bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of variance and total‐energy singular‐vectors
Authors: Reynolds C. A. , Gelaro R. , Rosmond T. E. 
Published: July 2005

AbstractThe analysis‐error variance estimates produced by the Naval Research Laboratory Atmospheric Variational Data Assimilation System are used to constrain singular vectors (SVs) at initial time (the final‐time metric is total energy). These ‘VAR SVs’ are compared to SVs for which total energy is both the initial‐ and final‐time metrics (TE SVs). The spatial distributions and structures of the VAR SVs and TE SVs are examined and their effectiveness in explaining forecast error is compared. Consistent with previous results, the VAR SVs have relatively larger amplitude than TE SVs in regions where analysis errors are larger (such as over oceans and polar regions). In contrast to previous results, the initial‐time VAR SV energy peaks at lower altitudes than the TE SV energy, reflecting the influence of the data‐assimilation‐error variance estimates. Despite these significant differences, the TE and VAR SVs explain comparable amounts of forecast error in both linear and nonlinear contexts. By projecting the VAR SV pseudo‐inverse perturbation onto the TE SVs, it is found that the component inside the TE‐SV subspace accounts for most of the forecast‐error reduction. The component outside the TE‐SV subspace has very little impact on error reduction. It is noteworthy that for both the TE and VAR SVs, nonlinear pseudo‐inverse forecast‐corrections are better than the expected linear corrections. Both sets of SVs exhibit a relationship between singular‐vector growth and forecast‐error total energy, when averaged over many cases. This indicates that the SVs have some utility in predicting forecast‐error variance. Copyright © 2005 Royal Meteorological Society.
Parametrization of ice‐particle size distributions for mid‐latitude stratiform cloud
Authors: Field P. R. , Hogan R. J. , Brown P. R. A. , Illingworth A. J. , Choularton T. W. , Cotton R. J. 
Published: July 2005

AbstractParticle size distributions measured by the UK C‐130 aircraft in ice stratiform cloud around the British Isles are analysed. Probability distribution functions over large scales show that the zeroth, second and fourth moments (equivalent to concentration, ice water content and radar reflectivity) as well as mean particle size have monomodal distributions. Rescaling of the size distributions requiring knowledge of two moments reveals a ‘universal’ distribution that has been fitted with analytically integrable functions. The existence of the ‘universal’ distribution implies that two‐moment microphysics schemes are adequate to represent particle size distributions (PSDs). In large‐scale models it may be difficult to predict two moments, and so power laws between moments have been found as functions of in‐cloud temperature. This means that a model capable of predicting ice water content and temperature can predict ice PSDs to use for calculations requiring knowledge of the size distribution (e.g. precipitation rate, radar reflectivity) or to make direct use of the power laws relating moments of the size distribution. © Royal Meteorological Society, 2005. Contributions by P. R. Field, P. R. A. Brown and R. J. Cotton are Crown copyright.
Resistance and heat‐transfer laws for stable and neutral planetary boundary layers: Old theory advanced and re‐evaluated
Authors: Zilitinkevich Sergej S. , Esau Igor N. 
Published: July 2005

AbstractThe planetary boundary layer (PBL) resistance and heat‐transfer laws express the surface fluxes of momentum and heat through the PBL governing parameters. Since the late sixties, the dimensionless coefficients (A, B and C) in these laws were considered as single‐valued functions of internal stability parameters: µ=u*/|f|Ls in the steady state PBLs, or h/Ls in the evolving PBLs (u* is the friction velocity, f is the Coriolis parameter, Ls is the surface Monin–Obukhov length, and h is the PBL depth). Numerous studies revealed very wide spread of data in empirical plots of A, B and C versus µ or h/Ls. It is not surprising that the above laws, although included in all modern textbooks on boundary‐layer meteorology, are not practically used. In the present paper the resistance and heat‐transfer laws are revised, accounting for the free‐flow stability, baroclinicity and the rise of a capping inversion. The coefficients A, B and C become functions not only of µ or h/Ls, but also of the external stability parameter µN=N/|f| (where N is the Brunt–Väisälä frequency in the free atmosphere above the PBL), the parameter of baroclinicity µΓ=Γ/N (or the free‐flow Richardson number Ri=(N/Γ)2=µΓ−2, where Γ is the geostrophic wind shear), and the ratio of the actual and equilibrium PBL depths h/hE. Moreover, the coefficient C is redefined to account for the effect of a capping inversion. It follows that A, B and C can be considered as single‐valued functions of µ only in the steady‐state, barotropic, nocturnal (that is short‐lived) PBL. On the other hand, the advanced laws cover a wide range of the PBL regimes. They are validated through large‐eddy simulations of different types of PBLs: truly neutral, conventionally neutral, nocturnal and long‐lived. This new development explains why prior formulations performed so poorly, and promotes advanced resistance and heat‐transfer laws as practical tools for use in environmental modelling applications. Copyright © 2005 Royal Meteorological Society.
Resonant gravity‐wave drag enhancement in linear stratified flow over mountains
Authors: Teixeira M. A. C. , Miranda P. M. A. , Argain J. L. , Valente M. A. 
Published: July 2005

AbstractHigh‐drag states produced in stratified flow over a 2D ridge and an axisymmetric mountain are investigated using a linear, hydrostatic, analytical model. A wind profile is assumed where the background velocity is constant up to a height z1 and then decreases linearly, and the internal gravity‐wave solutions are calculated exactly. In flow over a 2D ridge, the normalized surface drag is given by a closed‐form analytical expression, while in flow over an axisymmetric mountain it is given by an expression involving a simple 1D integral. The drag is found to depend on two dimensionless parameters: a dimensionless height formed with z1, and the Richardson number, Ri, in the shear layer. The drag oscillates as z1 increases, with a period of half the hydrostatic vertical wavelength of the gravity waves. The amplitude of this modulation increases as Ri decreases. This behaviour is due to wave reflection at z1. Drag maxima correspond to constructive interference of the upward‐ and downward‐propagating waves in the region z<z1, while drag minima correspond to destructive interference. The reflection coefficient at the interface z=z1 increases as Ri decreases. The critical level, zc, plays no role in the drag amplification. A preliminary numerical treatment of nonlinear effects is presented, where zc appears to become more relevant, and flow over a 2D ridge qualitatively changes its character. But these effects, and their connection with linear theory, still need to be better understood. Copyright © 2005 Royal Meteorological Society.
Linear criteria for gravity‐wave breaking in resonant stratified flow over a ridge
Authors: Teixeira M. A. C. , Miranda P. M. A. 
Published: July 2005

AbstractUsing linear theory, it is shown that, in resonant flow over a 2D mountain ridge, such as exists when a layer of uniform wind is topped by an environmental critical level, the conditions for internal gravity‐wave breaking are different from those determined in previous studies for non‐resonant flows. For Richardson numbers in the shear layer not exceeding 2.25, two zones of flow overturning exist, respectively below and downstream and above and upstream of the expected locations. Flow overturning occurs for values of the dimensionless height of the ridge smaller than those required for a uniform wind profile. These results may have implications for the physical understanding of high‐drag states. Copyright © 2005 Royal Meteorological Society.
Extension of an orographic‐drag parametrization scheme to incorporate orographic anisotropy and flow blocking
Authors: Kim Young‐joon , Doyle James D. 
Published: July 2005

AbstractThe Kim–Arakawa orographic gravity‐wave drag parametrization scheme, which is a component of the US Navy's NOGAPS ALPHA (Navy Operational Global Atmospheric Prediction System, Advanced‐Level Physics and High Altitude), is extended to include the effects of orographic anisotropy and low‐level flow blocking. The algorithms to calculate the orographic statistics needed for the parametrization are also revised. The extended scheme is evaluated against mountain waves explicitly simulated with COAMPS®† (Coupled Ocean/Atmosphere Mesoscale Prediction System) of NRL (Naval Research Laboratory).Mountain‐wave simulations over Boulder, Colorado, USA, are used for representing realistic situations of different wave activity including severe downslope windstorms. The simulations are area‐averaged and interpolated to the vertical grid of NOGAPS, and are used as the input to the extended Kim–Arakawa scheme. The scheme is calibrated by comparing the parametrized vertical distribution of the momentum fluxes with the counterpart obtained from the explicit mesoscale simulations. Overall, the calibrated scheme successfully represents the simulated magnitudes and vertical divergences of the momentum fluxes. A flow regime diagram is constructed utilizing a time series of the simulations to further evaluate the parametrization. The robustness of the orographic statistics, together with an approximate method to improve it, are also addressed. Copyright © 2005 Royal Meteorological Society.
Investigation of the sensitivity of the ECMWF radiation scheme to input parameters using the adjoint technique
Authors: Janiskov'a Marta , Morcrette Jean‐jacques 
Published: July 2005

AbstractThe potential of the adjoint technique for studying the sensitivity of a physical parametrization scheme to its input parameters is investigated. Compared with the standard evaluation approach, where the sensitivity of all the outputs is obtained by modifying one given input, the adjoint method offers a complementary and very efficient approach for sensitivity studies. The paper focuses on an estimation of the sensitivity of the ECMWF radiation schemes to changes in temperature, humidity, aerosols and cloud properties. The sensitivity of the topof‐atmosphere radiation fluxes in clear‐ and cloudy‐sky conditions, computed globally by the ECMWF model for the different seasons, is discussed in this study. This allows us to investigate spatial and temporal patterns in the sensitivity variations. The evaluation of the Jacobian of radiation fluxes by the adjoint technique provides an insight on the extent to which the various radiation fluxes are sensitive to the meteorological variables and confirms results usually obtained by more computationally intensive traditional methods. In addition, such a sensitivity study gives some indications on the importance and efficiency of particular types of observations in modifying the initial conditions of a model. Copyright © 2005 Royal Meteorological Society.
The impact of the stratosphere on the troposphere during the southern hemisphere stratospheric sudden warming, September 2002
Authors: Charlton A. J. , O'neill A. , Lahoz W. A. , Massacand A. C. , Berrisford P. 
Published: July 2005

AbstractRecent research has established that a small but statistically significant link exists between the stratosphere and the troposphere in the northern hemisphere extratropics. In this paper it is shown that a similar link exists between the stratosphere and troposphere during the unprecedented September 2002 sudden warming in the southern hemisphere. Two ensemble forecasts of the stratospheric sudden warming are run which have different stratospheric initial conditions and identical tropospheric initial conditions. Stratospheric initial conditions have an impact on the tropospheric flow at the peak of the major warming (5 days into the run) and on longer time‐scales (18 days into the run). The character of this influence is a localized, equatorward shift of the tropospheric storm track. The averaged impact of the change in the position of the storm‐track maps strongly onto the Southern Annular Mode structure, but does not have an annular character. Copyright © 2005 Royal Meteorological Society.
Consistent approximate models of the global atmosphere: shallow, deep, hydrostatic, quasi‐hydrostatic and non‐hydrostatic
Authors: White A. A. , Hoskins B. J. , Roulstone I. , Staniforth A. 
Published: July 2005

AbstractWe study global atmosphere models that are at least as accurate as the hydrostatic primitive equations (HPEs), reviewing known results and reporting some new ones. The HPEs make spherical geopotential and shallow atmosphere approximations in addition to the hydrostatic approximation. As is well known, a consistent application of the shallow atmosphere approximation requires omission of those Coriolis terms that vary as the cosine of latitude and of certain other terms in the components of the momentum equation. An approximate model is here regarded as consistent if it formally preserves conservation principles for axial angular momentum, energy and potential vorticity, and (following R. Müller) if its momentum component equations have Lagrange's form. Within these criteria, four consistent approximate global models, including the HPEs themselves, are identified in a height‐coordinate framework. The four models, each of which includes the spherical geopotential approximation, correspond to whether the shallow atmosphere and hydrostatic (or quasi‐hydrostatic) approximations are individually made or not made. Restrictions on representing the spatial variation of apparent gravity occur. Solution methods and the situation in a pressure‐coordinate framework are discussed. © Crown copyright 2005.
Spatial distribution of cloud droplets in a turbulent cloud‐chamber flow
Authors: Jaczewski A. , Malinowski S. P. 
Published: July 2005

AbstractWe present the results of a laboratory study of the spatial distribution of cloud droplets in a turbulent environment. An artificial, weakly turbulent cloud, consisting of droplets of diameter around 14µm, is observed in a laboratory chamber. Droplets on a vertical cross‐section through the cloud interior are imaged using laser sheet photography. Images are digitized and numerically processed in order to retrieve droplet positions in a vertical plane. The spatial distribution of droplets in the range of scales, l, from 4 to 80 mm is characterized by: the clustering index CI(l), the volume averaged pair correlation function η(l) and a local density defined on a basis of correlation analysis. The results indicate that, even in weak turbulence in the chamber that is less intense and less intermittent than turbulence observed in clouds, droplets are not spread according to the Poisson distribution. The importance of this deviation from the Poisson distribution is unclear when looking at CI(l) and η(l). The local density indicates that in small scales each droplet has, on average, more neighbours than expected from the average droplet concentration and gives a qualitative and intuitive measure of clustering. Copyright © 2005 Royal Meteorological Society.
Evaluation of probabilistic prediction systems for a scalar variable
Authors: Candille G. , Talagrand O. 
Published: July 2005

AbstractA systematic study is performed of a number of scores that can be used for objective validation of probabilistic prediction of scalar variables: Rank Histograms, Discrete and Continuous Ranked Probability Scores (DRPS and CRPS, respectively). The reliability‐resolution‐uncertainty decomposition, defined by Murphy for the DRPS, and extended here to the CRPS, is studied in detail. The decomposition is applied to the results of the Ensemble Prediction Systems of the European Centre for Medium‐range Weather Forecasts and the National Centers for Environmental Prediction. Comparison is made with the decomposition of the CRPS defined by Hersbach. The possibility of determining an accurate reliability‐resolution decomposition of the RPSs is severely limited by the unavoidably (relatively) small number of available realizations of the prediction system. The Hersbach decomposition may be an appropriate compromise between the competing needs for accuracy and practical computability. Copyright © 2005 Royal Meteorological Society.
On the use of the super compact scheme for spatial differencing in numerical models of the atmosphere
Authors: Esfahanian V. , Ghader S. , Mohebalhojeh A. R. 
Published: July 2005

AbstractThe ‘Super Compact Finite‐Difference Method’ (SCFDM) is applied to spatial differencing of some prototype linear and nonlinear geophysical fluid dynamics problems. An alternative form of the SCFDM relations for spatial derivatives is derived. The sixth‐order SCFDM is compared in detail with the conventional fourth‐order compact and the second‐order centred differencing. For the frequency of linear inertia‐gravity waves on different numerical grids (Arakawa's A–E and Randall's Z) related to the Rossby adjustment process, the sixth‐order SCFDM shows a substantial improvement on the conventional methods. For the Jacobians involved in vorticity advection by non‐divergent flow and in the Bolin–Charney balance equation, a general framework, valid for every finite‐difference method, is derived to present the discrete forms of the Jacobians. It is found that the sixth‐order SCFDM provides a noticeably more accurate representation of the wave‐number distribution of the Jacobians, when compared with the conventional methods. The problem of reconstructing the stream‐function field from the vorticity field on a sphere is also considered. For the Rossby–Haurwitz wave, the computation of a normalized global error at different horizontal resolutions in longitude and latitude directions shows that the sixth‐order SCFDM can markedly improve on the fourth‐order compact. The sixth‐order SCFDM is thus proposed as a viable method to improve the accuracy of finite‐difference models of the atmosphere. Copyright © 2005 Royal Meteorological Society.
Anvil glaciation in a deep cumulus updraught over Florida simulated with the Explicit Microphysics Model. I: Impact of various nucleation processes
Authors: Phillips Vaughan T. J. , Andronache Constantin , Sherwood Steven C. , Bansemer Aaron , Conant William C. , Demott Paul J. , Flagan Richard C. , Heymsfield Andy , Jonsson Haflidi , Poellot Micheal , Rissman Tracey A. , Seinfeld John H. , Vanreken Tim , Varutbangkul Varuntida , Wilson James C. 
Published: July 2005

AbstractSimulations of a cumulonimbus cloud observed in the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL‐FACE) with an advanced version of the Explicit Microphysics Model (EMM) are presented. The EMM has size‐resolved aerosols and predicts the time evolution of sizes, bulk densities and axial ratios of ice particles. Observations by multiple aircraft in the troposphere provide inputs to the model, including observations of the ice nuclei and of the entire size distribution of condensation nuclei.Homogeneous droplet freezing is found to be the source of almost all of the ice crystals in the anvil updraught of this particular model cloud. Most of the simulated droplets that freeze to form anvil crystals appear to be nucleated by activation of aerosols far above cloud base in the interior of the cloud (‘secondary’ or ‘in‐cloud’ droplet nucleation). This is partly because primary droplets formed at cloud base are invariably depleted by accretion before they can reach the anvil base in the updraught, which promotes an increase with height of the average supersaturation in the updraught aloft. More than half of these aerosols, activated far above cloud base, are entrained into the updraught of this model cloud from the lateral environment above about 5 km above mean sea level. This confirms the importance of remote sources of atmospheric aerosol for anvil glaciation.Other nucleation processes impinge indirectly upon the anvil glaciation by modifying the concentration of supercooled droplets in the upper levels of the mixed‐phase region. For instance, the warm‐rain process produces a massive indirect impact on the anvil crystal concentration, because it determines the mass of precipitation forming in the updraught. It competes with homogeneous freezing as a sink for cloud droplets. The effects from turbulent enhancement of the warm‐rain process and from other nucleation processes on the anvil ice properties are assessed. Copyright © 2005 Royal Meteorological Society.
Can error source terms in forecasting models be represented as Gaussian Markov noises?
Authors: Nicolis C. 
Published: July 2005

AbstractThe repercussions of model error on the long term climatological means and on the variability around them are analysed. The extent to which a stochastic representation of error source terms provides a universal correcting mechanism is addressed. General relations are derived linking the model error to the climatological means and the variability properties of a forecasting model subjected to a correcting Gaussian Markov noise on the basis of moment equations associated with Fokker–Planck and Liouville type equations. These relations are implemented in a variety of models giving rise to regular and to chaotic solutions. As it turns out, forecasting models fall into distinct universality classes differing in their response to the effect of noise according to the structure of the Jacobian and the Hessian matrices of the model phase‐space velocity. It is concluded that different trends may exist in which the ‘correcting’ noise tends to depress or, on the contrary, amplify the model error. Copyright © 2005 Royal Meteorological Society.
Dynamic System Identification Using a Step Input
Authors: Kosaka Manabu , Uda Hiroshi , Bamba Eiichi , Shibata Hiroshi 
Published: July 2005

In this paper, we propose a deterministic off-line identification method performed by using input and output data with a constant steady state output response such as a step response that causes noise or vibration from a mechanical system at the moment when it is applied but they are attenuated asymptotically. The method can directly acquire any order of reduced model without knowing the real order of a plant, in such a way that the intermediate parameters are uniquely determined so as to be orthogonal with respect to 0 ∼ N-tuple integral values of output error and irrelevant to the unmodelled dynamics. From the intermediate parameters, the coefficients of a rational transfer function are calculated. In consequence, the method can be executed for any plant without knowing or estimating its order at the beginning. The effectiveness of the method is illustrated by numerical simulations and also by applying it to a 2-mass system.