NCEP/NCAR Reanalysis

NCEP/NCAR Reanalysis
Name	NCEP/NCAR Reanalysis
Developer	National Centers for Environmental Prediction; National Center for Atmospheric Research
Initial release	1994
Latest release	Continuous updates
Genre	Atmospheric reanalysis; climate data assimilation
License	Public domain (US government data)

NCEP/NCAR Reanalysis is a global atmospheric reanalysis dataset produced by the National Centers for Environmental Prediction in collaboration with the National Center for Atmospheric Research. It provides a multidecadal, gridded record of atmospheric variables by combining historical observations with a fixed forecast model and data assimilation system, and it has become foundational for research at institutions such as NOAA, NASA, European Centre for Medium-Range Weather Forecasts, University of Reading, and Lamont–Doherty Earth Observatory. The dataset underpins studies by researchers at organizations like Scripps Institution of Oceanography, Potsdam Institute for Climate Impact Research, Met Office, and CIRES.

Overview

The project was initiated through collaboration among NCEP, NCAR, and the Cooperative Institute for Research in the Atmosphere to produce a consistent reanalysis from 1948 onward using the Global Forecast System dynamical core and the three-dimensional variational and successive correction assimilation frameworks developed at ECMWF and GFDL. The effort integrated observations from platforms including radiosonde networks, satellite remote sensing systems such as TIROS, NOAA satellites, ERS-1, and Nimbus, and in situ networks operated by WMO-affiliated services like British Met Office and Japan Meteorological Agency. The dataset has been widely cited in syntheses produced by Intergovernmental Panel on Climate Change authors and applied in analyses at Yale University, Columbia University, Princeton University, and ETH Zurich.

Data Sources and Methodology

Observational inputs include upper-air soundings from UK Met Office Radiosonde, surface synoptic observations compiled by WMO stations, marine reports collected by International Comprehensive Ocean-Atmosphere Data Set, and satellite radiances from instruments such as AVHRR, MSU, and HIRS. The assimilation system employed a fixed-version atmospheric model from NCEP with parameterizations influenced by research at NOAA Geophysical Fluid Dynamics Laboratory and NCAR. Data assimilation techniques drew on advances from Ralph Cess-era radiative transfer studies and operational practices at ECMWF and Met Office research groups. Ancillary datasets included sea surface temperatures from Reynolds SST and sea ice charts from NSIDC.

Products and Variables

Generated fields encompass standard atmospheric variables: three-dimensional wind components, temperature, geopotential height, relative vorticity, and specific humidity, as well as surface variables like sea level pressure, 2-meter temperature, and precipitation. Derived diagnostics include potential vorticity, storm-track indices, and planetary boundary layer metrics used by researchers at University of Colorado Boulder, University of Washington, and Massachusetts Institute of Technology. The archive serves climate indices such as North Atlantic Oscillation, El Niño–Southern Oscillation, Pacific Decadal Oscillation, and provides inputs for ocean reanalyses by NOAA ESRL and coupled model initialization by groups at Princeton University and Institute Pierre-Simon Laplace.

Validation and Uncertainty

Validation efforts compare reanalysis outputs with independent observations from TAO/TRITON buoys, Argo floats, and field campaigns like TOGA COARE and ARM. Inter-comparisons with contemporaneous datasets from ERA-40, ERA-Interim, and JRA-55 quantify systematic differences tied to model physics and observation coverage. Uncertainty arises from changes in observation systems (e.g., introduction of satellite sounding radiances), biases linked to model parameterizations developed at GFDL and NCAR, and homogenization challenges noted by analysts at Hadley Centre and Max Planck Institute for Meteorology.

Applications and Impact

The dataset has been instrumental for atmospheric research on synoptic climatology, trend detection, extreme-event attribution, and teaching in programs at Harvard University, Stanford University, and University of Oxford. It supports operational planning for agencies such as NOAA, US Fish and Wildlife Service, and USGS by providing historical climatologies and anomaly fields used in ecological and hydrological modeling by groups at USBR and EPA. The reanalysis has enabled cross-disciplinary work linking atmospheric states to cryospheric studies at NSIDC, paleoclimate reconstructions at Columbia University's Lamont–Doherty, and air quality research at EPA and University of California, Berkeley.

Limitations and Criticisms

Critics highlight temporal inhomogeneities caused by the evolving observing system—particularly the assimilation of satellite radiances in the late 1970s and 1980s—which can introduce artificial trends noted by investigators at NCAR and NOAA. Resolution limits of the used model restrict representation of mesoscale phenomena, leading groups at University of Miami and Florida State University to prefer higher-resolution regional reanalyses for tropical cyclone studies. Known biases in precipitation and surface fluxes have been characterized by teams at Lamont–Doherty Earth Observatory and University of Arizona, prompting development of successor products like NCEP Climate Forecast System Reanalysis and motivating methodological improvements at ECMWF and JMA.

Category:Reanalysis datasets