bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ozone perturbation experiments in a two‐dimensional circulation model
Authors: Haigh J. D. , Pyle J. A. 
Published: February 2007

AbstractA two‐dimensional circulation model is used to investigate the possible perturbation of the ozone layer by CO2 and chlorofluorocarbons (CFC's). Four experiments are described: a control run; a run including increasing levels of CO2 up to 625 ppm; a run including a source of chlorine compounds from the CFCs; and a run to investigate the coupled perturbation due to both CO2 and the CFC's. The dynamical and chemical behaviour of the runs is described.The control run reaffirms the conclusions of earlier experiments with this model (Harwood and Pyle 1980) that the summer stratopause is very close to radiative equilibrium. The strength of the polar night jet is also discussed.The perturbations due to CO2 and the CFC's have opposite effects on ozone with increasing CO2 producing an increase in column ozone which is greatest in high latitudes.The coupled perturbation is not a linear combination of the two individual experiments. This is investigated in terms of the photochemical scheme used. The reduced temperature dependence of the ozone concentration when chlorine compounds play a significant role is shown to produce the non‐linearity.
The Morning Glory: An extraordinary atmospheric undular bore
Authors: Smith Roger K. , Roff Greg , Crook Norman 
Published: February 2007

AbstractObservations made during an expedition in October 1980 to study ‘morning glory’ wind squalls in the Gulf of Carpentaria region of northern Australia are described. During a ten day period in Burketown, North Queensland, six squalls were documented on consecutive mornings (8–13 October), including two moving from the south, an apparently unusual direction. The unique data gathered from the latter confirm that these have the same character as their north‐easterly counterparts; that is, they are undular bores. The origin of southerly glories remains uncertain, but, at least, in some cases, appears to be linked with the northeast advance of a frontal trough across central Australia. While the data are equivocal, it seems possible that the motion of the front into the developing nocturnal inversion could generate waves, or hydraulic‐type disturbances, which run along the inversion layer, ahead of the front, as proposed by Tepper (1950). The efficacy of such a mechanism is demonstrated by a simple laboratory experiment.Evidence is presented which suggests that morning glory type events occur elsewhere in the world, sometimes as precursors to cold fronts. Observations in the Gulf of Carpentaria region show that they are effective triggers of deep convection when they advance into air with a sufficient degree of conditional instability.
Solar variability, weather and climate: An update
Authors: Barrie Csiro A. Pittock 
Published: February 2007

AbstractThis review substantially updates the earlier review by Pittock (1978) in the light of more than 100 papers published in the last few years. Note is made of an encouraging trend towards the study of physical mechanisms, as well as important new evidence on the short, intermediate, and longer time‐scales which must be taken into account. Notable amongst these are increasing doubts and controversy surrounding the claimed effects of solar magnetic field sector boundary crossings, new studies and ideas concerning correlations on the decadal time‐scales, and the availability of long series of proxy data on solar activity and climatic fluctuations on a thousand‐year time‐scale. The review concludes with a discussion of the controversy over solar variability, weather and climate as an example of scientific decision‐making in the face of inadequate data and other uncertainties, with reference to the statistical ideas of Type I and Type II errors and Weinberg's concept of a ‘republic of trans‐science’.
Some features of the structure of the tropical tropopause
Authors: Atticks M. G. , Robinson G. D. 
Published: February 2007

AbstractStatistics of the minimum saturation humidity mixing ratio are extracted from 2 500 radiosonde ascents in the tropics (10°N to 10°S) and in the region of the Asian summer monsoon. Two periods of approximately 20 days are examined, one in the northern winter and one in the northern summer. The relation of the observations to an hypothesis, proposed by A. W. Brewer in 1949, of mass exchange between troposphere and stratosphere is briefly discussed.
The steady, linear response of the stratosphere to tropospheric forcing
Authors: Karoly David J. , Hoskins Brian J. 
Published: February 2007

AbstractA linearized, steady‐state, 15–level numerical model is used to study the stationary planetary wave response of the stratosphere to thermal and orographic forcing in the troposphere. Zonally symmetric basic states representative of northern hemisphere winter and summer conditions are used. Solutions for each zonal wave‐number are considered separately. Eliassen‐Palm cross‐sections are used as a diagnostic of wave propagation.First, several simple thermal and orographic forcing distributions are used in the winter basic state. The response in the stratosphere is sensitive to changes in the zonal wind but its structure is insensitive to the forcing mechanism and to the dissipation used in the model. For representative northern hemisphere thermal and orographic forcing, solutions in winter agree well with observations except for wavenumber one, which has too small an amplitude and an incorrect structure.The solutions for wavenumbers one and two in the troposphere have small differences from those obtained using a similar 5–level model described by us earlier. For higher wavenumbers, the 15–level and 5–level solutions in the troposphere converge, as these waves are trapped in the troposphere.For the summer basic state, the planetary wave response has large amplitude in the troposphere only. It is necessary to use vorticity forcing in the upper troposphere to give a solution with a phase variation similar to that observed in summer.
A spectral model of the zonally averaged circulation in the middle atmosphere
Authors: Volland Hans 
Published: February 2007

AbstractMost papers dealing with numerical simulation of the zonally averaged atmospheric circulation start with the solar heat input as an external source that drives the circulation. In this paper, the reverse way will be followed. First, the meridional structure of the wave modes with zonal wavenumber m = 0 within the atmospheric waveguide is determined from tidal theory. Then the height structure of these modes is calculated numerically applying a heat source configuration per mode by trial and error such that the observed global zonal wind and temperature fields between 0 and 100km can be reproduced reasonably well.Observations during solstice and equinox conditions outside the equatorial regions can be grossly simulated by the four wave modes of lowest degree. These wave modes are driven by two heat sources, one centred near 3 km, the other near 50 km altitude. The symmetric component of the lower atmospheric heat source is strongly enhanced when compared with the expected direct solar heat input into the atmosphere, indicating the dominant influence of latent heat in redistributing solar energy. The antisymmetric component of the middle atmospheric heat source is enhanced by a factor of more than two when compared with direct solar heating. Here, dissipated energy of planetary waves may be the origin of the additional source. The absence of that source leads to wind and temperature changes within the middle atmosphere which strongly resemble the situation during a minor stratospheric warming.
Nonlinear mountain waves in two and three spatial dimensions
Authors: Peltier W. R. , Clark T. L. 
Published: February 2007

AbstractA three‐dimensional, time‐dependent, anelastic model is employed to simulate the evolution of nonlinear internal waves which are forced by stratified flow over isolated topography. Both two‐dimensional and three‐dimensional flows are considered. In the former case the discussion focusses upon the development of the wave field induced by a uniform mean flow with constant stability. The full three‐dimensional model is employed to study the nonlinear development of atmospheric ‘ship‐waves’ which have recently been observed in satellite photographs to the lee of oceanic islands in the Norwegian and Barents seas. The model is able to reproduce the characteristics of the observed wave patterns rather nicely when it is initialized with vertical profiles of wind and stability obtained through upper air ascents from stations located on the islands themselves. Detailed comparisons of the output of the nonlinear model with the results of three‐dimensional linear steady state theory are also provided. As is found to be the case in two‐dimensional analyses, linear theory may considerably underestimate the forced wave amplitude for symmetric topographic excitation.
Solutions to a model of a front forced by deformation
Authors: Cullen M. J. P. 
Published: February 2007

AbstractA semi‐geostrophic deformation model of a front studied by B. J. Hoskins and F. P. Bretherton is studied further. It is shown that a unique solution of the Lagrangian conservation laws governing the motion can still be constructed after the front has formed. This solution shows that separate upper and lower fronts propagate into the fluid, and are separated by a region where only smooth variations occur. Finite difference solutions of the primitive equations are also given which converge to a front with the correct mean slope and maximum long‐front velocity but without the correct variation in slope through the depth of the fluid.
The scavenging of particles by electrified drops: Radar echo intensification following lightning
Authors: Barker E. , Bicknell J. A. , Griffiths R. F. , Latham J. , Verma T. S. 
Published: February 2007

AbstractA series of laboratory experiments were performed in an effort to improve our understanding of the physics of the echo‐intensification phenomenon, in which the radar reflectivity of a region of a thundercloud increases rapidly immediately following the occurrence of lightning within it. Measurements were made of the charges, q, deposited on falling water drops when they engage in direct interactions with positive corona streamers in a uniform electric field, E, just above the limit for propagation, E0. As the drop radius increased from 12 to 950/μm, q increased from about 10−13 to about 10−10C; and q increased as E was raised above E0. These measurements yielded an estimate of 30μm and 108, respectively, for the radius of, and the number of elementary charges contained in, the tip of a propagating streamer at a pressure of one atmosphere.The collection efficiencies of drops in the radius range 40 to 120 μm carrying charges appropriate to the direct interaction process, for uncharged droplets of radius around 12 μm, were found to be about four times the non‐electrical values. It was concluded that this enhancement in collection resulted largely from dipole rather than coulomb forces. A simple analysis indicates that reported echo‐intensification observations cannot be explained in terms of these enhanced collection efficiencies, but could possibly be a consequence of the greatly enhanced velocities (and hence growth rates) of drops of radius ∼ 100 μm highly charged by direct interaction with corona streamers in the intense electric fields of a thundercloud.
Turbulent dispersion from an elevated line source: Markov chain simulations of concentration and flux profiles
Authors: Legg B. J. 
Published: February 2007

AbstractA Markov chain model that simulates the trajectories of fluid particles in turbulent flow is described. It incorporates fluctuations in vertical and streamwise velocity, and can be used with velocities that have a skewed probability distribution. The model is used to estimate the distribution of heat downwind from an elevated line source in the boundary layer above a rough surface, and the results are compared with those from a wind tunnel experiment. The simplest model, with fluctuations in vertical velocity only, underestimates the plume depth by 4% to 22% at various distances downwind, and underestimates the rise in the mean height of the plume by 1·5 mm in 25·5 mm. The inclusion of streamwise velocity fluctuations increases the vertical plume width by 6% and also improves the prediction of the mean height of the plume. The model also gives profiles of streamwise eddy flux of heat u'θ that agree closely with those measured. Skewed velocity distributions can be included in the model, but in the boundary layer above a rough surface Gaussian velocity distributions are quite adequate.
An observational study of the anvil of a winter maritime cumulonimbus cloud
Authors: Bennetts D. A. , Ouldridge M. 
Published: February 2007

AbstractThis paper reports on microphysical and dynamical measurements made from an aircraft in the anvil of a winter cumulonimbus cloud which grew in maritime air near the United Kingdom. The anvil had a well‐organized structure, with ice content in the central region exceeding 1 gm−3. The ice appeared to be distributed uniformly over the size range of crystals, with half the total mass contained in particles larger than 1 mm. The total particle concentration may have exceeded 1501−1 in places. A widespread supersaturation of typically 10% with respect to ice ensured that the ice crystals continued to grow by deposition. The microphysical and dynamical structures of the anvil are shown to be closely linked, and semi‐quantitative explanations are given for the evolution of particle size distributions in terms of deposition and gravitational settling.
Tropical cyclogenesis: A comparative study of two depressions in the northwest of Australia
Authors: Foster I. J. , Lyons T. J. 
Published: February 2007

AbstractA comparative study of two cloud clusters in the north‐west of Australia highlights synoptic influences on tropical cyclogenesis. Although both clusters developed over land in the same region, the large‐scale flow was conducive to the subsequent development of one cluster into tropical cyclone Enid and suppressed the development of the other cluster. The non‐developing low was under strong upper easterlies from an upper tropospheric ridge. An upper trough in the subtropical westerlies later split the ridge, bringing light and divergent upper winds over the low‐level monsoonal trough. This facilitated the development and intensification of a low‐level cyclonic circulation, tropical cyclone Enid.
Simulation of hydraulic jumps in the presence of rotation and mountains
Authors: Parrett C. A. , Cullen M. J. P. 
Published: February 2007

AbstractNumerical solutions of the shallow water equations in one dimension are presented. The formation and evolution of hydraulic jumps are predicted with a simple centred finite difference model and with a model utilizing Glimm's method. Glimm's method is a special one‐dimensional method, which has been proved to converge to the physically relevant solution of a number of equations in the presence of discontinuities. The solution from it is used to check the finite difference method.Cases presented include examples of jumps produced in the presence of rotation, and a variety of jumps forced by flow over orography. It is shown that a conservative finite difference method, with the addition of artificial diffusion, converges to the correct solution for almost all cases. However, the use of multipoint filters gives poor results. At low resolution, the errors in modelling the flow induced by the orography are larger than errors caused by not resolving the shape of the orography.
Mesospheric ozone — theory and observation
Authors: Vaughan G. 
Published: February 2007

AbstractThe predictions of a radiative‐photochemical model are compared with observations of the diurnal variation of mesospheric ozone obtained from rocket‐borne experiments. Temperature observations from the SAMS instrument on the Nimbus‐7 satellite are used to define the basic atmospheric state. Good agreement is found, provided that low water vapour abundances are accepted, together with slow rate coefficients for the recombination of odd hydrogen species. Sensitivity tests performed with the model show that uncertainties in the ozone calculations arise chiefly from uncertainties in water vapour concentrations, solar irradiance, O2 absorption cross‐sections and certain rate coefficients, and that the sensitivity of ozone to these parameters may be markedly different at different times of day, especially above 60 km. The model's representation of the ozone variation around dawn is also used to estimate the error caused by the assumption of spherical uniformity when deriving ozone concentrations from solar occultation experiments.
Transport of water vapour in a stratosphere‐troposphere general circulation model. II: Trajectories
Authors: Allam R. J. , Tuck A. F. 
Published: February 2007

AbstractTrajectories have been computed during a 10‐day period in January for approximately zonal rings of parcels in the upper troposphere and lower stratosphere of a general circulation model. Time histories of ozone and water vapour highlight the central role of the subtropical jet streams as mixing agents for tropospheric and stratospheric air. There is some evidence of inertial oscillations in the upper tropical troposphere, particularly at longitudes where there is no large‐scale convergence or divergence. The western tropical Pacific from about 150°E to 160°W appeared to be a centre of large‐scale motion, with pronounced upper tropospheric descent below about 10 km and ascent at and above 16 km, apparently linked to large‐scale ascent in the middle and high latitude stratosphere up to 30 km.
Interannual moisture variations near the surface of the tropical Pacific Ocean
Authors: Weare Bryan C. 
Published: February 2007

AbstractInterannual variations of surface specific humidity, surface latent heat flux out of the ocean and surface layer moisture divergence are analysed for the period 1957–76. Special emphasis is given to understanding the relationship between variations in these quantities and the El Niño/Southern Oscillation phenomenon. The analyses include eigenvectors, composites and time series. The results indicate spatially coherent temporally persistent variations, some of which are clearly linked to El Nino. The composite and time series analyses both suggest that during El Niño in the eastern Pacific moisture convergence changes precede those of sea surface temperature by one or more months, which in turn precede those of surface latent heat flux by a further one or more months. A hypothesis is suggested to relate these changes to variations of the South Pacific high.
Gradient distributions and flux profile relations above a rough forest
Authors: Lindroth A. 
Published: February 2007

AbstractTemperature and humidity gradients above a sparse pine forest (400 trees per hectare) in Sweden were measured using movable sensors. Under daytime conditions the gradients were remarkably small with a median value of −0.007 K m−1 for the potential temperature gradient and −3.8 × 10−6m−1 for the specific humidity gradient. The range of inferred Bowen ratios was −0.3 to 1.8 with a median value of 0.72.The starting point for the paper was a discrepancy between energy balance/Bowen ratio (EBBR) and water balance estimates of the forest evapotranspiration.There was no sign that insufficient fetch influenced the results but some evidence was obtained to suggest that the lowest measurement level, about one mean distance between trees above the mean tree level, was situated in a region of inhomogeneity in the heat and water flux field. Excluding this level from the calculations increased the inferred Bowen ratio by 30%. This change is not sufficient to account for the difference in estimates of evapotranspiration by the two methods. It is, however, concluded that the discrepancy could be explained by rather small, quite realistic errors in the gradient measurements.
On the dynamics of tropical cyclone structural changes
Authors: Holland Greg. J. , Merrill Robert T. 
Published: February 2007

AbstractTropical cyclone structural change is separated into three modes: intensity, strength and size. The possible physical mechanisms behind these three modes are examined using observations in the Australian/south‐west Pacific region and an axisymmetric diagnostic model.We propose that, though dependent on moist convection and other internal processes, the ultimate intensity, strength or size of a cyclone is regulated by interactions with its environment. Possible mechanisms whereby these interactions occur are described.
A diagnostic test of the closure assumption in Arakawa and Schubert's cumulus parametrization scheme
Authors: Dümenil Lydia , Ruprecht Eberhard 
Published: February 2007

AbstractThe parametrization of cumulus convection by Arakawa and Schubert is based on the assumption of quasi‐equilibrium between cumulus‐scale and large‐scale processes. Under these conditions, the cloud work function A(λ) should be constant. This assumption is tested in a diagnostic approach by using GATE data. Rawinsonde observations at the A/B‐scale ships were analysed for the period 30 August to 8 September 1974 and the cloud work functions are calculated for each observation time.The sensitivity of the cloud work function to temperature and humidity is studied. It is concluded that for the limited range of variations observed during GATE, the cloud work function can be regarded as constant for periods of up to 24 hours. Observed time changes of the large‐scale forcing indicate that a coupling between the time changes of the large‐scale temperatures and the moisture fields ensures that A(λ) remains constant.
Interannual displacements of convection and surface circulation over the equatorial Indian Ocean
Authors: Reverdin Gilles , Cadet Daniel L. , Gutzler David 
Published: February 2007

AbstractThe interannual variability of surface observations in the equatorial Indian Ocean is investigated from 23 years of ship reports (1954‐1976). In October and November, during certain years, the monthly analyses show strong wind anomalies in the eastern and central equatorial Indian Ocean. Simultaneously, cloud cover anomalies of opposite signs are observed in the eastern Indian Ocean and in the central Indian Ocean. A linear analysis of heat‐induced circulation suggests that the surface wind anomalies are forced by anomalies of rainfall. This circulation is probably dissipative with time scales in the range two to five days.The reasons for the maintenance of anomalous circulations are not well known. It is noted that during most El Niño events in the Pacific Ocean, anomalies are observed in the Indian Ocean. However, there are other years with the same anomalous pattern, 1961 for example. During the years with anomalously little cloudiness in the eastern Indian Ocean, sea surface temperatures lower than normal are found in the eastern Indian Ocean. This suggests that coupled air‐sea dynamics must be taken into account to understand the interannual variability.
Numerical experiments on the sensitivity of the monsoon circulation to differential heating
Authors: Chen Shou‐Jun , Dell'Osso Lorenzo 
Published: February 2007

AbstractSome numerical simulations from real data were carried out to examine the response of the monsoon circulation to moist processes. Two cases were selected: one for the monsoon onset and the other for the active (fully established) period. The results show that latent heat is the main feed‐back process in the monsoon circulation. The south‐west monsoon current from the Arabian Sea to the South China Sea in the lower troposphere and the easterly jet stream over southern Asia in the upper troposphere are greatly enhanced by this process both in the onset and active periods. The surface latent heat flux (mostly over the ocean) is important in the maintenance of the circulation during the active period but is less important for the onset.