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A key aim of climate monitoring is to place the current conditions of climate variables, such as surface air temperature and precipitation, in their historical context. In Europe, a leading provider of this information is the Copernicus Climate Change Service (C3S), which is implemented by the European Centre for Medium‐Range Weather Forecasts (ECMWF) on behalf of the European Commission. To undertake this activity in close‐to‐real time, C3S predominantly uses the ECMWF ERA5 reanalysis, and ERA5 precipitation is widely used as a proxy for observed precipitation for hydrological monitoring. However, for there to be confidence in the ERA5 data, it is essential to evaluate its ability to capture observed precipitation. In this study, we therefore evaluate ERA5 precipitation against observations globally to inform C3S monitoring activities and the broader climate science community. Using 24 hr precipitation observations at 5,637 stations from 2001 to 2020, results show that the smallest ERA5 random errors occur in the winter Extratropics and the largest ERA5 errors are in the Tropics. The errors grow in the summer Extratropics and the errors in the Tropics move with the intertropical convergence zone. These findings are mirrored in the stable equitable error in probability space (SEEPS) score, with the SEEPS signifying that ERA5 is more able to discriminate between different precipitation events in the Extratropics. In general, an ERA5 wet bias is also found. The assessment of annual maximum 1 day (RX1) precipitation accumulations and four extreme events shows that ERA5 cannot model the highest observed precipitation totals but that it can generally capture their locations and patterns. Furthermore, an evaluation of monthly precipitation corroborated that ERA5 is more skilful in the Extratropics. These results imply that users can have confidence in ERA5 precipitation in extratropical regions, and therefore it is recommended that ERA5 is mostly used for extratropical precipitation monitoring. [ABSTRACT FROM AUTHOR]

This report is the response to a request by the Committee on Space Research of the International Council for Science to prepare a roadmap on observation and integrated Earth-system science for the coming ten years. Its focus is on the combined use of observations and modelling to address the functioning, predictability and projected evolution of interacting components of the Earth system on timescales out to a century or so. It discusses how observations support integrated Earth-system science and its applications, and identifies planned enhancements to the contributing observing systems and other requirements for observations and their processing. All types of observation are considered, but emphasis is placed on those made from space. The origins and development of the integrated view of the Earth system are outlined, noting the interactions between the main components that lead to requirements for integrated science and modelling, and for the observations that guide and support them. What constitutes an Earth-system model is discussed. Summaries are given of key cycles within the Earth system. The nature of Earth observation and the arrangements for international coordination essential for effective operation of global observing systems are introduced. Instances are given of present types of observation, what is already on the roadmap for 2016–2025 and some of the issues to be faced. Observations that are organised on a systematic basis and observations that are made for process understanding and model development, or other research or demonstration purposes, are covered. Specific accounts are given for many of the variables of the Earth system. The current status and prospects for Earth-system modelling are summarized. The evolution towards applying Earth-system models for environmental monitoring and prediction as well as for climate simulation and projection is outlined. General aspects of the improvement of models, whether through refining the representations of processes that are already incorporated or through adding new processes or components, are discussed. Some important elements of Earth-system models are considered more fully. Data assimilation is discussed not only because it uses observations and models to generate datasets for monitoring the Earth system and for initiating and evaluating predictions, in particular through reanalysis, but also because of the feedback it provides on the quality of both the observations and the models employed. Inverse methods for surface-flux or model-parameter estimation are also covered. Reviews are given of the way observations and the processed datasets based on them are used for evaluating models, and of the combined use of observations and models for monitoring and interpreting the behaviour of the Earth system and for predicting and projecting its future. A set of concluding discussions covers general developmental needs, requirements for continuity of space-based observing systems, further long-term requirements for observations and other data, technological advances and data challenges, and the importance of enhanced international co-operation. [ABSTRACT FROM AUTHOR]

Near-surface and lower-tropospheric warming of the Arctic over the past 35 years is examined for several datasets. The new estimate for the near surface reported by Cowtan and Way in 2014 agrees reasonably well with the ERA-Interim reanalysis for this region. Both provide global averages with a little more warming over recent years than indicated by the widely used HadCRUT4 dataset, which has sparse coverage of the high Arctic. ERA-Interim is more sensitive than the Cowtan and Way estimate to the state of the underlying Arctic Ocean. Observational coverage of the Arctic varies considerably over the period. Surface air-temperature data of identified types are generally fitted well by ERA-Interim, especially data from ice stations, which appear of excellent quality. ERA-Interim nevertheless has a warm wintertime bias over sea-ice. Mean fits vary in magnitude as coverage varies, but their overall changes are much smaller than analysed temperature changes. This is also largely the case for fits to data for the free troposphere. Much of the information on trends and low-frequency variability provided by ERA-Interim comes from its background forecast, which carries forward information assimilated from a rich variety of earlier observations, rather than from its analysis of surface air-temperature observations. ERA-Interim agrees quite well with the new JRA-55 reanalysis, and with the MERRA reanalysis until recent years when MERRA exhibits weaker surface warming. Temperatures vary coherently between the surface and middle troposphere, with largest amplitude at the surface except in summer, when air temperatures are constrained by sea-ice and open-sea temperatures that differ little from 0°C. Much of the recent near-surface warming of the Arctic is associated with reduced cold-season sea-ice cover, with low temperatures over ice replaced by much higher ones over open sea. This occurs primarily in a relatively well-observed region around the northernmost islands of Europe and western Asia. [ABSTRACT FROM AUTHOR]

Breakup of the polar stratospheric vortex in the Northern Hemisphere is an event that is known to be predictable for up to a week or so ahead. This is illustrated using data from the 45-yr ECMWF Re-Analysis (ERA-40) for the sudden warmings of January 1958 and February 1979 and operational ECMWF data for February 2003. It is then shown that a similar level of skill was achieved in operational forecasts for the split of the southern stratospheric vortex in late September 2002. The highly unusual flow conditions nevertheless exposed a computational instability of the forecast model. Analyses and forecasts from reruns using improved versions of the forecasting system are presented. Isentropic maps of potential vorticity and specific humidity provide striking pictures of the advective processes at work. Forecasts as well as analyses are shown to be in good agreement with radiosonde measurements of the temperature changes associated with vortex movement, distortion, and breakup during August and September. Forecasts from 17 September onward capture the remarkable temperature rise of about 60°C recorded at 20 hPa by the Halley radiosonde station as the vortex split. Objective forecast verification and data denial experiments are used to characterize the performance of the observing and data assimilation systems and to infer overall forecast, analysis, and observation accuracy. The observations and analyses from 1957 onward in the ERA-40 archive confirm the extreme nature of the 2002 event. Secondary vortex development by barotropic instability is also discussed; in analyses for early October 2002, the process is active in the breakup of the weaker of the two vortices formed by the late-September split. [ABSTRACT FROM AUTHOR]

Studies the multiple chromosomes in photosynthetic eubacterium Rhodobacter sphaeroides. Isolation of trytophan auxotrophic strains; Mutagenization using Tn5; Existence of the trp genes and rpsA1 in a single copy within the genome.

Precipitation is an essential climate variable and a fundamental part of the global water cycle. Given its importance to society, precipitation is often assessed in climate monitoring activities, such as in those led by the Copernicus Climate Change Service (C3S). To undertake these activities, C3S predominantly uses ERA5 reanalysis precipitation. Research has shown that short‐range forecasts for precipitation made from this reanalysis can provide valuable estimates of the actual (observed) precipitation in extratropical regions but can be less useful in the tropics. While some of these limitations will be reduced with future reanalyses because of the latest advancements, there is potentially a more immediate way to improve the precipitation estimate. This is to use the precipitation modelled in the Four‐Dimensional Variational (4D‐Var) data assimilation window of the reanalysis, and it is the aim of this study to evaluate this approach. Using observed 24‐h precipitation accumulations at 5637 stations from 2001 to 2020, results show that smaller root‐mean‐square errors (RMSEs) and mean absolute errors are generally found by using the ERA5 4D‐Var precipitation. For example, for all available days from 2001 to 2020, 87.5% of stations have smaller RMSEs. These improvements are driven by reduced random errors in the 4D‐Var precipitation because it is better constrained by observations, which are themselves sensitive to or influence precipitation. However, there are regions (e.g., Europe) where larger biases occur, and via the decomposition of the Stable Equitable Error in Probability Space score, this is shown to be because the 4D‐Var precipitation has a wetter bias on 'dry' days than the standard ERA5 short‐range forecasts. The findings also highlight that the 4D‐Var precipitation does improve the discrimination of 'heavy' observed events. In conclusion, an improved ERA5 precipitation estimate is largely obtainable, and these results could prove useful for C3S activities and for future reanalyses, including ERA6. [ABSTRACT FROM AUTHOR]

The extension of the ERA5 reanalysis back to 1950 supplements the previously published segment covering 1979 to the present. It features the assimilation of additional conventional observations, as well as improved use of early satellite data. The number of observations assimilated increases from 53,000 per day in early 1950 to 570,000 per day by the end of 1978. Accordingly, the quality of the reanalysis improves throughout the period, generally joining seamlessly with the segment covering 1979 to the present. The fidelity of the extension is illustrated by the accurate depiction of the North Sea storm of 1953, and the events leading to the first discovery of sudden stratospheric warmings in 1952. Time series of ERA5 global surface temperature anomalies show temperatures to be relatively stable from 1950 until the late 1970s, in agreement with the other contemporary full-input reanalysis covering this period and with independent data sets, although there are significant differences in the accuracy of representing specific regions, Europe being well represented in the early period but Australia less so. The variability of ERA5 precipitation from month to month agrees well with observations for all continents, with correlations above 90% for most of Europe and generally in excess of 70% for North America, Asia and Australia. The evolution of upper air temperatures, humidities and winds shows smoothly varying behaviour, including tropospheric warming and stratospheric cooling, modulated by volcanic eruptions. The Quasi-Biennial Oscillation is well represented throughout. Aspects to be improved upon in future reanalyses include the assimilation of tropical cyclone data, the spin-up of soil moisture and stratospheric humidity, and the representation of surface temperatures over Australia. [ABSTRACT FROM AUTHOR]

This article describes an ensemble of ten atmospheric model integrations for the years 1899-2010, performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). Horizontal spectral resolution is T159 (about 125 km), using 91 levels in the vertical from the surface up to 1 Pa, and a time step of 1 h. This ensemble, denoted by ERA-20CM, formed the first step toward a twentieth-century reanalysis within ERA-CLIM, a three-year European funded project involving nine partners. Sea-surface temperature and sea-ice cover are prescribed by an ensemble of realizations (HadISST2), as recently produced by the Met Office Hadley Centre within ERA-CLIM. Variation in these realizations reflect uncertainties in the available observational sources on which this product is based. Forcing terms in the model radiation scheme follow CMIP5 recommendations. Any effect of their uncertainty is neglected. These terms include solar forcing, greenhouse gases, ozone and aerosols. Both the ocean surface and radiative forcing incorporate a proper long-term evolution of climate trends in the twentieth century, and the occurrence of major events, such as the El Niño-Southern Oscillations and volcanic eruptions. No atmospheric observations were assimilated. For this reason ERA-20CM is not able to reproduce actual synoptic situations. However, the ensemble is able to provide a statistical estimate of the climate. Overall, the temperature rise over land is in fair agreement with the CRUTEM4 observational product. Over the last two decades the warming over land exceeds the warming over sea, which is consistent with models participating in the CMIP5 project, as well as with the ECMWF ERA-Interim reanalysis. Some aspects of warming and of the hydrological cycle are discerned, and the model response to volcanic eruptions is qualitatively correct. The data from ERA-20CM are freely available, embracing monthly-mean fields for many atmospheric and ocean-wave quantities, and synoptic fields for a small, essential subset. [ABSTRACT FROM AUTHOR]

The reanalysis programs of numerical weather prediction (NWP) centers provide global, comprehensive descriptions of the atmosphere and of the earth’s surface over long periods of time. The high realism of their representation of key NWP parameters, like temperature and winds, implies some realism for less emblematic parameters, such as cloud cover, but the degree of this realism needs to be documented. This study aims to evaluate the high clouds over open oceans in the ECMWF 15- and 45-yr reanalyses. The assessment is based on a new 23-yr climatology of monthly frequencies of high-cloud occurrence retrieved from the infrared radiances measured by operational polar satellites. It is complemented by data from the International Satellite Cloud Climatology Project. It is shown that the 45-yr ECMWF reanalysis dramatically improves on the previous 15-yr reanalysis for the realism of seasonal and interannual variations in high clouds, despite remaining systematic errors. More than 60% of the observed anomalies during the January 1979–February 2002 period over large oceanic basins are captured by the latest reanalysis. However the realism of the analyses in the areas and in the years with sparse observations appears to be poor. Consequently, the interannual variations may not be reliable before January 1979 in most parts of the world. Possible improvements of the handling of assimilated satellite observations before and after this date are suggested. [ABSTRACT FROM AUTHOR]

Launched in 2006, the Formosa Satellite Mission 3-Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) was the first constellation of microsatellites carrying global positioning system (GPS) radio occultation (RO) receivers. Radio occultation is an active remote sensing technique that provides valuable information on the vertical variations of electron density in the ionosphere, and temperature, pressure, and water vapor in the stratosphere and troposphere. COSMIC has demonstrated the great value of RO data in ionosphere, climate, and meteorological research and operational weather forecasting. However, there are still challenges using RO data, particularly in the moist lower troposphere and upper stratosphere. A COSMIC follow-on constellation, COSMIC-2, was launched into equatorial orbit in 2019. With increased signal-to-noise ratio (SNR) from improved receivers and digital beam steering antennas, COSMIC-2 will produce at least 5,000 high-quality RO profiles daily in the tropics and subtropics. In this paper, we summarize 1) recent (since 2011 when the last review was published) contributions of COSMIC and other RO observations to weather, climate, and space weather science; 2) the remaining challenges in RO applications; and 3) potential contributions to research and operations of COSMIC-2. [ABSTRACT FROM AUTHOR]

Within the Copernicus Climate Change Service (C3S), ECMWF is producing the ERA5 reanalysis which, once completed, will embody a detailed record of the global atmosphere, land surface and ocean waves from 1950 onwards. This new reanalysis replaces the ERA‐Interim reanalysis (spanning 1979 onwards) which was started in 2006. ERA5 is based on the Integrated Forecasting System (IFS) Cy41r2 which was operational in 2016. ERA5 thus benefits from a decade of developments in model physics, core dynamics and data assimilation. In addition to a significantly enhanced horizontal resolution of 31 km, compared to 80 km for ERA‐Interim, ERA5 has hourly output throughout, and an uncertainty estimate from an ensemble (3‐hourly at half the horizontal resolution). This paper describes the general set‐up of ERA5, as well as a basic evaluation of characteristics and performance, with a focus on the dataset from 1979 onwards which is currently publicly available. Re‐forecasts from ERA5 analyses show a gain of up to one day in skill with respect to ERA‐Interim. Comparison with radiosonde and PILOT data prior to assimilation shows an improved fit for temperature, wind and humidity in the troposphere, but not the stratosphere. A comparison with independent buoy data shows a much improved fit for ocean wave height. The uncertainty estimate reflects the evolution of the observing systems used in ERA5. The enhanced temporal and spatial resolution allows for a detailed evolution of weather systems. For precipitation, global‐mean correlation with monthly‐mean GPCP data is increased from 67% to 77%. In general, low‐frequency variability is found to be well represented and from 10 hPa downwards general patterns of anomalies in temperature match those from the ERA‐Interim, MERRA‐2 and JRA‐55 reanalyses. [ABSTRACT FROM AUTHOR]

In recent years a number of reanalysis datasets have been published that cover the past century or more, including the 'Twentieth Century Reanalysis' 20CRv2 and the European Reanalysis of the twentieth century ERA-20C. These datasets are widely used, showing the need for, and possible benefit of, reanalysis data products designed for climate applications. The twentieth-century reanalyses so far have assimilated only surface observations, and rely on independent estimates of monthly averaged sea-surface temperatures and sea ice concentrations as boundary conditions. While 20CRv2 uses only observations of surface and sea-level pressure, ERA-20C additionally assimilates marine winds. Here we describe an experimental reanalysis, referred to as ERA-PreSAT, which covers the period 1939-1967 and also assimilates historical upper-air data. Assessments of this dataset including comparisons with independent data show that (i) temperature biases in the Northern Hemisphere are largely reduced compared to reanalyses that assimilate surface data only, (ii) concentration of 1940s upper-air data in the northern extratropics created a strong interhemispheric asymmetry which is likely not realistic, (iii) the forecast skill in the Northern Hemisphere has increased substantially compared to reanalyses that assimilate surface data only, (iv) day-to-day and (in the northern extratropics) month-to-month correlations with independent observations (of total column ozone, upper-air data) increase over time, (v) interannual variability is well captured in the reanalysis, (vi) a signature of the stratospheric Quasi-Biennial Oscillation is present as far back as the 1940s, and (vii) tropical cyclones are not well represented. The generally encouraging results from the experimental ERA-PreSAT reanalysis underline that early upper-air data greatly contribute to our knowledge on the troposphere and lower stratosphere over the twentieth century. [ABSTRACT FROM AUTHOR]

The ECMWF twentieth century reanalysis (ERA-20C; 1900-2010) assimilates surface pressure and marine wind observations. The reanalysis is single-member, and the background errors are spatiotemporally varying, derived from an ensemble. The atmospheric general circulation model uses the same configuration as the control member of the ERA-20CM ensemble, forced by observationally based analyses of sea surface temperature, sea ice cover, atmospheric composition changes, and solar forcing. The resulting climate trend estimations resemble ERA-20CM for temperature and the water cycle. The ERA-20C water cycle features stable precipitation minus evaporation global averages and no spurious jumps or trends. The assimilation of observations adds realism on synoptic time scales as compared to ERA-20CM in regions that are sufficiently well observed. Comparing to nighttime ship observations, ERA-20C air temperatures are 1 K colder. Generally, the synoptic quality of the product and the agreement in terms of climate indices with other products improve with the availability of observations. The MJO mean amplitude in ERA-20C is larger than in 20CR version 2c throughout the century, and in agreement with other reanalyses such as JRA-55. A novelty in ERA-20C is the availability of observation feedback information. As shown, this information can help assess the product's quality on selected time scales and regions. [ABSTRACT FROM AUTHOR]

Climate research, monitoring, prediction, and related services rely on accurate observations of the atmosphere, land, and ocean, adequately sampled globally and over sufficiently long time periods. The Global Climate Observing System, set up under the auspices of United Nations organizations and the International Council for Science to help ensure the availability of systematic observations of climate, developed the concept of essential climate variables (ECVs). ECV data records are intended to provide reliable, traceable, observation-based evidence for a range of applications, including monitoring, mitigating, adapting to, and attributing climate changes, as well as the empirical basis required to understand past, current, and possible future climate variability. The ECV concept has been broadly adopted worldwide as the guiding basis for observing climate, including by the United Nations Framework Convention on Climate Change (UNFCCC), WMO, and space agencies operating Earth observation satellites. This paper describes the rationale for these ECVs and their current selection, based on the principles of feasibility, relevance, and cost effectiveness. It also provides a view of how the ECV concept could evolve as a guide for rational and evidence-based monitoring of climate and environment. Selected examples are discussed to highlight the benefits, limitations, and future evolution of this approach. The article is intended to assist program managers to set priorities for climate observation, dataset generation and related research: for instance, within the emerging Global Framework for Climate Services (GFCS). It also helps the observation community and individual researchers to contribute to systematic climate observation, by promoting understanding of ECV choices and the opportunities to influence their evolution. [ABSTRACT FROM AUTHOR]

The article discusses a meeting of the World Meteorological Organization Commission for Climatology on September 7-9, 2010 sponsored by Great Britain's Meteorological Office. It states the meeting discussed the creation of a comprehensive, traceable data bank of global surface temperature and facilitate high-quality, robust data product creation to meet the needs of 21st century climate research. It commented on the need for increased openness and transparency in research data policy.

Historical records show that the A.D. 1783-1784 Laki eruption in Iceland caused severe environmental stress and posed a health hazard far beyond the borders of Iceland. Given the reasonable likelihood of such an event recurring, it is important to assess the scale on which a future eruption could impact society. We quantify the potential health effects caused by an increase in air pollution during a future Laki-style eruption using a global aerosol model together with concentration-response functions derived from current epidemiological studies. The concentration of particulate matter with diameters smaller than 2.5 μm is predicted to double across central, western, and northern Europe during the first 3 mo of the eruption. Over land areas of Europe, the current World Health Organization 24-h air quality guideline for particulate matter with diameters smaller than 2.5 Itm is exceeded an additional 36 d on average over the course of the eruption. Based on the changes in particulate air pollution, we estimate that approximately 142,000 additional cardiopulmonary fatalities (with a 95% confidence interval of 52,000-228,000) could occur in Europe. In terms of air pollution, such a volcanic eruption would therefore be a severe health hazard, increasing excess mortality in Europe on a scale that likely exceeds excess mortality due to seasonal influenza. [ABSTRACT FROM AUTHOR]

The article discusses the factors to be considered in dynamical climate reanalysis in climate research. It is said that major efforts are needed to bring together more of the available data into a coherent form that is suitable for climate reanalysis. A major problem with current reanalysis systems is the poor quality of surface fluxes of heat and freshwater over the oceans It is important to understand the atmospheric circulation. Uncertainty regarding the true multidecadal temperature trends aloft are highlighted by climate datasets of tropospheric temperature from satellites, radiosondes and reanalyses.

Several meteorological datasets, including U.K. Met Office (MetO), European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), and NASA’s Goddard Earth Observation System (GEOS-4) analyses, are being used in studies of the 2002 Southern Hemisphere (SH) stratospheric winter and Antarctic major warming. Diagnostics are compared to assess how these studies may be affected by the meteorological data used. While the overall structure and evolution of temperatures, winds, and wave diagnostics in the different analyses provide a consistent picture of the large-scale dynamics of the SH 2002 winter, several significant differences may affect detailed studies. The NCEP–NCAR reanalysis (REAN) and NCEP–Department of Energy (DOE) reanalysis-2 (REAN-2) datasets are not recommended for detailed studies, especially those related to polar processing, because of lower-stratospheric temperature biases that result in underestimates of polar processing potential, and because their winds and wave diagnostics show increasing differences from other analyses between ∼30 and 10 hPa (their top level). Southern Hemisphere polar stratospheric temperatures in the ECMWF 40-Yr Re-analysis (ERA-40) show unrealistic vertical structure, so this long-term reanalysis is also unsuited for quantitative studies. The NCEP/Climate Prediction Center (CPC) objective analyses give an inferior representation of the upper-stratospheric vortex. Polar vortex transport barriers are similar in all analyses, but there is large variation in the amount, patterns, and timing of mixing, even among the operational assimilated datasets (ECMWF, MetO, and GEOS-4). The higher-resolution GEOS-4 and ECMWF assimilations provide significantly better representation of filamentation and small-scale structure than the other analyses, even when fields gridded at reduced resolution are studied. The choice of which analysis to use is most critical for detailed transport studies (including polar process modeling) and studies involving synoptic evolution in the upper stratosphere. The operational assimilated datasets are better suited for most applications than the NCEP/CPC objective analyses and the reanalysis datasets (REAN/REAN-2 and ERA-40). [ABSTRACT FROM AUTHOR]

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 humidity analysis, from the operational data assimilation and forecasting system in 2002, and from the recently completed ERA-40 reanalysis project. Examples are shown of biases in the data and in the model that lead to biased humidity analyses. Although these biases are relatively small, they contribute to an overprediction of tropical precipitation and to an overly intense Hadley circulation at the start of the forecast, with rapid adjustments taking place during the first 6–12 h. It is shown that with an improved humidity analysis this long-standing “spindown” problem can be reduced. [ABSTRACT FROM AUTHOR]

An updated assessment of uncertainties in “observed” climatological winds and temperatures in the middle atmosphere (over altitudes ∼10–80 km) is provided by detailed intercomparisons of contemporary and historic datasets. These datasets include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements. The comparisons focus on a few basic circulation statistics (temperatures and zonal winds), with special attention given to tropical variability. Notable differences are found between analyses for temperatures near the tropical tropopause and polar lower stratosphere, temperatures near the global stratopause, and zonal winds throughout the Tropics. Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere. Detailed comparisons of the tropical semiannual oscillation (SAO) and quasi- biennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data. [ABSTRACT FROM AUTHOR]

At the European Centre for Medium-Range Weather Forecasts (ECMWF), reanalysis is a key contribution to the Copernicus Climate Change Service (C3S) that is implemented at ECMWF on behalf of the European Commission.The role of reanalyses in climate monitoring applications is now widely recognized. ECMWF's reanalysis ERA-Interim is periodically used, together with other datasets, as input to the World Meteorological Organization (WMO) annual assessment of the State of the Climate, routinely presented at the Conference of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC). ERA-Interim is also a resource for the production of Essential Climate Variables (ECVs) and Climate Indicators recommended by the Global Climate Observing System (GCOS). By optimally combining observations and models, reanalyses indeed provide consistent "maps without gaps" of ECVs and strive to ensure integrity and coherence in the representation of the main Earth system cycles (e.g. water, energy).This presentation focuses on the new ECMWF reanalysis ERA5, providing global estimates of the atmosphere, ocean waves and land surface quantities. It is produced at considerably higher resolution than ERA-Interim: hourly products are available at a horizontal resolution of 31 km on 137 levels in the vertical. ERA5 is publicly available from 1979 via the C3S Climate Data Store. A pre-extension back to 1950 is currently in production.Vast numbers of observations are assimilated using 4D-Var, both in situ and from satellites, that, jointly, are sensitive to a wide range of geophysical quantities throughout the atmosphere. ERA5 follows the evolution of greenhouse gases, volcanic eruptions, ozone and aerosols, as recommended by CMIP5. It uses a consistent reconstruction for sea-surface temperature and sea ice. ERA5 data products also include information about uncertainties, which is provided by a lower-resolution 10-member 4D-Var ensemble.The assimilation method includes a variational method for estimating observation biases that respects the heterogeneity within the observing system. This on one hand provides ERA5 products that are less sensitive to inhomogeneities and biases in its input data. On the other hand, the resulting bias estimates also provide a path towards more homogeneous long-term observational records.Updates are produced close to real time, which allow for an accurate and up-to-date climate monitoring, and provide information on climate variability, trends and extremes. As such, C3S publishes monthly-updated climate bulletins (https://climate.copernicus.eu/climate-bulletins), incorporating a global and European monitoring report covering surface air temperature, sea-ice and hydrological climate variables. [ABSTRACT FROM AUTHOR]