GHCN Global Gridded Precipitation Data

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Global Historical Climatology Network (GHCN)

Global Gridded Products

Overview and Description
of Temperature Data
Temperature Data
Set Development
Precipitation Data
Note
Data Access
Questions and Comments

Overview and Description of Data

This data set contains gridded mean temperature anomalies from the GHCN V2 monthly temperature data sets. GHCN homogeneity adjusted data was the primary source for developing the gridded fields. In grid boxes without homogeneity adjusted data, GHCN raw data was used to provide additional coverage when possible. Each month of data consists of 2592 gridded data points produced on a 5 X 5 degree basis for the entire globe (72 longitude X 36 latitude grid boxes).

Gridded data for every month from January 1880 to the most recent month is available. The data are temperature anomalies in degrees Celsius. Each gridded value was multiplied by 100 and written to file as an integer. Missing values are represented by the value -9999.

The data are formatted by year, month, latitude and longitude. There are 72 longitude grid values per line, so there is one line for each of the 36 latitude bands. Longitude values are written from 180 W to 180 E, and latitude values from 90 N to 90 S. Data for each month is preceded by a label containing the month and year of the gridded data.

for year = begyr to endyr
      for month = 1 to 12
        format(2i5) month,year
        for ylat = 1 to 36 (85-90N,80-85N,...,80-85S,85-90S)
          format(72i6) 180-175W,175-170W,...,170-175E,175-180E

The file has been compressed using 'gzip'. It can be uncompressed with 'WinZip' for those using Windows 95 or with 'gzip' from most UNIX platforms.

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Data Set Development

These datasets were created from station data using the Anomaly Method, a method that uses station averages during a specified base period (1961-1990 in this case) from which the monthly/seasonal/annual departures can be calculated. Prior to March 25, 2005 the First Difference Method (Peterson et al. 1998) was used in producing the Mean Temperature grid, and prior to February 24, 2004, the FD Method was used in producing the Maximum and Minimum Temperature grids. Due to recent efforts to restructure the GHCN station data by removing duplicates (see Peterson et al. 1997 for a discussion of duplicates), it became possible to develop grids for all temperature data sets using the Anomaly Method. The Anomaly Method can be considered to be superior to the FD Method when calculating gridbox size averages. The FD Method has been found to introduce random errors that increase with the number of time gaps in the data and with decreasing number of stations (Free et al. 2004). While the FD Method works well for large-scale means, these issues become serious on 5X5 degree scales.

Anomalies were calculated on a monthly basis for all adjusted stations having at least 25 years of data in the 1961-1990 base period. Station anomalies were then averaged within each 5 X 5 degree grid box to obtain the gridded anomalies. For those grid boxes without adjusted data, anomalies were calculated from the raw station data using the same technique.

References:

Free, M., J.K. Angell, I. Durre, J. Lanzante, T.C. Peterson and D.J. Seidel, 2004: Using first differences to reduce inhomogeneity in radiosonde temperature datasets, J. Climate, 21, 4171-4179.

Peterson, Thomas C. and Russell S. Vose, 1997: An overview of the Global Historical Climatology Network temperature data base, Bulletin of the American Meteorological Society, 78, 2837-2849.

Peterson, T.C., T.R. Karl, P.F. Jamason, R. Knight, and D.R. Easterling, 1998: The first difference method: maximizing station density for the calculation of long-term global temperature change. Journal of Geophysical Research, Atmospheres, 103 (D20), 25967-25974.

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Note

We developed these gridded data sets to produce the most accurate time series possible. However, this required that we treat months and grid boxes independently through time. The use of this data is most appropriate for analyzing the change in temperature within a particular grid box, or set of grid boxes, over a span of years. If one is more interested in analyzing temperature changes within individual years, e.g., the change in temperature between February and March, 1908, or between two regions in 1908, we recommend that the GHCN station data be used directly.

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Data Access

To obtain a copy of this dataset via your web browser follow these instructions:

Select Load To Local Disk from the Options menu.
Select any of the following items which you would like to download. You will be prompted to name the file to be saved on your local disk after each item that you select.
Select Load To Local Disk from the Options menu again to turn this option off.

1880 - 2009 Temperature Anomalies: 'grid_1880-2009_RVose.dat.gz'

Gridded Precipitation Data

*The use of temporal interpolation is a necessary step in the creation of gridded fields when using the first difference method. Missing first difference grid box values can cause the loss of gridded values before the missing year(s). By temporally interpolating across the missing years, a more complete gridded field in earlier years when station data were available (before the period of missing station data) can be created. The number of missing years over which temporal interpolation was performed was restricted to two years prior to March 2004. This span has now been increased to ten years to improve the spatial coverage of the gridded fields in earlier years without sacrificing data quality. All temporally interpolated gridded values were removed from the gridded field once the full first difference time series for each grid box was created. Examples of spatial coverage from May 1982 with the two-year and ten-year restriction illustrate the improved spatial coverage.

To access anonymous FTP at NCDC use the following information:

  Machine Address : ftp.ncdc.noaa.gov
  Login Name      : anonymous
  Password        : your email address
  Directory       : /pub/data/ghcn/v2/grid/
  Enter           : bin
  Enter           : get 'filename'

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Questions and Comments

For all climate questions, please contact the National Climatic Data Center's Climate Services Division::

Climate Services and Monitoring Division
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: +1-828-271-4876
phone: +1-828-271-4800
e-mail: ncdc.info@noaa.gov
To request climate data, please e-mail: ncdc.orders@noaa.gov

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