bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of cryoprecipitation during cardiopulmonary bypass in a patient with HIV-HCV co-infections
Authors: Fontana Massimiliano , Ruchat Patrick , Horisberger Judith , Aubert Vincent , Mayor Carole , Spertini François
Published: January 2007

Background: There are no guidelines for the management of patients with cryoglobulins during cardiopulmonary bypass (CPB) necessitating core hypothermia. Objective: To evaluate a simple, pragmatic protocol of in vitro temperature-dependent cryoprecipitation of serum in patients with cryoglobulinemia before elective cardiac surgery with CPB. Methods: A 44-year-old female patient was known for chronic hepatitis C and type III cryoglobulinemia. Elective surgery was planned for an aortic arch aneurysm. A differential serum cryoprecipitation profile was established in vitro prior to surgery. Results: Whereas, at temperatures ≤15°C, cryoglobulin levels were ≥0.112 g/L (normal value <0.05 g/L), at 20°C and above, the precipitate was ≤0.016 g/L. Accordingly, surgery was performed without any cryoglobulin-related complications at an extracorporeal circulation temperature of 22-24°C, to minimise the risk of cryoprecipitation. Conclusion: In elective cases of surgery with CPB and hypothermia, temperature-dependent differential serum cryoprecipitation profile may be an easy and efficient way to assess a safe peroperative level of temperature to avoid complications due to cryoglobulins, without enhancing the patient's tissue ischemia risks.
Isolated lung perfusion for pulmonary metastases, a review and work in progress
Authors: Grootenboers Marco JJH , Heeren Jos , Van putte Bart P , Hendriks Jeroen MH , Van boven Wim J , Van schil Paul EY , Schramel Franz MNH
Published: January 2007

Pulmonary metastasectomy is a widely accepted treatment for many patients with pulmonary metastases from various solid tumors. Nevertheless, 5–year survival is disappointing, with rates of 25–40%, and many patients develop recurrences. Isolated lung perfusion (ILuP) is a promising new technique to deliver high–dose chemotherapy to the lungs, while minimising systemic toxicities. This procedure is technically safe and feasible; however, clinical value and efficacy remain unclear. The aim of this paper is to give a review of literature on ILuP in humans, and to describe the development of the perfusion procedure in our institute.
Comparison of two different extracorporeal circuits on cerebral embolization during cardiopulmonary bypass in children
Authors: Rodriguez Rosendo A , Belway Dean
Published: January 2007

Objective: To compare the effect of two different extra-corporeal circuits on the counts of high-intensity transient signals (HITS) during pediatric cardiopulmonary bypass (CPB). Methods: Transcranial Doppler was used to detect HITS associated with extracorporeal sources during the period of aortic crossclamping in the middle cerebral artery of children undergoing CPB. Based on body size, children were assigned one of two extracorporeal circuits (A or B). Circuit A included a D-705 oxygenator and associated reservoir, and circuit B included a Lilliput oxygenator and reservoir. Patients were further classified into two groups according to the complexity of surgical repair: single simple lesions or multiple complex lesions. Results: We studied 109 pediatric patients. Surgery for multiple complex lesions was associated with longer periods of aortic crossclamping and CPB (p <0.0001). The median count of extra-corporeal HITS was 12 (25th, 75th percentiles: 3, 51). The type of extracorporeal circuit (p=0.012) and the complexity of surgical repair (p <0.0001) had an effect on the HITS counts. The use of circuit A was associated with higher HITS counts during surgery for multiple complex lesions compared to single simple lesions (p <0.0001). Conversely, no differences were found with the use of circuit B between these two surgical groups (p >0.25). During surgery for multiple complex lesions, patients treated with circuit A showed higher HITS counts than those with circuit B (p <0.01), but there were no circuit-related differences in HITS counts (p=0.30) during single simple lesions. Conclusion: Variations in the design characteristics of extracorporeal circuits can increase cerebral emboli during CPB in children. This may be related to the reduced ability of some circuits to remove emboli during long periods of CPB for complex congenital heart-surgery.
The contribution of arterio-venous extracorporeal lung assist to gas exchange in a porcine model of lavage-induced acute lung injury
Authors: Brederlau Jörg , Muellenbach Ralf , Kredel Markus , Schwemmer Ulrich , Anetseder Martin , Greim Clemens , Roewer Norbert
Published: January 2007

This prospective large-animal study was performed to evaluate the contribution of arterio-venous extracorporeal lung assist (AV-ECLA) to pulmonary gas exchange in a porcine lavage-induced acute lung injury model. Fifteen healthy female pigs, weighing 50.39±3.8 kg (mean±SD), were included.

After induction of general anaesthesia and controlled ventilation, an arterial line and a pulmonary artery catheter were inserted. Saline lung lavage was performed until the PaO2 decreased to 51±16 mmHg. After a stabilization period of 60 min, the femoral artery and vein were cannulated and a low-resistance membrane lung was interposed. Under apnoeic oxygenation, variations of sweep-gas flow were performed every 20 min in order to evaluate the membrane lung's efficacy, in terms of carbon dioxide (CO2) removal and oxygen (O2) uptake. Although AV-ECLA is highly effective in eliminating CO2, if combined with apnoeic oxygenation, normocapnia was not achievable. AV-ECLA's contribution to oxygenation during severe hypoxemia was antagonized by a significant increase in the pulmonary shunt fraction.
Anticoagulation management in patients undergoing open heart surgery by activated clotting time and whole blood heparin concentration
Authors: Federico Pappalardo , Annalisa Franco , Giuseppe Crescenzi , Francesco De Simone , Lucia Torracca , Alberto Zangrillo
Published: January 2007

Objective: To investigate the changes in perioperative anticoagulation management using a heparin-concentration-based system (HMS), and its effect on postoperative outcome. Methods: A total of 39 patients undergoing elective primary open heart surgery were randomly assigned to a heparin-concentration-based system approach (study group: 17 patients) or a standard ACT-based anticoagulation system (control group: 22 patients). Measurements and main results: Patients in the study group received a statistically significant higher dose of heparin (median 29 000 IU with IQR 22 500 33 500 IU versus median 19 000 IU with IQR 17 775 21 500 IU; p <0.001) and a smaller dose of protamine (median 170 mg with IQR 145 190 mg versus median 200 mg with IQR 180-250 mg; p=0.008) compared to the control group. Postoperative platelet count was significantly higher in the study group (164± 45×109/L versus 125±27 × 109/L, p=0.002). None of the study patients, but six patients in the control group required transfusion of blood products (p=0.02). No differences were recorded in postoperative antithrombin activity, bleeding, and other clinical outcomes. Conclusion: he HMS system, by facilitating maintenance of a stable heparin concentration, and by determining an appropriate dose of protamine, is associated with reduced platelet consumption and does not increase AT-III consumption and postoperative bleeding.
Photo-controlled Electrochemical Switch Based on Photochromic Tetraazaporphyrin Containing Ferrocene Units
Authors: Sun Lei , Wang Sheng , Tian He
Published: January 2007

A new photochromic compound of tetraazaporphyrin magnesium(II) appended with eight ferrocene units by ethynyl TPF was synthesized. Its photochromic properties and electrochemical properties were studied. As its redox potential was reversibly changed accompanying the open- and closed-ring photoisomerization of TPF with UV–vis light irradiation, TPF may be used as electrochemical switch controlled by light.
Limited‐area ensemble predictions at the Norwegian Meteorological Institute
Authors: Frogner Inger‐Lise , Haakenstad Hilde , Iversen Trond
Published: January 2007

This study aims at improving 0–3 day probabilistic forecasts of precipitation events in Norway. For this purpose a limited‐area ensemble prediction system (LAMEPS) is tested. The horizontal resolution of LAMEPS is 28 km, and there are 31 levels in the vertical. The state variables provided as initial and lateral boundary conditions for the limited‐area forecasts are perturbed using a dedicated version of the European Centre for Medium‐Range Weather Forecasts (ECMWF) global ensemble prediction system, TEPS. These are constructed by combining initial and evolved singular vectors that at final time (48 h) are targeted to maximize the total energy in a domain containing northern Europe and adjacent sea areas. The resolution of TEPS is T255 with 40 levels. The test period includes 45 cases with 21 ensemble members in each case. We focus on 24 h accumulated precipitation rates with special emphasis on intense events. We also investigate a combination of TEPS and LAMEPS resulting in a system (NORLAMEPS) with 42 ensemble members. NORLAMEPS is compared with the 21‐member LAMEPS and TEPS as well as the regular 51‐member EPS run at ECMWF. The benefit of using targeted singular vectors is seen by comparing the 21‐member TEPS with the 51‐member operational EPS, as TEPS has considerably larger spread between ensemble members. For other measures, such as Brier Skill Score (BSS) and Relative Operating Characteristic (ROC) curves, the scores of the two systems are for most cases comparable, despite the difference in ensemble size. NORLAMEPS has the largest ensemble spread of all four ensemble systems studied in this paper, while EPS has the smallest spread. Nevertheless, EPS has higher BSS with NORLAMEPS approaching for the highest precipitation thresholds. For the area under the ROC curve, NORLAMEPS is comparable with or better than EPS for medium to large thresholds. Copyright © 2006 Royal Meteorological Society
Influence of the Madden–Julian Oscillation on East African rainfall. I: Intraseasonal variability and regional dependency
Authors: Pohl Benjamin , Camberlin Pierre
Published: January 2007

The influence of the Madden–Julian Oscillation (MJO) on rainfall amounts over Equatorial East Africa (Kenya and northern Tanzania) is analysed for the period 1979–95 at the intraseasonal (pentad) time‐scale. The two rainy seasons (March to May and October to December) are considered. Intraseasonal wet events in East Africa are embedded in large‐scale zonal circulation anomaly patterns along the equator, showing distinct eastward propagation. It is further found that these ‘wet’ events display a clear phasing with respect to the MJO cycle. This phasing is expressed as out‐of‐phase variations between the Highland and the coastal areas. Such a pattern is suggested to reflect different rain‐causing mechanisms. MJO phases leading to wet spells in the western (Highland) region are those associated with the development of large‐scale convection in the Africa/Indian Ocean region. These events are unambiguously related to deep convection, fuelled by low‐level westerly moisture advection. MJO phases leading to wet spells in the eastern (coastal) region are often those associated with overall suppressed deep convection in the Africa/Indian Ocean region. However, these phases induce moisture advection from Indian Ocean. The possible role of stratiform rainfall or relatively shallow convection in the coastal wet spells observed in this phase is discussed. The contrasting rainfall conditions found in the two regions for the two opposite MJO phases are strongly correlated with the pressure gradient between the Indian and Atlantic Oceans. Copyright © 2006 Royal Meteorological Society
The Indian drought of 2002—a sub‐seasonal phenomenon?
Authors: Bhat G. S.
Published: January 2007

A major drought occurred over India in the year 2002 with a seasonal rainfall deficit of 21.5%, a result of 56% below normal rainfall in the month of July. The largest anomalies occurred in the western parts of India, when an Indian monsoon field experiment was in progress there. The present study is based primarily on data collected from a research ship that was deployed 100–250 km off the west coast of India for the experiment. Surface and upper air observations made over the eastern Arabian Sea during July 2002 are presented. Sea‐surface conditions were favourable for supporting deep convection over the study area. Strong atmospheric inversions around 800 hPa prevented the growth of cumulonimbus during the first half and towards the end of July. A second inversion above the melting level was also prominently present. The strength and persistence of the inversions are unusual. Back‐trajectory analysis reveals a major change in the low‐level circulation during July 2002 with frequent advection of dry air from over the deserts around the eastern Arabian Sea instead of marine air from across the equator. Copyright © 2006 Royal Meteorological Society
Microphysical and optical properties of midlatitude cirrus clouds observed in the southern hemisphere during INCA
Authors: Gayet Jean‐Francois , Shcherbakov Valery , Mannstein Hermann , Minikin Andeas , Schumann Ulrich , Ström Johan , Petzold Andreas , Ovarlez Joelle , Immler Franz
Published: January 2007

Airborne microphysical and optical properties of cirrus clouds, jet‐stream and wave clouds were measured at temperatures ranging from −25°C to −62°C in the southern hemisphere from Punta Arenas (53°S) in March and April 2000 during the INCA experiment (INterhemispheric differences in Cirrus properties from Anthropogenic emissions). The observations related to cirrus clouds show general decreases of the ice water content (18 mg m−3 to 0.05 mg m−3), extinction coefficient (0.70 km−1 to 0.08 km−1), ice particle concentration (2.2 cm−3 to 0.5 cm−3), and the effective diameter (80 µm to 17 µm) linked to the variation of ambient temperature (−25°C to −60°C). The lowest temperature at which supercooled water droplets were detected was −33°C. The asymmetry parameter shows relatively small variations, with the smallest values (0.758) observed at the lowest temperatures. High‐altitude clouds which form with a rapid vertical transport, i.e. jet‐stream cirrus and orographic‐wave ice‐cloud, are characterized by very high values of ice particle concentrations (up to 100 cm−3) compared to mean values as a whole (1.45 cm−3). These two kinds of high clouds are the subjects of detailed case‐studies. Although formed at a similar range of temperatures and with similar aerosol properties, the strong differences in cloud properties and humidity fields highlight the key role of the dynamical structure in controlling the formation, evolution and subsequent radiative properties of such high‐altitude clouds. Copyright © 2006 Royal Meteorological Society
Spatial and temporal distribution of long‐term short‐wave surface radiation over Greece
Authors: Fotiadi A. , Hatzianastassiou N. , Stackhouse P. W. , Matsoukas C. , Drakakis E. , Pavlakis K. G. , Hatzidimitriou D. , Vardavas I.
Published: January 2007

The short‐wave (SW) surface radiation budget (SRB, downward and absorbed fluxes) over Greece and surrounding areas has been computed for the first time, using a physical deterministic radiative‐transfer model. The model computations were performed on a monthly‐mean basis and at 2.5°×2.5° latitude–longitude resolution over the 17‐year period 1984–2000. Higher spatial resolution of 1°×1° was achieved using the new NASA‐Langley dataset but only for the shorter period 1985–1995. In the first case (2.5°×2.5° resolution), the model input data were taken from global datasets, such as the International Satellite Cloud Climatology Project (ISCCP), the TIROS Operational Vertical Sounder (TOVS) or the Global Aerosol Dataset (GADS), as well as from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) and European Centre for Medium Range Weather Forecasts (ECMWF) Global Re‐analysis Projects. In the second case (1°×1° resolution), the model input data were taken from the NASA‐Langley dataset supplemented by others (e.g., GADS). It is found that the annual mean values of the downward SW radiation at the surface (DSR) increase from about 150 W m−2 in the north of Greece to 210 W m−2 in the south. (Seasonal means are 50 and 100 W m−2, respectively, in the winter and 270 and 330 W m−2 in summer). The 1°×1° DSR fluxes reveal significant geographical features, indicating an important longitudinal variation, with smaller values along the central mountain axis and in the northern part of the country. The annual mean DSR flux, averaged over the study area, is 181.9±14.4 W m−2, calculated using the ISCCP‐D2 (1984–2000) data or 188.8±14.2 W m−2 using the NASA‐Langley (1985–1995) data. The corresponding averaged mean surface absorbed fluxes are 164.7±13.1 W m−2 and 170.7±13.2 W m−2. Computed time series of annual mean solar radiation arriving at the surface, and a linear fit applied to them, show an increase with time which may possibly be related to climatic change. Time series of annual amplitude of DSR (maximum minus minimum monthly values) indicate a year‐to‐year variation of DSR of about 245 W m−2, whereas a linear fit shows an increase with time but no systematic increase in summer maxima or decrease in winter minima. The model‐computed DSR fluxes are in good agreement with surface measurements, made at eight stations of the Hellenic National Meteorological Service and four other high‐standard stations run by Greek research organizations, with correlation coefficients in the range 0.91–0.99 and standard deviations smaller than 20 W m−2. The ratio of direct to diffuse DSR (an indicator of clear skies) peaks during the summer months at a value of 1.5 in Thessaloniki (northern Greece), at about three in Athens and nine in Crete. Copyright © 2006 Royal Meteorological Society
The surface energy balance and boundary layer over urban street canyons
Authors: Harman I. N. , Belcher S. E.
Published: January 2007

A model is developed for the energy balance of an urban area, represented as a sequence of two‐dimensional street canyons. The model incorporates a novel formulation for the sensible‐heat flux, that has previously been validated against wind tunnel models, and a formulation for radiation that includes multiple reflections and shadowing. This energy balance model is coupled to a model for the atmospheric boundary layer. Results are analysed to establish how the physical processes combine to produce the observed features of urban climate, and to establish the roles of building form and fabric on the urban modification to climate.

Over a diurnal cycle there are morning and evening transition periods when the net flux of radiation is largely balanced by the flux of heat into the surface. The urban surface has a large surface area in contact with the air, and hence a large active heat capacity, and so the urban area needs to absorb a larger amount of heat than a rural area to change the surface temperature. The morning and evening transitions are therefore prolonged over urban areas, delaying the onset of convective or stable boundary layers after sunrise and sunset. The model shows that the energy balance of the roof behaves very differently from the combined energy balance of the street canyon system of walls and street. The sensible‐heat flux from the street canyon into the boundary layer is increased by the increased surface area, but is decreased by the buildings reducing the local flow speeds. The net result is that, for the two‐dimensional geometry investigated here, the sensible‐heat flux from the canyon is not strongly sensitive to canyon geometry. The sensible‐heat flux from the roof is larger than from the street, and so the total sensible‐heat flux into the boundary layer, and hence also the air temperature, is strongly dependent on the fraction of plan area occupied by roofs. The radiation budget of the street canyon, which largely drives the temperatures of the canyon surfaces, is significantly changed by the limited sky view and multiple reflections caused by the local building form. The canyon surface temperatures thus depend strongly on local building morphology.

Finally, two mechanisms are suggested for how urban areas might maintain a positive sensible‐heat flux at night. Firstly, if the roof material has much lower heat capacity than the street canyon surfaces, then the roof can cool the boundary‐layer air faster than the street canyon surfaces cool, leading to a positive heat flux out of the street canyon. Secondly, advection decouples the boundary layer from the local surface energy balance. In this way, cool air, perhaps from a rural area, advected on to an urban surface can lead to a positive sensible‐heat flux which then tends to neutralize any stable stratification in the boundary layer. Copyright © 2006 Royal Meteorological Society
Improving simulations of severe winter storms by initial modification of potential vorticity in sensitive regions
Authors: RØsting B. , KristjÁnsson J. E.
Published: January 2007

In this paper simulations of three selected severe winter storms over the North Atlantic are presented. Modifications of potential vorticity (PV) fields according to features in water vapour (WV) images are combined with information from singular vectors (SVs) in an attempt to improve the initial state over data‐sparse regions. The apparent mismatch between features in the WV images and the upper‐level PV anomalies in the numerical analyses is corrected, mainly at levels indicated as sensitive by the fastest‐growing SVs. The procedure is based on the fact that modification of the analysis in regions where SVs show a pronounced signal may have a large impact on the simulation. Model reruns, based on the inverted corrected PV fields, were then performed. Three cases are presented: the two French Christmas storms of 1999, and the storm affecting UK, the North Sea and southern Norway on 30 October 2000. In these cases a substantial improvement of the simulations of the storms was achieved.

The PV modifications were carried out by a digital analysis system, implemented at the Norwegian Meteorological Institute. This system allows the PV modifications to be done interactively within an operational time limit. Copyright © 2006 Royal Meteorological Society
Development of a new wind‐rose for the British Isles using radiosonde data, and application to an atmospheric transport model
Authors: Dore A. J. , Vieno M. , Fournier N. , Weston K. J. , Sutton M. A.
Published: January 2007

A six‐hourly dataset of radiosonde ascents spanning a ten‐year period from four stations in the British Isles has been used to generate a set of wind frequency roses and wind speed roses for the pressure level range 950–900 hPa. The wind frequency rose showed close agreement with the long‐term series of the Jenkinson classification scheme. Small but significant inter‐station and interannual variations were observed. Seasonal analysis of the data revealed the higher incidence of north‐easterlies during spring months whilst the stronger wind speeds associated with the winter months were also evident. The use of a harmonic mean was found to be appropriate for calculating a directionally dependent wind speed for use in an atmospheric transport model. A harmonic mean wind speed value of 7.5 m s−1 was generated from the entire dataset, the same as that which has previously been used in other transport models. This is also the same value as the ‘optimized wind speed’ that was generated by Singles et al. The radiosonde wind frequency rose and wind speed rose were input to the FRAME atmospheric transport model. This resulted in an improved correlation with measurements of SO2 concentrations from a national monitoring network when compared to a model simulation using the earlier dataset of Jones. Copyright © 2006 Royal Meteorological Society
Laboratory studies of the effect of cloud conditions on graupel/crystal charge transfer in thunderstorm electrification
Authors: Saunders C. P. R. , Bax‐norman H. , Emersic C. , Avila E. E. , Castellano N. E.
Published: January 2007

Collisions between vapour‐grown ice crystals and a riming target, representing a graupel pellet falling in a thunderstorm, were shown by Reynolds, Brook and Gourley to transfer substantial charge, which they showed to be adequate to account for the development of charge centres leading to lightning in thunderstorms. Related experiments by Takahashi and Jayaratne et al. determined that the sign of charge transferred is dependent on the cloud liquid water content and on cloud temperature. There are marked differences between the results of Takahashi and Jayaratne in the details of the dependence they noted of the sign of graupel charging on cloud water and temperature. More recently, Pereyra et al. have shown that results somewhat similar in form to those of Takahashi are obtained by modifying the experimental technique used to prepare the clouds of ice crystals and supercooled water droplets used in the experiments.

In order to help resolve the reason for the differences in charge transfer results in various studies, work has continued in the Manchester laboratory with a modified cloud chamber in which the cloud conditions of the crystals and droplets may be controlled independently. Results indicate a profound effect on the charge sign of the particle growth conditions in the two clouds involved. For example, by suitable adjustments to the water contents of the two clouds, graupel is charged negatively by rebounding ice crystal collisions at higher cloud water contents than have been noted previously. It is suggested that the most important influence on charge sign is the relative diffusional growth rate of the two ice surfaces at the moment of impact and that this is affected by an increase in cloud supersaturation experienced by the ice crystals during the cloud mixing process just prior to collision. A range of cloud conditions is used in the present work in order to help determine the reasons for the various results reported previously.

Examination of some thunderstorm observations in the context of the present results points to the importance of mixing on the sign of the charge transferred during particle collisions when two cloud regions of different histories mix together. Copyright © 2006 Royal Meteorological Society
A data assimilation method for log‐normally distributed observational errors
Authors: Fletcher S. J. , Zupanski M.
Published: January 2007

In this paper we change the standard assumption made in the Bayesian framework of variational data assimilation to allow for observational errors that are log‐normally distributed. We address the question of which statistic best describes the distribution for the univariate and multivariate cases to justify our choice of the mode. From this choice we derive the associated cost function, Jacobian and Hessian with a normal background. We also find the solution to the Jacobian equal to zero in both model and observational space. Given the Hessian that we derive, we define a preconditioner to aid in the minimization of the cost function. We extend this to define a general form for the preconditioner, given a certain type of cost function. Copyright © 2006 Royal Meteorological Society
Influence of the Madden–Julian Oscillation on East African rainfall: II. March–May season extremes and interannual variability
Authors: Pohl Benjamin , Camberlin Pierre
Published: January 2007

The Madden–Julian Oscillation (MJO) was shown in Part I to have a significant impact on both East African rainy seasons at pentad time‐scale. The case of the ‘long rains’ (March–May) is further examined by considering both shorter (daily) and longer (interannual) time‐scales. Based on composite analyses, extreme daily rainfall events in the Highland (west) and in the coastal (east) regions of Equatorial East Africa (Kenya and Tanzania) are extracted. Low‐level westerly wind anomalies are seen to accompany wet events in the west and easterly ones in the east. These opposite circulation anomalies preferentially occur at distinct phases of the MJO, which indicates that the latter has a major influence on rainfall at the daily time‐scale.

However, this influence undergoes significant year‐to‐year variations. It is found that the common variance between smoothed rainfall time series (5‐day low‐pass filter) and MJO indices varies from 5% to 53% in the Highland region. Significantly lower air temperatures in the upper troposphere are recorded during the MJO cycles that present the highest common variance with East African rainfall. Such a cooling is seen to be related to the Kelvin wave propagation in the upper layers which favours upward atmospheric motion over the region.

At the interannual time‐scale, fluctuations in MJO amplitude contribute to the March–May rainfall variability, and 44% of the March–May seasonal rainfall variance in the 1979–95 period in East Africa is explained by this parameter. Years of high MJO amplitude are characterized by earlier onset of the rains, and higher seasonal amounts. Copyright © 2006 Royal Meteorological Society
Accounting for an imperfect model in 4D‐Var
Authors: Tr'emolet Yannick
Published: January 2007

In most operational implementations of four‐dimensional variational data assimilation (4D‐Var), it is assumed that the model used in the data assimilation process is perfect or, at least, that errors in the model can be neglected when compared to other errors in the system. In this paper, we study how model error could be accounted for in 4D‐Var.

We present three approaches for the formulation of weak‐constraint 4D‐Var: estimating explicitly a model‐error forcing term, estimating a representation of model bias or, estimating a four‐dimensional model state as the control variable. The consequences of these approaches with respect to the implementation and the properties of 4D‐Var are discussed.

We show that 4D‐Var with an additional model‐error representation as part of the control variable is essentially an initial‐value problem and that its characteristics are very similar to that of strong constraint 4D‐Var. Taking the four‐dimensional state as the control variable, however, leads to very different properties. In that case, weak‐constraint 4D‐Var can be interpreted as a coupling between successive strong‐constraint assimilation cycles. A possible extension towards long‐window 4D‐Var and possibilities for evolutions of the data assimilation system are presented. Copyright © 2006 Royal Meteorological Society
Synoptic‐scale weather patterns during Alpine heavy rain events
Authors: Hoinka Klaus P. , Schwierz Cornelia , Martius Olivia
Published: January 2007

Autumnal streamer‐type elongated troughs are related to heavy precipitation observed at the southside of the European Alps. In order to study the development of this configuration, the typical structural evolution of the ambient flow in the event of heavy rain is investigated by lagged analyses. The precipitation amounts, both observations at the Alpine southside and from ERA40 forecasts by the ECMWF, are chosen as parameters to be correlated with atmospheric fields provided by the ERA40 data. Indeed, the resulting statistics indicate that the preferable position of elongated streamers is quasi‐north–south aligned and extending southward over the Mediterranean Sea with its southern end located between the Pyrenees and northern Africa. A significant orographic impact on the streamer is revealed in the regression fields of the upper‐level potential vorticity showing an indentation above the western Alps. The lower‐tropospheric regression fields show a zonally elongated pressure signal due to the orographic influence. Up to two days in advance of heavy rain events a regressed meridional humidity flux occurs towards the south‐western Alps, which at the event's peak time is found impinging upon the entire Alpine ridge. The regressed vertical velocity fields exhibit two maxima south of the Alps, a strong one at the western and a weaker one over the eastern Alps. Copyright © 2006 Royal Meteorological Society
Assessment, correction and impact of the dry bias in radiosonde humidity data during the MAP SOP
Authors: Häberli Christian
Published: January 2007

This study reports on the characteristics of humidity measurements in the Mesoscale Alpine Programme (MAP) radiosonde dataset. During the Special Observing Period (SOP) of MAP from 9 September 1999 to 15 November 1999, about 10 100 soundings from 51 sites were collected in the so‐called ‘high‐resolution data domain’. Of these, 39 used Vaisala RS80A radiosondes, which delivered 81% of all soundings. Additionally, five sites providing about 10% of all soundings used either Meteolabor SRS‐400, Graw or VIZ sondes equipped with carbon hygristors for humidity measurements, six sites (8% of all soundings) used Meteolabor temperature sondes without humidity measurement, and one site used Vaisala RS90 sondes. Quality control and careful analysis of the MAP upper‐air dataset revealed several characteristics including the dry bias in Vaisala RS80 radiosondes. Since about two thirds of the stations are part of the routine synoptic network and were operated during the MAP SOP without major procedural changes, this evaluation also allows us to characterize the backbone of the operational upper‐air observations.

The dry bias of the Vaisala RS80 radiosonde was corrected using two different algorithms. The first algorithm raised the values of relative humidity of this sonde's profiles by about 4 measurement units (% relative humidity) in the lower troposphere and by 2 in the upper levels. The results of the second algorithm highly depend on the sonde's age. The relative humidity values are raised by 10% in the lower parts of the troposphere and by about 4% in the upper levels. These results are comparable to previous studies which mainly treated soundings from research stations in tropical regions. As in these studies, the increase of humidity in the soundings results in an increase of convective available potential energy and precipitable water, as well as a decrease of convection inhibition. Copyright © Royal Meteorological Society, 2006.
Understanding the variability of clear‐sky outgoing long‐wave radiation based on ship‐based temperature and water vapour measurements
Authors: John V. O. , Buehler S. A. , Engeln A. von , Eriksson P. , Kuhn T. , Brocard E. , Koenig‐langlo G.
Published: January 2007

High‐resolution radiative transfer model calculations with the Atmospheric Radiative Transfer Simulator (ARTS) were used to simulate the clear‐sky outgoing long‐wave radiative flux (OLR) at the top of the atmosphere. The unique set of radiosonde data collected by the research vessel Polarstern of the Alfred Wegener Institute for Polar and Marine Research during 27 expeditions in the years 1982 to 2003 was used to investigate the sources of clear‐sky OLR variability for ocean areas in different climate zones and seasons. For this dataset, tropospheric temperature variations contribute approximately 33 W m−2 OLR variability, tropospheric relative humidity variations 8.5 W m−2, and vertical structure 2.3–3.4 W m−2. Of these, 0.3–1.0 W m−2 are due to structures on a vertical scale smaller than 4 km, which cannot be resolved by conventional remote‐sensing instruments. It was also found that the poor absolute accuracy of current humidity data in the upper troposphere, approximately 40% relative error in relative humidity, leads to a significant uncertainty in OLR of about 3.8 W m−2 (for a midlatitude summer atmosphere), which should be put in the context of the double CO2 effect of only 2.6 W m−2 (for the same atmosphere).
Surface‐flux‐induced tropical cyclogenesis within an axisymmetric atmospheric balanced model
Authors: Frisius T.
Published: January 2007

The WISHE (wind‐induced surface heat exchange) instability theory for tropical atmospheric disturbances suggests that maximum warming occurs at the position of maximum surface wind. Applying this concept to axisymmetric cyclones leads to outward migration of the radius of maximum wind without amplification. Therefore, the fundamental WISHE feedback loop cannot explain tropical cyclogenesis on its own. Additional restrictions for the surface‐flux‐induced heating are necessary.

This study investigates in detail the effect of such restrictions on surface‐flux‐induced tropical cyclogenesis within the framework of a simple axisymmetric balanced model previously developed by the author. This model is based on the assumption of zero potential vorticity and formulated in potential‐radius coordinates. Heating is restricted by an efficiency parameter β that was previously introduced by Emanuel in a similar but more simplified model to account for the reduction of net latent heating in an unsaturated atmosphere. As in Emanuel's model it is found in the linearized and in the nonlinear model that a negative gradient of the efficiency parameter is necessary to initiate tropical cyclogenesis. In this case, wind amplification primarily takes place in the region where the gradient of the efficiency parameter is negative. This region migrates inward, shrinks due to frontogenesis and becomes the tropical cyclone's eyewall. It is shown that cyclogenesis becomes possible even when the surface heat exchange is wind‐speed independent. In the case of a zero β‐gradient outward propagation with no amplification takes place. If a cold anomaly is present at the vortex centre, the wind speed increases slightly but no cyclogenesis occurs. If on the other hand moisture fluxes can modify the initially uniform β‐profile, cyclogenesis appears after anegative β‐gradient is established. Horizontal diffusion is necessary to prevent a frontal collapse during the development and acts to transport momentum to regions where no wind is generated by heating. However, inward momentum diffusion does not accelerate the development as it was found previously in the model of Emanuel. This cyclogenesis process can already be qualitatively reproduced analytically by the linearized version of the model which additionally includes horizontal diffusion effects. Copyright © 2006 Royal Meteorological Society
Vertical discretizations giving optimal representation of normal modes: Sensitivity to the form of the pressure‐gradient term
Authors: Thuburn J.
Published: January 2007

The normal‐mode dispersion properties and structures of some vertical discretizations of the compressible Euler equations are re‐examined. It is shown that the dispersion properties can be sensitive to the form in which the pressure‐gradient term is expressed. For a height coordinate and for an isentropic vertical coordinate, discretizations are identified that have optimal dispersion properties and, at the same time, lend themselves to mass conservation by predicting the relevant density variable. Copyright © 2006 Royal Meteorological Society
The seasonal cycle in the lower troposphere over West Africa from sounding observations
Authors: Zhang Chidong , Woodworth Phoebe , Gu Guojun
Published: January 2007

In situ sounding observations from selected sites in West and Central Africa were used to document the seasonal cycle in the lower troposphere associated with the annual migration of precipitation. The main purpose of this exercise is to provide a description of the seasonal cycle free of the errors and biases of numerical models, which can be substantial in this region. Many features in the circulation typically associated with the West African Monsoon (WAM) exist through almost the entire seasonal cycle in the region. The low‐level easterly jet, known as the African Easterly Jet during the monsoon season, remains prominent and closely related to the rain band in other phases of the seasonal cycle, even when the rain band is located near the equator. The surface southerly monsoon onshore flow penetrates through the rain band in the entire season cycle. The depth of the southerly surface monsoon flow undergoes a seasonal variation, and is greatest during the peak season of the monsoon. A unique feature is a low‐level (∼700 hPa) northerly flow penetrating through the rain band in various phases of the seasonal cycle. Risking possible biases of land‐bound sounding data, these observations are synthesized into a schematic describing the salient features in the low‐level circulation associated with the rain band in different phases of the seasonal cycle. This synthesized circulation pattern in West Africa is in contrast to the traditional conceptual circulation pattern associated with the marine ITCZ and other monsoon systems. The results from this study call for more research attention to the low‐level meridional circulation for a full understanding of the dynamics of the WAM. This study also advocates the study of the WAM to be conducted in a broad context of the seasonal cycle in the region and in comparison to the marine ITCZ. Copyright © 2006 Royal Meteorological Society
Appraising qualitative research for inclusion in systematic reviews: a quantitative and qualitative comparison of three methods
Authors: Dixon-Woods Mary , Sutton Alex , Shaw Rachel , Miller Tina , Smith Jonathan , Young Bridget , Bonas Sheila , Booth Andrew , Jones David
Published: January 2007

Objective: Qualitative research is increasingly valued as part of the evidence for policy and practice, but how it should be appraised is contested. Various appraisal methods, including checklists and other structured approaches, have been proposed but rarely evaluated. We aimed to compare three methods for appraising qualitative research papers that were candidates for inclusion in a systematic review of evidence on support for breast-feeding.

Method: A sample of 12 research papers on support for breast-feeding was appraised by six qualitative reviewers using three appraisal methods: unprompted judgement, based on expert opinion; a UK Cabinet Office quality framework; and CASP, a Critical Appraisal Skills Programme tool. Papers were assigned, following appraisals, to 1 of 5 categories, which were dichotomized to indicate whether or not papers should be included in a systematic review. Patterns of agreement in categorization of papers were assessed quantitatively using κ statistics, and qualitatively using cross-case analysis.

Results: Agreement in categorizing papers across the three methods was slight ( κ =0.13; 95% CI 0.06–0.24). Structured approaches did not appear to yield higher agreement than that by unprompted judgement. Qualitative analysis revealed reviewers' dilemmas in deciding between the potential impact of findings and the quality of the research execution or reporting practice. Structured instruments appeared to make reviewers more explicit about the reasons for their judgements.

Conclusions: Structured approaches may not produce greater consistency of judgements about whether to include qualitative papers in a systematic review. Future research should address how appraisals of qualitative research should be incorporated in systematic reviews.
Waiting for cataract surgery – effects of a maximum waiting-time guarantee
Authors: Hanning Marianne , Lundström Mats
Published: January 2007

Objective: To evaluate the effects of the Maximum Waiting-time Guarantee (MWG) policy for cataract surgery on volume, indications, waiting times and priority setting in Sweden.

Methods: Comparison between 1993 and 1994, when the guarantee had been in force for one year, and 1998 and 1999, when the policy had been terminated for one year. Data from the National Cataract Registry covering 156,657 cataract operations for the years studied.

Results: The number of operations increased by 43% between the two study periods. Of this increase, 61% were patients with a visual acuity above 0.5 in the better eye, i.e. low-priority patients. Waiting times were longer for all patient categories in the later period and differences in waiting times between patients with differing priority diminished. Variations among the units in priority setting and waiting times were substantial, and increased after the Guarantee was terminated.

Conclusions: The Guarantee with its explicit indications was an effective policy instrument to limit waiting times and improve access for patients with the greatest need. It is unlikely that the Guarantee caused any 'crowding out' of other patient groups. When the Guarantee was not in force, indications for surgery widened. This, however, resulted in longer waiting times for all patient groups. After the Guarantee was terminated, the already substantial differences in access and indications among ophthalmic units became even greater.
Racial variations in the choice of on-pump versus off-pump coronary artery bypass grafting
Authors: Mukamel Dana , Glance Laurent , Weimer David , Pearson Thomas , Massey Todd , Gold Jeffery , Greenfield Sheldon , Jackson James , Mushlin Alvin
Published: January 2007

Objective: To examine explanations of differences in utilization rates of a newly reintroduced technique – off-pump coronary artery bypass grafting (CABG) – between racial minorities and Whites.

Method: The study was based on 15,313 CABG patients in the New York State Cardiac Surgery Reporting System covering all cardiac surgeons providing off-pump CABG in New York State. We estimated cross sectional, random effect regression models predicting the probability of off-pump versus on-pump surgery.

Results: Thirty one percent of Blacks, 20.7% of other races, and 23% of Whites underwent off-pump CABG ( P <0.0001). The higher rates for Blacks arose mostly from being treated by surgeons performing only a few off-pump procedures rather than from surgeons performing many off-pump surgeries. After adjusting for clinical characteristics and coronary anatomy, Blacks treated by surgeons with low volume off-pump procedures were 1.9 times ( P <0.01) more likely to have off-pump surgery compared with Whites treated by the same surgeons. There were no significant differences between Blacks and Whites treated by high volume surgeons.

Conclusions: These findings suggest that surgeons who are inexperienced with the off-pump techniques are more likely to perform this surgery on Black patients. Further research should examine potential explanations and the agenda addressing racial disparities should be expanded to address issues of treatment decisions.