Overview of current atmospheric reanalyses

Submitted by Cathy.Smith@noaa.gov on Thu, 10/07/2010 - 12:47


Ask a Question

Current / State-of-the-art: 

ASR | COSMO-REA | CERA-20C | ERA-20C | ERA-20CM | ERA-Interim | JRA-55, JRA-55C, JRA-55AMIP | MERRA-2 |  NCEP CFSR | NOAA-CIRES 20CRv2c

Possible issues: Consider other datasets for use in new research projects: NCEP/DOE II  | NCEP/NCAR NCEP NARR 

Superseded / Caution use for new research projects: ERA-40 | ERA-15 JRA-25

Model Change: NCEP CFSR (2011 and after)

Updated in real-time for public use (days behind): NCEP/DOE II  | NCEP/NCAR NCEP NARR  | NCEP CFSR? |  JRA-55 (2 days behind from JMA suite) |
Updated in near real-time for public use (months behind)ERA-Interim | JRA-55 | MERRA-2
Updated irregularly for public use (years behind): CERA-20C |ERA-20C | ERA-20CM | NOAA-CIRES 20CR NOAA-CIRES 20CRv2cNASA MERRA


Overview Comparison Table (Reanalyses.org)

Overview Comparison Table (ClimateDataGuide)

Overview Comparison Table (as of 2016, S-RIP)

Notes,questions, and discussion by dataset


Arctic System Reanalysis (ASR): 2000-2012

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

Assimilation: WRFDA-3DVAR

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/ds631.0/
ASRv2 30 km is expected early 2017

ASRv2 – 15 km (Currently updating through 2016 - available end of 2017)
Model Resolution: 15 km, 71 sigma levels
Dataset location: https://rda.ucar.edu/datasets/ds631.1/

Data Access: Polar Meteorology Group

References | ClimateDataGuide


COSMO Regional Reanalyses: 1995-present

Several reanalysis systems are developed to generate high-resolution regional reanalysis data sets for Europe based on the NWP model COSMO. The first available data set at a horizontal resolution of 6km covers the entire European continent for the years 1995-2015 with output of model variables being available for every hour. A subsequent second data set covers large parts of Central Europe in a convection-permitting setup with 2km horizontal resolution and is available for the period 2007-2013.  

Reanalysis consortium: Hans-Ertel-Centre - Climate Monitoring and Diagnostics, German Meteorological Service (DWD) - Climate and Environment, Meteorological Institute of the University of Bonn, Institute for Geophysics and Meteorology of the University of Cologne

Time Range: 1995-2015

Assimilation: Continuous nudging, separate DA modules for soil moisture, snow, SST and sea ice, latent heat nudging scheme

Dataset Output Times: 15 minutes for surface, hourly for upper air fields

COSMO-REA6 – 6.2 km
Model Resolution: 6.2 km, 40 eta levels
Period available: 1995-2015, production for year 2016 is currently under way, will be updated regularly
Domain: Europe (CORDEX-11 domain)
Production of a second (updated) version of COSMO-REA6 is expected to start late 2017 / early 2018

COSMO-REA2 – 2 km
Model Resolution: 2 km, 50 eta levels
Period available: 2007-2013, production for 2014-2015 is currently under way, will be updated regularly
Domain: Central Europe

Data Access: COMSO reanalysis website



ECMWF CERA-20C: 1901-2010

CERA-20C is a global 20th-century reanalysis which aims to reconstruct the past weather and climate of the Earth system including the atmosphere, ocean, land, waves and sea ice. CERA-20C is part of the EU-funded ERA-CLIM2 project and extends the reanalysis capability developed in ERA-20C to the ocean and sea-ice components.

A new assimilation system (CERA) has been developed to simultaneously ingest atmospheric and ocean observations in the coupled Earth system model used for ECMWF’s ensemble forecasts. It is based on a variational method with a common 24-hour assimilation window. Air-sea interactions are taken into account when observation misfits are computed and when the increments are applied to the initial condition. In this context, ocean observations can have a direct impact on the atmospheric analysis and, conversely, atmospheric observations can have an immediate impact on the analysed state of the ocean.

CERA-20C assimilates only surface pressure and marine wind observations (ISPDv3.2.6 and ICOADSv2.5.1) as well as ocean temperature and salinity profiles (EN4). The air-sea interface is relaxed towards the sea-surface temperature from the HadISST2 monthly product to avoid model drift while enabling the simulation of coupled processes. No data assimilation is performed in the land, wave and sea-ice components, but the use of the coupled model ensures some dynamical consistency.

The evolution of the global weather for the period 1901–2010 is represented by a ten-member ensemble of 3-hourly estimates for ocean, surface and upper-air parameters. The resolution of the atmospheric model is set to TL159L91 (IFS version 41r2), which corresponds to a 1.125° horizontal grid (125 km) with 91 vertical levels going up to 0.1hPa. The ocean model (NEMO version 3.4) uses the ORCA1 grid, which has approximately 1° horizontal resolution with meridional refinement at the equator. There are 42 vertical ocean levels with a first-layer thickness of 10m.

Data Access: ECMWF

References | Data documentation | ClimateDataGuide


ECMWF ERA-20C: 1900 - 2010

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 | NCAR

References | ClimateDataGuide


ECMWF ERA-20CM Model integration (no data assimilation): 1900 - 2010

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.

Access: ECMWF

References | ClimateDataGuide

ECMWF Interim Reanalysis (ERA-Interim): 1979-present

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.

Data Access: ECMWF | NCAR

References | ClimateDataGuide


ECMWF 40 Year Reanalysis (ERA-40): Sep 1957-Aug 2002

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.

Data Access: ECMWF  | NCAR

References | ClimateDataGuide

ECMWF 15 Year Reanalysis (ERA-15): Jan 1979-Dec 1993

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.

Data Access: ECMWF  | NCAR

References | ClimateDataGuide

Japanese 25-year Reanalysis (JRA-25): 1979-2004, JCDAS: 2005-Jan.2014

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

Homepage | Atlas | References | ClimateDataGuide

Japanese 55-year Reanalysis (JRA-55): 1958-2012,  and extended to present
     [JRA-55C(1972-2012) and JRA-55AMIP(1958-2012)] <-- not extended to present

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 DataMonthly Means and Variances) (JRA-55C: Daily(3-hourly,6-hourly), Monthly) (JRA-55AMIP: Daily(3-hourly,6-hourly), Monthly) | ESGF/NASA/WCRP | ECMWF |

Homepage | References | JRA-55 Atlas |



NASA Modern Era Reanalysis for Research and Applications (MERRA): 1979-2016(Feb)

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.

Data Access: GES MDISC | ESGF

Home Page | References | FAQ | Atlas | ClimateDataGuide | AMS Special Collection

NASA Modern Era Reanalysis for Research and Applications Version-2 (MERRA-2): 1980-present

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.

Data Access: GES MDISC | FTP Subsetter

Home Page | File Specification | Documentation | AMS Special Collection



NCEP Climate Forecast System Reanalysis (CFSR): 1979-present

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.

Data Access: NCEP | NCDC NOMADS | NCAR (includes real time CFSv2) | ESGF

References | ClimateDataGuide


NCEP/DOE Reanalysis II: 1979-near present

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.


References | ClimateDataGuide

NCEP/NCAR Reanalysis I: 1948-present

This reanalysis was the first of its 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.


References | FAQ | FGDC | ClimateDataGuide

NCEP North American Regional Reanalysis (NARR): 1979-near present

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.


References | FAQ | ClimateDataGuide

NOAA-CIRES 20th Century Reanalysis version 2 (20CRv2): 1871-2012

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.


Homepage | References | Related Publications | ClimateDataGuide

NOAA-CIRES 20th Century Reanalysis version 2c (20CRv2c): 1851-2012 [2013-2014]

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. 

Data Access: ESRL |  NCAR | ESGF | NERSC (every member)

Homepage | References | Related Publications ClimateDataGuide



Have a question or comment on a specific reanalysis dataset or in general?

Use this link to Post Notes, Questions, and Comments on specific reanalyses



Dear Alima, Is there a particular dataset whose land/sea mask you are trying to get? Depending on the dataset, the mask could be different. NCL could possibly be used to make a general conversion from the built-in mask http://www.ncl.ucar.edu/ but I have not test this. best wishes, gil

Remo Beerli (not verified)

Mon, 12/09/2013 - 02:35

Hi everyone, Is there a mask of the elevation of the topography of every grid point in 20CR? If yes, where can I access it? Thanks in advance for any help or suggestions!

Dear Remo, One source is to see the files listed at http://www.esrl.noaa.gov/psd/data/gridded/data.20thC_ReanV2.monolevel.html You want the file from the table for Time-Invariant Either Geopotential Height Surface 2x2 ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/time_invariant/hgt.sfc.nc or Geopotential Height Surface (gaussian grid) ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/gaussian/time_invariant/hgt.sfc.nc best wishes, gil compo

Hi Remo, The 20CR surface geometric height is contained in the file sflxgrbfg_orography.t62.grib, which can be downloaded at the following URL: http://rda.ucar.edu/datasets/ds131.1/index.html#sfol-wl-/data/ds131.1?g=309 You will need to sign in at the NCAR RDA website before downloading the file. Additionally, the ISPDv2, which was assimilated into the 20CR, contains the station elevation data and modified elevation for all stations in the ISPDv2. These data may be accessed from the NCAR RDA website at the following URL: http://rda.ucar.edu/datasets/ds132.0/ - Tom Cram

Anonymous (not verified)

Thu, 09/26/2013 - 06:02

Is NCEP reanalysis more accurate (lower bias and RMS) in summer (JJA) than in winter (DJF) in the stratosphere and troposphere of the northern hemisphere? If so, why? How about in the southern hemisphere? Thanks!

What variables are referring to? In general, your question is a research question that depends on your interests. More broadly, the paper Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J. Woollen, Y. Zhu, A. Leetmaa, R. Reynolds, M. Chelliah, W. Ebisuzaki, W. Higgins, J. Janowiak, K. C. Mo, C. Ropelewski, J. Wang, R. Jenne, D. Joseph, 1996: The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, doi: 10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2. describes the expected level of reliability of the various variables. With more than 10,000 papers having used the dataset, it is possible that someone has already looked into your question, but without more detail, it is difficult to provide any additional direction. Links to additional information (FAQ, ClimateDataGuide) can be found at http://reanalyses.org/atmosphere/overview-current-reanalyses#NCEP1 best wishes, gil compo U. of Colorado CIRES & NOAA Earth System Research Laboratory

Paul Trimble (not verified)

Wed, 09/25/2013 - 06:31

Is the NARR going to be run back to 1900 with 20th Century Reanalysis being used for its boundary coniditions? This would be very useful for studying regional climate and hydrologic within the early portion of the 20th Century. Thanks Paul

Dear Paul, There are no plans that I know of do anything like this specifically. You may be interested in the dynamically downscaled data described in DiNapoli, S. M. and V. Misra, 2012: Reconstructing the 20th century high-resolution climate of the southeastern United States, J. Geophys. Res., 117, D19113, doi:10.1029/2012JD018303. best wishes, gil compo

Nirvikar Dashora (not verified)

Thu, 09/12/2013 - 08:16

Thanks a lot to all of you who responded to my query regarding GPS based water vapor estimation and high res. data. I, indeed, am thankful to you all and at the moment feeling overwhelmed to receive four replies and all are supporting and relevant. So now, let see how all comments work-out. I would like to come back with my findings again to this forum. It has been useful to post a comment here.

ndashora (not verified)

Fri, 09/06/2013 - 03:05

While working for estimation of IWV using GPS, I learned that the diurnal variations in GPS-IWV can be obtained if we use high resolution (better than 6 hours i.e. 3 hourly) surface temperature and pressure values. These values, in turn are required to obtain the hydrostatic delay over the GPS site for estimation of wet delay. I would really appreciate if somebody can provide information about a reanalysis product that has temporal resolution of 3 hours and spatial resolution about 100 km or better. I downloaded MERRA 3-hour product, but observations from our AWS do not match with this data for shorter scales (like diurnal variations and range of variations of parameters).

Dear ndashora, It would be very helpful if you would make a Page on the site and post a figure illustrating the issue. If you do not have an account, go to https://reanalyses.org/user/register to make one. A listing of the spatial and temporal resolution of the atmospheric reanalysis datasets is given at https://reanalyses.org/atmosphere/comparison-table see the Model Output Resolution column and Publicly Available Dataset Resolution column. Links to Data Access can be found under the descriptions at https://reanalyses.org/atmosphere/overview-current-reanalyses Oh, you may want to spell out the acronym IWV. Other users refer to is as Water Vapor Path or other names.

David (not verified)

Thu, 08/22/2013 - 15:07

I didn't quite formulate my question earlier. Let me retry. The general question is what the kg/m2 means in NARR in monthly files? My assumption is that for these "transports" that the value is an accumulation over 3hr. So, to get to a daily value of, say, ssrun, one would simply multiply by 8. And to a monthly integral just days per month. Could someone confirm this? Regards, David

Dick Dee (not verified)

Tue, 07/30/2013 - 04:05

The main ECMWF reanalysis webpage (www.ecmwf.int/research/era) has some information about observations used in ERA-Interim, including a timeline (http://www.ecmwf.int/research/era/do/get/index/29/29?showfile=true) and a complete inventory of radiosonde observations (http://www.ecmwf.int/research/era/do/get/index/29/28). We are working on a system that will allow users to view and download all observations used in our reanalyses - stay tuned.

Christopher (not verified)

Sat, 07/27/2013 - 05:29

Hello, I am looking for the PFT maps used in NCEP I (and other reanalysis, but NCEP I is the first one I'd like to use)? So, the underlying classification of land grid cells according to vegetation or similar used in the reanalysis. I have had no luck finding these online so wanted to ask here? Thanks, Christopher


Mon, 07/29/2013 - 11:26

In reply to by Christopher (not verified)

I think the files are here (monthly) ftp://ftp.emc.ncep.noaa.gov/mmb/gcp/sfcflds/test/fixed/README_albedo_gfrac.txt NCAR has ncep R1 files and lists vegetation (grib 225). I'm not sure which set of products it is in. http://rda.ucar.edu/datasets/ds090.0/#description Cathy

It looks like NCAR has the variable Vegetation Species for the NCEP/NCAR Reanalysis at http://rda.ucar.edu/datasets/ds090.0/#description The University of Maryland table describing the land cover for 1 degree data from which the NCEP/NCAR vegetation species is presumably derived is at http://glcf.umd.edu/data/landcover/ (after consulting with Mike Ek of NOAA). best wishes, gil compo

asimnicol (not verified)

Tue, 07/23/2013 - 04:30

Has anyone worked with the uncertainties of monthly values derived from the 20th Century Reanalysis product? I know there are monthly mean values of sub-daily ensemble spread available, but these are not the same as the spread of the monthly averages calculated using each ensemble. That sentence is confusing, because I am confused! Would be very grateful for any advice or ideas.

Dear Asimnicol, Your comment had spam lines, which have been deleted. At portal.nersc.gov, you can find each member of selected variables averaged to a daily mean and to a monthly mean. From this, you can construct your own ensemble spread or other statistic. Please let me know of any additional questions. best wishes, gil compo (University of Colorado/CIRES and NOAA/Earth System Research Laboratory/Physical Sciences Division)

Tade (not verified)

Mon, 07/08/2013 - 14:59

hello there, I'm wondering if anyone out there could provide and /or confirm on the availability of ERA interim reanalysis at 0.25 degree spatial resolution and sub daily or daily temporal resolution for public access. Apparently, I read from ECMWF portal that ERA interim reanalysis data has approximately 80 km resolution. I'm interested to use a global reanalysis data to force hydrological models such as SWAT for a meso watershed with sparse hydrometeorological stations. I would appreciate if you drop me any piece of information on the availability of global reanalysis data with resolution in the order of 20 -30km at daily scale or shorter. So far I saw CFSR with 38 km which has a potential use but I'm hoping if there is more resoluted one. Many thanks, Tade

Tade, To date, there is no global reanalysis dataset at the resolution you are requesting. See the overview table at http://reanalyses.org/atmosphere/comparison-table There are regional reanalyses that come close to your desired resolution. Again, see the table. best wishes, gil compo (University of Colorado/CIRES and NOAA/Earth System Research Laboratory/Physical Sciences Division)

Anonymous (not verified)

Mon, 06/17/2013 - 06:39

Hi Dears, Where can I find the list of surface station observations used in ERA-Interim? Where can I find the list of radiosonde station observations used in ERA-Interim? Thanks, Celeste

I just took a quick look at the MERRA assimilated observations in Jan2000. I can see data near Summit in surface pressure, but not near Humbolt, GITS, Tunu-N or Petermann. I'm not so familiar with the stations data availability. If they were in the GTS, then they would be input. Note, that MERRA assimilates surface pressure from surface meteorology stations, not temperature, moisture or wind.

To look at this, I used MERRA's Gridded Innovations and Observations data, on openDAP at: http://opendap.nccs.nasa.gov/dods/MerraObs

It can also be downloaded from GES DISC: http://disc.sci.gsfc.nasa.gov/mdisc/data-holdings/merra-innov

These are not yet well documented.

We did not use these data in ERA-Interim - they are also not used by the ECMWF operational forecast system. Most of the Greenland station data that currently arrive at ECMWF are from coastal stations. Those inland stations could be very valuable for forecasting (and reanalysis, of course).

For the 20th Century Reanalysis (20CR, http://reanalyses.org/atmosphere/overview-current-reanalyses#TWENT ), you can obtain all of the observations used from the International Surface Pressure Databank version 2 ( http://reanalyses.org/observations/international-surface-pressure-datab… ) for the entire global domain and time period (1871-2010) or for a subset period or region using the tools
courtesy of the Data Support Section of the Computational and Information Systems Laboratory at the National Center for Atmospheric Research from http://rda.ucar.edu/datasets/ds132.0/.

Maps of the stations available to the 20CR can be viewed at http://www.esrl.noaa.gov/psd/data/ISPD/v2.0/.
A text file with the stations available is at http://reanalyses.org/sites/default/files/groups/users/gilbert.p.compo/… .
See the ISPD home page http://reanalyses.org/observations/international-surface-pressure-datab… for more information.

Please let me know if I can of more help.

best wishes,
gil compo

Gijs de Boer (not verified)

Wed, 02/20/2013 - 14:02

I have a couple of quick questions about ERA-Interim. The documentation is a bit fuzzy on this, but as far as I can tell, the radiation scheme used in Interim is RRTM, is that correct? Also, am I reading correctly that SST and sea ice come from the NCEP analysis for years prior to June 2001, then the NOAA OISST from July 2001-December 2001, the NCEP RTG from January of 2002-January 2009 and finally OSTIA from February 2009 onwards? Thanks, Gijs de Boer

Please take a look at http://www.ecmwf.int/research/era, specifically the links to the IFS documentation, which has all the details about the radiation scheme used in the model, and links to 'known quality issues' which include the inconsistent use of SST products.

I did look at the documentation before posting my questions. However, I was not convinced that I had all of the answers to the questions I posed. For longwave radiation, the model documentation states: "Since cycle Cy22r3, two longwave radiation schemes are available in the ECMWF model, the pre-cycle Cy22r3 by Morcrette (1991), and the current longwave radiation transfer scheme, the Rapid Radiation Transfer Model (RRTM)." It is not stated (as far as I can tell), which version is used for the ERA-Interim runs, which is what I am trying to figure out... While those at ECMWF are likely versed in which model versions are used for the ERA-I production runs, unfortunately I'm not. If I am reading the documentation correctly, the shortwave portion of the radiative transfer scheme is described in Fouquart and Bonnel (1980), and RRTM is NOT used for shortwave radiation. As far as SST goes, the model documentation states: "For the operational ten-day forecasts, ECMWF uses the NCEP daily real-time global SST product (RTG_SST) at 0.5 degree resolution." In the Dee et al. paper, it states that ERA-Interim uses NCEP RTG between 01/02 and 01/09. I was just trying to confirm that this is the case, given the documentation's description. Thanks for providing the hint about searching under the "known quality issues" section, where what I describe above appears to be confirmed. Thanks again for any insight that folks may be able to provide on the longwave radiation scheme used for the ERA-I runs.

Sorry about that - there is a lot of information available but unfortunately it is not all in one place, and not always clear, and it could certainly be much better organised. We tried to be thorough in Dee et al 2011, which is the basic reference for ERA-Interim. In fact it is just as you say - in ERA-Interim LW radiation is computed using RRTM while SW is still based on Fouquart and Bonnel with six spectral intervals.

Brian Walsh (not verified)

Thu, 01/31/2013 - 13:52

I'm looking for high resolution surface wind (10 metres above ground) for 5 years (2008-2012) off Western Greenland. We'd prefer something less than 20 km in spatial resolution and at least 6 or 12 hourly time steps. Is that available from any reanalysis dataset?


Mon, 01/21/2013 - 03:23


I would like to compare globally gridded monthly means of cloud products derived from satellite observations (AVHRR,MODIS) with reanalysis products. I am tending towards using ERA-Interim but would be interested in the general opinion on this question. I would also be very interested in any recommendations which products to look at. I am aiming for cloud fractional coverage, cloud liquid and ice water path and possibly cloud top height. Any comments on this also wrt common traps and problems, parameters to investigate etc. are highly appreciated.



I can't say which you should compare, as it ultimately depends on your metrics and purpose. However, direct cloud data comparisons have been tricky, in my experience, since there are inherent differences in what is observed, and how the background models compute cloud quantities. Part of this is also the motivation for data simulators (e.g. ISSCP Simulator). I would encourage you to include radiation observations into the comparison, as those should be another variable where the feedback from clouds to the atmosphere manifests.

Thanks for your answer. You are certainly raising an important point. We might include direct radiation comparisons but the current scope of the project will not allow us to do much. Therefore, we may have to stick with direct cloud data comparisons for the time being.



Anonymous (not verified)

Tue, 10/23/2012 - 20:51

Hi all, I am studying the surface energy balance problem and using the ERA-Interim solar radiation data, the fields are accumulated from the start of the forecast, so in order to get averaged values I divided the data by the length of the forecast step as the ERA-Interim website FAQs : ( FLD( STEP2)- FLD( STEP1))/(( STEP2-STEP1)*3600) while I get some negative values which I think is impossible,so can you tell me the right to handle the accumuliate field?Thanks. X.L

Paul (not verified)

Thu, 10/25/2012 - 06:08

In reply to by Anonymous (not verified)

In order to obtain average values from accumulated values you need to divide by the number of seconds in the STEP ie STEP*3600 because the accumulation is from the beginning of the forecast to the STEP (in hours) in question. If you require the average value from STEP1 to STEP2 then the formula you quote is correct provided that STEP2 is larger than STEP1. If you obtained netCDF data from the ECMWF data server at http://data-portal.ecmwf.int/ then you need to be aware that the data are packed, see the data FAQ at http://www.ecmwf.int/products/data/archive/data_faq.html#netcdfintegers, and that the scale_factor and add_offset vary with date, time and STEP etc.

Dick Dee (not verified)

Tue, 09/18/2012 - 05:15

Dear anonymous, your question would make a good subject for a paper. It is probably too general for this forum. I can say that we are reasonably confident about lower-tropospheric humidity in ERA-Interim, especially over land areas, based on the quality of the precipitation estimates generated by the model - see Dee et al QJ 2011 (http://onlinelibrary.wiley.com/doi/10.1002/qj.828/abstract). ERA-Interim humidity near the surface compares very well with independent observations - see Simmons et al JGR 2010 (doi:10.1029/2009JD012442). We have also looked at the variability of upper-tropospheric humidity and temperature in the tropics which seems reasonably good - see my presentation at the WCRP Open Science Conference in Denver last year (http://conference2011.wcrp-climate.org/orals/B4/Dee_B4.pdf) Dick


Fri, 09/07/2012 - 00:39

Hello all,
I am studying applicability of met parameter (P, T & Rh) derived from reanalysis products to GPS PWV estimation. I selected NCEP R1, NCEP FNL and ERA-Interim for a decade and use the values (P, T & Rh) derived from them for inter-comparison. R1 and ERA-Interim are reanalysis products whereas FNL is operational GDAS analysis. Is it feasible to use them for inter-comparison? Any help will be highly appreciated.



Fri, 08/03/2012 - 03:47

Hello all,

I have a question regarding the CFSV2. UCAR website states that it is a continuation of CFSR. But is it a reanalysis like CFSR or is it an analysis? Can we consider that the quality of CFSV2 data are the same than CFSR?



Linden Ashcroft (not verified)

Thu, 07/05/2012 - 23:52

Has anyone worked with the uncertainties of monthly values derived from the 20th Century Reanalysis product? I know there are monthly mean values of sub-daily ensemble spread available, but these are not the same as the spread of the monthly averages calculated using each ensemble. That sentence is confusing, because I am confused! Would be very grateful for any advice or ideas.

Dear Linden, You are right that monthly means of sub-daily ensemble spread are not the same as the ensemble spread of the monthly averages. The "correct" spread will always only results from doing all analyses for each member separately and then analyse the spread of the results (e.g., averages, trends, any other statistics). The monthly means of sub-daily ensemble spread can only tell you something about the ensemble spread of the monthly averages if you have a way to consider the autocorrrelation. In my view, it is still valuable as an upper-limit estimation. Maybe I am too simplistic, but some part of the spread will be close to random and thus its contribution is expected to decrease with the square root of n, so the true spread of the monthly means will be lower.

megha (not verified)

Tue, 03/27/2012 - 00:27

kindly suggest me that can we take two different parameters from two different grid data set of NCEP/NCAR reanalysis 2 to calculate a variable in which both the parameters have been involved? for example-can i take skin temperature from surface data grid and all other from pressure data grid to calculate latent heat flux ?

If I understand correctly, you would like to use data from N/N surface files and pressure level files, together, to make a new calculation of Latent heat flux? Ultimately, I don't think there is a specific reason that would prevent it. You would need to be careful about time step an grid centers (if all not identical). However, the reanalysis should produce it's own latent heat flux. Is the LE not sufficient? Can you offer more details or clarification?

The typical output would provide data centered on a grid box, and at the listed pressure level. However, for certain purposes, data offset to the edges are more accurate, but these should be easily identifiable. When in doubt, check the model or system documentation for a description of the grid and data format.

Huug van den Dool (not verified)

Thu, 03/22/2012 - 08:31

Yes, you understand correctly. The solar constant varies, but by the same % irradiance variation for each freq band. Moorthi or Yu-Tai can answer as to whether ozone varies in that set-up. Huug

Stergios (not verified)

Tue, 03/20/2012 - 03:48

Some questions regarding the 20th century reanalysis Which reconstruction of solar irradiance is used to force the model? Is the model forced with total or spectral solar irradiances? Is there a 11-yr solar cycle? Was the stratospheric one kept constant? Thank you very much.

The reconstruction is described in http://www.cpc.ncep.noaa.gov/products/people/wd51hd/vddoolpubs/solar_reconstruction.doc The NCEP model is forced by a spectral distribution of solar radiation. We do include the abt 11 yr cycle, even with a forecast to 2020. Not sure what is meant by the stratosphere question. Huug van den Dool (no need for anonymity on my part)

Thank you very much for the quick reply.

The NCEP model is forced by spectral irradiances but, if i understood correctly, the solar cycle variation refers to total solar irradiance only. This means that every spectral band of the radiation code increases equally (~0.1%) from the minimum to the maximum phase of the 11-yr solar cycle.
The last question was referring to stratospheric ozone. There is a prognostic equation for ozone, right? So, i guess there is a weak ozone variation in the course of the 11-yr solar cycle.

Stergios Misios

bastin (not verified)

Tue, 07/26/2011 - 00:39

So which is the best analysis for wind related long term calculations.......NCEP/NCAR reanalysis or NOAA-CIRES 20th Century Reanalysis V2 (20CR): 1871-2008

It depends on your needs, and which winds you are referring to. Ocean/SHem will have diffs in N/N when satellite data becomes available. 20CR is an ensemble of surface pressure only assimilation, no wind assimilation. the pressure gradients where obs are available should help the low level winds, but there is no upper level wind assimilation.

bottom line is that the 20CR is so new, you will likely have to determine this for your self, and we hope that you can share that information back here, as others may have similar questions. Be sure to search for new papers coming out and conference papers, 20CR is getting a lot of attention!

Add new comment

This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.