bluuebunny/crossref_metadata_2025_split huggingface dataset:
Broadband solar fluxes and heating rates for atmospheres with 3D broken clouds
Authors: Barker Howard W. , Morcrette Jean‐Jacques , Alexander G. David 
Published: February 2007

AbstractA 3D Monte Carlo photon transport algorithm is presented that computes broadband solar fluxes and heating rates. It treats attenuation by cloud droplets and gases separately and can produce 3D distributions of constituent absorptances. Underlying surfaces are accounted for and diurnal‐mean calculations can be achieved in the same time as typical single‐zenith‐angle experiments. Domain‐averaged fluxes and heating rate profiles are presented for two very different 3D cloud fields: (i) scattered, shallow cumuli inferred from Landsat imagery; and (ii) towering clouds simulated by a cloud‐resolving model. Plane‐parallel, homogeneous (PPH), independent column approximation (ICA), and clear‐sky versions of the 3D fields were generated and used as well.For both cloud fields, total atmospheric absorptance depends very weakly on cloud geometry. Cloud geometry does, however, invoke major differences in surface absorptance and, hence, reflectance to space. At high sun, albedos for 3D clouds are less than corresponding PPH values, but are in almost perfect agreement with ICA estimates. This indicates that simple horizontal variability of cloud optical depth outweighs the impact of cloud sides. At very low sun 3D fields reflect most because of interception of radiation by cloud sides, while PPH and ICA albedos come into better agreement. For the towering cloud field, radiative fluxes are determined largely by clouds below 6 km, despite some clouds reaching 12 km. Heating rate profiles are also affected by cloud geometry. For most sun angles, PPH clouds exhibit anomalously large heating near cloud tops and anomalously small heating beneath clouds. On the other hand, profiles for 3D and ICA fields are very similar and depend much less on altitude; partly because of side illumination but also because the dense cores of inhomogeneous clouds are often radiatively‐shielded (unlike their PPH counterparts).Finally, regular arrays of idealized cloud forms are used to demonstrate the potential ambiguity of using cloud radiative forcing ratios, R, as proxy measures for the impact of clouds on atmospheric absorptance. In essence, R depends not only on how clouds influence atmospheric absorption, but also on how they partition radiation between albedo and transmittance.
Transport of near‐tropopause air into the lower midlatitude stratosphere
Authors: Vaughan G. , Timmis C. 
Published: February 2007

AbstractDuring the last week of January 1992 ozonesonde observations over Europe revealed a layer of very low ozone concentrations in the stratosphere—below 100 parts per billion (109) by volume in the potential‐temperature range 360–380 K. A coincident lidar observation revealed that the air was virtually free of volcanic aerosol, which filled the lower stratosphere at that time. The layer corresponded well with low potential vorticity (PV) in ECMWF analysis fields. Trajectory calculations confirmed a subtropical origin for the layer, and PV fields suggest that it was formed in a streamer of low‐PV air drawn from the troposphere over North America as the sub‐tropical jet stream turned northwards on 25 January. Ozone profiles on the equatorward flank of the subtropical jet stream contain similar mixing ratios to those seen in the layer over Europe in the same potential‐temperature range. The mass of the layer at its maximum extent is estimated as 6 × 1015 kg. Most of the air in the layer eventually returned to the subtropics after mixing with ambient midlatitude air.
Thermodynamic analytic fields from Doppler‐radar data by means of the MANDOP analysis
Authors: Protat A. , Lemaitre Y. , Scialom G. 
Published: February 2007

AbstractThe paper is devoted to scale interaction studies. It presents a new approach for retrieving mesoscale and convective‐scale thermodynamic fields from Doppler‐radar data in order to diagnose processes involved in these interactions. Thermodynamic fields are retrieved analytically, using the analytic form of the three‐dimensional wind field obtained by the MANDOP analysis in the non‐dissipative and stationary first‐order anelastic approximation of the equation of motion. Applications on simulated data and experimental data from the TOGA‐COARE show the capability of this new method to retrieve the pressure and temperature fields at various scales of motion, and in particular at mesoscale. This new analysis will be used intensively on Doppler‐radar data collected during the Fronts and Atlantic Storm Tracks Experiment in order to diagnose the multiscale interaction processes associated with frontal‐wave and/or secondary cyclogenesis.
The ECMWF implementation of three‐dimensional variational assimilation (3D‐Var). II: Structure functions
Authors: Rabier F. , McNally A. , Andersson E. , Courtier P. , Undén P. , Eyre J. , Hollingsworth A. , Bouttier F. 
Published: February 2007

AbstractStructure functions for the 3D‐Var assimilation scheme of the European Centre for Medium‐Range Weather Forecasts are evaluated from statistics of the differences between two forecasts valid at the same time. Results compare satisfactorily with those reported in the existing literature. Non‐separability of the correlation functions is a pervasive feature. Accounting for non‐separability in 3D‐Var is necessary to reproduce geostrophic characteristics of the statistics, such as the increase of length‐scale with height for the horizontal correlation of the mass variable, sharper vertical correlations for wind than for mass and shorter horizontal length‐scales for temperature than for mass. In our non‐separable 3D‐Var, the vertical correlations vary with total wave‐number and the horizontal correlation functions vary with vertical level.
Stratospheric water vapour and tropical tropopause temperatures in Ecmwf analyses and multi‐year simulations
Authors: Simmons A. J. , Untch A. , Jakob C. , Kållberg P. , Undén P. 
Published: February 2007

AbstractStratospheric humidity analyses produced operationally by the European Centre for Medium‐Range Weather Forecasts (ECMWF) are discussed for the period since late January 1996 when the practice of resetting the upperlevel specific humidity to a fixed value at each analysis time was abandoned. Near‐tropopause analyses are in reasonable overall agreement with independent observations. Very low humidities occur in conjunction with deep convection and a particularly cold tropopause over the equatorial western Pacific during the northern winter. Drying occurs also in the cold core of the Antarctic polar‐night vortex. the lower stratosphere is moistened in the outer tropics and subtropics in summer and autumn, predominantly in the northern hemisphere. Changes associated with the latest occurrence of El Niño are illustrated.Analysed temperatures near the tropical tropopause are generally in good agreement with corresponding radiosonde measurements, with standard‐level biases of the order of 0.5 degC or less. the past two years are the coldest by about 1 degC in a series of tropical mean 100 hPa analyses extending back to 1979. A cooling trend of about 0.6 degC per decade is seen in the global means of the 100 hPa analyses.Moisture is spread zonally and upward from the tropical tropopause as the data assimilation proceeds, but the rate of upward transfer is much faster than observed. Substantial lateral mixing can occur within the stratosphere over the course of a season. Moistening at middle and high latitudes due to mixing with more humid tropospheric air is confined, realistically, to a shallow layer at the base of the stratosphere.The rate of upward transfer of tropical stratospheric moisture is much more realistic in a multi‐year simulation using a version of the model that has finer stratospheric resolution than the version used for the operational data assimilation. Temperatures at the tropical tropopause and in the Antarctic polar night are accurately simulated, apart from excessive persistence of cold south‐polar temperatures in late winter and early spring. the latter is conducive to drying the model stratosphere; lack of a parametrization of moistening due to methane oxidation is an obvious deficiency in this regard.
The marine atmospheric boundary layer during semaphore. I: Mean vertical structure and non‐axisymmetry of turbulence
Authors: Lambert D. , Durand P. 
Published: February 2007

AbstractThis paper describes the vertical structure of the marine atmospheric boundary layer, analysed using aircraft measurements in the Azores region during SEMAPHORE (Structure des Echanges Mer‐Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale). the flights were performed in the middle of the solar day, during near‐anticyclonic conditions, with weak‐to‐moderate winds and weak surface sensible‐heat flux, over a homogeneous oceanic area. the boundary layer was characterized by a mixed layer, driven by surface fluxes, which was not coupled to the overlying, broken stratocumulus, layer. This decoupling is demonstrated by the shape of the continuous profile of the dissipation rate of turbulent kinetic energy, computed from the continuous slant profiles performed by the aircraft. This method makes it possible to determine the thickness of the mixed layer, which is a relevant scale for the parametrization of the profiles. the turbulence field is analysed through the wavelength of the spectrum peak of the vertical velocity, computed on 392 runs more or less parallel or perpendicular to the mean wind. It demonstrates a stretching of the most energetic eddies along the mean wind. the consequences of this non‐axisymmetric behaviour of the turbulent field on the flux estimates from aircraft data are discussed.
A GCM study of climate change in response to the 11‐year solar cycle
Authors: Haigh Joanna D. 
Published: February 2007

AbstractA general‐circulation model (GCM) is used to investigate the impact of the 11‐year solar‐activity cycle on the climate of the lower atmosphere. Solar forcing is represented by changes in both incident irradiance and stratospheric ozone concentrations. Experiments are carried out with realistic and factor‐ten enhanced solar irradiance changes and with ozone changes based on two‐dimensional photochemical model results and loosely based on Total Ozone Mapping Spectrometer ozone column data. A pattern of response, consistent across all the experiments, is found in which the tropical Hadley cells weaken and broaden, and the sub‐tropical jets and mid‐latitude Ferrel cells move polewards. This causes sub‐tropical warming and a characteristic vertical banding of mid‐latitudes temperature changes in both the summer and winter hemispheres. the GCM results suggest that the precise response of the atmosphere depends on the magnitude and distribution of the ozone changes. This is confirmed by use of an equal‐area model of the tropical Hadley cells in which the input radiative equilibrium‐temperature anomalies are determined from the downward irradiance (both solar and long wave) at the tropopause as calculated in the GCM. As both the magnitude of the solar irradiance change and, more particularly, the latitude‐height structure of solar‐induced ozone changes over the 11‐year cycle are not yet well established, the GCM study may well underestimate the solar effects.
Electrodynamic trapping and manipulation of ice crystals
Authors: Swanson Brian D. , Bacon Neil J. , Davis E. James , Baker Marcia B. 
Published: February 2007

AbstractWe have developed a double‐ring double‐disk electrodynamic balance with humidity control provided by an internal thermal diffusion chamber to study several atmospherically important processes involving 10‐200 μm ice particles. the balance constants needed to quantify the particle size and mass were determined by a three‐dimensional relaxation‐method calculation of the non‐axisymmetric electric fields, and by experimental measurement of the onset of particle stability using polystyrene latex microspheres of known size and mass. We have levitated frost particles of various shapes and sizes under a range of atmospherically relevant temperature and humidity conditions. the measured mass changes during growth and sublimation are consistent with predictions based on vapour and thermal diffusion to equivalent spheres. the electrodynamic balance is shown to be a useful tool for exploring single particle growth and sublimation rates, and for measuring their light‐scattering characteristics.
Effects of cloud‐droplet spectra on the average surface‐temperature of ice accreted on fixed cylindrical collectors
Authors: Avila E. E. , Castellano N. E. , Saunders C. P. R. 
Published: February 2007

AbstractAn experimental study of the heat balance of a stationary cylindrical collector accreting supercooled water droplets has shown a new dependence on the sizes of the water droplets in the laboratory cloud. In a study in 1967, MacKlin and Payne related the steady‐state heat‐release during accretion to the heat loss by convection and conduction; their equation involved a numerical factor χ for which they assumed a value of 0.28. the present study has shown that χ is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s‐1 for a mean volume‐weighted droplet‐diameter of 18 μm, and that χ approaches 0.3 for droplets greater than 30 μm diameter. the results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water‐droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice‐crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.
An investigation into convectively generated potential‐vorticity anomalies using a mass‐forcing model
Authors: Gray M. E. B. 
Published: February 2007

AbstractA mass‐forcing model is used to investigate how the potential‐vorticity (PV) anomalies, formed as a response to changes in the mass field due to convection in a rotating, stratified fluid, are dependent upon the horizontal distribution of the vertical mass transfer.It is found that when the mass is concentrated within a single convective plume a stronger PV anomaly results than when an equivalent total mass is distributed about an ensemble of plumes. When the ensemble is well separated the resultant balanced energy is approximately proportional to the sum of each plume's convected mass to the five‐thirds. As the separation of the ensemble is reduced below that of a Rossby radius the ensemble behaves more like a single system. However, as the PV anomalies interact they coalesce and energy lost in this coalescence process, plus the entrainment of environmental PV, results in less balanced energy than predicted from the above quantitative relationship.Further experiments show that the final PV anomalies show only a little sensitivity to the horizontal scale of the mass transfer, and it is argued that the final balanced energy is primarily a function of the convected mass. However, when the local intensity of the mass transfer is high, such as when the mass is forced through smaller scales, there is a much stronger fast manifold response in the form of inertia‐gravity waves. This complements other studies which argue that convective heating on scales less than a Rossby radius will mostly excite inertia‐gravity waves, whilst when on scales greater than a Rossby radius will strengthen the balanced flow.
The effect of the cloud‐droplet spectrum on electrical‐charge transfer during individual ice‐ice collisions
Authors: Avila E. E. , Pereyra R. G. , Varela G. G. Aguirre , Caranti G. M. 
Published: February 2007

AbstractExperiments were conducted with a wind tunnel in a cold room, in order to investigate the influence of the cloud‐droplet spectrum on the charges transferred when individual ice spheres collided with a fixed artificial graupel pellet growing by riming. the experiments were carried out with ice spheres of about 100 μm in diameter, impact velocities around 4 m s−1, temperatures between −10°C and −30°C and effective water contents representative of real clouds. Two different cloud‐droplet spectra were used. One had more than 30% of the droplets with sizes greater than 13 μm, and the other had more than 50% of the droplets greater than that. the new results show that the size distribution of the droplets is very important to the sign of electric charge transferred. the target graupel charged positively over all the temperature range covered when the smaller‐droplet spectrum was used, but negatively at temperatures below −18°C for the larger‐droplet spectrum. These results show the importance of droplet sizes to thunderstorm charging.
Role of salient potential‐vorticity elements in an event of frontal‐wave cyclogenesis
Authors: Fehlmann René , Davies Huw C. 
Published: February 2007

AbstractExtratropical cyclogenesis is usually accompanied by both an upper‐level trough and a surface front with its cloud‐diabatic accoutrements. In the present study these distinctive structures are interpreted as salient elements of the atmosphere's potential vorticity (PV) distribution, and their role examined for one particular event of frontal‐wave cyclogenesis.The strategy adopted is a form of diagnosis by PV dismemberment. It entails adopting a ‘successful’ forecast with a limited‐area model as a surrogate for the actual event, and then performing a sequence of simulations with modified initial conditions that correspond in each case to the removal of one (or more) of the salient PV elements. This approach provides an assessment of the relative significance of the individual elements, permits an insightful comparison of various extant theories of cyclogenesis, and pinpoints the particular PV elements influencing the event's predictability.It is shown that the replication of the simulated cyclone requires an adequate representation both of specific fine‐scale PV features at tropopause levels and of the diabatically maintained low‐level pre‐frontal PV band. Thus, a tenable theory of cyclogenesis that incorporates this not atypical event should both recognize and help clarify the dependence of cyclogenesis upon the relative locations, movement, scales and structures of the aforementioned salient PV elements.
Least action principle for a general, non‐hydrostatic, compressible, acoustically non‐filtered pressure‐coordinate model
Authors: Rõõm Rein 
Published: February 2007

AbstractThe least action principle is described for general (non‐hydrostatic, compressible, acoustically non‐filtered) pressure‐coordinate equations of atmospheric dynamics (Rõõm 1989), which represents a generalization of the Least Action Principle, first developed for the pressure‐coordinate representation of atmospheric dynamics by Salmon and Smith (1994).
Large‐eddy simulations of neutrally stratified flow over surfaces with spatially varying roughness length
Authors: Hobson J. M. , Wood N. , Brown A. R. 
Published: February 2007

AbstractLarge‐eddy simulations of neutrally stratified flow over a homogeneous surface (with constant roughness length) are used to help determine the requirements for a credible large‐eddy simulation of similar flow over a heterogeneous surface (with varying roughness length). It transpires that particular attention must be paid to simulating the unperturbed mean profiles correctly and to using appropriately high grid resolution. Results from heterogeneous large‐eddy simulations are then compared with those obtained using a first‐order mixing‐length closure model. Finally, the implications of the results for the validity of the effective‐roughness‐length parametrizations that are used in many numerical weather prediction models are considered.
Ensemble simulations of eurasian snow‐depth anomalies and their influence on the summer Asian monsoon
Authors: Ferranti L. , Molteni F. 
Published: February 2007

AbstractThe effect of springtime surface conditions over Eurasia on the monsoon circulation is addressed by using several simulations with the model used by the European Centre for Medium‐Range Weather Forecasts (ECMWF). the simulations have been specially designed to investigate whether the Eurasian snow‐anomaly is a passive response to the tropical forcing, implying that the ultimate relationship exists only between the El Niño/Southern Oscillation (ENSO) and the monsoon as suggested by previous studies, or plays an active independent role in the monsoon modulation. Preliminary results suggest that the Eurasian snow depth is probabilistically predictable, and that it does influence the seasonal‐mean monsoon independently of the ENSO phase. Therefore, proper observations and simulations of the Eurasian snow field can provide an additional and independent contribution to monsoon prediction.
A case‐study of a partially cloudy boundary layer
Authors: Price Jeremy D. 
Published: February 2007

AbstractA case‐study of a partially cloudy boundary layer consisting of cumulus and stratocumulus is presented, and the main dynamical processes responsible for its evolution are identified. Measurements were made with the UK Meteorological Office tethered‐balloon facility which was located in Hampshire, southern England, during the Doppler Radar Observation Project, September 1998.Results show that fair weather cumulus formed during the morning of the third and quickly overdeveloped into patches of stratocumulus. A characteristic of this day was a relatively weak capping inversion which allowed a significant amount of encroachment/entrainment to occur. Between 1100 and 1400 GMT this was calculated at 153 kg m−2. The ratio of entrapment to encroachment was found to be 0.6.Data analysis, together with a simple model, shows that encroachment/entrainment of warm air into the upper pan of the boundary layer significantly increased the stability there and caused a reduction in the cloud area. The data were used to assess the UK Meteorological Office cloud parametrization, and show that during the middle of the day cloud amount was underestimated.