Overview of current atmospheric reanalyses
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Updated in near real-time for public use (months behind): ERA-Interim | JRA-55 | MERRA-2
Updated irregularly for public use (years behind): ERA-20C | ERA-20CM | NOAA-CIRES 20CR | NOAA-CIRES 20CRv2c | NASA MERRA
The Arctic System Reanalysis (ASR), a high-resolution regional assimilation of model output, observations, and satellite data across the mid- and high latitudes of the Northern Hemisphere for the period 2000 – 2012 has been performed at 30 km (ASRv1) and 15 km (ASRv2) horizontal resolution using the polar version of the Weather Research and Forecasting (WRF) model and the WRF Data Assimilation (WRFDA) System.
Source: Polar Meteorology Group, Byrd Polar & Climate Research Center, The Ohio State University
Time Range: 2000-2012
Dataset Output Times and Time Averaging: 3-hourly for surface and upper air fields, Monthly means of selected variables
ASRv1 – 30 km
Model Resolution: 30 km, 71 sigma levels
Dataset location: http://rda.ucar.edu/datasets/ds631.4/
ASRv2 30 km is expected early 2017
ASRv2 – 15 km
Model Resolution: 15 km, 71 sigma levels
Dataset location: http://rda.ucar.edu/datasets/ds631.4/ - Will become available during second half of 2016
Data Access: Polar Meteorology Group
ERA-20C is ECMWF's first atmospheric reanalysis of the 20th century, from 1900-2010. It is an outcome of the ERA-CLIM project.
ERA-20C was produced with the same surface and atmospheric forcings as the final version of the atmospheric model integration ERA-20CM. A coupled Atmosphere/Land-surface/Ocean-waves model is used to reanalyse the weather, by assimilating surface observations. The ERA-20C products describe the spatio-temporal evolution of the atmosphere (on 91 vertical levels, between the surface and 0.01 hPa), the land-surface (on 4 soil layers), and the ocean waves (on 25 frequencies and 12 directions). The horizontal resolution is approximately 125 km (spectral truncation T159). Note, atmospheric data are not only available on the native 91 model levels, but also on 37 pressure levels (as in ERA-Interim), 16 potential temperature levels, and the 2 PVU potential vorticity level. Monthly means, daily, and invariant data are available. The temporal resolution of the daily products is usually 3-hourly.
The assimilation methodology is 24-hour 4D-Var analysis, with variational bias correction of surface pressure observations. Analysis increments are at T95 horizontal resolution (aprox. 210 km). The analyses provide the initial conditions for subsequent forecasts that serve as backgrounds to the next analyses. A 10-member ensemble was produced initially, to estimate the spatio-temporal evolution of the background errors.
The observations assimilated in ERA-20C include surface pressures and mean sea level pressures from ISPDv3.2.6 and ICOADSv2.5.1, and surface marine winds from ICOADSv2.5.1. The observation feedback from ERA-20C is available. It includes the observations but also departures before and after assimilation and usage flags.
Data Access: ECMWF
The ERA-20CM atmospheric model integrations were produced in the framework of the ERA-CLIM project.
There are two versions, ERA-20CM and ERA-20CMv0, each comprising of a 10-member ensemble. The first version is 'final', the second is 'experimental'. The 'experimental' version was an early production and should not be used to initiate new research.
The model integration is forced by radiative forcing from CMIP5 and also by sea-surface temperature (SST) and sea ice cover from HadISST2.
References | ClimateDataGuide
ERA-Interim was originally planned as an 'interim' reanalysis in preparation for the next-generation extended reanalysis to replace ERA-40. It uses a December 2006 version of the ECMWF Integrated Forecast Model (IFS Cy31r2). It originally covered dates from 1 Jan 1989 but an additional decade, from 1 January 1979, was added later. ERA-Interim is being continued in real time. The spectral resolution is T255 (about 80 km) and there are 60 vertical levels, with the model top at 0.1 hPa (about 64 km). The data assimilation is based on a 12-hourly four-dimensional variational analysis (4D-Var) with adaptive estimation of biases in satellite radiance data (VarBC). With some exceptions, ERA-Interim uses input observations prepared for ERA-40 until 2002, and data from ECMWF's operational archive thereafter. See Dee et al. (2011) in the references below for a full description of the ERA-Interim system.
Completed in 2003, ERA-40 is a global atmospheric reanalysis of the 45-year period 1 September 1957 - 31 August 2002. It was produced using a June 2001 version of the ECMWF Integrated Forecast Model (IFS Cy28r3). The spectral resolution is T159 (about 125 km) and there are 60 vertical levels, with the model top at 0.1 hPa (about 64 km). Observations were assimilated using a 6-hourly 3D variational analysis (3D-Var). Satellite data used include Vertical Temperature Profile Radiometer radiances starting in 1972, followed by TOVS, SSM/I, ERS and ATOVS data. Cloud Motion Winds are used from 1979 onwards. Various data from past field experiments were used, such as the 1974 Atlantic Tropical Experiment of the Global Atmospheric Research Program, GATE, 1979 FGGE, 1982 Alpine Experiment, ALPEX and 1992-1993 TOGA-COARE.
Completed in 1996, ERA-15 is a global atmospheric reanalysis of the 15-year period 1 January 1979 - 31 December 1993. It was produced using an April 1995 version of the ECMWF Integrated Forecast Model (IFS Cy13r4). The spectral resolution is T106 (about 190 km) and there are 31 vertical levels, with the model top at 10 hPa (about 31 km altitude). Observations were assimilated using a 6-hourly Optimum Interpolation analysis (OI). Satellite data used were limited to cloud-cleared TOVS radiances and Cloud Motion Winds from GOES, GMS, and METEOSAT. Pseudo-observations of surface pressure (PAOBS) were also used, as well various data from past field experiments: 1979 FGGE, 1982 Alpine Experiment (ALPEX), TOGA, SUBDUCTION, and those found in the COADS dataset.
The Japanese 25-year Reanalysis (JRA-25) represents the first long-term global atmospheric reanalysis undertaken in Asia. Covering the period 1979-2004, it was completed using the Japan Meteorological Agency (JMA) numerical assimilation and forecast system and specially collected and prepared observational and satellite data from many sources including the European Center for Medium-Range Weather Forecasts (ECMWF), the National Climatic Data Center (NCDC), and the Meteorological Research Institute (MRI) of JMA. A primary goal of JRA-25 is to provide a consistent and high-quality reanalysis dataset for climate research, monitoring, and operational forecasts, especially by improving the coverage and quality of analysis in the Asian region. JRA-25 was conducted by JMA and CRIEPI (Central Research Institute of Electric Power Industry). It had been continued as JCDAS (JMA Climate Data Assimilation System) operated by JMA in near real time basis. The data assimilation systems of JRA-25 and JCDAS are the same. Users can use JRA-25 and JCDAS as one continuous reanalysis dataset. JCDAS data provision was terminated in early Feburay 2014 because it was replaced with JRA-55 in operational. The available data period of JRA-25/JCDAS is for 35 years and 1 month (January 1979 to January 2014).
Data Access: NCAR
JMA has carried out the second reanalysis project named the Japanese 55-year Reanalysis (JRA-55) (nicknamed JRA Go! Go!) using a more sophisticated NWP system, which is based on the operational system as of December 2009, and newly prepared past observations. The analysis period is extended to 55 years starting from 1958, when the regular radiosonde observations became operational on the global basis. Many of deficiencies in JRA-25 have been diminished or reduced in JRA-55 because many improvements achieved after JRA-25 have been introduced. JRA-55 provides a consistent climate dataset over the last half century. JRA-55 has been continued in near real time basis after 2013. If you need real time basis (2 days behind) data, please access to JMA. The real time basis data are also provided to other cooperating organizations (Note: half year behind). Note that the products for extended period after 2013 are also called JRA-55. As "JRA-55 family", there are two subproducts JRA-55C and JRA-55AMIP produced by MRI/JMA. JRA-55C assimilated conventional observations only. JRA-55C covers from 1972 to 2012. Before 1971, use JRA-55 instead because no satellite data was assimilated in JRA-55 before 1971. JRA-55AMIP (AMIP type run of JRA-55, with no observations) covers 1958 to 2012. JRA-55C and JRA-55AMIP data are available from DIAS and NCAR. Note that JRA-55C and JRA-55AMIP are not extended to present. JRA-55 Atlas (climate charts) is now available.
Data Access: JMA | DIAS (JRA-55) (JRA-55C) (JRA-55AMIP) | NCAR (JRA-55: Daily 3-Hourly and 6-Hourly Data, Monthly Means and Variances) (JRA-55C: Daily(3-hourly,6-hourly), Monthly) (JRA-55AMIP: Daily(3-hourly,6-hourly), Monthly) | ESGF/NASA/WCRP | ECMWF |
MERRA is a NASA reanalysis for the satellite era using a major new version (circa 2008) of the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) produced by the NASA GSFC Global Modeling and Assimilation Office (GMAO). The Project focused on historical analyses of the hydrological cycle on a broad range of weather and climate time scales and placed the NASA EOS suite of observations in a climate context.
MERRA-2 is a NASA reanalysis for the satellite era using a major new version of the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) produced by the NASA GSFC Global Modeling and Assimilation Office (GMAO). MERRA-2 assimilates observations not available to MERRA during the 2010s, and therefore, will continue processing in real time longer than MERRA. There are numerous improvements and updates to the data assimilaiton, model and observing system. One notable change is the assimilation of aerosol observations, including black and organic carbon, sulfate and dust. Production began in the spring of 2014 and is presently available for access.
The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) spans 1979 to present. The CFSR was designed and executed as a global, high resolution, coupled atmosphere-ocean-land surface-sea ice system to provide the best estimate of the state of these coupled domains over this period. The T382 resolution atmospheric data spans 1979 to 2010. The current T574 analysis is an extension of the CFSR as an operational, real time CFSv2 product from 2011 into the future.
NCEP produced a second version of their first reanalysis starting from the beginning of the major satellite era. More observations were added, assimilation errors were corrected and a better version of the model was used.
This reanalysis was the first of it's kind for NOAA. NCEP used the same climate model that were initialized with a wide variety of weather observations: ships, planes, RAOBS, station data, satellite observations and many more. By using the same model, scientists can examine climate/weather statistics and dynamic processes without the complication that model changes can cause. The dataset is kept current using near real-time observations.
The NARR reanalysis was done to produce very high resolution output over the North American region. Observational inputs were similar to NCEP I with the addition of assimilated precipitation. The NARR model region was nested in a global, lower resolution model. Outputs are similar to the NCEP I and II models but with more snow, ice and precipitation related variables.
The 20th Century Reanalysis version 2 (20CRv2) dataset contains global weather conditions and their uncertainty in six hour intervals from the year 1871 to 2012. Surface and sea level pressure observations are combined with a short-term forecast from an ensemble of 56 integrations of an NCEP numerical weather prediction model using the Ensemble Kalman Filter technique to produce an estimate of the complete state of the atmosphere, and the uncertainty in that estimate. The uncertainty is approximately inversely proportional to the density of observations. Additional observations and a newer version of the NCEP model that includes time-varying CO2 concentrations, solar variability, and volcanic aerosols are used in version 2. The long time range of this dataset allows scientists to examine better long time scale climate processes such as the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation as well as looking at the dynamics of historical climate and weather events. Verification tests have shown that using only pressure creates reasonable atmospheric fields up to the tropopause. Additional tests suggest some correspondence with observed variations in the lower stratosphere.
The 20th Century Reanalysis version 2 (20CRv2c) dataset contains global weather conditions and their uncertainty in six hour intervals from the year 1851 to 2012. Surface and sea level pressure observations are combined with a short-term forecast from an ensemble of 56 integrations of an NCEP numerical weather prediction model using the Ensemble Kalman Filter technique to produce an estimate of the complete state of the atmosphere, and the uncertainty in that estimate. The uncertainty is approximately inversely proportional to the density of observations. Additional observations from ISPDv3.2.9 and new boundary conditions from the Simple Ocean Data Assimilation with sparse observational input (SODAsi.2) pentad sea surface temperature and COBE-SST2 monthly sea ice concentration are used. For the 2013 and 2014 extension, SSTs are from the NOAA daily 1/4 degree Optimal Interpolation version 2. 2014 does not include tropical cyclone pressure observations after April.