Showing papers on "Meteorological reanalysis published in 2005"

The ERA‐40 re‐analysis

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.

Assimilation and Modeling of the Atmospheric Hydrological Cycle in the ECMWF Forecasting System

Abstract: Several new types of satellite instrument will provide improved measurements of Earth's hydrological cycle and the humidity of the atmosphere. In an effort to make the best possible use of these data, the modeling and assimilation of humidity, clouds, and precipitation are currently the subjects of a comprehensive research program at the European Centre for Medium-Range Weather Forecasts (ECMWF). Impacts on weather prediction and climate reanalysis can be expected. The preparations for cloud and rain assimilation within ECMWF's four-dimensional variational data assimilation system include the development of linearized moist physics, the development of fast radiative transfer codes for cloudy and precipitating conditions, and a reformulation of the humidity analysis scheme. Results of model validations against in situ moisture data are presented, indicating generally good agreement—often to within the absolute calibration accuracy of the measurements. Evidence is also presented of shortcomings in ECMWF's h...

Evaluation of maximum and minimum temperature of NCEP-NCAR reanalysis data over Greece

Abstract: Assessment of the reliability of NCEP-NCAR reanalysis data has been the subject of much recent climatological research. In this study, an attempt is made to evaluate the reanalysis data for maximum and minimum temperatures over Greece for the period 1958–2000. Considering that available observations for Greek stations are not included as input in the NCEP-NCAR reanalysis data, the evaluation was made using gridded observational data derived from long time series for the examined area, using an objective scheme. The reanalysis data were compared with respect to the intra-annual variability for extreme years, the inter-annual variability of the corresponding temperature anomalies, and their ability to represent cold and warm spells. Also, the correlation patterns between the two datasets of daily and monthly values were examined. In general, it was found that there was good agreement between the two datasets, although some regional and seasonal differences existed and these were associated with topographical features not correctly represented by the reanalysis model resolution, such as land-sea distribution and orography.

Improving Regional Model Simulations with Precipitation Assimilation

Abstract: Although large-scale atmospheric reanalyses are now providing physical, realistic fields for many variables, precipitation remains problematic. As shown in recent studies, using a regional model to downscale the global reanalysis only marginally alleviates the precipitation simulation problems. For this reason, later-generation analyses, including the recent National Centers for Environmental Prediction regional reanalysis, are using precipitation assimilation as a methodology to provide superior precipitation fields. This methodology can also be applied to regional model simulations to substantially improve the precipitation fields downscaled from global reanalysis. As an illustration of the regional model precipitation assimilation impact, the authors describe here an extended-range simulation comparison over South America. The numerical experiments cover the beginning of the Large-Scale Biosphere–Atmosphere wet season campaign of January 1999. Evaluations using radiosonde datasets obtained dur...

Differences of the Bi-level Structure of Hadley Cells between Two Different Reanalysis Data

Abstract: The NCEP/NCAR and ECMWF reanalysis data were used to analyze the difference of zonally mean meridional wind and mass stream functions between the two data sets from 1979 to 1989The result shows that the Hadley cell in the ECMWF data had an obvious bi-level structure,but there was no such phenomena in the NCEP/NCAR dataAlthough this paper cannot verify whether Hadley cell actually has a bi-level structure or not,it does clarify that the choice of data has direct effect on the research result of the low-latitude general circulation

Tropospheric ozone and its precursors: reanalysis over the past 45 years and projections for 2030

Abstract: Within the European Union project RETRO a reconstruction is made of the chemical composition of the troposphere since 1960 with the focus on ozone and its precursors. Long-term simulations are currently being performed using several global chemistry-transport and chemistry-climate models. Meteorological input is provided by the 45-year reanalysis ERA-40, which has recently been completed by the European Centre for Medium-Range Weather Forecasts (ECMWF). Changes in anthropogenic emissions are taken into account by a new inventory covering the whole period; estimates of the interannual variability of biomass burning and biogenic emissions are also included in the models. In this paper we present some preliminary results of this chemical reanalysis, which eventually should include changes in tropospheric ozone and precursor gases as well as in the associated radiative forcing. The results of the reconstruction will also be discussed in the context of future changes to be expected on the basis of the ‘2030 Photcomp’ experiment, which has recently been performed as a contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). In this experiment, projections are made of the air quality and the tropospheric composition for the year 2030 based on the new International Institute for Applied Systems Analysis (IIASA) emission scenarios ‘Current Legislation’ and ‘Maximum Technically Feasible Reduction’ as well as the IPCC Special Report on Emission Scenarios (SRES) scenario A2.