North American Regional Reanalysis (NARR)

Data Sources

Data assimilated to initialize the model to real-world conditions include:

• Temperatures, winds, and moisture from radiosondes
• Pressure data from surface observations
• Dropsondes
• Pibals
• Aircraft temperatures and winds
• Satellite radiance (a measure of heat) from polar (orbiting Earth) satellites
• Cloud drift winds from geostationary (fixed at one location viewing Earth) satellites

Precipitation

Precipitation data is a major component of the NARR model. The precipitation dataset has a variety of sources for different parts of the North American continent:

• Continental United States: A 1/8-degree gauge dataset analyzed using PRISM and a least-squares distance-weighting algorithm.
• Canada and Mexico: 1-degree gauge datasets.

Much of the rest of the domain's precipitation comes from the Climate Prediction Center (CPC) CMAP (CPC Merged Analysis of Precipitation), and a merged combination of satellite and gauge precipitation.

Additional Datasets

• Winds and precipitable water from Television Infrared Observations Satellite (TIROS) Operational Vertical Sounder (TOVS) satellite radiances
• Wind and moisture from hourly and 3-hourly surface stations
• Ship and buoy data
• Snow depth from the 512x512 Air Force snow dataset
• Sea surface temperatures (SSTs) contain a 1-degree Reynolds dataset, including the Great Lakes
• Sea ice data come from a satellite dataset used for the NCAR/NCEP Reanalysis-I
• Canadian lake ice from the Canadian Ice Center.

NARR fields use earth-relative winds, which do not need adjustment when used with the Gridded Analysis and Display System (GrADS) and the GrADS Data Server (GDS).

Naming Conventions

For each analysis time, GRIB files are named as below:

narr-a_YYYYMMDD_HH00_000.grb
narr-b_YYYYMMDD_HH00_000.grb

The date code YYYYMMDDHH corresponds to the analysis time or the starting time of the forecast for model predicted quantities such as flux or precipitation. The possible HH are 0,03, 06, 09, 12, 15, 18, and 21. All times are in UTC.

One GrADS control file is used for each day:

narr-a_YYYYMMDD_0000_000.ctl
narr-b_YYYYMMDD_0000_000.ctl

The eight 3-hour time increments covered by the specific day (YYYYMMDD), are defined as forecast hours 1 through 8. However, these files do not contain forecast data.

GrADS and File Differences

The data for each analysis time is split into two files to be compatible with GrADS software. The "narr-b" file is much smaller and contains fields that are similar to those in the larger file but excludes fields that GrADS does not recognize. For example, narr-b has a 3-hour forecast of the sensible heat flux, whereas the larger file contains the average from the 00-03 hour forecast and has only one time variable.

Example:

• File A: Analysis at 2004-01-01-00Z
• File B: 3-hour forecast valid at 2004-01-01-00Z

GrADS can combine datasets such as the "A" files in the example, and make a plot for the time-stamp 2004-01-01-18Z. However, it cannot process analyses and forecasts simultaneously. To avoid this limitation, all data were put into the "A" files except the forecasts that cause the timing confusion.

Data Usage Notes

29 Apr 2016

Ingest of NARR at NCEI has ended. NARR data after 02Oct2014 may be found at the National Center for Atmospheric Research (NCAR) Research Data Archive (RDA), dataset ds608.0.

References

Mesinger, F., G. DiMego, E. Kalnay, K. Mitchell, and Coauthors, 2006: North American Regional Reanalysis. Bulletin of the American Meteorological Society, 87, 343–360, doi:10.1175/BAMS-87-3-343.

Additional Documentation

• Presentation to NESDIS Archive Requirements Council (ARC)
• NCEI DSI 6175 NARR Dataset Documentation
• Content of NARR Output GRIB Files

Links

• NCEP NARR Home Page
• Earth System Research Laboratory (ESRL) NARR Home Page