New Program: REGRID
Motivation
The current Datagrid program is hardwired to access a few global
datasets from NCAR's archive, and then interpolate the global lat/long
data to mesoscale grid as defined in program Terrain. As the number
of users outside academic community and abroad increases, and as
more datasets become available at NCAR (such as NCEP/NCAR reanalysis),
the need to have a program that is more flexible to adapt different
datasets and be able to run on different platforms is clear.
This new program, REGRID, is designed to overcome these problems
by separating data acquisition, which is often variable and may
require user effort, from the simple task of interpolation.
To find out more about REGRID, please see Manning
and Gill (1998) published in the 1998 MM5 Users' Workshop preprint.
Program Function
The REGRID program is comprised of two sub-programs called pregrid
and regridder. The pregrid program reads a global dataset
and rewrites it to a specified simple format. The regridder program
then reads in this reformatted data and interpolates it to mesoscale
grid.
If an user wants to input a different dataset than those supported
(see the list below), all the user needs to do is to read the dataset
and write it to the simple format, and then run regridder.
The program is written in Fortran 90 and can be run on various
workstations and Cray.
Input Data Format to regridder
The files are written as unformatted FORTRAN 32-bit IEEE records.
Four records are used for every horizontal slab.
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Record 1:
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IFV
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Record 2:
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HDATE, XFCST, FIELD, UNITS, DESC, XLVL, NX, NY, IPROJ
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if (IPROJ == 0) (Cylindrical equidistant grid)
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Record 3:
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STARTLAT, STARTLON, DELTALAT, DELTALON
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if (IPROJ == 3) (Lambert conformal grid)
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Record 3:
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STARTLAT, STARTLON, DX, DY, XLONC, TRUELAT1, TRUELAT2
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if (IPROJ == 5) (Polar-stereographic grid)
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Record 3:
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STARTLAT, STARTLON, DX, DY, XLONC, TRUELAT1
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Record 4:
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SLAB
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Where:
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integer
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::
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IFV
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!
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The PREGRID format version number, currently 2
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character*24
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::
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HDATE
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!
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The time, in format "YYYY-MM-DD_HH:mm:ss "
(only the first 19 characters are used)
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real
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::
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XFCST
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!
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Forecast time (in hours) of the data in the slab
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character*8
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FIELD
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!
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A field name. Names with special meaning are described in
section 4.
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character*16
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::
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UNITS
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!
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Units describing the field in the slab
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character*56
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DESC
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!
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Text description of the field.
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real
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::
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XLVL
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!
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Pressure-level (Pa) of the data.
200100 Pa indicates surface data;
201300 Pa indicates sea-level pressure
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integer
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NX
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!
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Slab dimension in the X direction
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integer
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NY
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!
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Slab dimension in the Y direction
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integer
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::
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IPROJ
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!
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Flag denoting the projection. Recognized values are:
0: Cylindrical Equidistant (Lat/lon) grid.
3: Lambert-conformal projection
5: Polar-stereographic projection
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real
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STARTLAT
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!
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Starting latitude (degrees)
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real
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STARTLON
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Starting longitude (degrees)
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real
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DELTALAT
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!
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Latitude increment (degrees) for lat/lon grid
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real
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DELTALON
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!
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Longitude increment (degrees) for lat/lon grid
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real
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DX
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Grid-spacing in x (km at TRUELAT1 (and TRUELAT2))
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real
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DY
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!
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Grid-spacing in y (km at TRUELAT1 (and TRUELAT2))
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real
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XLONC
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!
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Center longitude of the projection.
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real
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::
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TRUELAT1
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!
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Extra latitude used for defining Polar Stereographic and
Lambert conformal projections
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real
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TRUELAT2
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!
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A second extra latitude used for defining Lambert conformal
projection
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real
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SLAB(NX,NY)
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Two-dimensional array of data.
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Supported
Datasets
Several datasets are currently supported by the pregrid program:
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NCEP GDAS analysis (in ON84 format, discontinued in April
1997);
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NCEP GDAS analysis (in GRIB format, beginning in April 1997);
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TOGA basic level-III anlaysis (GRIB);
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NCEP/NCAR reanalysis archived at NCAR (GRIB);
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NCEP ETA 212 forecast, available on OSO server (GRIB);
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ECMWF reanalysis (GRIB);
For a description of GRIB format, you may find NCEP Office Note
388 useful. You can download it from this site:
ftp://ftp.ncep.noaa.gov/pub/nws/nmc/docs/gribed1.
Program
Documents
An overview for program pregrid.
A README file from program regridder.
Source
tar file
ftp://ftp.ucar.edu/mesouser/MM5v2/Regrid/regrid.tar.gz
Major
Bug Fixes
-
Updated July 29, 1999
-
A correction is put in REGRID/pregrid for processing NCEP
GDAS temperature data in ON84 format. The temperature in the
dataset is virtual temperature, but the previous releases
of REGRID assumed it to be temperature This affects the data
obtained from NCAR DSS082.0 or mesouser/catalog.nmc for the
period up to March 1997.
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