bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field studies of the optical and microphysical characteristics of clouds enveloping Great Dun Fell
Authors: Choularton T. W. , Consterdine I. E. , Gardiner B. A. , Gay M. J. , Hill M. K. , Latham J. , Stromberg I. M. 
Published: February 2007

AbstractIn an effort to study aspects of their evolution, simultaneous measurements have been made, in two separate studies, of the microphysical properties of cap clouds over Great Dun Fell, in Cumbria, at two vertically displaced sites along the line of the wind. Dynamical, optical (10.6 γm) and acoustic sounder measurements were also made.Influences upon the cloud properties of humidity fluctuations near to cloud base, turbulent deposition of droplets to ground, additional activation caused by orographically induced accelerations within the clouds, entrainment of environmental air and long‐wave radiation to space were identified and examined.The clouds studied exhibited structure in their microphysical and optical properties on all scales from a few metres to several hundred metres.The cloud model of Carruthers and Choularton was found to predict the optical and microphysical characteristics of clouds not significantly influenced by entrainment, to a reasonable degree of accuracy.
Systematic errors of the ECMWF operational forecasting model in mid‐latitudes
Authors: Arpe K. , Klinker E. 
Published: February 2007

AbstractThe systematic errors of the ECMWF spectral operational model (April 1983 to April 1985) in midlatitudes are described. The main errors are:* a zonalization of the time‐mean flow with considerably reduced diffluent flow at the jet exits;* a wavenumber‐2 pattern in the mean height error field with forecast heights too low over Europe and the Bering Strait, and too high over Canada and Siberia;* an upward shift of the subtropical jet and the tropopause;* a cooling of the stratosphere;* a cooling of the middle troposphere which decreases the static stability in the lower troposphere;* an increase of the horizontal and vertical tilts of baroclinic waves;* changes in the geographical distributions of baroclinic waves and cyclones, with enhanced activity near jet exits and reduced activity near areas of cyclogenesis;* a drop of eddy kinetic energy during the 10‐day forecasts, first in the baroclinic waves and later in the long waves.The errors in both hemispheres have similar characteristics.The relations between the different errors and possible causes are discussed and comparisons with the errors of the former ECMWF operational grid point model are made. The introduction of the spectral model has led to significant improvements in the speed of baroclinic waves, which are now predicted more accurately up to day 3.
Super‐rotation and diffusion of axial angular momentum: I. ‘Speed limits’ for axisymmetric flow in a rotating cylindrical fluid annulus
Authors: Read P. L. 
Published: February 2007

Abstract‘Super‐rotation’ can be defined with respect to the limitations on the magnitude of specific angular momentum, m, in an inviscid fluid. In a viscous fluid, a steady, super‐rotating axisymmetric flow is shown to require diffusion of m against its gradient ∇m in the meridional plane. The conditions under which m can be diffused in an incompressible fluid by molecular viscosity against ∇m in a cylindrical system are shown to be consistent with the normal properties of isotropic Newtonian viscosity (i.e. appropriate for the laminar flow of a viscous liquid in the laboratory) when cylindrical curvature is fully represented. A series of numerical simulations of thermally‐driven axisymmetric circulations in a cylindrical fluid annulus, subject to various mechanical boundary conditions, is then presented. The role of diffusion in the angular momentum budget of the simulations is examined by diagnosing m, its diffusive flux F (due to molecular viscosity) and divergence ∇·F from the final equilibrium (steady) flow. Up‐gradient diffusion (with respect to ∇m) is found to be particularly important for flows in a system with stress‐free top and side boundaries and a non‐slip base. Similar up‐gradient diffusion can also result in angular momentum expulsion effects in a system confined entirely by stress‐free boundaries. The characteristic dynamics of super‐rotation in a viscous fluid, and the associated limitations upon its magnitude and dependence upon the external conditions and fluid properties, are then explored in a scale analysis for the cylindrical annulus with a non‐slip base (based on a scheme due to Hignett, Ibbetson and Killworth). The most rapid super‐rotation (with zonal Rossby number > 1) is found to be favoured at moderate rotation rates, with strong cylindrical curvature, and a large meridional aspect ratio and Prandtl number. The results of the scale analysis are verified by means of further numerical experiments.
Conditional symmetric instability and mesoscale rainbands
Authors: Xu Qin 
Published: February 2007

AbstractThe linear theory of conditional symmetric instability (CSI) is re‐examined in a rigorous framework. In comparison with symmetric instability a new feature of CSI is that the moist updraught tends to be narrow, as with conditional buoyancy instability (CBI). As the width of the moist updraught varies from its tolerance maximum to infinitesimal, the inviscid growth rate increases from zero to its maximum and the slope of the moist updraught increases from the absolute momentum surface to the moist most unstable surface. The fact that CSI circulations absorb energy from the basic shear and moist thermal field but lose energy to the dry basic thermal field is responsible for the narrow and slant feature of the moist updraught. When a bulk viscosity is accounted for, the most rapidly growing CSI modes bear a qualitative resemblance to some observed rainbands. The stability criterion of viscous CSI also shows a better comparison with observational data than inviscid CSI. The linear CSI theory here predicts that the isolated mode is preferred to other non‐isolated (periodic or irregular spacing) modes. The preference of non‐isolated modes is speculated to occur in the nonlinear stage.
Diurnal variation and cloud in a general circulation model
Authors: Wilson C. A. , Mitchell J. F. B. 
Published: February 2007

AbstractIt is shown that changing the resolution of the diurnal cycle of cloud and radiative fluxes in an atmospheric general circulation model can affect the simulated climate. The effect on radiative forcing of using a temporal resolution which is unable to represent accurately the phase of diurnal variation in cloud is illustrated using a radiative‐convective version of the model. Similar results are found in the full model simulation for July, especially over land in the tropics. A detailed study of the changes over North Africa shows that the reduction in solar heating at the surface leads to a reduction in low‐level convergence and rainfall, and increased low cloud. The results indicate that cloud amounts need to be updated more frequently than four times a day if the model simulation is not to be degraded when the diurnal cycle is represented.
Momentum exchange at the sea surface by wind stress and understress
Authors: Bye John A. T. 
Published: February 2007

AbstractMomentum exchange at the interface between two fluids is considered using general reasoning on energy dissipation in the coupled planetary boundary layers.It is shown that the surface shearing stress can be expressed as a function of the relative surface geostrophic velocity between the two fluids, and that the surface velocity is a linear combination of the two surface geostrophic velocities. This latter result is in agreement with a result previously derived by E. B. Kraus directly from the momentum equations.The analysis enables the ratio of the dissipation rates between the two fluids in the interfacial boundary layer to be determined. For the coupled ocean‐atmosphere, we find this ratio to be approximately (p1/p2)12 : where p1 and p2 are the densities of air and water, and we have made use of observations of the surface drift velocity and a dimensional argument which both suggest that the drag coefficients in the two fluids are approximately equal.From the form of the expression for the surface shearing stress, it is clear that both fluids lose energy in the coupled boundary layer, and also that they either transfer energy to each other or extract energy from each other by interaction at the interface.These energy fluxes are carried by two elemental stresses due to the general circulations of the atmosphere and the ocean respectively and which we call ‘wind stress’ and ‘understress’.The mutual loss of energy implies that the interface exerts a drag on both the atmosphere and the ocean, and the interfacial energy exchanges show that the ocean does work on the atmosphere analogous to the work done by the atmosphere on the ocean.
Comparative energetics of the observed and simulated global circulation during the special observing periods of FGGE
Authors: Kung E. C. , Baker W. E. 
Published: February 2007

AbstractEnergetics of the observed and simulated global circulation are evaluated in the zonal spectral domain for the special observing periods of FGGE. The study utilizes GLA analyses of FGGE observational data and parallel simulation experiments. There are noticeable differences in energy transformations between the observation and simulation during SOP‐1. These include the baroclinic conversion C(n) by the zonal mean motion and short‐wave disturbances, and the nonlinear wave‐wave interaction L(n) at the long and short waves. The energy transformations of the short‐wave disturbances are much more intense in the simulated circulation than in the observation. However, good agreement is noted in the conversion and dissipation of kinetic energy in the large‐ and cyclone‐wave range n = 1–10. Spectral distributions of global energy transformations at the long‐ and cyclone‐wave range indicate that the SOP‐2 simulation agrees more closely with the observed fields than the SOP‐1 simulation. Other pertinent points of energetics diagnosis are also included in the discussion.
A study of wintertime circulation anomalies during past El Niño events using a high resolution general circulation model. I: Influence of model climatology
Authors: Palmer T. N. , Mansfield D. A. 
Published: February 2007

AbstractIn this paper the response of an 11‐layer general circulation model (GCM) to an enhanced composite El Niño sea surface temperature (s.s.t.) anomaly is studied. The integrations were run for 540 days in a perpetual January mode, and had either mean or envelope orography.A basic objective of this paper is to study the influence of model climatology on the response to a tropical s.s.t. anomaly. This was done both by comparing our results with those from a lower resolution GCM (the NCAR Community Climate Model) with an identical s.s.t. anomaly, and by performing control and anomaly integrations with both mean and envelope orography. The specification of orography strongly influences the strength of the mean zonal flow, and stationary and transient wave activity in our model. Whereas the runs with envelope orography produced an anomalous Pacific/North American (PNA) teleconnection pattern in the northern hemisphere, the runs with mean orography did not. In the extratropical southern hemisphere. our model produced a statistically significant response which had a substantial zonally symmetric component. By contrast, the NCAR model, with weaker zonal flow, produced a weaker and mainly statistically insignificant response in the southern hemisphere. Finally, in the tropics, over the Central and Eastern Pacific, the anomalous rainfall and vorticity fields correlated strongly with the corresponding fields in the control integration. Overall, therefore, we conclude that a GCM's response is strongly sensitive to the basic model climatology.In trying to understand dynamically the GCM response it was concluded that the PNA pattern may not simply be the result of Rossby wave dispersion from a tropical source. The PNA pattern may also be associated with a combination of two separate influences, the interaction with the anomalous mean flow of enhanced storm track activity over the Pacific, and with orography on the North American continent.The implications of the model's tropical response for simple linear theory were also discussed. In these composite El Niño anomaly experiments enhanced rainfall and upper divergence occurred well to the west of the upper tropical anticyclone pairs, implying that a Sverdrup type balance in the vorticity equation cannot hold. It is suggested that the strength of the anomalous vortex stretching term could be a small residual compared with the horizontal advection terms, and that a simple linear relationship between anomalous latent heating and the position and strength of the anomalous anticyclone pairs is not always valid. An alternative qualitative explanation for the relative position of these anticyclone pairs is given in terms of a reduction in the zonally asymmetric component of upper tropospheric vorticity across the tropical Pacific, whilst the position of the rainfall maximum is located close to the s.s.t. maximum.
A new convective adjustment scheme. Part II: Single column tests using GATE wave, BOMEX, ATEX and arctic air‐mass data sets
Authors: Betts A. K. , Miller M. J. 
Published: February 2007

AbstractThe schemes proposed in part I are tested using single‐column data sets from tropical field experiments (GATE, BOMEX, ATEX) and an arctic air‐mass transformation. Both the deep and shallow schemes perform well. The sensitivity of the schemes to adjustable parameters is also studied. Preliminary global forecasts show significant improvements in the global surface fluxes and mean tropical temperature tendency over the operational Kuo convection scheme.
Trace constituents in the Austral stratosphere
Authors: Galbally I. E. , Roy C. R. , O'Brien R. S. , Ridley B. A. , Hastie D. R. , Evans W. F. J. , McElroy C. T. , Kerr J. B. , Plumb R. A. , Hyson P. , Laby J. E. 
Published: February 2007

AbstractMeasurements of NO, NO2, HNO3, O3, N2O, CCl3F, H2O, CH4 and aerosol were made during balloon flights in the stratosphere over Australia at 23°S and 34°S from March to October 1979. These data and ground‐based column density measurements of O3 and NO2 are presented and compared with previous measurements of the same species in the southern hemisphere stratosphere.Diurnal variations of NO and NO2 are presented. These measurements show that there is a temporary reservoir which, during the daytime, releases perhaps one third of the total NOx present at sunset.Vertical and latitudinal variations of NOy (NO + NO2 + HNO3) and the partitioning between the three species are presented. There is a substantial increase in NOy towards high latitudes. HNO3 is a larger fraction of NOy in the mid‐latitude westerlies compared with the subtropical easterlies as observed in a mixing event involving air from higher latitudes.Unusual profiles of aerosol, CCl3F and NO were observed that can be explained by an intrusion of air from lower altitude into the 27 to 32 km height range in the equatorial and temperate latitudes of the southern hemisphere during March to May 1979.
Multiple state stochastic models for the long‐range transport and removal of atmospheric tracers
Authors: Egbert Gary D. , Baker Marcia B. 
Published: February 2007

AbstractWe discuss a general mathematical framework for modelling long‐term average concentration and deposition patterns for atmospheric tracers which are subject to removal and transformation. For a generalized ‘particle’ which can exist in a finite number of states, the joint statistics of random particle transport and interstate transformation can be used to calculate long‐term mean fields for deposition and concentration. We show that a number of models presented in the recent literature can be considered as simple cases of this formulation. These models generally assume a weak statistical relationship between vertical transport, horizontal transport and removal processes. We consider a general approach to linking these processes, based on calculating approximate transport statistics conditional on particle states. We demonstrate this approach with a rather schematic, but almost analytically solvable, stochastic model which allows for the linkage of transport and removal processes. We use these ideas to construct a two‐layer model of the transport and removal of sulphur in a region of convective precipitation, demonstrating how the correlation of vertical transport and precipitation can change the precipitation statistics in the particles' Lagrangian frame and hence affect deposition patterns.
The effect of rimer surface temperature on ice splinter production by the Hallett‐Mossop process
Authors: Griggs D. J. , Choularton T. W. 
Published: February 2007

AbstractThe effects of rimer surface temperature and environment temperature on spike production as supercooled water droplets are accreted by an ice surface immersed in a liquid bath have been investigated.When the rimer surface temperature and the environment temperature were the same, spikes were produced only in the temperature range −3° to −9 °C. However, when they were varied independently it was found that the upper temperature limit for spike production of −3 °C is controlled more by the rimer surface temperature, provided that the environmental temperature is at or below −3 °C. By contrast, the low temperature cut‐off for spike production at −9 °C is almost independent of the rimer surface temperature and is controlled more by the environmental temperature.If applicable, this could suggest that the Hallett‐Mossop process will not be displaced to lower temperatures when rapid riming of hailstones occurs in clouds with high liquid water contents.
Studies of internal gravity waves at Halley Base, Antarctica, using wind observations
Authors: Rees J. M. , Mobbs S. D. 
Published: February 2007

AbstractAt Halley Base, which is situated on the Brunt Ice Shelf in Antarctica, internal gravity waves are frequently observed in the stably stratified atmospheric boundary layer. In this paper, time series of wind speed and direction at a height of 8 m, observed from three meteorological masts, are used to determine some of the physical properties of the waves, such as their wavelengths, phase speeds and directions of propagation. The relationship of the results to various theories of the generation of internal gravity waves is considered. It is shown that the waves do not usually propagate in the direction of the surface wind; typically the direction of propagation is rotated about 45° clockwise from the wind vector. The waves most frequently propagate from a direction of about 135°, which is perpendicular both to the Hinge Line (line where the ice shelf meets the land) and to the ridges in the ice shelf, suggesting a topographic influence. It is shown that the waves obey a dispersion relation similar to that for neutral, trapped internal gravity waves.
On the nitrogen budget for the United Kingdom and north‐west Europe
Authors: Derwent R. G. , Dollard G. J. , Metcalfe S. E. 
Published: February 2007

AbstractThe application of a simple trajectory model approach to the emission, transformation and deposition of a coupled series of atmospheric pollutants including SO2, NOx and ammonia is described. A detailed comparison of the model results with observations is provided using United Kingdom monitoring data. Whilst reasonable agreement can justifiably be claimed for some species, whether in the gas phase, aerosol or precipitation, it is clear that for the others there are either severe disagreements or a lack of suitable data for comparison purposes. Background sources of these pollutants are assessed by applying wind sector analysis to precipitation measurements at remote sites. The budgets for the United Kingdom and north‐west Europe have a similar balance between wet and dry deposition to that given in the literature for the global nitrogen budget. This is in conflict with some literature budgets for Europe as a whole which have apparently overestimated the dry deposition terms.
A dual‐satellite algorithm for deriving sea surface temperature
Authors: Dudhia Anu 
Published: February 2007

AbstractThis paper describes an extension of conventional multichannel s.s.t. algorithms for NOAA‐7 AVHRR/2 data to include data from the Meteosat‐2 IR1 (11 μm) channel, generally viewing through a different zenith angle. This provides a combination of multichannel and dual‐angle techniques for determining the atmospheric correction. These algorithms, derived statistically from the results of transmission calculations on a number of temperature/humidity profiles, were tested under ‘pseudo‐operational’ conditions against ship measurements of s.s.t., and the results compared with the AVHRR‐only algorithms of other workers. The conclusion is that the technique is feasible but, due to the uncertainties in the Meteosat radiances caused by residual cloud contamination, the additional data are given only a low weight in the algorithms and the influence on retrieved s.s.t. is small. There were also opportunities to test the Rutherford‐Appleton Laboratory transmission model used in deriving the algorithms, and the results suggest that the model underestimates the absorption by the water vapour continuum in the 11 μm window.
A global numerical weather prediction model with variable resolution: Application to the shallow‐water equations
Authors: Courtier Philippe , Geleyn Jean‐Francois 
Published: February 2007

AbstractWe follow the approach suggested by F. Schmidt to implement a spectral global shallow‐water model with variable resolution. A conformal mapping is built between the earth and a computational sphere and the equations are discretized on the latter using the standard spectral technique associated with a collocation (Gaussian) grid. We prove that the only non‐trivial conformal mapping which exists between the two spheres is based on the transformation introduced by Schmidt, but the pole of the collocation grid has no longer to coincide with the pole of dilatation. We implement the technique in an explicit model, where only minor modifications to a uniform resolution model are needed. The semi‐implicit scheme and the nonlinear normal mode initialization are proved to work satisfactorily. 24‐hour forecasts show that the method is successful in dealing with the shallow‐water equations and allow us to discuss the potential of the approach.