bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiative cooling near the top of a cloudy mixed layer
Authors: Nieuwstadt F. T. M. , Businger J. A. 
Published: February 2007

AbstractThe role of radiation above a cloudy mixed layer is examined. We find that whereas turbulent entrainment can be identified with a very sharp temperature jump at the cloud top, the effect of radiative flux divergence above the cloud leads to a much more gradual temperature increase. With adequate observations the two can easily be distinguished. The development of the boundary layer can be described in terms of equations in which above‐cloud radiation plays no role.
Modelling tracer budgets in the stratosphere
Authors: Pyle J. A. , Rogers C. F. 
Published: February 2007

AbstractThe ozone budget in the stratosphere of a modified diabatic circulation model is compared with traditional Eulerian calculations. The importance of the chemical contribution in comparison with net dynamical contributions, even in the lower stratosphere, is stressed. Furthermore the chemical dependence of the eddy transports is shown to introduce significant differences in the meridional transport and points to a potentially important source of error in two‐dimensional simulations of tracer distributions in the stratosphere. Other aspects arising from photochemistry, the photochemical eddy term and the eddy coupling of different species, are also considered.
Finite amplitude, steady Rossby waves and mean flows: Analytical illustrations of the Charney‐Drazin non‐acceleration theorem
Authors: White A. A. 
Published: February 2007

AbstractExact steady‐state solutions of the nonlinear quasi‐geostrophic equations are used to illustrate some important repercussions of the Charney—Drazin theorem on the non‐acceleration of zonal mean flows by steady conservative waves. The solutions, which are similar to those discussed by Kuo in 1959, consist of spatially non‐uniform zonal flows and barotropic and baroclinic Rossby waves each having the same three‐dimensional wavenumber; a uniform zonal flow is also allowed. Two examples, both consisting of an internal jet zonal flow, a barotropic Rossby wave and a baroclinic Rossby wave, are considered. The absence of wave/mean interaction in these steady‐state solutions is clearly reflected in the absence of poleward eddy potential vorticity fluxes, but is disguised by the existence of non‐zero poleward eddy heat and zonal momentum fluxes and active Lorenz energy cycles. The solutions thus exhibit the same behaviour as the linearized examples discussed previously by various workers, and emphasize the danger of inferring from incomplete vorticity, energy or heat budget analyses that wave forcing (or maintenance) of Eulerian mean flows by eddy motion is taking place.One of the solutions (which is valid in a laterally open domain) is examined as a possible theoretical model of the steady waves seen in rotating annulus experiments. The spatial variations of the zonal mean flow and the eddy heat and momentum fluxes are in reasonable agreement with the results of a numerical simulation of a steady annulus wave, but the analytical solution is unsatisfactory in some other respects. It is clear that dissipative effects must be represented in any complete theoretical model of these steady waves.
Zonal wind components in the stratosphere and troposphere over India
Authors: Reddy C. A. , Reddi C. Raghava , Mohankumar K. G. 
Published: February 2007

AbstractUsing rocket and balloon data for 1979 and 1980, the stratospheric and tropospheric zonal wind components are quantified for three rocket ranges in India: (a) Thumba (8.5°N 76.9°E); (b) Sriharikota (13.7°N 80.2°E); and (c) Balasore (21.5°N 86.9°E). Values of the mean zonal wind and the amplitudes and phases of the quasibiennial oscillation (QBO), the annual oscillation (AO), and the semi‐annual oscillation (SAO) in the altitude range 2–60 km are presented. By subtracting the combined contribution of these long‐period components from the measured winds, the shorter‐period fluctuations of zonal wind, attributable to wave disturbances, are obtained. These fluctuations show a significant decrease in amplitude in the height region where the QBO is dominant, signifying a loss of wave momentum in that region. The fluctuations also indicate that some wave modes propagate into the mesosphere without significant attenuation. Significant inter‐annual variability in the AO and the SAO is present. The significance of the observational results is discussed in relation to earlier observations and current theoretical ideas.
Rain from clouds with tops warmer than – 10°C in Israel
Authors: Rangno Arthur L. 
Published: February 2007

AbstractRawinsonde observations combined with surface synoptic reports and satellite data, indicate that in Israel rain often falls from clouds with top temperatures ≥− 10° C. This suggests the presence of relatively large cloud droplets and/or high concentrations of ice particles at these temperatures, and a relatively efficient natural precipitation‐forming process.
Sensitivity of medium‐range weather forecasts to the use of an envelope orography
Authors: Jarraud M. , Simmons A. J. , Kanamitsu M. 
Published: February 2007

AbstractThe performances of grid‐square mean and enhanced ‘envelope’ orographies are compared in a set of 10‐day forecasts performed using the ECMWF spectral model at horizontal resolutions T21, T42, T63 and T106. Twenty‐four cases chosen at monthly intervals from May 1983 to April 1985 are examined, and for diagnosis of results for the northern hemisphere these are divided into 12 ‘winter’ (November to April) and 12 ‘summer’ (May to October) situations.The winter results in many respects confirm those of previous studies. Apart from T21 resolution, use of the envelope orography in this season is clearly beneficial in general, and synoptic assessment illustrates how mountain barrier effects are better represented by the envelope. Conversely, in summer the envelope has a detrimental effect (according to some, though not all measures) at T42 and T63 resolutions, though not at T106. This appears to be at least in part due to the more northerly position of the (northern hemisphere) jet in summer, which interacts with mountains that are less of a barrier, with T106 giving a better separation of the localized orographic features of these regions. Some problems are seen at all seasons with the envelope representation of the Asian relief.Results for the southern hemisphere are, not surprisingly, generally less sensitive to the representation of mountains, the principal impact coming from the southern Andes and Antarctic Peninsula to the south. A small beneficial impact of the envelope orography is found in the tropics.In individual cases, the use of envelope rather than mean orographv gives rise to local forecast differences near mountains which tend to propagate and amplify (principally on synoptic scales), following the upper‐level flow. Much of the hemisphere can be influenced in 7–10 days. Ensemble‐ and time‐averaged errors are generally reduced by use of the envelope, though not dramatically, and not at all locations.
The development of tropical cyclones in the north‐west of Australia
Authors: Foster I. J. , Lyons T. J. 
Published: February 2007

AbstractCase studies of developing and non‐developing tropical depressions in the north‐west Australian region during the 1979/80 and 1980/81 cyclone seasons have been constructed using conventional and satellite observations. These show that enhanced low‐level winds can occur during the lifetime of non‐developing disturbances and are not exclusively associated with cyclogenesis. Both types of system possessed lower‐level cyclonic circulations and there was an overlapping such that non‐developing storms could have stronger circulations than some developers. At upper levels, development was associated with the subtropical ridge being situated over the surface position of the disturbance. In contrast, the ridge tended to be located southwards of non‐developers.These findings are supported by calculations of area‐averaged vorticity at 850 and 200 mb. Cross‐sections of zonal winds show that non‐developing systems could exhibit weaker vertical wind shears than some developing storms. Developers had only moderate shears at worst and maintained a well organized lower cyclonic circulation.Such features are consistent with both classes of disturbance existing within the monsoon shearline. Non‐development was caused by interactions with large‐scale flows in the southern hemisphere that prevented the necessary conditions for cyclogenesis from being all fulfilled. This suggests a need for greater understanding of the influence of mid‐latitude events on depressions within the monsoon trough.
Wavenumber transition and wavenumber vacillation in Eady‐type baroclinic flows
Authors: Weng H.‐Y. , Barcilon A. 
Published: February 2007

AbstractWavenumber transition and wavenumber vacillation are studied numerically in a ‘maximum simplification’ model of the Eady type with uneven Ekman dissipation. The spectral wave solution contains three waves having adjacent zonal wavenumbers and the gravest meridional mode. The model only allows for wave‐mean‐flow interaction.As the stratification parameter decreases away from the upper symmetric flow, we observe that baroclinic forcing increases faster than dissipation, implying the prevalence of a higher wave energy state. This state is realized by an increase in wave amplitude, number of temporal and/or spatial degrees of freedom, or dominant wavenumber. The first two occur first, but for small enough stratification, the flow transits to a higher wavenumber in order to realize the increased energy.Wavenumber vacillation is a flow regime observed at some parameter settings when the flow has at least two spatial and three temporal degrees of freedom. This regime is usually found in the region of parameter space where wavenumber transitions occur as parameters change.The balance between baroclinic forcing and damping adjusted by wave‐mean‐flow interaction seems to be a basic mechanism for wavenumber transition and wavenumber vacillation. Wave‐wave interaction is not necessary for such phenomena to exist.
Updraught characteristics of a Florida thunderstorm
Authors: Hill R. D. 
Published: February 2007

AbstractBecause of possible significance in understanding lightning, the characteristics of an updraught velocity enhancement observed in a typical Florida thunderstorm are investigated. The most probable explanation of the sudden velocity enhancement is increased buoyancy resulting from the release of latent heat of freezing of supercooled droplets on to rime in the updraught. From information on updraughts in two different cells in the same storm, it is tentatively concluded that enhanced electrical activity, in typical Florida coastal thunderstorm cells, is probably associated with the mechanism of the initial charging of ice particles.
Comments on ‘Objective quality control using Bayesian methods’ by A. C. Lorenc and O. Hammon (January B 1988, 114, 515–543)
Authors: Thiebaux H. Jean 
Published: February 2007

AbstractThe proposals for quality control (QC) with automatic updating of the QC system, which Lorenc and Hammon (LH) have presented are important and forward‐looking contributions to the future of operational numerical weather prediction. With expanding computer capabilities for data management, including the maintenance of archives which keep up‐to‐date records of data quality by observation type and location, it is possible to make use of highly relevant information whose assemblage previously was unpractical. Lorenc and Hammon have suggested mechanisms for doing this; and their proposals offer promise for significant improvements in objective quality control. My comments are designed to enhance practical development of the authors' ideas, by focusing on some implications of the underlying theory.The objective of the work under discussion is to establish an algorithm whose application will result in the retention of observations which are within credible range of a background (or forecast) field, together with numerical assignment of their ‘credibilities’, and the rejection of observations which are not judged to be credible. Furthermore, part of its exercise will be renewal of the criterion of ‘within credible range of the background’, using information stored in quality control performance files.
A study of the stratospheric final warming of 1982 in the southern hemisphere
Authors: Mechoso C. R. , O'Neill A. , Pope V. D. , Farrara J. D. 
Published: February 2007

AbstractThe three‐dimensional evolution of the final warming that takes place in the stratosphere of the southern hemisphere during spring is studied using data from a satellite. The event of spring 1982 is discussed in detail, and other events from an 8‐year set are briefly surveyed. The zonal‐mean westerly jet moves poleward and downward in spring as strong, planetary‐scale disturbances develop which contribute to the weakening of the stratospheric westerly vortex. The processes governing this weakening are discussed by reference to isentropic maps of Ertel's potential vorticity and associated area diagnostics. The vortex breaks down first in the upper stratosphere and then later (and more slowly) in the middle stratosphere. This behaviour is broadly reproduced year after year. Repeating life‐cycles of growth, eastward movement and decay of anticyclones in the stratosphere are described and related to the behaviour of quasi‐stationary wave 1 and eastward‐travelling wave 2. Evidence that the topography of the southern hemisphere exerts a strong influence on the evolution of the final warming is presented. An association is found between the location of anticylones in the upper stratosphere, warm pools of air in the lower stratosphere and a climatological split of the westerly jet stream in the upper troposphere.
Humidity measurements in the free troposphere using Raman backscatter
Authors: Vaughan G. , Wareing D. P. , Thomas L. , Mitev V. 
Published: February 2007

AbstractA lidar system has been developed to measure the mixing ratio of atmospheric water vapour using Raman scattering from water vapour and nitrogen. The system uses the third harmonic of a neodymium‐YAG laser at 354.7 nm, with interference filters to isolate the vibrational Raman bands. Humidity profiles extending from about 2 km to the tropopause have been obtained, with a resolution of 30 m vertically and 20 minutes in time below 5 km, and > 300m vertically and several hours in time above 10 km. Good agreement was found between the lidar profiles and those of coincident radiosondes. Distinctive layers in the humidity profiles are presented, and measurements in the vicinity of cirrus clouds indicate sharp transitions from supersaturation to saturation with respect to ice at the cloud boundary.
Aircraft measurements of the solar absorption by broken cloud fields: A case study
Authors: Rawlins F. 
Published: February 2007

AbstractMeasurements of broad‐band radiation at solar (0.3–3.0 μm) and near‐infrared (0.7–3.0 μm) wavelengths are presented for three flights of the Meteorological Research Flight C130 aircraft in broken cloud fields. The solar absorption is determined from observations made above cloud top and below cloud base, using data in the two spectral bands to minimize errors of cloud sampling between different runs and to reduce the scatter due to cloud edge effects. The method assumes that cloud layer absorption in the visible region is negligible compared with that in the near‐infrared. This allows average absorption to be calculated for small sections of the aircraft track, which will generally include both fully clear and totally overcast cases. The smallest absorption measured is about 2%, in agreement with model results for the clear atmosphere. The largest absorption was found to be 8–12% (for a maximum cloud depth of 1 km), which is similar to measurements reported for layer cloud. An additional finding is that absorption by the broken cloud field varies uniformly with albedo, indicating that the parametrization of absorption in numerical models can be adequately described as a simple function of the albedo in partially cloudy areas.
A field study of the oxidation of SO2 in a cap cloud at Great Dun Fell
Authors: Chandler A. S. , Choularton T. W. , Dollard G. J. , Gay M. J. , Gallagher M. W. , Hill T. A. , Jones B. M. R. , Penkett S. A. , Tyler B. J. , Bandy B. 
Published: February 2007

AbstractA series of field experiments has been performed in natural cloud on Great Dun Fell to investigate the multiphase oxidation of sulphur dioxide by hydrogen peroxide and ozone. This has been done by observing the decay of hydrogen peroxide and the generation of sulphate ions in the cloud water. It is demonstrated that the apparent field reaction rate between SO2 and hydrogen peroxide is considerably faster than would be expected from recent laboratory studies. It was found that hydrogen peroxide was generally the most important oxidant for sulphate in the cloud. Significant quantities of this oxidant can be entrained from the free troposphere into the cloud and this may be rate‐determining for the production of sulphate over longer timescales. When the pH of the cloud water was maintained above about 4.8 (probably due to gas phase ammonia) ozone was found to be the major oxidant. It is also clear that these processes will also be important in free clouds remote from the ground with oxidation by hydrogen peroxide being dominant away from ground‐based ammonia sources.
On the influence of small‐scale topography on precipitation
Authors: Grabowski Wojciech W. 
Published: February 2007

AbstractA simple model of the influence of small‐scale topography on precipitation via the ‘seeder‐feeder’ mechanism is presented. In the model the large‐scale stratiform seeder cloud and the subcloud layer are modified by the airflow perturbations caused by small‐scale topography. Two separate scales of motion are considered; the large scale, with the updraught maintaining the seeder cloud, and the small scale tied to topography. In the diagnostic numerical model the interaction of these two scales is simulated. Two basic situations are considered: rain with a ground temperature of 12°C and snow with –5°C. Results of the model application to a bell‐shaped solitary hill are presented and compared with previous theoretical studies and field observations in the Welsh hills. The influence of orographic airflow perturbations on snow growth above the melting level may explain the observed strong dependence of rain enhancement on the horizontal wind speed. Simple considerations for the complex topography are also presented with reference to observations made near Uppsala, Sweden. It is suggested that the observed rain distribution may again result from influences on snow growth, with both the amplitude of airflow perturbations near the melting level and its phase relative to the topography beneath being very important.
Representativeness errors for radiosonde observations
Authors: Kitchen M. 
Published: February 2007

AbstractData from the United Kingdom operational upper air network, as well as from special radiosonde trials, have been analysed to provide statistics of spatial and temporal atmospheric variations. These statistics are applied to a study of the network performance and of representativeness errors associated with the use of the data in synoptic analysis. The results also have application to comparisons between measurements from radiosondes and those from other observing systems. For example, it is demonstrated that minimum collocation errors associated with radiosonde temperature measurements located at the centre of a satellite radiometer scan spot of radius 55 km are <1 degC for levels in the troposphere and lower stratosphere.
On the incorporation of atmospheric boundary layer effects into a balanced model
Authors: Cullen M. J. P. 
Published: February 2007

AbstractA method of coupling the thermal and frictional forcing in the atmospheric boundary layer to a semi‐geostrophic model of the internal dynamics is developed. It is illustrated by two‐dimensional sea‐breeze simulations, which are compared with those of a two‐dimensional primitive equation model. It is demonstrated that the main features of the circulation on a horizontal scale larger than 20 km can be simulated with the semi‐geostrophic model, but the detailed local circulations cannot.
Ground truth confirmation and theoretical limits of an experimental VLF arrival time difference lightning flash locating system
Authors: Lee A. C. L. 
Published: February 2007

AbstractDuring trials of a VLF Arrival Time Difference (ATD) technique for long range lightning flash location, an apparently well organized and isolated flash sequence was located. Internal ATD evidence suggests flashes were located at a thousand‐kilometre range to within 5 km. ‘Ground truth’ based on synoptic/mesoscale considerations, observer reports, and lightning damage claims confirms locations to 10–15 km. In addition, elimination of systematic effects from internal ATD evidence demonstrates relative flash location errors of 0.9‐1.8 km, and a ‘tight cluster’ of ATD fixes features scatter in location which is not inconsistent with these values. The nature of VLF lightning flash observation is examined, and shown to be consistent with errors even smaller than this.
Airflow over a two‐dimensional escarpment. II: Hydrostatic flow
Authors: Pitts R. O. , Lyons T. J. 
Published: February 2007

AbstractHydrostatically dominated forced flow over the asymmetric topography of the Darling Scarp, Western Australia, is modelled using a hydrostatic numerical mesoscale model and compared with observations. Simulations reproduce the essential features of wave overturning and the development of a shooting hydraulic flow. This response is dependent on the wind profile but not on the existence of a critical level. the high backsheared environment leads to a high ratio of the Brunt‐Väisälä frequency to wind speed throughout the profile, resulting in short wavelengths, high nonlinearity and overturning. With the ratio of the halfwidth of the topography to the boundary‐layer depth being small, the flow fields are shown to be sensitive to the boundary layer.