bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of the flow structure around Ailsa Craig, a steep, three‐dimensional, isolated hill
Authors: Jenkins G. J. , Mason P. J. , Moores W. H. , Sykes R. I. 
Published: July 2010

AbstractObservations of neutral flow around an isolated island are presented. the island has a fairly smooth shape with slopes of about 30° and a horizontal section which is roughly elliptical with axis ratio 1.5. the flow field 4 m above the surface shows a speed‐up around the sides and over the summit, with reverse flow on the lee slope. Measurements with an instrumented aircraft, of the mean flow in the wake of the island reveal a single very powerful trailing vortex, with axis close to the upstream wind direction. There are indications that the single vortex was a consequence of the asymmetry caused by the island's elliptical shape. Measurements of fluctuating quantities with a tethered balloon system show marked changes in the components of the turbulence energy in the flow around the side of the hill.
Kinematic analysis of the large‐scale mean state during phases I, II and III of GATE
Authors: Vincent Dayton G. 
Published: July 2010

AbstractAn analysis is presented of the large‐scale mean state kinematic properties of the wind field based on observed rawinsonde data taken over western Africa and the eastern Atlantic during Phases I, II, and III of GATE. Variables presented are wind direction and speed, zonal wind component, temporal standard deviation of the zonal wind component, vertical p‐velocity and relative vorticity. Wind direction and speed and temporal standard deviation of zonal wind were subjectively analysed at the surface, 850mb, 700mb, 500mb, 400mb, 300mb, 250mb, 200mb, 150mb and 100mb. Grid point data were extracted from analyzed charts at increments of 2° latitude and longitude and used to compute vertical motion and vorticity. Resultant analyses are examined to determine kinematic properties common to all three phases of GATE, trends in these properties from one phase to the next, and differences between properties over western Africa (land) and the eastern Atlantic (water). Features of the mean state are compared with results obtained by other investigators for such phenomena as large‐scale westward propagating wave disturbances, low‐level cyclonic vortices, satellite‐derived precipitation and cloud clusters associated with squall lines.
Mechanistic limitations to the release of latent heat during the natural and artificial glaciation of deep convective clouds
Authors: Lamb Dennis , Hallett John , Sax R. I. 
Published: July 2010

AbstractThe latent heat thermodynamically available in the supercooled water of deep convective clouds is released at rates governed by the glaciation mechanism, presumed here to involve primary nucleation, capture nucleation of rain by small ice particles and secondary ice production (rime‐splintering hypothesis). A simple microphysical model of the glaciation shows the importance of regenerative feed‐back on the evolution of ice when the primary nucleation and regenerative processes proceed simultaneously, leading to insensitivity to the primary ice nucleus concentration. This allows rapid glaciation and heat release to occur naturally in clouds exhibiting a broad supercooled drop size spectrum.New observational data and model results of artificially induced glaciation are consistent with the idea that the primary microphysical role of seeding is the creation of many small ice particles which substitute for the secondary ice splinters of naturally induced glaciation. the aerodynamic capture of the splinters by the supercooled rain leads to the formation of new graupel particles and the rapid release of fusional heat, shown by calculation to dominate the heat release mechanisms. With a seeding agent acting in the contact mode the small (cloud drop) end of the spectrum is required, since Brownian scavenging of the nuclei by the few large rain drops is inefficient. the quantitative analysis of these glaciation concepts also demonstrates that realistic seeding under conditions conducive to ice multiplication could increase materially the rate of heat release and offer opportunities for artificially invigorating the dynamic structure of a cloud if glaciation is induced to occur within a relatively narrow ‘time window’ for seeding.
Water vapour absorption in the 3.5‐4.2μm atmospheric window
Authors: Barton I. J. 
Published: July 2010

AbstractAn analysis of Nimbus 5 Selective Chopper Radiometer data supports the measurements of Bignell (1970) and Watkins et al. (1979) which both show considerable ‘e‐type’ absorption by water vapour in the 3.5‐4.2 μm atmospheric window.
The response of numerical weather prediction systems to fgge level iib data. Part II: Forecast verifications and implications for predictability
Authors: Arpe By K. , Hollingsworth A. , Tracton M. S. , Lorenc A. C. , Uppala S. , Kållberg P. 
Published: July 2010

AbstractThe purpose of our two‐part study is to assess the importance of the differences between three independent analyses of the same FGGE level IIb observational dataset. Part I is concerned with the nature and origin of the differences among the analyses. Part II of the study is concerned with the implications of the analysis differences for forecast skill, and for estimates of predictability.Our experimental material is a set of forecasts by two models from the three ensembles of analyses. the energetics of the analyses are different, and this is reflected in differences in the energetics of the forecasts based on the analyses.A study of the objective forecast verifications shows that there are clear differences in the forecast skill of the two models we used. the verifications also show a marked sensitivity to the choice of initial data.We studied in some detail how forecasts made with the same model from different analyses diverge from one another, with particular attention to three aspects: (i) the growth rate at small amplitude; (ii) the time taken for the differences to reach an asymptotic level; (iii) the amplitude of this level relative to that of persistence. the results for small amplitude growth rates are consistent with earlier results in giving a doubling time of 2·0 days in the height field in the day 1‐2 forecasts but with slower growth rates (doubling times of 2·6 days) in the wind field. the baroclinic waves show faster growth, with about 0·25 days shorter doubling times. the forecast differences reach an asymptotic level more rapidly in this than in earlier investigations. This suggests that earlier estimates of the purely dynamical potential for predictability of instantaneous weather patterns may be overoptimistic.We combined the measures of forecast skill and forecast divergence in an error budget which separated the contributions to forecast error arising from model error and analysis error, subject to some simplifying assumptions. the results show that between day 2 and day 5 the model error grows linearly in time and the analysis error grows exponentially. the model is the main source of forecast error in this time range. the analysis error is the main source of forecast error in the short‐range forecasts, and is a substantial contributor after about day 5. These results are very sensitive to the magnitude of the initial analysis errors.Taken together with the synoptic results of part I, these statistical results emphasize the importance of analysis technique for the success of forecasting, particularly in the medium range. Given identical data of good quality, three advanced analysis systems produced analyses which lead to rather different forecasts.The results are based on a small sample over a period of 21/2 days, which represent essentially the same synoptic situation; therefore the generality of the results should be tested on further experiments.
Microphysical properties of supercooled cumulus clouds in which an ice particle multiplication process operated
Authors: Mossop S. C. 
Published: July 2010

AbstractMicrophysical measurements made in small wintertime cumuli on five days in June 1981 are described. On all days an ice crystal multiplication process was active. the main conditions for the operation of the Hallett‐Mossop multiplication process were fulfilled—namely, the presence of both graupel particles and drops ≃ 24m̈m in diameter in the cloud zone between the ‐3 and ‐8°C levels. Shortcomings of the available theoretical models prevented any worth‐while comparisons between their predictions and the observed cloud behaviour. In these clouds, large drops (⩾300 m̈m diameter) grew by coalescence and appeared in a concentration of ≃0.1 per litre at about the same time as ice particles (graupel) of similar size. the drops reached a concentration of ≃5 per litre and then disappeared while the graupel continued to increase to concentrations of ≃10 per litre. There is evidence to indicate that the concentration of ice particles increased exponentially with time, being multiplied by a factor of 10 every 10 min between the values of 1 and 100 per litre. It is likely that the original ice nuclei activated were more numerous than the generally accepted average concentration of about 10m−3 at ‐10°C.
Initialization using laplace transforms
Authors: Lynch By Peter 
Published: July 2010

AbstractThe initialization of limited area models is complicated by the difficulty of determining the linear normal modes and of allowing for general boundary conditions. A new method of initialization is devised, which does not require explicit knowledge of the normal modes. the method is based on a filtering procedure which uses a modified inverse Laplace transform. the efficacy of the method is demonstrated by application to a one‐dimensional model, and the rationale for application to a general forecasting model is discussed. the method is closely related to the nonlinear normal mode method of initialization.
The calculation of stratospheric air parcel trajectories using satellite data
Authors: Austin John , Tuck A. F. 
Published: July 2010

AbstractAir parcel trajectories are calculated for the mid‐stratosphere using data from the stratospheric sounding unit on board NOAA‐6. In the analysis method all the orbital data for each 24 h period are combined into a single global analysis. Three trajectory methods are used‐isobaric, isentropic and quasi‐isentropic‐and the results are compared and contrasted. For the quasi‐isentropic method a radiation model is used, via the thermodynamic equation, to imply cross‐isentrope flow at regular intervals along the trajectory. the positions of the parcels, computed using the three methods, are found in general to be in good agreement when projected on to a horizontal plane. However, the altitude varies according to the trajectory method used and changes by about 1 km along a quiescent trajectory and as much as 2 km along a disturbed trajectory, during a 10‐day period. This has important implications in the study of chemistry along parcel trajectories during disturbed periods since the temperature‐ and pressure‐dependent reactions will proceed at different rates under the different assumptions. Also, the high lapse rate in the vertical mixing ratio profile of ozone implies that the detailed photochemistry will depend critically on the height of the air parcel.Further, potential vorticity and potential temperature are used as quasi‐conservative Lagrangian tracers, to try to determine which trajectory method is most realistic. For the quiescent period studied (June 1979 in the southern hemisphere) the isobaric and isentropic methods produced similar results throughout the ten days of the trajectory but the quasi‐isentropic method was clearly superior. A disturbed period was also studied (the February 1979 stratospheric warming), but the results from the trajectories studied were consistent with the Lagrangian conservation laws for only 6 days, at most. These results illustrate the need for caution, particularly with regard to sensitivity to initial horizontal position, in using trajectories calculated for disturbed periods.
Aircraft observations of the ekman layer during the joint air‐sea interaction experiment
Authors: Nicholls S. 
Published: July 2010

AbstractResults are presented from an observational study of the mid‐latitude atmospheric boundary layer over the sea. the data were obtained mainly by instrumented aircraft as part of the Joint Air‐Sea Interaction Experiment (JASIN).The eight occasions chosen for study are characterized by small surface buoyancy fluxes and the conditions are well described as near neutral and barotropic. In the absence of low‐level inversions, a well‐mixed Ekman layer is observed on each occasion but is limited to a depth of approximately 0.2u */f. Accurate measurements of horizontal gradients (including pressure) together with improved wind observations and turbulent flux measurements enabled each of the terms of the momentum balance to be evaluated throughout the depth of this layer. These terms were found to balance quite closely, were well described by Ekman scaling and were consistent with the requirements of the measured turbulent kinetic energy balance. the latter suggests that the main shear production terms are dissipated locally and that little is exported to upper levels in the Ekman layer to enable significant deepening by entrainment although only a slight increase in instability appears to be needed to alter this balance. Conditions in which such boundary layer structure might be observed are suggested. Values of various coefficients used in schemes for relating surface fluxes to mean quantities (CD, CE, Cg, A, B) are derived and compared with previous measurements.Spectral analysis reveals that most of the turbulent transport is confined to a distinct high wavenumber region whose characteristics vary as a function of Ekman layer depth and stability parameters. This is superimposed on larger‐scale fluctuations which do not vary appreciably within the Ekman layer and which therefore dominate the variances in the upper regions as the intensity of the smaller‐scale turbulence decreases strongly with height.Finally, further implications of this interpretation are discussed with particular reference to the heat and water vapour balance. These imply that removal of water vapour from the Ekman layer is accomplished by transfer related to cloud activity, marking a significant change in the mechanism of turbulent transport at the top of this layer. the relationship between these and similar results obtained concurrently by different methods is also discussed.
Mesoscale analysis of a polar trough interacting with a polar front
Authors: Browning K. A. , Hill F. F. 
Published: July 2010

AbstractThe interaction of a polar trough with a polar front can lead to a characteristic satellite cloud pattern commonly referred to as an instant occlusion. the detailed structure and development of an event rather resembling an instant occlusion is analysed in this paper using routine data supplemented by additional radiosondes, soundings and cloud imagery from NOAA‐7 and Meteosat, and radar network pictures. the event presented differs from an instant occlusion as described by Anderson and others in that a band of polar front cloud developed simultaneously with the band of cloud associated with the polar trough rather than being a pre‐existing feature. Thus we refer to it under the different name of pseudo‐occlusion in order to keep this distinction in mind. A conceptual model of the pseudo‐occlusion is developed in which the key elements are (i) a moist, relatively warm, low‐level jet associated with the polar trough, referred to as the ‘polar trough conveyor belt’, and (ii) a major upper‐level jet streak associated with the polar front, referred to as the ‘polar front conveyor belt’. the two conveyor belts intersect almost at right angles. Precipitation associated with the polar front is predominantly from stratiform cloud, whereas that associated with the polar trough is a mixture of stratiform and convective. Just on the poleward side of the upper jet the cloud top drops abruptly. Here, dry air having recently descended beneath the tropopause fold, suppresses the depth of the moist air associated with the polar trough conveyor belt. This leads to a minimum in the intensity of precipitation between the rain areas associated with the trough and the front. Although the air overrunning the trough just on the poleward side of the polar front is dry as a result of earlier descent, the air in this location is likely to have begun ascending as part of the indirect circulation in the exit region of the upper level jet streak. the polar trough low‐level jet probably forms part of this circulation.
An airborne study of the microphysical structure of cumulus clouds
Authors: Hill T. A. , Choularton T. W. 
Published: July 2010

AbstractData are presented from aircraft passes through cumulus clouds studied during a cooperative convective precipitation experiment on the plains of Montana in 1981. It is found that small concentrations of large drops are produced which exceed the size predicted by growth in a closed parcel model. These concentrations are higher in young, rapidly ascending turrets than in older clouds and coalescence‐size drops are found in turrets less than ten minutes old. It is concluded that dry air entrainment is responsible for the production of these large drops in ascending turrets.
On the detection of temperature changes induced by increasing atmospheric carbon dioxide
Authors: Parker D. E. 
Published: July 2010

AbstractRadiosonde data for approximately the past 25 years have been used to search for the lower‐stratospheric cooling and lesser upper‐tropospheric warming expected, according to many modelling studies, as a result of the increasing concentration of carbon dioxide in the atmosphere. There are no clear indications that the hypothesized temperature changes have occurred. Settling of volcanic dust after the 1963 eruption of Agung, and inhomogeneity in the data resulting from changes in design of radiosondes, may have caused observed loẃer‐stratospheric temperatures to fall in the late 1960s at some stations. Even in the absence of instrumental shortcomings, a further 35 years of radiosonde data, or 20‐25 years of satellite stratospheric sounding data, are a prerequisite for detection of temperature trends of the size predicted by global circulation models for the present rate of increase of atmospheric carbon dioxide concentration.
A comparison of observed and forecast energetics over North America
Authors: Baker Wayman E. , Brin Yevgenia 
Published: July 2010

AbstractThe observed kinetic energy balance is calculated over North America and compared with that computed from forecast fields for the 13‐15 January 1979 cyclone. the FGGE upper‐air rawinsonde network serves as the observational database while the forecast energetics are derived from a numerical integration with the GLAS fourth‐order general circulation model initialized at 00 GMT 13 January.Maps of the observed and predicted kinetic energy and eddy conversion are in good qualitative agreement, although the model eddy conversion tends to be 2 to 3 times stronger than the observed values. Both the forecast and observations exhibit the lower and upper tropospheric maxima in vertical profiles of kinetic energy generation and dissipation typically found in cyclonic disturbances. an interesting time lag is noted in the observational analysis with the maximum observed kinetic energy occurring 12 h later than the maximum eddy conversion over the same region.
On systematic errors in parametrized calculations of longwave radiation transfer
Authors: Morcrette Jean‐Jacques , Fouquart Yves 
Published: July 2010

AbstractA detailed narrow band model of longwave radiation transfer in a clear‐sky atmosphere is used to study the impact on cooling rate profiles and radiative fluxes of some approximations commonly used in GCM‐type radiation codes.Systematic errors in the results arise when economies are made in the vertical and spectral resolution. A coarse discretization of the vertical profiles of temperature and humidity overestimates atmospheric absorption (by as much as +5 W m−2), as does (by as much as +5 W m−2) the use of mean values of the temperature and humidity in each model layer. Overestimation of the absorption (up to +7 W m−2) also results from the use of the strong line approximation for H2O and CO2, or of the weak line approximation for O3.Decreasing the order of the vertical quadrature used for the vertical integration tends to decrease the absorption. Effects of the water vapour continuum absorption outside the 800‐1250 cm−1 window region cannot be neglected, as this absorption accounts respectively for 21 and 8 W m−2 of the downward radiation at the surface for a tropical and a subarctic winter atmosphere, and decreases the corresponding outgoing radiation at the top of the atmosphere by 5 and 0.3 W m−2 respectively. Neglecting N2O and CH3 decreases absorption by about 5 W m−2. Restricting CO2 absorption to the 500‐800 cm−1 interval, and O3 absorption to the 970‐1110 cm−1 interval further decreases by 5 W m−2 the absorption in the tropical atmosphere.For transmission functions described by statistical models, a widening of the spectral intervals reinforces the influence of the strong lines and leads to an overestimation of the absorption, which is partly compensated by a weaker temperature dependence.
Systematic errors of the ecmwf operational forecasting model in tropical regions
Authors: Heckley William A. 
Published: July 2010

AbstractThe performance of the ECMWF forecasting system in tropical prediction is discussed in terms of objective scores and systematic errors. the temperature, humidity and wind errors appear to be mutually consistent. the forecasts exhibit a cooling in the tropical stratosphere, warming at and below the tropical tropopause and a cooling in the mid and lower tropical troposphere. the analyses appear too humid in the lower troposphere, while the forecasts show a drying. Precipitation and evaporation are both too weak; a new energy balance within the model is slowly established through cooling, this new balance having a reduced total energy (Lq + cqT). the associated wind errors are seen to have a highly baroclinic structure and a meridional extent such as to affect significantly the baroclinicity of the mid‐latitude flow, particularly over the North and South Atlantic. Systematic errors are large compared to the variability of the fields themselves and show a remarkable temporal consistency from month to month.