bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium atmospheres of a two‐column radiative‐convective model
Authors: Nilsson J. , Emanuel K. A. 
Published: February 2007

AbstractInteraction between steady, large‐scale atmospheric circulations and a radiative‐convective environment is considered. As a model tool, we use a two‐column radiative‐convective model with an explicit hydrological cycle that uses clear‐sky conditions in the radiation calculation. A flow field is calculated by the linearized, hydrostatic equations of motion in a non‐rotating frame of reference. Mechanical damping is represented by vertical diffusion of momentum and surface drag. the flow advects heat and moisture, and thereby modifies the local radiative‐convective equilibrium. A dynamically passive ocean mixed layer is situated below the model atmosphere.All externally specified parameters are identical in the two columns, implying that local radiative‐convective equilibrium is a steady solution. For weak mechanical damping (or small column length), the local equilibrium is generally unstable due to a positive feedback between large‐scale subsidence and infrared cooling, which operates via advective drying. A circulating equilibrium, in which the air ascends in one column and descends in the other, is attained. Due to a reduced content of clear‐sky water vapour, which is the major infrared absorber in the model, the circulating equilibrium can emit the absorbed solar radiation at a significantly lower surface temperature than the corresponding local equilibrium.In the limit of a nearly inviscid atmosphere, the intensity of the large‐scale circulation is controlled chiefly by the mid‐tropospheric radiative cooling in the downdraught column. In this regime, we find two distinct equilibria with circulation that are distinguished by the features of the downdraught column: one branch with deep convection but where the integrated convective heating vanishes due to evaporation of precipitation; and one branch with shallow (or no) convection where the surface boundary layer is disconnected from the free atmosphere.
3D‐Var Hessian singular vectors and their potential use in the ECMWF ensemble prediction system
Authors: Barkmeijer J. , Buizza R. , Palmer T. N. 
Published: February 2007

AbstractSingular vectors are computed which are consistent with 3D‐Var (three‐dimensional variational) estimates of analysis error statistics. This is achieved by defining the norm at initial time in terms of the full Hessian of the 3D‐Var cost function. At final time the total energy norm is used. the properties of these Hessian singular vectors (HSVs) differ considerably from total energy singular vectors (TESVs) in such aspects as energy spectrum and growth rate. Despite these differences, the leading 25 TESVs and HSVs explain nearly the same part of the 2‐day forecast error.Two experimental ensemble configurations are studied. One configuration uses perturbations based on HSVs in the computation of initial perturbation, the other uses TESVs and 2‐day linearly evolved singular vectors (ESVs) of two days before. the latter approach provides a way to include more stable and large‐scale structures in the perturbations. Ten pairs of ensembles are compared to the operational European Centre for Medium‐Range Weather Forecasts Ensemble Prediction System. the ensembles using ESVs perform slightly better. the ensembles based on HSVs show a slightly worse performance and are lacking some spread in the medium range. Possible directions to improve the computation of HSVs are discussed.
Variational analysis of effective soil moisture from screen‐level atmospheric parameters: Application to a short‐range weather forecast model
Authors: Rhodin A. , Kucharski F. , Callies U. , Eppel D. P. , Wergen W. 
Published: February 2007

AbstractA variational analysis scheme for soil moisture that assimilates analysed fields of screen‐level atmospheric temperatures and relative humidities in the domain of the operational regional weather forecast model of the Deutscher Wetterdienst, is investigated over a five‐day period in March 1994.To reduce the computational load implied by the variational analysis scheme, a stand‐alone system comprising the soil module plus a simplified atmospheric boundary‐layer description has been isolated from the full forecast model. the coupling between the two systems is mediated via boundary conditions and source terms.The retrieved soil moisture values are consistently much lower than those in the operational reference run. They can be regarded as tuned effective parameters providing optimum lower‐boundary conditions for the atmosphere. the improved quality of the resulting sensible‐ and latent‐heat fluxes can be substantiated by better atmospheric forecasts.Numerical experiments give estimates of the influence on analysed soil moistures of the misspecification of radiative forcing. Soil moisture values derived from observations of atmospheric relative humidity alone are more stable with respect to radiation errors than those derived from atmospheric temperature observations.
Conceptual models of upper‐level frontogenesis in south‐westerly and north‐westerly flow
Authors: Schultz David M. , Doswell Charles A. 
Published: February 2007

AbstractThe conceptual model proposed by Shapiro as it is applied to the evolution of an upper‐level frontal zone within a baroclinic wave is reviewed and its limitations are investigated through previous literature and two casestudies presented in this paper. the early stages in the evolutions of these two cases are used to examine specific limitations of this conceptual model: (1) upper‐level frontogenesis in south‐westerly flow that evolves from a state of equivalent barotropy to a state of cold advection along the front, and (2) upper‐level frontogenesis in northwesterly flow with along‐front variation in the sign of the thermal advection, such that warm advection occurs upstream of cold advection in the thermal trough.Vector‐frontogenesis diagnostics for the Lagrangian rate of change of the magnitude and direction of the horizontal potential‐temperature gradient, including tilting due to vertical motion, are derived. These diagnostics are applied to the two cases to examine the maintenance of the potential‐temperature gradient and the development of cold advection along each upper‐level front. the upper‐level front in south‐westerly (north‐westerly) flow was maintained primarily by deformation (tilting) frontogenesis, in agreement with previous research. the increasing cold advection along the upper‐level front in both cases was related to an upstream vorticity maximum. For the case in south‐westerly flow, the pre‐existing vorticity maximum approached a downstream equivalent‐barotropic upper‐level front in a manner similar to an instant occlusion, resulting in cold advection along the length of the upper‐level front. For the case in north‐westerly flow, an intensifying vorticity maximum concentrated the cold advection in the base of the thermal trough, as warm advection developed upstream.These two cases are compared to upper‐level fronts in previous literature and a climatology of upper‐level fronts associated with landfalling cyclones over the eastern North Pacific Ocean. the results indicate that these two cases are typical of early evolutions of upper‐level fronts that can occur in south‐westerly and north‐westerly flow. Therefore, a revised version of the Shapiro conceptual model is presented that represents more accurately the early evolutions exhibited in the present and previous studies.
Frontogenesis and frontal motion due to confluent deformation with a translating dilatation axis
Authors: Cunningham P. , Keyser D. 
Published: February 2007

AbstractA two‐dimensional model of primitive‐equation frontogenesis is formulated in which the forcing is due to a basic‐state field of confluent deformation with a dilatation axis that translates in the cross‐front direction. Although the translation speed and direction of motion of the basic‐state dilatation axis have no effect on frontal structure when the total deformation is spatially uniform, they can influence considerably the motion of the front. At the surface, this motion may be separated into two components: (i) internal motion, directed towards the warm air, which is associated with the secondary ageostrophic circulation of the front itself; and (ii) external motion, either towards cold or warm air, which is associated with the initial location and translation speed of the basicstate dilatation axis. the latter component ultimately dominates, and thus the motion of a mature front may be thought of as being controlled by the large‐scale flow. However, the former may dominate early on in the frontal evolution, resulting in significantly different frontal trajectories depending on the initial location of the basic‐state dilatation axis and on whether this axis is moving towards the cold or the warm air. the relative locations of various conventional frontal measures are examined in the special case of a uniformly translating dilatation axis. of these measures the axes of maximum baroclinicity and vorticity become collocated at the surface as the front intensifies. However, the basic‐state dilatation axis and the confluence axis, the latter being defined as the location of zero total wind in the cross‐front direction, may be displaced considerably from this merger point, with this displacement depending on the initial location and subsequent motion of the basic‐state dilatation axis. Potential extensions of the model are discussed with regard to improved understanding of the difference in structure and motion between cold and warm fronts.
The January 1992 stratospheric sudden warming: A role for tropical inertial instability?
Authors: Rosier Suzanne M. , Lawrence Bryan N. 
Published: February 2007

AbstractTwelve simulations of the stratosphere and mesosphere have been performed to investigate the near‐major stratospheric warming of January 1992. All were initialized close to the observed warming. the resulting simulations fall into two classes: those that accurately reproduce the timing and anticyclonic merger mechanism of the observed warming and those that fail. the model used was a mechanistic stratosphere‐mesosphere model. with a prescribed troposphere; thus differences among the simulations must only be due to differences among the initial conditions, which were constructed using different combinations of observed and climatological data. the main differences between the initial conditions of those simulations that succeed and those that fail are in low latitudes. A detailed analysis of two contrasting simulations reveals that the one which fails does not accurately reproduce the observed conveyor belt feeding tropical low‐potential‐vorticity (PV) air into the Aleutian high. Several factors appear to have combined to make the difference between the successful and the unsuccessful simulation of this sudden warming. the amount of low PV already present in higher latitudes in the initial condition appears to have an influence, as does the strength of the subtropical PV barrier. Also important is the Rossby wave structure which, by determining the degree of zonal asymmetry of the PV barrier, influences the injection of low PV into higher latitudes. In addition, however, we propose that the inertial stability of the tropical upper stratosphere might have played a significant role. In the unsuccessful simulation the tropical upper stratosphere is more inertially unstable than in the successful simulation; in this region more vigorous small‐scale roll structures develop which, in stabilizing the flow, might have inhibited the northward transport of tropical air that appears to be a key part of the development of the observed sudden warming.
Observations of non‐dimensional wind shear in the coastal zone
Authors: Vickers Dean , Mahrt L. 
Published: February 2007

AbstractVertical profiles of the time‐averaged wind stress, wind speed and buoyancy flux from the off‐shore tower site in the Risø Air Sea Experiment are used to evaluate similarity theory in the coastal zone. the observed dependence of the non‐dimensional wind shear on stability is compared to the traditional parametrization. Relationships between the non‐dimensional shear, development of internal boundary layers and wave state are explored.We find that the largest‐scale turbulent eddies are suppressed in shallow convective internal boundary layers, leading to larger non‐dimensional shear than that of the traditional prediction based only on stability. In shallow stable boundary layers, elevated generation of turbulence leads to smaller non‐dimensional shear compared to the traditional prediction. Over young growing waves in stable stratification, the observed non‐dimensional shear is less than that over older more mature waves in otherwise similar conditions. the non‐dimensional shear is a function of wave state for stable conditions even though the observations are well above the wave boundary layer. We conclude that development of shallow internal boundary layers and young growing‐wave fields, both of which are common in the coastal zone, can lead to substantial departures of the non‐dimensional shear from the prediction based only on stability.
Direct retrieval of wind from total ozone mapping spectrometer (TOMS) data: Examples from FASTEX
Authors: Davis Christopher , Low‐Nam Simon , Shapiro Melvyn A. , Zou Xiaolei , Krueger Arlin J. 
Published: February 2007

AbstractThe quantitative relationship between ozone and potential vorticity, and hence balanced wind and temperature, is examined using observations collected for a one‐month period by the total ozone mapping spectrometer (TOMS). Ozone data are compared with Ertel potential vorticity (PV) integrated vertically from 500 to 50 mb, obtained from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis archive. By performing a simple time filtering we isolate synoptic‐scale transients in the ozone and PV. We show that the previously reported high correlation between PV and ozone is actually variable from day to day. the correlation also shows strong latitudinal dependence, with essentially no correlation in the tropics and high correlation in middle latitudes.A method is introduced to derive a three‐dimensional PV representation from ozone data and a background field taken from the reanalysis data. PV‐inversion methods are then used to recover balanced winds and temperatures and geopotential heights which may be compared to the analysed fields. Results suggest that many of the upper‐tropospheric synoptic‐scale wind perturbations may be recovered from the ozone data. A systematic error in the retrieval method used here is the understimation of the strength of upper‐level ridges, corresponding to an excess of vertically integrated ozone compared with integrated PV. We discuss reasons for this difference.
FASTEX IOP17 cyclone: Introductory synoptic study with field data
Authors: Cammas Jean‐Pierre , Pouponneau Béatrice , Desroziers Gerald , Santurette Patrick , Joly Alain , Arbogast Philippe , Mallet Isabelle , Caniaux Guy , Mascart Patrick 
Published: February 2007

AbstractThis paper introduces the study of the early development phase of the IOP17 frontal cyclone of the FASTEX field experiment (Fronts and Atlantic Storm‐Track EXperiment). With the support of observations from FASTEX observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational Météo‐France ARPEGE (Action de Recherche Petite Echelle Grand Echelle) analysis cycle, i.e. cloud head, dry wedge and upper‐level jet outflow. A discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well‐known conceptual models of maritime cyclone life cycles: (i) the indirect role of an upper‐level precursor in triggering the surface low; (ii) the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone. These two mechanisms are the subject of two companion papers.
Effects of a low‐level precursor and frontal stability on cyclogenesis during FASTEX IOP17
Authors: Mallet Isabelle , Arbogast Philippe , Baehr Christophe , Cammas Jean‐Pierre , Mascart Patrick 
Published: February 2007

AbstractThe Fronts and Atlantic Storm‐Track EXperiment (FASTEX) has provided comprehensive data to document the life‐cycle of secondary frontal cyclones over the North Atlantic, and to improve the understanding of cyclogenesis mechanisms. This study analyses the processes leading to the triggering of a particularly well‐sampled frontal cyclone that developed on the trailing cold front of a mature primary cyclone during FASTEX Intensive Observation Period 17 (IOP17) between 16 and 20 February 1997.The case features both a classical low‐level vorticity strip along the primary front where the frontal cyclone develops and, more unexpectedly, a pre‐existing continental surface low further west, the importance of which is revealed in the pilot study of Arbogast and Joly. In order to study possible cyclogenetic contributions along the primary front, the domain‐independent vorticity‐divergence attribution technique of Bishop is used to partition the flow into contributions from the continental low and from the large‐scale environment. Results indicate that the frontal cyclone is triggered where and when along‐front stretching decreases below the theoretical critical threshold of Bishop and Thorpe. It is shown that the cyclone is developing under normalized strain less than 1, in agreement with other case‐studies. Finally, the role of the continental low is investigated using a series of numerical forecasts made from different initial conditions manipulated with a potential‐vorticity inversion tool. the wind attributable to the continental low accounts for roughly 30% of the along‐front stretching decrease. the continental low also has a frontolytic effect on the western part of the primary front where its thermal advection pattern favours cyclogenesis.In general terms, the frontal‐cyclone triggering seems to support the Bishop and Thorpe theoretical framework of frontal instability in low‐strain areas. However, a more complex picture arises when considering the role of the continental surface low, which also acts as a low‐level precursor.
Mesoscale analysis of arc rainbands in a dry slot
Authors: Browning K. A. , Roberts N. M. 
Published: February 2007

AbstractA series of almost concentric, are‐shaped narrow rainbands was observed travelling at 140 km h−1 and producing severe wind gusts over parts of England. Their structure and environment have been analysed using radar and satellite imagery, mesoscale‐model diagnostics, surface observations and additional rawinsonde ascents obtained during the Fronts and Atlantic Storm‐Track EXperiment (FASTEX). the multiple‐rainband event is shown to have been associated with part of a dry intrusion characterized by a mesoscale vortex/cold pool. the event occurred within the ‘dry slot’ region of a small frontal cyclone where the mesoscale pool of cold dry air was overrunning warm‐sector air. Continuous wind profiles from a UHF radar, together with a well‐located rawinsonde at the ‘epicentre’ of the arc rainbands, showed that the major anomaly in the cold pool was an area of locally stronger winds (>40 m s−1) at 800 hPa colocated with the temperature minimum at that level. the observed orientation of the rainbands is explained in terms of the cold‐frontal structure at this level triggering ascent of the underlying warm moist air. the multiple nature of the arc rainbands remains unexplained; the possibilities of mesoscale gravity waves and conditional symmetric instability are both considered.
Improved retrieval of tropospheric temperatures from remote measurements of thermal radiation using the adiabatic lapse rate as a constraint
Authors: Peckham G. E. , Grippa M. 
Published: February 2007

AbstractSpace‐borne radiometers now form an important part of the global network of atmospheric observing systems which provide data for weather forecasting and studies of climate change. However, achieving adequate vertical resolution remains a problem, particularly for the retrieval of profiles of temperature and of water‐vapour concentrations in the troposphere. The problem of retrieving these profiles from radiance measurements is ill‐posed in that there is no unique answer‐solutions may be unstable and excessively sensitive to measurement noise. A technique known as regularization may be used to stabilize the solution by biasing the retrieved profiles toward an acceptable form. Similar inverse problems occur in many areas of science and engineering. Work on image enhancement has shown that regularization which includes a constraint, such as non‐negativity of the solution, can provide retrievals with improved accuracy over other regularization methods. We note that the adiabatic lapse rate provides an effective constraint on tropospheric temperature profiles and we exploit this to develop a regularization scheme for the retrieval of atmospheric temperatures. We demonstrate that the retrieved profiles are indeed more accurate than those obtained without this constraint.
Remote sensing of bubble clouds in sea water
Authors: Flatau Piotr J. , Flatau Maria , Zaneveld J. R. V. , Mobley Curtis D. 
Published: February 2007

AbstractWe report on the influence of submerged bubble clouds on the re mote‐sensing properties of water. We show that the optical effect of bubbles on radiative transfer and on the estimate of the ocean colour is significant. We present a global map of the volume fraction of air in water derived from daily wind speed data. This map, together with the parametrization of the microphysical properties, shows the possible significance of bubble clouds on the albedo to incoming solar energy.