Until 2010, the longest globally-complete estimate of the four-dimensional atmospheric circulation was from a dataset produced jointly by NOAA's National Centers for Environmental Prediction and the National Center for Atmospheric Research: the NCEP-NCAR Reanalysis. This dataset of computer-generated weather map reconstructions or "reanalyses" starts from 1948, leaving many important climate events such as 1930's Dust Bowl drought uncovered. To expand the coverage of global gridded reanalyses, the 20th Century Reanalysis Project is an effort led by NOAA's Earth System Research Laboratory Physical Sciences Division and the University of Colorado CIRES Climate Diagnostics Center to produce a reanalysis dataset spanning the entire twentieth century, assimilating only surface observations of synoptic pressure, monthly sea surface temperature and sea ice distribution. The pressure observations have been assembled through international cooperation under the auspices of the Atmospheric Circulation Reconstructions over the Earth initiative, ACRE, and working groups of the Global Climate Observing System and World Climate Research Program. The Project uses a recently-developed Ensemble Filter data assimilation method which directly yields each six-hourly reanalysis field or weather map as the most likely state of the global atmosphere, and also estimates uncertainty in that map. This dataset will provide the first estimates of global tropospheric variability spanning 1871 to present at six-hourly temporal resolution and 2 degree longitude by 2 degree latitude resolution.
There are 3 sample animations of the data available for Science On a Sphere®. All three animations are showing columnar averaged precipitable water (that is, the total amount of water vapor there is in a column extending from the surface to the top of the atmosphere). Water isn't directly assimilated into the 20th Century dataset but is produced by the atmospheric circulation interacting with water sources such as the oceans. It is a good tracer of atmospheric motions.
This dataset shows the atmosphere throughout the two years of 1902 to 1903. The dot that appears in the Antarctic Region is the location of one of the many sources of observed data that were included in the reanalysis. In this case, it is the ship "Discovery" frozen in the ice continuously for two years. The Discovery was the vessel used for the British National Antarctic Expedition of 1901-1904. Among their many scientific observations, frequent pressure measurements were taken on board the ship and have been included in the reanalysis. The scientific expedition was perceived as a success and launched the careers of many famous explorers including Ernest Shackleton and Captain Robert Scott.
The second datasest, Precipitable Water - El Nino 1917-1919 , illustrates a La Nina(1917) and El Nino (1919). Note that during the La Nina, most of the atmospheric water in the tropical Pacific tended to be in the west while during El Nino, it shifts eastward to the central Pacific.
The third dataset, Precipitable Water - Galveston Hurricane, illustrates the hurricane that made landfall on Galveston, Texas on Sep 8 1900. The hurricane was a class 4 (135+mph) and caused an estimated 8000 deaths, making it the deadliest for the mainland United States history.
The Twentieth Century Reanalysis Project used resources of the National Energy Research Scientific Computing Center and of the National Center for Computational Sciences at Oak Ridge National Laboratory, which are supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and Contract No. DE-AC05-00OR22725, respectively.
More information of the 20th Century Datasets along with the ability to plot the data can be found on the NOAA/ESRL PSD's 20th Century Reanalysis Documentation Web Page
- Longest objective estimate of observed weather
- Reconstruction of global tropospheric variations at 6 hourly resolution
- Puts current atmospheric events in a historical perspective