GHCN Gridded Products

Overview and Description of Data

September 2014 Land Surface Temperature Anomalies
September 2014 Land Surface Precipitation Anomalies

Temperature

This data set contains gridded mean temperature anomalies from the Global Historical Climatology Network-Monthly (GHCN-M) version 3.2.1 temperature data set. The gridded anomalies were produced from GHCN-M bias corrected data. Each month of data consists of 2,592 gridded data points produced on a 5° by 5° basis for the entire globe (72 longitude by 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 = begYear to endYear
       for month = 1 to 12
         format(2i5) month,year
         for lat = 1 to 36 (85-90N,80-85N,...,80-85S,85-90S)
           format(72i6) 180-175W,175-170W,...,170-175E,175-180E
    

Precipitation

This data set contains gridded precipitation anomalies calculated from the GHCN version 2 monthly precipitation data set. 2,064 homogeneity adjusted precipitation stations (from the U.S., Canada, and Former Soviet Union) were combined with a data set containing 20,590 raw precipitation stations throughout the world to create these gridded fields. Grid boxes with no homogeneity adjusted data, GHCN raw data was used to provide the greatest possible global coverage. Each month of data consists of 2,592 gridded data points produced on a 5° by 5° basis for the entire globe (72 longitude by 36 latitude grid boxes).

Gridded data for every month from January 1900 to the most recent month is available. The data are precipitation anomalies in millimeters. Each gridded value was multiplied by 100 and written to file as an integer. Missing values are represented by the value -32768.

The data are formatted by year, month, latitude and longitude. There are twelve longitude grid values per line, so there are 6 lines (72/12 = 6) 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 = begYear to endYear
       for month = 1 to 12
         format(2i7) month,year
         for lat = 1 to 36 (85-90N,80-85N,...,80-85S,85-90S)
           format(12i7) 180-175W,175-170W,...,130-125W,125-120W
           format(12i7) 120-115W,175-170W,...,70-65W,65-60W
           format(12i7) 60-55W,55-50W,...,10-5W,5-0W
           format(12i7) 0-5E,5-10E,...,50-55E,55-60E
           format(12i7) 60-65E,65-70E,...,110-115E,115-120E
           format(12i7) 120-125E,125-130E,...,170-175E,175-180E
    

Data Set Development for Temperature and Precipitation

These datasets were created from station data using the Anomaly Method, a method that uses station averages during a specified base period from which the monthly/seasonal/annual departures can be calculated. Anomalies were calculated on a monthly basis for all adjusted stations having at least 20 years of data in the 1961–1990 base period. Station anomalies were then averaged within each 5° by 5° 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. Please note that the gridded temperature anomalies were readjusted to be with respect to the 1981–2010 base period.

References:

  • Jones, P. D., and A. Moberg, 2003: Hemispheric and Largescale Surface Air Temperature Variations: An extensive Revision and an Update to 2001, J. Climate, 16, 206–223.
  • 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.

Global Average Anomalies

After the creation of the 5° by 5° anomaly grid, the grid boxes are averaged across the globe using cosine weighting to obtain the global average temperature and precipitation anomaly for each month. The global temperature anomalies can be accessed via the Global Surface Temperature Anomalies page.

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 these data sets 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.

Data Access

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Note: GHCN-M Data Notice

An omission in processing a correction algorithm led to some small errors on the Global Historical Climatology Network-Monthly dataset (GHCN-M v3.2.0). This led to small errors in the reported land surface temperatures in the October, November, December and Annual U.S. and global climate reports. On February 14, 2013, NCDC fixed this error in its software, included an additional improvement (described below), and implemented both changes as GHCN-M version 3.2.1. With this update to GHCN-M, the Merged Land and Ocean Surface Temperature dataset also is subsequently revised as MLOST version 3.5.3.

The net result of this new version of GHCN-M reveals very small changes in temperature and ranks. The 2012 U.S. temperature is 0.01°F higher than reported in early January, but still remains approximately 1.0°F warmer than the next warmest year, and approximately 3.25°F warmer than the 20th century average. The U.S. annual time series from version 3.2.1 is almost identical to the series from version 3.2.0 and that the 1895-2012 annual temperature trend remains 0.13°F/decade. The trend for certain calendar months changed more than others (discussed below). For the globe, ranks of individual years changed in some instances by a few positions, but global land temperature trends changed no more than 0.01°C/century for any month since 1880.

NCDC uses two correction processes to remove inhomogeneities associated with factors unrelated to climate such as changes in observer practices, instrumentation, and changes in station location and environment that have occurred through time. The first correction for time of observation changes in the United States was inadvertently disabled during late 2012. That algorithm provides for a physically based correction for observing time changes based on station history information. NCDC also routinely runs a .pairwise correction. algorithm that addresses such issues, but in an indirect manner. It successfully corrected for many of the time of observation issues, which minimized the effect of this processing omission.

The version 3.2.1 release also includes the use of updated data to improve quality control and correction processes of other U.S. stations and neighboring stations in Canada and Mexico.

Compared to analyses released in January 2013, the trend for certain calendar months has changed more than others. This effect is related to the seasonal nature of the reintroduced time-of-observation correction. Trends in U.S. winter temperature are higher while trends in summer temperatures are lower. For the globe, ranks of individual years changed in some instances by a few positions, but global temperature trends changed no more than 0.01°C/century for any month since 1880.

More complete information about this issue is available at this supplemental page.

NCDC will not update the static reports from October through December 2012 and the 2012 U.S and Global annual reports, but will use the current dataset (GHCN-M v. 3.2.1 and MLOST v. 3.5.3) for the January 2013 report and other comparisons to previous months and years.

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Please note that the anomalies for the precipitation are with respect to the 1961–1990 base period. The temperature anomalies are with respect to the 1981–2010 base period.

Files have been compressed using gzip.

HTTP Access:

GHCN version 3.2.1 Land Temperature Anomalies grid file:
grid-mntp-1880-current-v3.2.1.dat.gz

Land and Ocean Temperature Anomalies grid file using GHCN version 3.2.1:
ncdc-merged-sfc-mntp.dat.gz

GHCN version 2 Land Precipitation Anomalies grid file:
grid_prcp_1900-current.dat.gz

FTP Access:

    FTP Site   : ftp.ncdc.noaa.gov
    Login Name : anonymous
    Password   : your email address
    Enter      : bin
    

GHCN version 3.2.1 Land Temperature Anomalies grid file

    Directory : /pub/data/ghcn/v3/grid/
    Enter     : get grid-mntp-1880-current-v3.2.1.dat.gz
    

Land and Ocean Temperature Anomalies grid file using GHCN version 3.2.1

    Directory : /pub/data/ghcn/blended/
    Enter     : get ncdc-merged-sfc-mntp.dat.gz
    

GHCN version 2 Land Precipitation Anomalies grid file

    Directory : /pub/data/ghcn/v2/grid/
    Enter     : get grid_prcp_1900-current.dat.gz