bluuebunny/crossref_metadata_2025_split huggingface dataset:
Horizontal structure of height‐forecast errors over the Southern part of South America
Authors: Vera Carolina 
Published: February 2007

AbstractA study of the height‐forecast error autocovariances was made for a simple intermittent data‐assimilation system (SADI) applied over the southern part of South America. The main objective of this study was to determine from the data the height‐forecast error autocorrelation, and to provide new estimations of the forecast‐ and observation‐error standard deviations. In performing this derivation several significant differences were found between the estimates obtained with a simple forecast model in an area which is data sparse, and those derived for data‐rich regions and advanced forecast models. The forecast‐error correlations were fitted to the Fourier—Bessel series and also to a negative square exponential (NSE) function at the six model levels. The fitted Fourier—Bessel series was able to represent more accurately the wavelength range resolved by the analysis scheme than the fitted NSE function. New estimations of forecast and observation errors have been obtained from the Fourier—Bessel expansion. As the representative errors are much larger because of the coarse resolution of the network and the low‐order truncation of the fit, the observation errors are greater than those used for the northern hemisphere analysis systems. Results also show that the forecast errors are dominated by the synoptic‐scale components in all the levels considered. An evaluation of the impact of using the new set of horizontal covariances was done and it mainly showed that the analysis done with the fitted Fourier‐Bessel series better represents the data than both the original SADI system and an analysis system using a fitted NSE function.
A pole problem in the reduced Gaussian grid
Authors: Courtier P. , Naughton M. 
Published: February 2007

AbstractIt is shown that a pole problem may arise from the use of a reduced Gaussian grid in the spectral transform method on the sphere. The problem is related to an asymptotic property of the associated Legendre functions and can be solved by slightly increasing the number of points close to the pole.It is also shown that the reduced grid controls aliasing arising from quadratic terms only as an asymptotic property. Nevertheless, a small increase in the number of points (everywhere) is enough to reduce the aliasing to a negligible level.
The effect of the passage of cold fronts on the vertical distribution of ozone at the CHMI observatory at Prague‐Libuš
Authors: Halenka T. , LašTovička J. , Radicella S. 
Published: February 2007

AbstractThe response of the total ozone content to meteorological phenomena of a synoptic scale has been studied for many years and is relatively well known now. Much less is known about the response of the ozone profile to such meteorological phenomena. In this paper the response of the shape of the ozone profile to the passage of intense cold fronts and to strong advection from a significantly northern direction is investigated using the results of ozone soundings carried out by the observatory of the Czech Hydrometeorological Institute (CHMI) in Prague‐Libuš during the period January to April for the years 1981 to 1990. Some data from Uccle (Belgium) have also been used.The synoptic patterns studied here were those that were followed by the occurrence of secondary peaks in ozone profiles between the tropopause height (often significantly decreased during such events) and the usual height of the main ozone maximum. Such secondary peaks can be sometimes even larger than the usual ozone maximum. The observed changes in ozone profiles could be explained by the transport of air of polar origin having a greater ozone content in the lower stratosphere behind the upper‐level frontal zone.
Large‐eddy simulation of stable atmospheric boundary layers with a revised stochastic subgrid model
Authors: Brown A. R. , Derbyshire S. H. , Mason P. J. 
Published: February 2007

AbstractSimulations of stable atmospheric boundary layers have been conducted at various stabilities with a revised, stochastic backscatter model based on Mason and Thomson's theoretical and numerical results. Compared to the previous results of Mason and Derbyshire, there is more turbulence and a deeper boundary layer, as was expected from the tendency of the parametrization change to increase the surface stress. Scatterplots of various local non‐dimensional quantities against the gradient Richardson number are presented which indicate a high degree of collapse to a single local scaling curve. Agreement of the non‐dimensional gradients with the surface‐layer observations is greatly improved by the inclusion of backscatter.
Diagnosis of hydrometeor profiles from area‐mean vertical‐velocity data
Authors: Braun Scott A. , Houze Robert A. 
Published: February 2007

AbstractA simple one‐dimensional microphysical retrieval model is developed for estimating vertical profiles of liquid and frozen hydrometeor mixing ratios from observed vertical profiles of area‐mean vertical velocity in regions of convective and/or stratiform precipitation. The mean vertical‐velocity profiles can be obtained from Doppler radar (single and dual) or other means. The one‐dimensional results are shown to be in good agreement with two‐dimensional microphysical fields from a previous study. Sensitivity tests are performed.
The parametrization of surface fluxes in large‐scale models under free convection
Authors: Beljaars Anton C. M. 
Published: February 2007

AbstractThis paper investigates the idea of formulating free convection in large‐scale models as a special case of forced convection. In free convection, the wind speed in the surface transfer law is related to the velocity of the large eddies in the mixed layer and is proportional to the convection velocity scale. The empirical coefficient is estimated with the help of large eddy simulation data by Sykes et al. (1993) and the resulting formulation is compared with field data by Stull (1994). This concept is shown to be applicable to smooth ocean surfaces as well as rough land surfaces. It is argued that within this framework, free convection is a natural extension of forced convection and only needs a minor modification of traditional transfer laws.
Rotating convective disturbances in the trades
Authors: Raymond David J. , Lewis Sharon A. 
Published: February 2007

AbstractObservations of rotating convective disturbances in the trade‐wind region just east of Hawaii are presented. Rotation results from stretching of vertical ambient vorticity in the convective regions. Surface friction is shown to play a significant dissipative role in these disturbances. Ekman pumping associated with the rotation is probably only of secondary importance. Convection is found to be associated with weak local maxima in the boundary‐layer equivalent potential temperature. This suggests that convection occurs where such anomalies make the buoyancy of surface parcels larger than average. Convective available potential energies are found to be small, which means that such equivalent‐potential‐temperature anomalies are important in determining parcel buoyancy. It is hypothesized that mesoscale circulations induced by the ascending motion of convection reinforce the anomalies, resulting in the intensification of the circulations. The equivalent potential temperature of the boundary layer results from a balance between surface fluxes and entrainment from above. Ascending motion apparently reduces entrainmcnt, thus allowing the equivalent potential temperature to rise, whereas subsidence has the opposite effect.
Mesoscale aspects of a dry intrusion within a vigorous cyclone
Authors: Browning K. A. , Golding B. W. 
Published: February 2007

AbstractThe results of a diagnostic study using radar and satellite imagery, together with surface reports and output from regional and mesoscale models, are presented for an occasion of a rapidly deepening cyclone that crossed the British Isles. The study shows how air descended from near‐tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front. One of the dry intrusions is analysed in detail, because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band: in some places the precipitation was entirely suppressed, whilst in other places the precipitation became convective, with a tornadic squall line developing. Although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar, the approach of the dry intrusion was also clearly detected in the satellite water‐vapour imagery, and foreshadowed in the model forecasts.The mesoscale model, despite some limitations, reproduced many of the observed mesoscale features. It also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line. It showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity (PV) which was extruded from the lower part of a large region of high PV near a low tropopause. The extruded PV anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt. The dry intrusion was also characterized by relatively low wet‐bulb potential temperature, θw, and it led to potential instability where it overran the warm air. The warm conveyor belt itself was characterized not only by a high θw but also by a separate strip of high PV generated locally, mainly by condensation. The quality of the mesoscale‐model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when, as in this case, they are orchestrated by resolved larger‐scale dynamics.
Global processing of satellite sounding radiances in a numerical weather prediction system
Authors: Gadd A. J. , Barwell B. R. , Cox S. J. , Renshaw R. J. 
Published: February 2007

AbstractThis paper gives an account of the global soundings system (GLOSS), which is the new method introduced at the Meteorological Office at Bracknell for the processing of global TOVS radiance data for assimilation into numerical weather prediction (NWP) models. The assimilating NWP models themselves provide the prior information necessary to infer temperature and humidity information from radiances. After a brief summary of the historical background, the GLOSS processing is described, noting in particular the differences from similar work elsewhere. Results are then presented from NWP impact studies of the assimilation of temperature profiles derived from satellite soundings. An advantage is demonstrated for the GLOSS temperature retrievals relative to the retrievals distributed by NESDIS and produced from the same radiance data. The advantage of GLOSS is clear and consistent in the extratropical regions of the northern hemisphere and, especially, of the southern hemisphere. In the tropics the results are more mixed. The paper concludes with a note of additional work required before operational implementation of GLOSS, and with an outline of other expected future developments.
Data sparsity and the tropical‐cyclone analysis and prediction problem: Some simulation experiments with a barotropic numerical model
Authors: Weber Harry C. , Smith Roger K. 
Published: February 2007

AbstractSome simulation experiments relevant to the problem of determining the minimum data requirements for the accurate reconstruction of tropical‐cyclone‐scale vortices from given sparse data distributions are described. Also, the accuracy with which the vortex track can be predicted using these data is investigated. The experiments are based on a 96‐hour numerical integration of the barotropic vorticity equation on a beta‐plane, starting with a symmetric tropical‐cyclone‐scale vortex embedded in zonal shear flow. After 48 hours, when asymmetries in the vortex circulation have developed, the model fields in this ‘control’ calculation are used as a ‘perfect’ data set to assess the analysis strategy described. The 20 km horizontal resolution of these new initial data is progressively degraded to test the ability of the analysis procedure to reconstruct the perfect analysis. The analyses of the degraded data sets are used as an initial condition for a further 48‐hour integration of the model, and the resulting vortex tracks are compared with that in the second half of the control run. The influence of the analysed vortex asymmetry on the subsequent vortex track is also studied.As the resolution of the simulated initial data is degraded, so is the information that these data provide on the symmetric circulation and the vortex‐induced asymmetries, and ultimately it becomes necessary to introduce ‘synthetic’ data in the analysis. The calculations indicate some of the problems that need to be overcome to introduce such data properly.The analysis method provides a general way to partition the flow into four components: the large‐scale environment, the symmetric vortex, the vortex asymmetry, and the small‐scale environment. The large‐scale environment is characterized by the lowest few wave numbers in a two‐dimensional Fourier analysis. The residual field is subjected to an azimuthal Fourier analysis about the cyclone centre, and the last three components of the partition are defined by the symmetric component, the wave‐number‐one component and the sum of all higher wave‐number components of this analysis, respectively. An attractive feature of such a partition is that the total flow across the centre of the symmetric vortex, which governs the vortex motion in a barotropic model, is contained in only two components: the large‐scale environment and the vortex asymmetry.
Simulated sensitivity of the earth's radiation budget to 'changes in cloud properties
Authors: Sinha A. , Shine K. P. 
Published: February 2007

AbstractSimulations are made of the long‐term mean clear‐sky and total‐scene components of the earth's radiation budget (ERB), using detailed solar and thermal infrared radiative transfer schemes. These employ as input a wide range of multi‐year observations of atmospheric, surface and cloud parameters. For clear skies, differences between the simulations and results from the Earth Radiation Budget Experiment (ERBE) are generally within the expected accuracy of the observations and calculations, with the most notable disagreement at high latitudes. For cloudy skies, the agreement is less good, but still generally within the systematic error bounds. the absorbed shortwave radiation (ASR) is simulated least well over oceanic regions, with the pattern of disagreement resembling the pattern of response when low cloud cover or liquid water path is perturbed; this suggests that the representation of low cloud cover or liquid water path dominates the ASR discrepancy between the simulation and ERBE. the simulated outgoing longwave radiation (OLR), which is sensitive to the high‐cloud emissivity, differs most from the ERBE OLR in deep convective regions; whilst assuming the high cloud to be black lessens agreement between the simulation and observations in some areas, agreement is substantially improved in others. This indicates that better knowledge of high‐cloud emissivity remains an important issue. the spatial and temporal variations of the sensitivity of the ERB to perturbations to low, mid and high cloud properties are investigated. Principal results include (a) the dominant importance of cloud amount, as compared to cloud temperature, in determining the sensitivity of the ERB to high‐cloud properties, and (b) the greater sensitivity of the net ERB to low‐cloud properties than to those of mid and high cloud. A major uncertainty in the calculations is the degree of cloud overlap; the inclusion of overlapping clouds is found to be capable of reversing the net high‐cloud sensitivities in certain locations. Global mean sensitivity to low cloud perturbations are compared with previous results obtained using a GCM. the simulated sensitivity of the ERB to low cloud cover is substantially larger than in the previous results, although the effects of changes in liquid water path are similar.
A realistic three‐component planetary wave model, with a wave‐breaking parametrization
Authors: Kinnersley J. S. , Kinnersley Jonathan S. 
Published: February 2007

AbstractA fairly simple stratospheric model of the three longest planetary waves is constructed, which includes interference terms between the three wave components, and a diffusive parametrization of wave breaking in regions where the local meridional potential vorticity gradient is negative. In order to allow comparison with the observed behaviour of planetary waves the model is forced near the tropopause with observed wave amplitudes and the model waves propagate over the observed zonal‐mean state. the model is able to mimic the behaviour of the observed waves fairly accurately, with the thermal damping, interference and wave breaking terms all being important to its success. Good results are obtained with a value of local wave‐breaking diffusion coefficient between 106 and 107m2s−1. It is shown that the deficiencies in Matsuno's (1970) model are probably due mainly to the neglect of wave‐wave interactions and an over‐simplified zonal‐mean temperature structure.It is shown that Garcia's (1991) idea that wave breaking completely absorbs any build‐up of zonal‐mean wave activity is probably too severe, but that better results are obtained if the local nature of the wave‐breaking is taken into account.The zonal‐mean diffusion coefficient sometimes has large values within the vortex, as well as in the midlatitude surf zone, with the two regions of diffusion being separated by the vortex edge.The difficulty in estimating the diffusion coefficient required for a tracer is discussed, as well as the behaviour of the zonal‐mean potential vorticity flux during a wave‐breaking episode. the assumption of turbulent diffusion in reversed‐gradient regions implies a positive diffusive contribution to the potential vorticity flux.It was also found that changes in the equatorial zonal wind result in a modulation of the extra‐tropical potential vorticity flux similar to that found by Dunkerton and Baldwin (1991), but that the modulation did not depend strongly on a movement of the tropical zero‐wind line.
The role of ozone‐induced diabatic heating anomalies in the quasi‐biennial oscillation
Authors: Li Dingmin , Shine K. P. , Gray L. J. 
Published: February 2007

AbstractThe diabatic effects of the quasi‐biennial oscillation (QBO) in ozone on the oscillation of temperature and zonal mean winds are investigated using a 2‐dimensional model with full interaction between dynamics, radiation and photochemistry. It is found that the temperature anomaly caused by the ozone QBO makes a significant (25%) contribution to the total temperature anomaly of the QBO although the corresponding change in wind is smaller (about 10%). It is shown that the diabatic effects of the ozone QBO should not be neglected in attempts to simulate the QBO in other parameters.
Evaluation of physical processes in an idealized extratropical cyclone using adjoint sensitivity
Authors: Langland Rolf H. , Elsberry Russell L. , Errico Ronald M. 
Published: February 2007

AbstractAn adjoint model is used to examine the sensitivity of an idealized dry extratropical cyclogenesis simulation to perturbations of predictive variables and parameters during the cyclone life cycle. the adjoint sensitivity indicates how small perturbations of model variables or parameters anywhere in the model domain can influence cyclone central pressure. Largest sensitivity for both temperature and wind perturbations is located between 600 and 900 hPa in the baroclinic zone above the developing cyclone. Perturbations of a given size have more influence on cyclone intensity when located in high‐sensitivity regions (the middle and lower troposphere in this simulation). the effects of physical processes can be interpreted with adjoint sensitivity by considering perturbations that are proportional to temperature and wind tendencies in the basic state (nonlinear forecast). In the early phase of the cyclone life cycle, temperature advection near the steering level in the lower troposphere (about 800 hPa) is strongly cyclogenetic and resembles a Charney mode of baroclinic instability. During the phase of most rapid deepening, temperature advection in the lower troposphere remains important, while interpretation of sensitivity to wind perturbations suggests that increased vorticity in the middle and upper troposphere above the surface low‐pressure centre may also be significant for cyclone intensification.Adjoint techniques can provide insight into spatial and temporal sensitivity not easily obtained from other methods. Higher sea surface temperature (SST) has a cyclogenetic effect mainly in a localized region corresponding to the cyclone warm sector. Outside the areas of high sensitivity, small perturbations of SST have very little effect on central pressure of the forecast cyclone. When strong upward sensible‐heat flux, Fs, exists, it can have a cyclogenetic (preconditioning) influence early in the cyclone life cycle, although downward Fs in the cyclone warm sector is anticyclogenetic during the phase of most rapid deepening. the sensitivity indicates that Fs can be cyclogenetic in one location and anticyclogenetic at the same time in another location, so that Fs effects on cyclone intensity are partially self‐cancelling. Surface momentum stress is anticyclogenetic, with sensitivity highly localized in the cyclone warm sector.
Airborne radiometric observations of cloud liquid‐water emission at 89 and 157 GHz: Application to retrieval of liquid‐water path
Authors: English S. J. 
Published: February 2007

AbstractMeasurements of the microwave brightness temperature of stratocumulus cloud at 89 and 157 GHz using the Microwave Airborne Radiometer Scanning System on the UK Meteorological Research Flight's C‐130 aircraft have been analysed. Comparisons of observed and calculated brightness temperature using models available in the literature have given good agreement for sea‐surface emission and atmospheric attenuation in clear and cloudy skies. A nonlinear retrieval scheme has been applied to the observations to retrieve cloud liquid‐water paths for comparison with the in situ measurements. Validation of the retrieved liquid‐water paths to within 50 g m−2 has been achieved. Ambiguities between cloud retrievals and water vapour and surface parameters are discussed. the observed differences between the retrieval and the in situ measurement are not found to correlate strongly with cloud temperature, but a higher than expected correlation is found with the drop‐size distribution. It is demonstrated that the scheme is applicable to satellite soundings of cloud, and that a similar level of accuracy should be achieved.