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A 3-D animated image of Reanalysis-2 data for the first ten days of July 1979, in six-hourly intervals. This animation shows a constant 100mph 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 zero degrees Celsius 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 (IDV) 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 gives a level playing field for all instruments throughout the historical record.

The following reanalysis datasets are available through NOMADS: