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Specifications

NLDAS-E will run with the following specifications:

Spatial Extent North America
Spatial Resolution 12 km
Time Period 1996-2002
Temporal Resolution Hourly
Land Surface Models MOSAIC, CLM, NOAH, Catchment
Atmospheric Model NCEP's 12km Eta
Output Format GRIB


GRID INFORMATION

The NLDAS-E project will use the same rotated, semi-staggered Arakawa-E grid as is used by NCEP's 12km Eta model. A more specific description of the grid is given by the following:


ARAKAWA SEMI-STAGGERED E-GRID
ON ROTATED LATITUDE/LONGITUDE GRID

Grid Characteristics
Grib Projection number
96
Data Representation Type
203
Total number of points along X axis
1211
Total mass points on odd (even) rows
606 (605)
Total number of points along Y axis
1067
La1 - latitude of first grid point
3.441S
Lo1 - longitude of first grid point
211.201E = 148.799
La2 - latitude of center of the grid
50.000N
Lo2 - longitude of center of the grid
249.000E = 111.000W
Di - Longitudinal Direction Increment
88 millidegrees (=53/605 deg)
Dj - Latitudinal Direction Increment
75 millidegrees (=40/533 deg)

Note:
The rotation of the latitude/longitude grid is such that the intersection of the "prime meridian" and the "equator" has been located at the central latitude and longitude of the area represented.




NLDAS-E and the Eta model use the semi-staggered Arakawa E grid (see visual below). Prognostic variables at mass (H) points are surface pressure, temperature, and specific humidity. Zonal and meridional wind components are carried at velocity (V) points. The E grid is mapped to a rotated latitude-longitude grid which is centered at 50N and 111W for the current operational Eta with 12 km resolution. Two rotations are involved. One moves the Greenwich meridian to 111 W, and the second shifts the equator to 50 N. Each row of the E grid lies along a line of constant rotated latitude; each column lies along a line of constant rotated longitude.

The 12km Eta grid representation in GRIB follows a 2-D grid format, whereby the grid is staggered row by row, wind and mass, and the same number of points (1211) are in each row. 606 (605) mass points exist on odd (even) rows, and vice versa for wind points. 

     
      Staggered, 2-D E-grid indexing
        
   3   H   V   H   V   H   V   H  (V)

J  2   V   H   V   H   V   H   V  (H)

   1   H   V   H   V   H   V   H  (V)      () points are "extra"
        \ /     \ /     \ /     \ /        included in grid but not
         1       2       3       4         used in integration
                     I

      Data Representation Type 203 - Arakawa staggered E-grid on rotated
                                     latitude/longitude grid

What area does the NLDAS-E Grid Domain cover?

NLDAS-E Domain
Black outlines the NLDAS-E 12 km domain. Green outlines the NLDAS 1/8th degree domain.

Sample plots illustrating NLDASE domain
NASA webpageLDAS webpage LDAS Web Page
Developed and Maintained at NASA/GSFC		Matthew Rodell: Matthew.Rodell@gsfc.nasa.gov
Brian Cosgrove: Brian.Cosgrove@gsfc.nasa.gov
GSFC webpage