Description and Directions for Daily 1° x 1° Grids
20 May 2004
Description
The 1° x 1° degree data contained on this CD were produced using daily surface observations
from the U.S. National Weather Service (NWS) cooperative station network (available from the
National Climatic Data Center’s TD3200 dataset) and Canadian daily surface observations (from
R. Brown, Meteorological Service of Canada, pre-processed at Rutgers University Climate Lab).
The data were reformatted if necessary into TD3200 format so that all data were in a consistent
format for further processing. Station lists were created with basic metadata for each site,
including latitude and longitude, elevation, station name, and the state or province in which the
station was located.
The National Climatic Data Center (NCDC) performs quality control procedures on all
cooperative data, and the TD3200 format data gives two flag codes for each data entry regarding
the accuracy and source of the information. The quality control procedures that the Canadian
data were subject to were different from the US data. The data were strictly examined using
criteria set forth by Robinson (Physical Geography, 10, 120-130, 1989). This was accomplished
by adding an additional quality control flag to the data.
Once the quality control was complete, initial 0.25° latitude x 0.25° longitude grids were created
using the station data. This task was accomplished by means of the Spheremap spatial
interpolation program, developed at the Center for Climatic Research, Department of Geography,
University of Delaware. This software was used because of its ability to create a 2-D grid in
Cartesian space through input of an irregularly spaced point system where distances and station
locations are not necessarily preserved. Spheremap uses a modified version of Shepard’s (D.
Shepard, Proceedings – 1968 ACM National Conference) procedure. The routine computes the
distance and directional relationships among the input data points in spherical space, then uses
them to interpolate from irregularly spaced data to the nodes of a spherical lattice. Within the
program, the search radius changes according to the minimum and maximum number of data
points allowed for the interpolation. For the dataset described here, a minimum of 5 points and a
maximum of 25 points were set as the boundaries.
Upon completion of the 0.25° x 0.25° grids, the final 1° x 1° grids were prepared. This was done
by utilizing the 16 individual 0.25° grid cells that comprise a 1° x 1° grid cell. In order to
minimize file size and irrelevant data, a masking routine was developed and applied that
effectively removed all 0.25° grid cells that did not directly fall over a land surface.
Data Organization
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The gridded data are organized on this CD in yearly files, utilizing the UNIX tar utility, each
containing the daily 1° x 1° grids for that year. The daily grid files contained in the yearly files
are compressed using the UNIX gzip utility. In order to extract and uncompress the daily grids
for a given year, the following commands must be typed at a UNIX command prompt:


tar –xvf NorAm.YYYY.SNWD.1x1degree.grids.tar
gunzip *.gz
where YYYY is the year and TYPE is the data type. See the section File Naming Convention
for more information regarding available data types and their respective identifiers.
The first line untars the yearly data files, yielding the daily grids for that year. The second line
uncompresses the daily grid files, allowing them to be accessed directly.
File Naming Convention
The yearly tarred datasets are labeled based on year, data type, geographical coverage, and grid
resolution. The daily gzipped filenames are similar, except they include the month and day of
the gridded data. The following is an example filename of a yearly tarred file, followed by an
example of a daily gzipped file:
NorAm.YYYY.TYPE.1x1degree.grids.tar
NorAm.YYYY.MM.DD.TYPE.final.grid.gz
NorAm
Refers to North America, which in the case of these data refer to the United States and
Canada
YYYY
Year
MM
Month
DD
Day
TYPE
Data type, based on NCDC names. Data types include the following:
TMAX – maximum daily recorded surface temperature
TMIN – minimum daily recorded surface temperature
PRCP – total daily precipitation (frozen and liquid)
SNOW – total daily frozen precipitation
SNWD – instantaneous daily snow depth
1x1degree
Grid resolution
Data Units
The units for the data are as follows:
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TMAX – Degree Celsius
TMIN – Degree Celsius
PRCP – Millimeters
SNOW – Millimeters
SNWD – Centimeters
Format
The daily 1° x 1° grid files each contain 9 columns and 2891 rows of values for a given day. The
eight columns contain the following data, respectively:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Longitude
Latitude
Maximum value
Minimum value
Median value
Mean value
Standard deviation
Number of valid points over land
Number of invalid (missing) points over land
The longitude and latitude values refer to the lower left corner of the 1° x 1° grid cell. The data
values are calculated based on the 0.25° x 0.25° grid cells used to compute the 1° x 1° grid. See
the Description section for more details regarding the creation of the grids.
In order to read the data from the daily grid files, the following FORTRAN format statement can
be used:
format (2(f10.2),4(f8.1),2(i8))
Contacts
For problems, questions, or comments on the data contained on this CD, please contact either
Thomas Mote (tmote@uga.edu) or Jamie Dyer (dyerlive@uga.edu) at the following address:
Climatology Research Laboratory
Department of Geography
University of Georgia
Athens, GA 30602
Phone: (706) 542-2856
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