolution of general circulation anomalies, as well as noise in predictors may contribute to forecast failures. However, the severe 1958 drought was eminently predictable from the methodology developed here. The most important predictors are atmospheric and oceanic parameters in key areas of the tropical Atlantic; the timely acquisition of such observations consistent with a reference climatology being essential for the implementation of the prediction method on an operational basis.
A radiation boundary condition for multi‐dimensional flows
Authors: Raymond William H. , Kuo H. L. 
Published: February 2007

AbstractA radiation boundary condition designed for use at open or computational boundaries with multidimensional flows is formulated and tested on three two‐dimensional problems. Two of the problems simulate a simple wave propagation and possess analytic solutions so that the effectiveness of the boundary condition can be measured in terms of a r.m.s. error. A more subjective analysis must be used in the final problem, which is the simulation of an atmospheric cold front. The proposed radiation boundary condition utilizes the phase velocity projection in each coordinate direction or equivalently a weighted configuration of the phase velocities. This approach greatly reduces the sensitivity on the spatial derivative normally displayed in the phase velocity calculations. Comparisons are made against the traditionally used Sommerfeld radiation condition and various numerical schemes are tested. For multi‐dimensional flows the proposed radiation boundary condition is found to give significant improvement over the traditional Sommerfeld radiation condition.
A numerical model investigation of the storm surge of 31 January and 1 February 1953 in the North Sea
Authors: Flather Roger A. 
Published: February 2007

AbstractTwo numerical finite difference models, developed for operational surge prediction, are used to simulate the great storm surge of 31 January/1 February 1953 in the North Sea. The required meteorological forcing is derived from an analysis of observed atmospheric pressures.Both models reproduce the surges observed at the coast with good accuracy. A discussion of the surge generation and development is presented on the basis of the model solutions. Estimates of the work done by the wind stress and by gradients of atmospheric pressure indicate that the surge was generated within the North Sea primarily by the wind. Much of the surge generation took place in a few areas of limited extent, where the strongest winds and strong currents occurred in a favourable combination.