A 3–D animated image of Reanalysis-2 data for the first 10 days of July 1979, in six-hourly intervals. This animation shows a constant 100 mph wind speed surface in red. (Note the stronger, more widespread, polar jet stream in the Southern Hemisphere—this is July, during the southern winter.) A cyan-colored, constant temperature sheet of 0°C ripples across the globe, showing the freezing level. Near-surface wind flow is denoted by white flowlines. This image was generated with plots from Unidata's Integrated Data Viewer combined with ImageMagick.
Reanalysis of past weather data presents a clear picture of past weather, independent of the many varieties of instruments used to take measurements over the years. Through a variety of methods, observations from various instruments are added together onto a regularly spaced grid of data. Placing all instrument observations onto a regularly spaced grid makes comparing the actual observations with other gridded datasets easier. In addition to putting observations onto a grid, reanalysis also holds the gridding model constant—it doesn't change the programming—keeping the historical record uninfluenced by artificial factors. Reanalysis helps ensure a level playing field for all instruments throughout the historical record.
The following reanalysis datasets are available through NOAA's National Operational Model Archive and Distribution System (NOMADS).
Climate Forecast System Reanalysis (CFSR)
CFSR provides a global reanalysis (a best estimate of the observed state of the atmosphere) of past weather from January 1979 through March 2011 at a horizontal resolution of 0.5°.
North American Regional Reanalysis (NARR)
NARR is a regional reanalysis of North America containing temperatures, winds, moisture, soil data, and dozens of other parameters at 32 km horizontal resolution.
Reanalysis-1 / Reanalysis-2
Reanalysis-1 / Reanalysis-2 are two global reanalyses of atmospheric data spanning 1948/1979 to the present at a 2.5° horizontal resolution.