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BackgroundAtypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive CNS tumors of infancy and early childhood. Hallmark is the surprisingly simple genome with inactivating mutations or deletions in the SMARCB1 gene as the oncogenic driver. Nevertheless, AT/RTs are infiltrated by immune cells and even clonally expanded T cells. However, it is unclear which epitopes T cells might recognize on AT/RT cells.MethodsHere, we report a comprehensive mass spectrometry (MS)-based analysis of naturally presented human leukocyte antigen (HLA) class I and class II ligands on 23 AT/RTs. MS data were validated by matching with a human proteome dataset and exclusion of peptides that are part of the human benignome. Cryptic peptide ligands were identified using Peptide-PRISM.ResultsComparative HLA ligandome analysis of the HLA ligandome revealed 55 class I and 139 class II tumor-exclusive peptides. No peptide originated from the SMARCB1 region. In addition, 61 HLA class I tumor-exclusive peptide sequences derived from non-canonically translated proteins. Combination of peptides from natural and cryptic class I and class II origin gave optimal representation of tumor cell compartments. Substantial overlap existed with the cryptic immunopeptidome of glioblastomas, but no concordance was found with extracranial tumors. More than 80% of AT/RT exclusive peptides were able to successfully prime CD8+T cells, whereas naturally occurring memory responses in AT/RT patients could only be detected for class II epitopes. Interestingly, >50% of AT/RT exclusive class II ligands were also recognized by T cells from glioblastoma patients but not from healthy donors.ConclusionsThese findings highlight that AT/RTs, potentially paradigmatic for other pediatric tumors with a low mutational load, present a variety of highly immunogenic HLA class I and class II peptides from canonical as well as non-canonical protein sources. Inclusion of such cryptic peptides into therapeutic vaccines would enable an optimized mapping of the tumor cell surface, thereby reducing the likelihood of immune evasion.

Allogeneic innate lymphocytes such as Vγ9Vδ2 T cells are attractive candidates for cancer immunotherapy as they provide MHC-unrestricted antitumor activity without clinical evidence for inducing graft-versus-host disease (GvHD). However, current cellular immunotherapy approaches lack predictive biomarkers identifying patient cohorts most susceptible to immune attack. For this purpose we performed a comprehensive analysis of clinical, genetic, metabolic, and immunophenotypic features of 19 primary acute myeloid leukemia (AML) samples and correlated these factors with AML blast recognition by allogeneic Vγ9Vδ2 T cells. We show that 36% of primary AML samples were intrinsically susceptible to allogeneic Vγ9Vδ2 T cells. Among several evaluated features, only UL-16 binding protein 1 (ULBP1) expression (P

Results from 3 ½-yr experimental program of extended-range integrations of the ECMWF numerical weather prediction model are summarized. The topics discussed include: 1) The evolution of extended-range systematic errors and skill in forecasting large-scale weather regime transitions ; 2) The dependence of extended-range systematic error and skill on model horizontal resolution ; 3) Monthly mean forecast of tropical rainfall ; 4) Tropical/extratropical interaction, and the influence of tropical low-frequency variability on extratropical forecast skill ; 5) Ensemble forecasting, including the impact of ensemble averaging on forecast skill, and ensemble dispersion as a measure of forecast reliability ; and 6) Probabilistic forecasting using phase-space cluster analysis. Our results are broadly consistent with those from other major centers evaluating the feasibility of dynamical extended-range prediction. We believe that operational extende-range forecasting using the ECMWF model may be viable to day 20 – and possibly beyond – following further research on techniques for Monte Carlo forecasting, and when model systematic error in the tropics has been reduced significantly.

On the occasion of the 70th annual meeting of the American Academy of Dermatology in San Diego the ILDS Executive Committee hosted a cocktail reception in the evening of 18 March. The reception, held at the Marriott Hotel on an evening of several competing attractions, was well attended by friends of the ILDS, who stopped by for a drink and a chat. Jean Bolognia and Chris Griffiths acted as official ILDS meeters and greeters for the guests. Our president, Wolfram Sterry gave a short speech of welcome and provided an update for those present on the recent achievements of and plans for the ILDS. The announcement of the Berlin summit was particularly well received by our member societies. Jerry Shapiro then took the floor to apprise us of the arrangements for the Vancouver World Congress, these too were greeted with enthusiasm...

Bullous pemphigoid (BP) is an autoimmune blistering skin disease associated with circulating autoantibodies to the hemidesmosomal antigens BP180 and BP230. We report two cases of therapy-refractory BP adjuvantly treated by tryptophan immunoadsorption. In both patients, this treatment was associated with rapid clinical improvement and reduction in the required corticosteroid dosage. In addition, levels of circulating anti-BP180 autoantibodies decreased markedly. Antibodies that were eluted from the tryptophan matrix bound to BP180 and induced dermal-epidermal separation in cryosections of human skin. Our observations suggest that immunoadsorption may be a helpful adjuvant treatment in severe BP.

In Part II of this study the ECMWF Ensemble Prediction System (EPS) is used to study the probabilistic predictability of three major European storms of the twentieth century. The storms considered are the Dutch storm of 1 February 1953, the Hamburg storm of 17 February 1962, and the British/French storm of October 1987 (Great October storm). Common to all these storms is their severity that caused large loss of life and widespread damage. In Part I of this study it has been found that deterministic predictability of the Dutch and Hamburg storms amount to 48 and 84 hours, respectively. Here, it is shown that the ensemble forecasts supplement the deterministic forecasts. The large number of members in the 48 and 84 hour ensemble forecasts of the Dutch and Hamburg storms, respectively, suggest that at this forecast range and for these storms the sensitivity of the forecasts to analysis and model uncertainties is rather small. From these results, therefore, it is argued that reliable warnings (i.e. low probability for the occurrence of a forecast failure) for the Dutch and Hamburg storms could have been issued 48 and 84 hours, respectively, in advance, had the current ECMWF EPS been available. For the Great October storm it has been found in Part I of this study that short-range and medium-range forecasts of the intensity and track of the storm were very skilful with a high-resolution model of the ECWMF model. The actual timing of the storm, however, was difficult to predict. Here, it is shown that the EPS is capable of predicting large forecast uncertainties associated with the timing of the Great October storm up to 4 days in advance. It is argued that reliable warnings could have been issued at least 96 hours in advance had the ECMWF EPS been available. From the results presented in this study it is concluded that an Ensemble Prediction System is an important component of every early warning system for it allows an a priori quantification of the probability of the occurrence of severe wind storms. Copyright © 2005 Royal Meteorological Society

In Part I of this study recent versions of the ECWMF Integrated Forecasting System (IFS) are used together with historical observational data to carry out reanalyses and deterministic reforecasts of three major north-west European wind storms of the twentieth century. The storms considered are the Dutch storm of 1 February 1953, the Hamburg storm of 17 February 1962, and the British October storm of 1987 (Great October Storm). Common to all these storms is their severity, which caused large loss of life and widespread damage. Reanalysis of the storms is based on a 3D-Var and 4D-Var assimilation scheme at a horizontal resolution of TL159(≈ 125 km) and TL511(≈ 50 km), respectively. Similarly, two different horizontal resolutions (TL159 and TL511) are used to investigate the deterministic predictability of these storms. The lower-resolution system is exactly that used in the ERA-40 reanalysis project. The high-resolution system is a more recent version of the ECMWF IFS. It is shown that the basic characteristics of the Dutch and Hamburg storms that gave rise to the storm surge are well predicted by the single deterministic forecasts up to about 48 and 84 hours, respectively, in advance. Our capability to predict the Great October Storm is more difficult to assess. On the one hand, even recent versions of the ECMWF IFS underestimate the severity of the storm in the very short-range (12–24-hour forecasts started at 12 UTC 15 October 1987). On the other hand, the high-resolution version of the ECMWF IFS provides excellent deterministic forecasts of the track and intensity of the storm up to 96 hours in advance. However, there are errors in the timing of the storm (12 hours for the 96 hour forecast). From the results presented in this study it is concluded – bearing in mind the limited number of cases considered – that with the current ECMWF forecasting system reliable deterministic predictions of some European wind storms are possible several days in advance. Copyright © 2004 Royal Meteorological Society.

SummaryBackground Pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are autoimmune blistering skin diseases usually treated with high-dose systemic corticosteroids and other immunosuppressants that may cause severe side-effects. Plasmapheresis also has been demonstrated to be of benefit in the treatment of pemphigus. In contrast to plasmapheresis, staphylococcal protein A immunoadsorption (PA–IA) specifically removes immunoglobulin from the circulation, allows treatment of larger plasma volumes, and does not require the substitution of plasma components. Objectives To determine the effectiveness and side-effects of PA–IA in patients with severe pemphigus. Methods Five patients with severe pemphigus (PV, n = 4; PF, n = 1) were treated by PA–IA. Three of these patients had been refractory to various treatment regimens. In addition to PA–IA, methylprednisolone, 0·5 mg kg−1 body weight day−1 was given initially and subsequently tapered. Results In all patients, a dramatic clinical improvement was seen within 2 weeks after initiation of therapy. Patients were free of lesions after 3, 4, 4, 10 and 21 weeks of treatment, respectively. Concurrently, autoantibody levels decreased rapidly. Conclusions PA–IA is a rational, effective, and safe adjuvant therapy for severe pemphigus and warrants wider use for this indication. A controlled study should compare side-effects and effectiveness of PA–IA with other treatment options for pemphigus.

Singular-value decomposition (SVD) analysis is employed to study flow-dependent forecast errors. The results presented are based on ECMWF operational forecasts and verifying analysis of 500 hPa heights for the most recent seven winter periods. Beyond forecast day 3 the flow-dependent errors are mainly localized over the Atlantic sector and are associated with the North Atlantic Oscillation- (NAO)-like circulation anomalies. The forecasts systematically underestimate the intensity of pressure anomalies centred over Iceland with the effect of reducing the anomalous westerly/easterly flow over the eastern north Atlantic/western Europe. The flowdependent component of the errors explains about 10% of the total forecast-error variance. However, since it is associated with the NAO mode that dominates the variability of the European weather on longer time-scales, it is essential to identify the model limitations in predicting this flow anomaly in order to guide future work on improving forecasts over Europe. The relationship between forecast-error variability and NAO fluctuations is effectively described by an SVD analysis performed on fields of forecast-error magnitude and analyses. Regions with large (small) forecast-error anomalies are located over the maximum of the anomalous westerly (easterly) jet, while on the flanks of the jet the error anomaly is expected to be minimum/maximum. Copyright © 2002 Royal Meteorological Society.

The first two papers of this series describe the development of the operational four-dimensional variational assimilation (4D-Var) configuration implemented at the European Centre for Medium-Range Weather Forecasts (ECMWF). The basic features are a 6-hour incremental 4D-Var set-up with two minimization steps, using very simplified physics in the first minimization and a more complete set of linear physics in the second. This paper describes the validation of this configuration. Prior to implementation, 12 weeks of experimentation showed a consistent improvement relative to 3D-Var. After an additional 6 weeks of encouraging parallel operation with the then current operational suite, 4D-Var with physics was introduced in operations at ECMWF in November 1997. The difference in scores is statistically significant, and the fast-growing components of the 4D-Var analysis errors are shown to be smaller than their 3D-Var counterparts. The performance of this new operational assimilation system is studied for the month of January 1998, for which the 4D-Var analyses exhibit more realistic baroclinic waves than the 3D-Var, especially in the Pacific area. A case-study illustrates the improvement one can expect in forecast terms in the mid latitudes. The 4D-Var system improved the forecast skill in the Tropics in general. Observing-system experiments show that the current 4D-Var operational system benefits from the assimilation both of satellite data and conventional observations.

An iteration procedure minimizing the short-range forecast error leads, after some iterations, to so-called key analysis errors. These are estimates of the part of analysis errors that is largely responsible for the short-range forecast errors. The first step of the minimization procedure provides a scaled gradient of the two-day forecast errors for which the ‘energy’ inner-product provides an efficient way of identifying the analysis errors at scales that are relevant for forecast error growth. By using an ‘enstrophy’ like inner-product as an alternative to ‘energy’ the sensitivity gradient obtains an unrealistically large scale. Performing a few more steps in the minimization provides better estimates of the analysis error in the directions spanned by the leading singular vectors of the tangent-linear model. On a case study it is shown that three steps provide key analysis increments which, when added to the analysis, both significantly improve the fit to the available data, and substantially improve the subsequent model integration. It does not appear to be beneficial to do more steps of the minimization because of the uncertainty in the definition of the short-range forecast error, and of approximations in the tangent-linear model. Key analysis errors represent an improved estimate of analysis errors compared to the scaled gradient of day-2 forecast errors. In particular the geographical distribution shows the stability dependence of the scaled gradient. The projection of the gradient on the fastest growing errors limits maximum sensitivity to the major baroclinic zones. The close correspondence of evolved key analysis errors and forecast errors shows that key analysis errors are more realistically projecting on to full analysis errors. The close link between the stability of the flow and the gradient of the forecast errors implies an unreasonably strong seasonal variation of analysis errors estimates. In contrast, key analysis errors are nearly seasonally independent, which means that their detrimental effect on forecast errors in absolute terms in summer and winter is comparable.

We examine the large-scale effects of organized convective systems in the tropical western Pacific observed during the Tropical-Ocean Global-Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). In a case-study approach, we examine realizations of a supercluster, associated with the onset of the December 1992 westerly wind burst, in the T213 operational medium-range weather forecasting model of the European Centre for Medium-Range Weather Forecasts (ECMWF). We idealize a supercluster as a hierarchy of three interacting scales, namely organized cumulonimbus C 1 , mesoscale convective systems C 2 , and the supercluster component C 3 . It is shown that the ECMWF model represents this hierarchy as a C 3 -like surrogate whose influence dominates the effect of parametrized convection. This causes over-prediction of the model tendencies which, in the case of zonal momentum, is explained in elementary terms. The structure of the resolved-scale momentum flux is explained by Moncrieff's (1992) archetypal theory of organized convection which has been verified against observations and cloud-resolving model data-sets. The parametrization of subgrid-scale convective momentum-flux in the ECMWF model, based on a momentum mixing concept, produces subgrid-scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow. We outline a strategy for parametrizing the momentum flux by the C 1 component based on the archetypal model. The C 2 component, which is part-resolved and part-parametrized, is at odds with the assumptions of scale separation underpinning parametrization. It is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus. Finally, we suggest cloud-resolving modelling studies to further quantify the structure and large-scale impact of superclusters in a westerly-wind-burst environment, ranging from idealized models to models having data assimilation capability.

The adjoint method has been used to calculate the sensitivity of short-range forecast errors to the initial conditions. The gradient of the energy of the day 2 forecast error with respect to the initial conditions can be interpreted as a sum of rapidly growing components of the analysis error. An analysis modified by subtracting an appropriately scaled vector, proportional to the gradient, provides initial conditions for a ‘sensitivity integration’ that can be used to diagnose the effect of initial-data errors on forecast errors. Statistics of sensitivity calculations for the month of April 1994 characterize the sensitivity patterns as small-scale, middle or lower tropospheric structures which are tilted in the vertical. The general pattern of these structures is known to be associated with the fastest possible growth of forecast error. When used as initial perturbations, they evolve rapidly into synoptic-scale structures, propagating both downstream and to higher atmospheric levels. On average, the sensitivity integration corrects for about a tenth of the day 2 forecast error, which indicates that indeed not all of the error is in the fastest-amplifying modes. But the fraction of the error corrected at day 2 is important for an improvement in the medium-range, as this fraction continues to grow substantially in the non-linear regime. These results have proved that there is still scope for great improvement in the medium-range forecast, particularly over Europe, by a better description of the initial conditions. The sensitivity experimentation suggests that many cases of major forecast-errors may be explained by defects in the analysis. A small but well-chosen change in the analysis can frequently improve the forecast quality.

The relationship between boundary-layer thermodynamic structure and cloud fields and their diurnal variation are explored using seven days of data from dw R/V Valdivia during the Atlantic Stratocumulus Transition Experiment. Cloudiness is at a maximum before dawn, when the boundary layer (BL) has the thermodynamic structure of a partially mixed, conditionally unstable stratocumulus layer, which is close to mean saturation below the inversion. Cloudiness falls during the daytime, and in the late afternoon the BL has two distinct layers: a warmer, drier cloud layer (characteristic of trade cumulus) above a more well-mixed subcloud layer. The observed mean profiles are consistent with an earlier suggestion that there is a cloud-cover transition once the BL mixing-line slope exceeds half that of the moist adiabat. In contrast, the BL structure in the ECMWF model for the same week has a much drier, warmer, more stable “cloud” layer than the observations.

Cloud fraction is a widely used parameter for estimating the effects of boundary-layer cloud on radiative transfer. During the Atlantic Stratocumulus Transition Experiment (ASTEX) during June 1992, ceilometer and satellite-based measurements of boundary-layer cloud fraction were made in the subtropical North Atlantic, a region typified by a 1–2 km deep marine boundary layer with cumulus clouds rising into a broken stratocumulus layer underneath an inversion. Both the diurnal cycle and day-to-day variations in low-cloud fraction are examined. It is shown that ECMWF low cloudiness analyses do not correlate with the observed variations in cloudiness and substantially underestimate the mean low cloudiness. In these analyses, the parameterization of low cloud fraction is primarily based on the inversion strength. A comparison of ECMWF analyses and ASTEX soundings (most of which were assimilated into the analyses) shows that the thermodynamic structure of the boundary layer and the inversion strength a...

Elimination of pathogenic autoantibodies by immunoadsorption (IA) has been described as an effective adjuvant treatment in severe bullous autoimmune diseases, especially in pemphigus. There is much less experience in the treatment of bullous pemphigoid (BP). BP was diagnosed in a 62-year-old Caucasian woman presenting a pruritic rash with multiple tense blisters. Standard treatments with topical and oral corticosteroids, steroid-sparing agents including dapsone, azathioprine, mycophenolate mofetil (MMF) and intravenous immunoglobulins were ineffective or had to be discontinued due to adverse events. An immediate clinical response could be achieved by two treatment cycles of adjuvant protein A immunoadsorption (PA-IA) in addition to continued treatment with MMF (2 g/day) and prednisolone (1 mg/kg/day). Tolerance was excellent. Clinical improvement remained stable after discontinuation of IA and went along with sustained reduction of circulating autoantibodies. Our data demonstrate that PA-IA might be a safe and effective adjuvant treatment in severe and recalcitrant BP.

Some applications of satellite radiance data in the medium range weather forecasting environment are described. In the first, data is used as a proxy for rainfall rates, which may be used for diabatic initialization of the model. The second uses the data to study the behaviour of the parametrized radiation scheme within the forecast model. Finally there is an example of a verification of the integrity of the analyses by a comparison of observed and inferred radiances.

The momentum budget for January 1987 is evaluated with global observations analyzed at the European Centre for Medium-Range Weather Forecasts (ECMWF). The dissipation term is diagnosed from the budget as a balance requirement, that is, as that required to balance the sum of the advection, Coriolis, pressure gradient, and local tendency terms. This is then compared with the parameterized subgrid-scale effects in the ECMWF model's momentum equation, with a view of identifying possible errors in those parameterizations. The balance requirement does not support the high parameterized values of orographically induced gravity-wave drag in the lower stratosphere. A deeper analysis also does not suggest a major role for turbulent vertical transports above the boundary layer. On the other hand, our budget does indicate that more effort be spent on a better representation of the potential enstrophy cascade associated with Rossby wave breaking in the upper troposphere. These statements are qualified by the ...

The systematic errors of the ECMWF forecast model have been investigated by relaxing forecasts towards analyses in selected regions. This method proved to be a useful tool to study the initial error growth in a certain region and the subsequent error propagation. The forecast fields in the tropics were relaxed towards the analysis by adding a contribution proportional to the current forecast error to the tendencies of temperature and momentum. From the comparison of control forecasts with tropically relaxed forecasts it was possible to separate large errors generated in the extra-tropics from comparatively small errors penetrating from the tropics into the extra-tropics. Relaxation in the major mountain regions showed different results for the Rocky Mountains and the Himalayas. the errors originating from the Rocky Mountains are substantial contributors to errors of both transient eddies and stationary eddies. the baroclinic waves in the Atlantic storm track are weakened and the stationary eddies develop a wave-train-like error pattern which is typical for many operational forecasts in the winter season. The errors in the Pacific are much less dependent on errors from the mountainous region. the error structure of the transient and stationary eddies, as revealed from experiments in which the Asian mountains are excluded or included from the relaxation, shows little similarity to operational forecast errors.

Summary Background. Pemphigus vulgaris is a life-threatening autoimmune blistering skin disease, usually treated with high-dose corticosteroids in combination with other immunosuppressants. However, this regimen may prove inadequate in severe cases and can cause dangerous side-effects. We have recently reported protein A immunoadsorption (PAIA) to be an effective adjuvant treatment for induction of remission in severe pemphigus. However, in a significant number of cases, the disease rapidly recurred once PAIA and immunosuppressive medication were tapered. Aims. The aim of the present study was to develop a PAIA-based therapeutic regimen that would result in a more prolonged remission of pemphigus. Methods. Nine patients with pemphigus vulgaris were treated with a modified protocol characterized by a combination of PAIA with a higher initial dose of systemic methylprednisolone (2 mg/kg). In addition, azathioprine or mycophenolate mofetil was administered as a steroid-sparing agent. Results. In all nine patients treated with this regimen, we observed a sharp decline of circulating autoantibody levels and dramatic improvement of cutaneous and mucosal lesions within 4 weeks of therapy. The patients remained free of clinical disease for up to 26 months after PAIA treatment was discontinued. Conclusion. The improved treatment protocol appears to combine highly effective induction of clinical remission in severe or treatment-resistant pemphigus with a prolonged subsequent symptom-free interval.

The Group on Earth Observations System of Systems, GEOSS, is a co-ordinated initiative by many nations to address the needs for earth-system information expressed by the 2002 World Summit on Sustainable Development. We discuss the role of earth-system modelling and data assimilation in transforming earth-system observations into the predictive and status-assessment products required by GEOSS, across many areas of socio-economic interest. First we review recent gains in the predictive skill of operational global earth-system models, on time-scales of days to several seasons. We then discuss recent work to develop from the global predictions a diverse set of end-user applications which can meet GEOSS requirements for information of socio-economic benefit; examples include forecasts of coastal storm surges, floods in large river basins, seasonal crop yield forecasts and seasonal lead-time alerts for malaria epidemics. We note ongoing efforts to extend operational earth-system modelling and assimilation capabilities to atmospheric composition, in support of improved services for air-quality forecasts and for treaty assessment. We next sketch likely GEOSS observational requirements in the coming decades. In concluding, we reflect on the cost of earth observations relative to the modest cost of transforming the observations into information of socio-economic value.

The temporal variability of convection at short time-scales (from diurnal to intra-seasonal) is an important characteristic outlining the response of the tropical atmosphere to astronomical forcing and its interaction with dynamical forcing. The spatial organisation of the convective cells into larger clusters of different sizes also is a strong characteristic of tropical convection. This paper presents analyses that can be used to evaluate the spatio-temporal variability in GCMs from measurements of geostationary meteorological satellites. The aim is not only to evaluate the description of the convective activity but also to trace the source of the cloud radiative forcing obtained in GCMs. These analyses make use of the modelled radiance in the infrared window and are compared to satellite data in a “model-to-satellite”approach. As an illustration, we present some preliminary results obtained from a comparison between the ECMWF model and Meteosat data over Africa and the Atlantic Ocean. Three model time series are used based either on “first guess” or on two runs without assimilation. The aim of the “first guess” time series is to validate the response of the cloud parameterization to realistic (i.e. close to the analysis) dynamical and thermodynamical fields. Two runs of three months without assimilation, identical except for the cloud scheme, are also analysed.

EnglishIn this paper, ensemble prediction is shown to be more suitable for predicting severe weather events than standard deterministic forecasting. Moreover, as ensemble prediction leads to a probabilistic formulation of weather forecasts, it is a valuable decision-making tool for weather-sensitive economic or social activities. Although computationally demanding, this weather forecasting technique could therefore become a useful quantitative tool for meteorological risk management. francaisDans cet article, on montre que la prevision d'ensemble est plus apte a prevoir les phenomenes meteorologiques dangereux que la prevision deterministe classique. De plus, la possibilite de formuler les previsions du temps de facon probabiliste fait de la prevision d'ensemble un outil d'aide a la decision bien adapte aux activites economiques ou sociales sensibles aux conditions meteorologiques. Bien que gourmande en calcul, cette technique de prevision du temps pourrait donc devenir un excellent outil de gestion du risque meteorologique.

EnglishECMWF made a major step by switching its operational data assimilation method to four-dimensional data assimilation (4D-VAR). 4D-VAR uses all the tools from the previous operational system, 3D-VAR (same 6-hour assimilation window, same observations and same background term). The new ingredient is the temporal dimension. Over the 6-hour data assimilation window, 4D-VAR seeks the atmospheric model trajectory best fitting the observations and the background while satisfying an approximate geostrophic balance constraint. This allows to make a better use of the observations, in a way consistent with the dynamics, leading to better forecasts at all ranges in mid-latitudes. More over, a set of sub-grid scale physical processes has been introduced in the linearised versions of the forecast model used to solve the 4D-VAR variational problem. These physical processes describe deep moist convection, large-scale precipitation, vertical diffusion, longwave radiation and sub-grid-scale orographic effects. Because of the cost, these physical processes have been introduced in only a fraction of the variational processes. Nevertheless, their impact is significant for the humidity field in the Tropics, with a better performance of forecast quality in this region. 4D-VAR has been tested in parallel with the previous 3D-VAR for several months. A significant improvement of the forecast quality has been observed in both hemispheres. francaisLe Centre europeen pour les previsions meteorologiques a moyen terme (CEPMMT) a franchi le 25 novembre 1997 une etape majeure en adoptant l'assimilation variationnelle quadridimensionnelle (4D-VAR) en tant que methode d'assimilation de donnees pour la prevision numerique du temps. L'assimilation 4D-VAR emploie tous les ingredients du systeme precedent, le 3D-VAR (meme fenetre temporelle de six heures, memes observations et meme terme d'ecart a l'ebauche), auxquels elle ajoute la dimension temporelle. Sur la fenetre temporelle de six heures, le 4D-VAR recherche la trajectoire du modele atmospherique qui passe « au plus pres » des observations et de l'ebauche, tout en satisfaisant une contrainte d'equilibre geostrophique approche. Cela permet de mieux prendre en compte les observations, de facon coherente avec la dynamique. D'ou des previsions ameliorees a toutes les echeances aux latitudes temperees. De plus, un ensemble de processus physiques d'echelle sous-maille a ete introduit dans les versions linearisees du modele de prevision qui servent a resoudre le probleme variationnel que traite le 4D-VAR. Ces processus physiques representent les effets de la convection profonde, des precipitations stratiformes, de la diffusion turbulente, des processus radiatifs de grande longueur d'onde et de la partie du relief non resolue par les modeles. Pour des raisons de cout, ces processus physiques n'ont ete introduits que dans une partie du traitement variationnel. Ils ont cependant un effet significatif sur la description du champ d'humidite en zone tropicale, avec pour consequence une amelioration de la qualite des previsions dans ces regions. La technique 4D-VAR a ete testee en parallele avec l'ancienne methode 3D-VAR pendant plusieurs mois. On a observe une amelioration notable des performances de la prevision dans les deux hemispheres.

EnglishThe adjoint model, which is used in four-dimensional variational assimilation of meteorological data, can also tielp to investigate the sensitivity of forecast error to initial conditions in a diagnostic manner. Results obtained by this method over the month of April 1994 show that many cases of relatively poor model performance can be explained by weaknesses in the analysis. A slight modification of the analysis can be sufficient for improving substantially the quality of the forecast. francaisLe modele adjoint, qui est utilise pour mettre en oeuvre l'assimilation variationnelle quadridimensionnelle de donnees meteorologiques, peut egalement servir a evaluer la sensibilite de l'erreur de prevision aux conditions initiales. Les resultats obtenus par cette methode sur le mois d'avril 1994 montrent que de nombreux cas d'echecs relatifs de la prevision peuvent etre expliques par des faiblesses de l'analyse. Une modification mineure de cette derniere est souvent suffisante pour ameliorer notablement la qualite de la prevision.

The systematic errors of the ECMWF spectral operational model (April 1983 to April 1985) in midlatitudes are described. The main errors are: * a zonalization of the time-mean flow with considerably reduced diffluent flow at the jet exits; * a wavenumber-2 pattern in the mean height error field with forecast heights too low over Europe and the Bering Strait, and too high over Canada and Siberia; * an upward shift of the subtropical jet and the tropopause; * a cooling of the stratosphere; * a cooling of the middle troposphere which decreases the static stability in the lower troposphere; * an increase of the horizontal and vertical tilts of baroclinic waves; * changes in the geographical distributions of baroclinic waves and cyclones, with enhanced activity near jet exits and reduced activity near areas of cyclogenesis; * a drop of eddy kinetic energy during the 10-day forecasts, first in the baroclinic waves and later in the long waves. The errors in both hemispheres have similar characteristics. The relations between the different errors and possible causes are discussed and comparisons with the errors of the former ECMWF operational grid point model are made. The introduction of the spectral model has led to significant improvements in the speed of baroclinic waves, which are now predicted more accurately up to day 3.

Gridded data from the ECMWF archives are analyzed spectrally in order to determine the structure and characteristics of the African wave disturbances observed during August–September 1985. Major findings are: (1) The most prominent peaks in the 850 mb meridional wind spectra occurred at periods of 3–5 days. Co-spectrum analysis revealed that the 3–5-day oscillations were produced by waves of approximately 2500 km wavelength that travelled westward at speeds of about 8 m s−1. (2) Patterns of vorticity variance in the 3–5-day frequency band indicated that the waves originated primarily in two regions, one centered near 10°E and 22°N and the other centered near 10°E and 12°N, and that the storm tracks emanating from these regions merged into a single track, located between 15° and 20°N, over the Atlantic. (3) The energetics of the waves, inferred from covariance patterns of temperature, vertical velocity and meridional and zonal winds, indicated that the waves formed as a result of the joint baroclinic/barotropic instability of the African Easterly Jet. There was evidence that wave-CISK enhanced the growth of the waves that followed the southerly storm track.

An observational and modeling study is made of tropical-extratropical interactions on time scales relevant to medium and extended range forecasting. First, an empirical orthogonal function (EOF) analysis is made of outgoing longwave radiation (OLR) in the tropics over seven winters. Having removed the seasonal cycle and interannual variability, the two leading EOFs describe the 30–60 day oscillation. A composite of extratropical 500 mb geopotential height correlated simultaneously with this mode of tropical variability is constructed. In its two phase-quadrature components, this composite has significant projection onto the Pacific/North American teleconnection pattern and onto the North Atlantic oscillation pattern, respectively. The 500 mb height composite is compared with the Simmons, Wallace and Branstator (SWB) mode of barotropic instability, which has similar periodicity and similar spatial structure in both its phase-quadrature components. A simple theoretical analysis shows that the SWB m...

A comprehensive set of physical parametrizations has been linearized for use in the European Centre for Medium-Range Weather Forecasts (ECMWF's) incremental four-dimensional variational (4D-Var) system described in Part I. The following processes are represented: vertical diffusion, subgrid-scale orographic effects, large-scale precipitation, deep moist convection and long-wave radiation. The tangent-linear approximation is examined for finite-size perturbations. Significant improvements are illustrated for surface wind and specific humidity with respect to a simplified vertical diffusion scheme. Singular vectors computed over 6 hours (compatible with the 4D-Var assimilation window) have lower amplification rates when the improved physical package is included, due to a more realistic description of dissipative processes, even though latent-heat release contributes to amplify the potential energy of perturbations in rainy areas. A direct consequence is a larger value of the observation term of the cost-function at the end of the minimization process when improved physics is included in 4D-Var. However, the larger departure of the analysis state from observations in the lower-resolution inner-loop is in better agreement with the behaviour of the full nonlinear model at high resolution. More precisely, the improved physics produces smaller discontinuities in the value of the cost-function when going from low to high resolution. In order to reduce the computational cost of the linear physics, a new configuration of the incremental 4D-Var system using two outer-loops is defined. In a first outer-loop, a minimization is performed at low resolution with simplified physics (50 iterations), while in the second loop a second minimization is performed with improved physics (20 iterations) after an update of the model trajectory at high resolution. In this configuration the extra cost of the physics is only 25%, and results from a 2-week assimilation period show positive impacts in terms of quality of the forecasts in the Tropics (reduced spin-down of precipitation, lower root-mean-square errors in wind scores). This 4D-Var configuration with improved physics and two outer-loops was implemented operationally at ECMWF in November 1997.

SUMMARY In this third and final paper of a series, we assess the performance of the three-dimensional variational data assimilation scheme, in the light of the results from the extensive pre-operational programme of numerical experimentation. Its performance is compared with that of the previous operational scheme at the European Centre for Medium-Range Weather Forecasts, which was based on Optimal Interpolation. The main features of the new scheme are illustrated, in particular the effects of non-separable structure functions and the improved data usage. TIROS-N Operational Vertical Sounder cloud-cleared radiances, for example, are used directly without a separate retrieval step. Scatterometer data are assimilated in the form of ambiguous winds with the ambiguity removal taking place within the analysis itself. Problems encountered during the tests are discussed and the solutions implemented are explained. The overall impact on forecast accuracy in the troposphere of the northern hemisphere extratropics is neutral for geopotential and positive for wind and temperature. The impact is neutral in the tropics, and significantly positive in the southern hemisphere. Analyses and forecasts for the stratosphere have improved in all regions. Other positive results include a clear improvement in analyses of near-surface winds over oceans, particularly in the vicinity of tropical storms. This is predominantly because of the assimilation of scatterometer wind-data.