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European Centre (european + centre)
Selected AbstractsSeasonal and inter-annual variability of the moisture sources for Alpine precipitation during 1995,2002INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2010Harald Sodemann Abstract This study presents a first quantitative climatology of the moisture sources for precipitation in the European Alps, covering a 7-year period from January 1995 to August 2002. Using a Lagrangian moisture source diagnostic and data from the ERA-40: European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis, the contribution of the following moisture sources to annual mean precipitation has been diagnosed: North Atlantic ocean 39.6%, Mediterranean 23.3%, North Sea and Baltic Sea 16.6%, and European land surface 20.8%. However, strong seasonal variability of the influence of various moisture sources is evident. Most notably, moisture transport to the Alps changes from an oceanic mode characterised by dominantly North Atlantic moisture sources during winter to a continental mode during summer with a marked contribution from Central European land areas. The method identifies inter-annual variability with respect to the location of the moisture sources in the North Atlantic, and the importance of precipitation recycling during summer. Despite the smoothed Alpine orography in the ERA-40 model, the Alps act as an effective barrier for meridional moisture transport, leading to distinct mean moisture source locations at their northern and southern slopes. The Northern Alps are predominantly influenced by the North Atlantic ocean and Central European land sources with a clear seasonality and limited monthly variability. In contrast, the Southern Alps receive a large fraction of precipitation from the Mediterranean with considerable month-to-month variability. Possible implications of these differences for precipitation extremes and stable isotopes in precipitation are discussed. Copyright © 2009 Royal Meteorological Society [source] The surface radiation budget over North America: gridded data assessment and evaluation of regional climate modelsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2009Marko Markovic Abstract While surface station observations of downwelling radiation offer accuracy at high temporal resolution, they do not easily allow an evaluation of model surface radiation budgets (SRB) over a wide geographical area. We evaluate three gridded SRB data sets against detailed observations from six surface radiation sites from the US surface radiation (SURFRAD) network. We subsequently use the most accurate surrogate observational data set for evaluation of model-simulated SRB. The data sets assessed are: ERA40,reanalysis of European Centre for Medium-Range Weather Forecasts (ECMWF), North American Regional Reanalysis (NARR),regional reanalysis of National Centres for Environmental Prediction (NCEP) and the surface radiative budget (SRB) from the International Satellite Cloud Climatology Project (ISCCP). Due to varying constraints with respect to temporal coverage of each data set, the evaluation period used in this study is 1996,2001, inclusive. The ERA40 downwelling longwave radiation (DLR) appears the most accurate surrogate observation, while both ERA40 and ISCCP show accurate results when the incoming shortwave radiation (ISR) is considered across the annual cycle. Winter DLR is less accurate in ISCCP with a positive bias and lack of very low (<200 Wm,2) flux values. The NARR SRB shows a large positive bias in the ISR throughout the annual cycle, linked to a significant underestimate of cloud cover. The ERA40 data are subsequently used to evaluate the simulated SRB in three regional climate models across North America. With respect to solar radiation, cloud cover biases are seen to be crucial, while for longwave fluxes both cloud fraction and in-cloud water content are important to simulate correctly. Inclusion of trace gases beyond H2O, CO2 and O3 appears necessary for an accurate calculation of clear-sky longwave radiation. Error compensation frequently occurs between the various components contributing to a model total-sky SRB. This is important to consider when trying to identify the underlying causes of errors in the simulated total SRB. Copyright © 2009 Royal Meteorological Society [source] Global atmospheric energetics from NCEP,Reanalysis 2 and ECMWF,ERA40 ReanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2009Carlos A. F. Marques Abstract The global atmospheric energy cycle is estimated on an annual basis using Reanalysis 2 data from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR), and ERA 40 Reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1979,2001. A formalism to avoid belowground data on pressure levels intercepted by topography is adopted. No appreciable differences were found between the two datasets from the energetics point of view. The so-called ,, and v·grad z formulations were both used for the conversions from zonal available potential energy into zonal kinetic energy (CZ) and from eddy available potential energy into eddy kinetic energy (CE). Results with both formulations are comparable only when using the formalism preventing belowground data to enter into the computations. Atmospheric energetics are also computed using ECMWF Reanalyses for the period 1958,1978. A significant increase was found in the eddy kinetic and eddy available potential energies from the early period to the later period, likely related to the assimilation in the reanalyses of satellite data after 1979. The conversion rate, CZ, was found to change its sign throughout the years. The atmospheric energy cycle using the ECMWF Reanalyses data is compared with five previous estimates. Differences in the direction of the conversion rate, CZ, between the various estimates may be explained by the different time periods chosen for averaging. Owing to the omission of belowground data, the conversion from zonal available potential energy into eddy available potential energy (CA) was somewhat smaller in ECMWF Reanalyses than in the previous estimates. Despite those differences, an overall agreement may be found between the various estimates for the atmospheric energy cycle. Copyright © 2008 Royal Meteorological Society [source] Atmospheric moisture budget over Antarctica and the Southern Ocean based on the ERA-40 reanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2008Hanna Tietäväinen Abstract The atmospheric moisture budget over Antarctica and the Southern Ocean was analysed for the period 1979,2001 on the basis of the ERA-40 reanalysis of the European Centre for Medium-Range Weather Forecasts. Meridional transport by transient eddies makes the largest contribution to the southward water vapour transport. The mean meridional circulation contributes to the northward transport in the Antarctic coastal areas, but this effect is compensated by the southward transport by stationary eddies. The convergence of meridional water vapour transport is at its largest at 64,68°S, while the convergence of zonal transport is regionally important in areas of high cyclolysis. Inter-annual variations in water vapour transport are related to the southern annular mode (SAM). The eastward transport has a significant (95% confidence level) positive correlation with the SAM index, while the northward transport has a significant negative correlation with SAM near 60°S. Hydrological balance is well-achieved in the ERA-40 reanalysis: the difference between the water vapour flux convergence (based on analysis) and the net precipitation (precipitation minus evaporation, based on 24-h forecasts) is only 13 mm yr,1 (3%) over the Southern Ocean and , 8 mm yr,1 (5%) over the continental ice sheet. Over the open ocean, the analysis methodology favours the accuracy of the flux convergence. For the whole study region, the annual mean flux convergence exceeded net precipitation by 11 mm yr,1 (3%). The ERA-40 result for the mean precipitation over the Antarctic continental ice sheet in 1979,2001 is 177 ± 8 mm yr,1, while previous estimates range from 173 to 215 mm yr,1. For the period 1979,2001, the ERA-40 data do not show any statistically significant trend in precipitation over the Antarctic grounded ice sheet and ice shelves. From the ERA-40 data, the annual average net evaporation (evaporation minus condensation) is positive over the whole continent. Copyright © 2008 Royal Meteorological Society [source] Global summer monsoon rainy seasonsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2008Suping Zhang Abstract A concise and objective definition of monsoon rainy season characteristics is proposed for worldwide monsoon regions. The result highlights six major summer monsoon rainy season domains and the mean dates of the local onset, peak and withdrawal phases of the summer monsoon rainy season. The onset phases occur progressively later poleward in the continental domains but primarily eastward in the oceanic monsoon regions. The rainy season retreats equatorward over the continental and oceanic monsoon regions. The length of the rainy season decreases poleward and shorter rainy season can also be found over the outskirts of warm water. Some exceptions exist in terms of the characteristics of rainy season, e.g. the westward advance of rainy season over North Africa and an apparently prolonged rainy season in the Korean peninsula. The results here are basically compatible with those obtained in previous studies on regional monsoons. A definition of the seasonal wind overturning is proposed. Combining rainfall and winds, we stratify the global monsoon into strong and weak categories. The strong monsoons are typically in the regions with both concentration of summer rainfall and annual reversal of low-level winds, while the weak monsoon features only a contrasting wet,dry season. Seemingly, some mid-latitude regions with wind reversals are not monsoonal because of the reversals being opposite to the monsoon overturning and the rainfall patterns being more or less Mediterranean. The comparison between the monsoon domains derived from Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the 40-year European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), the Japanese 25-year Reanalysis (JRA-25) and National Centers for Environmental Prediction (NCEP) datasets show good capabilities of the reanalyses in demarcation of the major monsoon rainy season domains in the tropics and subtropics. But the reanalyses are less realistic in the mid-latitudes of Eurasia and North America. The result here provides the simple yet objective definitions of monsoon domain, onset, peak and withdrawal which are useful for validation of GCMs. Copyright © 2008 Royal Meteorological Society [source] Recent accumulation variability and change on the Antarctic Peninsula from the ERA40 reanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2008Georgina M. Miles Abstract The Antarctic Peninsula has displayed significant climate change over recent decades. Understanding contemporaneous changes in accumulation is made difficult because the region's complex orography means that ice-core data are not necessarily representative of a wider area. In this paper, the patterns of regional spatial accumulation variability across the Antarctic Peninsula region are presented, based on an Empirical Orthogonal Function (EOF) analysis of European Centre for Medium Range Forecasts Reanalysis (ERA40) data over the 23-year period from 1979 through 2001. Annual and seasonal trends in the sign and strength of these patterns are identified, as is their relationship with mean sea level pressure, temperature and indices of large-scale circulation variability. The results reveal that the first pattern of accumulation variability on the Peninsula is primarily related to pressure in the circumpolar trough and the second pattern to temperature: together the two EOFs explain ,45,65% of the annual/seasonal accumulation. The strongest positive trend in an EOF occurs with EOF2 in the austral autumn March-April-May (MAM). This is highly correlated with the Southern Annular Mode (SAM) in this season, suggesting stronger westerly winds have caused an increase in orographic precipitation along the west Antarctic Peninsula. A significant correlation with ENSO occurs only in the winter EOF1, associated with blocking in the Bellingshausen Sea. Inter-annual ERA40 accumulation is shown to compare favourably with an ice core in the south of the Peninsula, but, for a variety of reasons, correlates poorly with accumulation as measured in an ice core from the northern tip. Opposite trends in accumulation at these two sites can be explained by the spatial pattern and trend of EOF2 in MAM and thus by recent changes in the SAM. The results of this study will aid in the understanding of temporal accumulation changes observed in the regional ice-core record. Copyright © 2007 Royal Meteorological Society [source] Simulation of Indian summer monsoon: sensitivity to cumulus parameterization in a GCMINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2007S. K. Deb Abstract Hindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from a series of numerical simulations performed with a general circulation model using different cumulus parameterization schemes. Ten sets of ensemble simulations have been produced without using any vegetation scheme but by prescribing the monthly observed SST from the ECMWF (European Centre for Medium Range Weather Forecasts) analyses. For each ensemble, ten simulations have been realised with different initial conditions that are also prepared from the ECMWF data: five each from the April and May analyses of both the years. Stream function, velocity potential with divergent winds at 200 hPa, winds at 850 hPa and rainfall patterns with their anomalies have been analysed and interpreted. The large-scale upper and lower level circulation features are simulated satisfactorily. The spatial structure of predicted July monsoon rainfall over India shows a fair agreement with the GPCP (observed) pentad rainfall distribution. The variability associated with all-India June,July simulated rainfall time series matches reasonably well with the observations in 2003, but the model fails to simulate the observed variability in July 2002. Further evaluation of the model-produced precipitation in seasonal simulations is done with the help of empirical orthogonal functions (EOFs) of the GPCP rainfall over India. Since the first four EOFs explain a significant part of the total variance of the observed rainfall, the simulated precipitation is projected on to these modes. Thus, the differences in simulated and observed rainfall fields manifest in the time series of their expansion coefficients, which are utilised for inter-comparison/evaluation of model simulations. Copyright © 2006 Royal Meteorological Society [source] A study on the effect of Eurasian snow on the summer monsoon circulation and rainfall using a spectral GCMINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2006S. K. Dash Abstract Many studies based on observed data indicate the inverse relationship between the Eurasian snow cover/depth and the Indian summer monsoon rainfall (ISMR). The purpose of this study is to confirm the inverse snow,ISMR relationship by using the observed snow depth data as boundary conditions in the spectral general circulation model (GCM) of Indian Institute of Technology, Delhi (IITD), and to examine the influence of Eurasian snow depth on the monsoon circulation. The original model belonging to the European Centre for Medium range Weather Forecasts (ECMWF) at resolution T21 has been modified extensively to a higher resolution of T80L18 at IITD. A two-dimensional Lanczos digital filter has been used to represent the orography realistically. The Historical Soviet Daily Snow Depth (HSDSD) version II data set has been used for conducting sensitivity experiments using the above model. Two sensitivity experiments have been designed, corresponding to two contrasting cases: one with high Eurasian snow depth in spring followed by deficient ISMR and the second with low snow depth followed by excess ISMR. The difference fields of mean monsoon circulation simulated in the above two experiments are examined in detail in order to confirm the influence of Eurasian snow depth on ISMR and to examine the Asian summer monsoon circulation and rainfall. Copyright © 2006 Royal Meteorological Society [source] Ten-year climatology of summer monsoon over South China and its surroundings simulated from a regional climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2006Yiming Liu Abstract In a previous study by the authors, a regional climate model (hereafter the RCM) developed to study the summer monsoon over South China (SC) and the South China Sea (SCS) has been tested and found to be able to simulate to a large extent the precipitation over this region for the months of May and June. To examine the interannual variability of the summer monsoon here, it is necessary to establish a model climatology to serve as a comparison and to reduce or even remove any systematic model biases. This paper presents the analyses of such a 10-year climatology (1991,2000). The model was initialized on 1 April and integrated up to the end of June for the ten years. The initial atmospheric conditions and lateral boundary data used in this study are from the European Centre for Medium-range Weather Forecasts ,40-year' reanalyses. The RCM can reproduce well the main features of the monsoon circulation and vertical structure of the atmosphere. The RCM can simulate the intensification and northwestward displacement of the south Asian upper anticyclones from May to June, as well as the low-level moisture transport from the Bay of Bengal to SC. In the simulation, the average SCS summer monsoon onset occurs in the fourth pentad of May, which is consistent with the results from previous observational research. In addition, the RCM can reproduce the main characteristics of the onset such as the change of the low-level zonal flow from easterly to westerly as well as the rapid increase in daily precipitation. The SC and SCS precipitation anomalies have the correct sign in almost all the years. The shortcomings of the model simulation include an under-prediction of the strength of the subtropical high over the Northwest Pacific and the moisture transport from the Bay of Bengal to the Indochina Peninsula (IC) and SCS. A cold bias in surface air temperature is also observed, with the 10-year mean biases of the simulated surface air temperature over SC, SCS and IC in May and June being about ,2.1 °C, ,2.4 °C and ,1.4 °C respectively. The 10-year mean biases of the simulated daily precipitation rate over SC, SCS and IC are about 2.0, ,3.8 and 3.5 mm d,1 respectively. Copyright © 2005 Royal Meteorological Society. [source] Trends in storminess over the Netherlands, 1962,2002INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2005A. Smits Abstract Trends in the annual number of independent wind events over the Netherlands are studied for the period 1962,2002. The events are selected out of 13 hourly 10 m wind speed records that are part of a high quality dataset of near-surface wind observations at Dutch meteorological stations. Comparisons are made with trends in independent wind events selected from geostrophic wind speed records and reanalysis data. The results for moderate wind events (that occur on average 10 times per year) and strong wind events (that occur on average twice a year) indicate a decrease in storminess over the Netherlands between 5 and 10%/decade. This result is inconsistent with National Centers for Environmental Prediction,National Center for Atmospheric Research or European Centre for Medium-Range Weather Forecasts reanalysis data, which suggest increased storminess during the same 41 year period. Possible explanations are given for the discrepancy between the trends in storminess based on station data and the trends in storminess based on reanalysis data. Evaluation of trends in geostrophic wind, both from station data and reanalysis data, and evaluation of trends in vector-averaged (upscaled) 10 m wind over the Netherlands point towards inhomogeneities in the reanalysis data as the main cause of the discrepancy. We conclude that it is likely that the decrease in storminess observed in Dutch station records of near-surface wind in the past four decades is closer to reality than the increase suggested by the reanalysis data. Copyright © 2005 Royal Meteorological Society. [source] The impact of non-stationarities in the climate system on the definition of ,a normal wind year': a case study from the BalticINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005S. C. Pryor Abstract Wind speeds over the Baltic significantly increased over the second half of the 20th century (C20th), with the majority of the increase being focused on the upper quartile of the wind speed distribution and in the southwest of the region. These changes have potentially profound implications for the wind energy resource. For example, based on the National Centers for Environmental Prediction,National Center for Atmospheric Research (NCEP,NCAR) reanalysis data it is shown that, owing to this non-stationarity, using the normalization period of 1987,98 to determine the wind resource (as in the Danish wind index) leads to overestimation of the wind energy index (and hence the wind energy resource) in western Denmark relative to 1958,2001 by approximately 10%. To address whether the increased prevalence of high wind speeds at the end of the C20th will be maintained in the future, we provide a first prognosis of annual wind indices from the HadCM3 coupled atmosphere,ocean general circulation model. The results suggest the 21st century (C21st) will be similar to the 1958,2001 period with respect to the wind energy density, but that the northeastern Baltic will exhibit slightly higher wind energy indices over the course of the C21st relative to the latter half of the C20th, whereas the southwest of the Baltic exhibits some evidence of declining wind indices towards the end of the C21st. These changes may indicate a tendency in HadCM3 towards more northerly tracking of mid-latitude cyclones in the future, possibly due to evolution of the North Atlantic oscillation. As a caveat to this finding, it should be noted that the NCEP,NCAR and European Centre for Medium-Range Weather Forecasts reanalysis data sets and HadCM3 simulations, although exhibiting commonalities during the period of overlap, differ quantitatively in terms of the spatial fields and empirical cumulative probability distributions at individual grid cells. Copyright © 2005 Royal Meteorological Society [source] Towards ice-core-based synoptic reconstructions of west antarctic climate with artificial neural networksINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2005David B. Reusch Abstract Ice cores have, in recent decades, produced a wealth of palaeoclimatic insights over widely ranging temporal and spatial scales. Nonetheless, interpretation of ice-core-based climate proxies is still problematic due to a variety of issues unrelated to the quality of the ice-core data. Instead, many of these problems are related to our poor understanding of key transfer functions that link the atmosphere to the ice. This study uses two tools from the field of artificial neural networks (ANNs) to investigate the relationship between the atmosphere and surface records of climate in West Antarctica. The first, self-organizing maps (SOMs), provides an unsupervised classification of variables from the mid-troposphere (700 hPa temperature, geopotential height and specific humidity) into groups of similar synoptic patterns. An SOM-based climatology at annual resolution (to match ice-core data) has been developed for the period 1979,93 based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 15-year reanalysis (ERA-15) dataset. This analysis produced a robust mapping of years to annual-average synoptic conditions as generalized atmospheric patterns or states. Feed-forward ANNs, our second ANN-based tool, were then used to upscale from surface data to the SOM-based classifications, thereby relating the surface sampling of the atmosphere to the large-scale circulation of the mid-troposphere. Two recorders of surface climate were used in this step: automatic weather stations (AWSs) and ice cores. Six AWS sites provided 15 years of near-surface temperature and pressure data. Four ice-core sites provided 40 years of annual accumulation and major ion chemistry. Although the ANN training methodology was properly designed and followed standard principles, limited training data and noise in the ice-core data reduced the effectiveness of the upscaling predictions. Despite these shortcomings, which might be expected to preclude successful analyses, we find that the combined techniques do allow ice-core reconstruction of annual-average synoptic conditions with some skill. We thus consider the ANN-based approach to upscaling to be a useful tool, but one that would benefit from additional training data. Copyright © 2005 Royal Meteorological Society. [source] A 10 year cloud climatology over Scandinavia derived from NOAA Advanced Very High Resolution Radiometer imageryINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2003Karl-Göran Karlsson Abstract Results from a satellite-based method to compile regional cloud climatologies covering the Scandinavian region are presented. Systematic processing of multispectral image data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument has been utilized to provide monthly cloud climatologies covering the period 1991,2000. Considerable local-scale variation of cloud amounts was found in the region. The inland Baltic Sea and adjacent land areas exhibited a large-amplitude annual cycle in cloudiness (high cloud amounts in winter, low cloud amounts in summer) whereas a weak-amplitude reversed annual cycle (high cloud amounts with a weak maximum in summer) was found for the Scandinavian mountain range. As a contrast, conditions over the Norwegian Sea showed high and almost unchanged cloud amounts during the course of the year. Some interesting exceptions to these patterns were also seen locally. The quality of the satellite-derived cloud climatology was examined through comparisons with climatologies derived from surface cloud observations, from the International Satellite Cloud Climatology Project (ISCCP) and from the European Centre for Medium-range Weather Forecasts ERA-40 data set. In general, cloud amount deviations from surface observations were smaller than 10% except for some individual winter months, when the separability between clouds and snow-covered cold land surfaces is often poor. The ISCCP data set showed a weaker annual cycle in cloudiness, generally caused by higher summer-time cloud amounts in the region. Very good agreement was found with the ERA-40 data set, especially for the summer season. However, ERA-40 showed higher cloud amounts than SCANDIA and ISCCP during the winter season. The derived cloud climatology is affected by errors due to temporal AVHRR sensor degradation, but they appear to be small for this particular study. The data set is proposed as a valuable data set for validation of cloud description in numerical weather prediction and regional climate simulation models. Copyright © 2003 Royal Meteorological Society [source] Validation of ECMWF (re)analysis surface climate data, 1979,1998, for Greenland and implications for mass balance modelling of the ice sheetINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2001Edward Hanna Abstract Climate (re)analysis products are potentially valuable tools, when properly verified, for helping to constrain the surface mass balance of the Greenland Ice Sheet (GIS). Monthly surface fields from European Centre for Medium-Range Weather Forecasts (ECMWF) operational- and re-analyses spanning 1979,1998 were validated using in situ data (surface air pressure and temperature, precipitation, cloud cover, short-/all-wave radiation, and wind speed/direction). These validation data are from coastal or near-coastal Danish Meteorological Institute (DMI) synoptic stations, inland Greenland Climate Network (GC-Net) and University of Wisconsin Automatic Weather Stations (AWSs), and two energy balance stations near the southern ice margin. The ECMWF analyses closely reproduce the seasonal patterns and interannual variations of much of the in situ data. Differences in the mean values of surface air pressure and temperature can mainly be ascribed to orography errors in the analyses' schemes, compared with the latest available accurate digital elevation model. Much of the GIS margin as modelled by ECMWF was too cold, on average by 4°C, and ECMWF precipitation averaged some 136% of the DMI station values. The misrepresentation of the (relatively) steep ice-sheet margin, which tends to be broadened and systematically over-elevated by several hundred metres, orographically reduced temperature and enhanced precipitation there in the ECMWF models. The cloud-cover comparison revealed not dissimilar annual mean cloud covers (ECMWF ,8%) but the ECMWF analyses had too little cloud and were too ,sunny' during the critical summer melt-season. ECMWF-modelled surface albedo in summer was ,11% lower than GC-Net values, which was mainly responsible for the disagreement of modelled surface short-wave radiation fluxes with observations. Model albedo and cloud errors need to be rectified if the analyses are to be used effectively to drive energy balance models of Greenland snowmelt. ECMWF wind speed averaged 66% (62%) of the DMI station (AWS) values. The validation results provide useful insights into how one can best improve the ECMWF Greenland climate data for use in glaciological and climatological studies. Copyright © 2001 Royal Meteorological Society [source] Dynamic fade restoration in Ka-band satellite systemsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2002A. Paraboni Atmospheric precipitation can seriously affect the propagation of centimeter and millimeter electromagnetic waves. As a consequence, in some applications, it is necessary to make use of a fade countermeasure technique in order to satisfy the system availability and quality requirements. This study analyses the performance of a satellite-based system in geo-stationary orbit operating at 20 GHz, dynamically assigning the antenna directivity pattern to counteract tropospheric attenuation. The on-board power is spatially distributed over the covered region to minimize, at any time, the number of users undergoing outage because of the tropospheric attenuation. Both the aspects of broadcasting and telecommunication services are addressed. The reflector antenna of the system is supposed to be illuminated by a cluster of feeds driven by a set of excitation coefficients, continuously modified and optimized according to the meteorological information derived by processing METEOSAT satellite data and ECMWF (European Centre for Medium-Range Weather Forecasts) data. Copyright © 2002 John Wiley & Sons, Ltd. [source] Review article: influenza A (H1N1) virus in patients with inflammatory bowel diseaseALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 1 2010J.-F. RAHIER Summary Background, Infection with influenza A (H1N1)v (swine flu) has caused widespread anxiety, among patients who are potentially immunocompromised, such as those being treated for inflammatory bowel disease. Aim, To provide guidance for physicians and their patients on the risk, prevention and management of influenza A (H1N1)v infection. Methods, Medline was searched using the following key words: ,swine flu', ,immunosuppression', inflammatory bowel disease', ,recommendations', ,immunization', ,vaccination'. Organizations such as European Centre for Disease Prevention and Control, the Centers for Disease Control and Prevention and the World Health Organization were consulted for recent papers and recommendations regarding immunocompromised patients and influenza A (H1N1)v infection. Results, Pandemic influenza A (H1N1) virus predominantly affects young patients. Those who are immunocompromised because of underlying disease or treatment are considered at higher risk of complications from influenza A (H1N1). They should be offered prevention (vaccination, postexposure prophylaxis) or treatment with antiviral drugs, if affected. Pneumococcal infection is a complication of influenza infection; therefore, pneumococcal vaccination appears advisable. Seasonal influenza vaccination is also recommended. Withdrawal of immunosuppressive treatment appears advisable during severe active infection if possible. Conclusions, Pragmatic advice is the best that can be offered in the current circumstances because of paucity of evidence. Investigation into the impact of influenza A (H1N1)v infection in young people with chronic conditions is needed. [source] On the use of the intensity-scale verification technique to assess operational precipitation forecastsMETEOROLOGICAL APPLICATIONS, Issue 1 2008Gabriella Csima Abstract The article describes the attempt to include the intensity-scale technique introduced by Casati et al. (2004) into a set of standardized verifications used in operational centres. The intensity-scale verification approach accounts for the spatial structure of the forecast field and allows the skill to be diagnosed as a function of the scale of the forecast error and intensity of the precipitation events. The intensity-scale method has been used to verify two different resolutions of the European Centre for Medium-Range Weather Forecasts (ECMWF) operational quantitative precipitation forecast (QPF) over France, and to compare the performance of the ECMWF and the Hungarian Meteorological Service operational model (ALADIN) forecasts, run over Hungary. Two case studies have been introduced, which show some interesting insight into the spatial scale of the error. The distribution of daily skill score for an extended period of time is also presented. The intensity-scale technique shows that the forecasts in general exhibit better skill for large-scale events, and lower skill for small-scale and intense events. In the paper, it is mentioned how some of the stringent assumptions on the domain over which the method can be applied, and the availability of the matched forecasts and observations, can limit its usability in an operational environment. Copyright © 2008 Royal Meteorological Society [source] How much does simplification of probability forecasts reduce forecast quality?METEOROLOGICAL APPLICATIONS, Issue 1 2008F. J. Doblas-Reyes Abstract Probability forecasts from an ensemble are often discretized into a small set of categories before being distributed to the users. This study investigates how such simplification can affect the forecast quality of probabilistic predictions as measured by the Brier score (BS). An example from the European Centre for Medium-Range Weather Forecasts (ECMWF) operational seasonal ensemble forecast system is used to show that the simplification of the forecast probabilities reduces the Brier skill score (BSS) by as much as 57% with respect to the skill score obtained with the full set of probabilities issued from the ensemble. This is more obvious for a small number of probability categories and is mainly due to a decrease in forecast resolution of up to 36%. The impact of the simplification as a function of the ensemble size is also discussed. The results suggest that forecast quality should be made available for the set of probabilities that the forecast user has access to as well as for the complete set of probabilities issued by the ensemble forecasting system. Copyright © 2008 Royal Meteorological Society [source] Storm prediction over Europe using the ECMWF Ensemble Prediction SystemMETEOROLOGICAL APPLICATIONS, Issue 3 2002Roberto Buizza Three severe storms caused great damage in Europe in December 1999. The first storm hit Denmark and Germany on 3 and 4 December, and the other two storms crossed France and Germany on 26 and 28 December. In this study, the performance of the Ensemble Prediction System (EPS) at the European Centre for Medium-Range Weather Forecast (ECMWF) in predicting these intense storms is investigated. Results indicate that the EPS gave early indications of possible severe storm occurrence, and was especially useful when the deterministic TL319L60 forecasts issued on successive days were highly inconsistent. These results indicate that the EPS is a valuable tool for assessing quantitatively the risk of severe weather and issuing early warnings of possible disruptions. The impact of an increase of the ensemble system horizontal resolution (TL255 integration from a TL511 analysis instead of the operational TL159 integration from a TL319 analysis) on the system performance is also investigated. Results show that the resolution increase enhances the ensemble performance in predicting the position and the intensity of intense storms. Copyright © 2002 Royal Meteorological Society. [source] Statistical interpretation of NWP products in IndiaMETEOROLOGICAL APPLICATIONS, Issue 1 2002Parvinder Maini Although numerical weather prediction (NWP) models provide an objective forecast, poor representation of local topography and other features in these models, necessitates statistical interpretation (SI) of NWP products in terms of local weather. The Perfect Prognostic Method (PPM) is one of the techniques for accomplishing this. At the National Center for Medium Range Weather Forecasting, PPM models for precipitation (quantitative, probability, yes/no) and maximum/minimum temperatures are developed for monsoon season by using analyses from the European Centre for Medium-Range Weather Forecasts. The SI forecast is then obtained by using these PPM models and output from the operational NWP model at the Center. Direct model output (DMO) obtained from the NWP model and the SI forecast are verified against the actual observations. The present study shows the verification scores obtained during the 1997 monsoon season for 10 locations in India. The results show that the SI forecast has good skill and is an improvement over DMO. Copyright © 2002 Royal Meteorological Society. [source] Comparison of the atmosphere above the South Pole, Dome C and Dome A: first attemptMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008S. Hagelin ABSTRACT The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly time-scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid-latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented. [source] Capacity and capacity development: Coping with complexityPUBLIC ADMINISTRATION & DEVELOPMENT, Issue 1 2010Derick W. Brinkerhoff This overview article introduces the topic of capacity and capacity development (CD), noting the vagueness and multiplicity of definitions and approaches. It presents the model of capacity developed by the European Centre for Development Policy Management (ECDPM) study, and reviews our evolving understanding of CD. Brief summaries of the contributions to the symposium highlight the main findings and key points. The contents of the symposium include four country cases,Pakistan, Tanzania, Brazil, and Papua New Guinea (PNG),and one conceptual piece on CD in fragile states. Several common themes emerge: the benefits of viewing capacity and CD through systems lenses, the salience of the politics of CD; and the need to change how donors and capacity builders approach the practice of CD. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simulation of the Madden, Julian Oscillation and its teleconnections in the ECMWF forecast systemTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010Frédéric Vitart Abstract A series of 46-day ensemble integrations starting on the 15th of each month from 1989 to 2008 has been completed with the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast system. The Madden, Julian Oscillation (MJO) simulated by the hindcasts is diagnosed using an index based on combined empirical orthogonal functions (EOFs) of zonal winds at 200 and 850 hPa and outgoing long-wave radiation. Results indicate that the dynamical model is able to maintain the amplitude of the MJO during the 46 days of integrations and the model displays skill for up to about 20 days to predict the evolution of the MJO. However, the MJO simulated by the model has a too slow eastward propagation and has difficulties crossing the Maritime Continent. The MJO teleconnections simulated by the ECMWF forecast system have been compared to reanalyses. In the Tropics, the impact of the MJO on precipitation is generally consistent with reanalysis. In the Northern Extratropics, the MJO simulated by the model has an impact on North Atlantic weather regimes, but with a smaller amplitude than in reanalysis which can be partly explained by the too slow eastward propagation of the simulated MJO events. The impact of the MJO on the probabilistic skill scores has been assessed. Results indicate that the MJO simulated by the model has a statistically significant impact on weekly mean probabilistic skill scores in the Northern Extratropics, particularly at the time range 19, 25 days. At this time range, the reliability of the probabilistic forecasts over Europe depends strongly on the presence of an MJO event in the initial conditions. This result confirms that the MJO is a major source of predictability in the Extratropics in the sub-seasonal time-scale. Copyright © 2010 Royal Meteorological Society [source] Estimates of spatial and interchannel observation-error characteristics for current sounder radiances for numerical weather prediction.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010I: Methods, application to ATOVS data Abstract This is the first part of a two-part article that uses three methods to estimate observation errors and their correlations for clear-sky sounder radiances used in the European Centre for Medium-Range Weather Forecasts (ECMWF) assimilation system. The analysis is based on covariances derived from pairs of first-guess and analysis departures. The methods used are the so-called Hollingsworth/Lönnberg method, a method based on subtracting a scaled version of mapped assumed background errors from first-guess departure covariances and the Desroziers diagnostic. The present article reports the results for the three Advanced TIROS Operational Vertical Sounder (ATOVS) instruments: the Advanced Microwave Sounding Unit (AMSU)-A, High-Resolution Infrared Radiation Sounder (HIRS) and Microwave Humidity Sounder (MHS). The findings suggest that all AMSU-A sounding channels show little or no interchannel or spatial observation-error correlations, except for surface-sensitive channels over land. Estimates for the observation error are mostly close to the instrument noise. In contrast, HIRS temperature-sounding channels exhibit some interchannel error correlations, and these are stronger for surface-sensitive channels. There are also indications for stronger spatial-error correlations for the HIRS short-wave channels. There is good agreement between the estimates from the three methods for temperature-sounding channels. Estimating observation errors for humidity-sounding channels of MHS and HIRS appears more difficult. A considerable proportion of the observation error for humidity-sounding channels appears correlated spatially for short separation distances, as well as between channels. Observation error estimates for humidity channels are generally considerably larger than the instrument noise. Observation error estimates from this study are consistently lower than those assumed in the ECMWF assimilation system. As error correlations are small for AMSU-A, the study suggests that the current use of AMSU-A data in the ECMWF system in terms of observation-error or thinning-scale choices is fairly conservative. Copyright © 2010 Royal Meteorological Society [source] 4D-Var assimilation of MERIS total column water-vapour retrievals over landTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 644 2009Peter Bauer Abstract Experiments with the active assimilation of total column water-vapour retrievals from Envisat MERIS observations have been performed at the European Centre for Medium-Range Weather Forecasts (ECMWF), focusing on the summer 2006 African Monsoon Multidisciplinary Analysis (AMMA) field campaign period. A mechanism for data quality control, observation error definition and variational bias correction has been developed so that the data can be safely treated within 4D-Var, like other observations that are currently assimilated in the operational system. While data density is limited due to the restriction to daylight and cloud-free conditions, a systematic impact on mean moisture analysis was found, with distinct regional and seasonal features. The impact can last 1--2 days into the forecast but has little effect on forecast accuracy in terms of both moisture and dynamics. This is mainly explained by the weak dynamic activity in the areas of largest data impact. Analysis and short-range forecast evaluation with radiosonde observations revealed a strong dependence on radiosonde type. Compared with Vaisala RS92 observations, the addition of MERIS total column water-vapour observations produced neutral to positive impact, while contradictory results were obtained when all radiosonde types were used in generating the statistics. This highlights the issue of radiosonde moisture biases and the importance of sonde humidity bias correction in numerical weather prediction (NWP). Copyright © 2009 Royal Meteorological Society [source] The characteristics of Hessian singular vectors using an advanced data assimilation schemeTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 642 2009A. R. Lawrence Abstract Initial condition uncertainty is a significant source of forecast error in numerical weather prediction. Singular vectors of the tangent linear propagator can identify directions in phase-space where initial errors are likely to make the largest contribution to forecast-error variance. The physical characteristics of these singular vectors depend on the choice of initial-time metric used to represent analysis-error covariances: the total-energy norm serves as a proxy to the analysis-error covariance matrix, whereas the Hessian of the cost function of a 4D-Var assimilation scheme represents a more sophisticated estimate of the analysis-error covariances, consistent with observation and background-error covariances used in the 4D-Var scheme. This study examines and compares the structure of singular vectors computed with the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System using these two types of initial metrics. Unlike earlier studies that use background errors derived from lagged forecast differences (the NMC method), the background-error covariance matrix in the Hessian metric is based on statistics from an ensemble of 4D-Vars using perturbed observations, which produces tighter correlations of background-error statistics than in previous formulations. In light of these new background-error statistics, this article re-examines the properties of Hessian singular vectors (and their relationship to total-energy singular vectors) using cases from different periods between 2003 and 2005. Energy profiles and wavenumber spectra reveal that the total-energy singular vectors are similar to Hessian singular vectors that use all observation types in the operational 4D-Var assimilation. This is in contrast to the structure of Hessian singular vectors without observations. Increasing the observation density tends to reduce the spatial scale of the Hessian singular vectors. Copyright © 2009 Royal Meteorological Society [source] Medium-range multimodel ensemble combination and calibrationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 640 2009Christine Johnson Abstract As part of its contribution to The Observing System Research and Predictability Experiment (THORPEX), the Met Office has developed a global, 15 day multimodel ensemble. The multimodel ensemble combines ensembles from the European Centre for Medium-Range Weather Forecasts (ECMWF), Met Office and National Centers for Environmental Prediction (NCEP) and is calibrated to give further improvements. The ensemble post-processing includes bias correction, model-dependent weights and variance adjustment, all of which are based on linear-filter estimates using past forecast-verification pairs, calculated separately for each grid point and forecast lead time. Verification shows that the multimodel ensemble gives an improvement in comparison with a calibrated single-model ensemble, particularly for surface temperature. However, the benefits are smaller for mean-sea-level pressure (mslp) and 500 hPa height. This is attributed to the higher degree of forecast-error similarity between the component ensembles for mslp and 500 hPa height than for temperature. The results also show only small improvements from the use of the model-dependent weights and the variance adjustment. This is because the component ensembles have similar levels of skill, and the multimodel ensemble variance is already generally well calibrated. In conclusion, we demonstrate that the multimodel ensemble does give benefit over a single-model ensemble. However, as expected, the benefits are small if the ensembles are similar to each other and further post-processing gives only relatively small improvements. © Crown Copyright 2009. Reproduced with the permission of HMSO. Published by John Wiley & Sons Ltd. [source] Retrieval validation during the European Aqua Thermodynamic ExperimentTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S3 2007Daniel K. Zhou Abstract Atmospheric and surface thermodynamic parameters retrieved with advanced hyperspectral remote sensors aboard Earth observing satellites are critical to weather prediction and scientific research. The retrieval algorithms and retrieved parameters from satellite sounders must be validated to demonstrate the capability and accuracy of both observation and data processing systems. The European Aqua Thermodynamic Experiment (EAQUATE) was conducted not only for validation of the Atmospheric InfraRed Sounder on the Aqua satellite, but also for assessment of validation systems of both ground-based and aircraft-based instruments that will be used for other satellite systems, such as the Infrared Atmospheric Sounding Interferometer on the European MetOp satellite, the Cross-track Infrared Sounder from the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project and the continuing series of NPOESS satellites. Detailed intercomparisons were conducted and presented using different retrieval methodologies: measurements from airborne ultraspectral Fourier transform spectrometers, aircraft in situ instruments, dedicated dropsondes and radiosondes, ground-based Raman lidar, as well as the European Centre for Medium-range Weather Forecasting modelled thermal structures. The results of this study not only illustrate the quality of the measurements and retrieval products, but also demonstrate the capability of the validation systems put in place to validate current and future hyperspectral sounding instruments and their scientific products. Copyright © 2007 Royal Meteorological Society [source] Limited-area ensemble predictions at the Norwegian Meteorological InstituteTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 621 2006Inger-Lise Frogner Abstract 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 [source] The ERA-40 re-analysisTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 612 2005S. M. Uppala Abstract ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized. A number of results indicative of the overall performance of the data assimilation system, and implicitly of the observing system, are presented and discussed. The comparison of background (short-range) forecasts and analyses with observations, the consistency of the global mass budget, the magnitude of differences between analysis and background fields and the accuracy of medium-range forecasts run from the ERA-40 analyses are illustrated. Several results demonstrate the marked improvement that was made to the observing system for the southern hemisphere in the 1970s, particularly towards the end of the decade. In contrast, the synoptic quality of the analysis for the northern hemisphere is sufficient to provide forecasts that remain skilful well into the medium range for all years. Two particular problems are also examined: excessive precipitation over tropical oceans and a too strong Brewer-Dobson circulation, both of which are pronounced in later years. Several other aspects of the quality of the re-analyses revealed by monitoring and validation studies are summarized. Expectations that the ,second-generation' ERA-40 re-analysis would provide products that are better than those from the firstgeneration ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases. © Royal Meteorological Society, 2005. The contributions of N. A. Rayner and R. W. Saunders are Crown copyright. [source] | ||||||||||||||||