Global Historical Climatology Network

Many researchers could benefit from the use of Global Historical Climatology Network (GHCN) data. But one of the problems they face with the data (other than downloading and uncompressing/unzipping those monster-size data files) is extracting data from the stations they need. There is some extraction code available on both GHCN download sites, but it isn't user friendly nor is it completely functional. Therefore I have reworked an extraction program I developed while at the Tree-Ring Laboratory at Lamont-Doherty Earth Observatory (of Columbia University (in the City of New York)).

According to the World Data Center for Meteorology in Asheville, North Carolina, the GHCN "is a comprehensive global baseline climate data set comprised of land surface station observations of temperature, precipitation, and pressure. All GHCN data are on a monthly basis with the earliest record dating from 1697."

There are now three versions of the GHCN. The initial version, GHCN1, was released in 1992. It contains monthly temperature, precipitation, station pressure and sea-level pressure data. The second version, GHCN2, contains monthly mean, maximum and minimum temperature, precipitation, and sea-level pressure data. The temperature data were released in 1997, the precipitation data were released in 1999, and the sea-level pressure data were released in 2002 or 2003. (I admit, I missed the release of the sea-level pressure data at the time.)

As of the summer of 2011, GHCN2 was supplanted by GHCN3. I have just added the ability to search GHCN3 files to ClimExWin.

Where you obtain the data depends on what version you would like to obtain.

I originally had two programs, one for extracting data from GHCN1 files and one for GHCN2 files. I had also supported both 16-bit and 32-bit versions of the ClimExWin programs, but on 23 July 2003 decided to no longer make the 16-bit versions available. On 31 July 2003 I decided to combine GHCN1 and GHCN2 search functions into one program. The older 32-bit version did not work on later 32-bit operating systems (such as Windows Vista), but until June 2011 I did not have a computer capable of compiling code for newer computers. I do now.

The original versions of ClimExWin were written in Fortran, but this new version -- a full-featured Windows version -- is written in Free Pascal using the Lazarus Integrated Development Environment. It represents a complete overhaul of the original code. In addition, the additional help documentation was upgraded to the new Windows HTML Help format.

The current ClimExWin can, like its predecessor, search and extract data from GHCN1 and GHCN2 files. Unlike its predecessor, it can also extract data from GHCN3 files. ClimExWin is a native 64-bit Windows program. The current version number is I have compiled and tested it in Windows 7.

I have also compiled a 32-bit version that works in Windows Vista.

To use the program, download the setup file and save it to a temporary directory. Run the setup program from the temporary directory and follow its instructions. Contact me if you need any assistance.

ClimExWin installers

ClimExWin_setup.exe (64-bit version).

ClimExWin32_setup.exe (32-bit version).

Potential issues

QC data skipped in GHCN2 searches

In early tests, the program occasionally skipped some of the data in the quality control (QC in GHCN2, flag in GHCN1 parlance) files, even in the simplest read-and-write routines. I was unable to discover the cause of the skips.

Part of the problem may line in a change in formatting of GHCN quality control data. In GHCN1, a flag value is given for every monthly value in the corresponding climate file. In GHCN2, NCDC switched a one-entry-per-line format in which only monthly values with questionable data points are listed. Such a format saves a tremendous amount of space, but is more of a challenge (for me) to write appropriate search codes for.

There were no patterns to the data omissions that I could discern, but I continued to revise the search procedures until I at least minimized the problem.

Given the apparent random nature of the skipping, I cannot be completely sure that successful tests on my part represent a successful correction, therefore I recommend you compare the GHCN2 flag output with the original GHCN2 QC files to see if there are any gaps.

Missing files error in GHCN2 searches

Depending on where you obtained the GHCN2 data, you may get a "File not found" error when running GHCN2 searches. That is because the primary FTP site does not include two of the GHCN2 files the code includes in all GHCN2 searches.

The missing files are:

The files can be downloaded from my Web site using the links above, or from the NCDC ftp site at: Install them in the same directory as the rest of the GHCN2 database.



Below are links to help documentation for the program as well as the source databases.


GHCN Version 1:

Vose, R. S., Richard L. Schmoyer, Peter M. Steurer, Thomas C. Peterson, Richard Heim, Thomas R. Karl, and J. Eischeid, 1992: The Global Historical Climatology Network: long-term monthly temperature, precipitation, sea level pressure, and station pressure data. ORNL/CDIAC-53, NDP-041. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

GHCN Version 2:

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, Thomas C., Russell S. Vose, Richard Schmoyer, and Vyachevslav Razuvaev, 1997: Quality control of monthly temperature data: The GHCN experience. International Journal of Climatology, submitted.

Easterling, David R., Thomas C. Peterson, and Thomas R. Karl, 1996: On the development and use of homogenized climate data sets. Journal of Climate, 9, 1429-1434.

Easterling, D.R. and T.C. Peterson, 1995: The effect of artificial discontinuities on recent trends in minimum and maximum temperatures. Atmospheric Research, 37, 19-26.

Easterling, David R. and Thomas C. Peterson, 1995: A new method for detecting and adjusting for undocumented discontinuities in climatological time series. International Journal of Climatology, 15, 369-377.

Peterson, Thomas C. and David R. Easterling, 1994: Creation of homogeneous composite climatological reference series. International Journal of Climatology, 14, 671-679.

GHCN Version 3:

Durre, I., M.J. Menne, and R.S. Vose, 2008: Strategies for evaluating quality assurance procedures. Journal of Applied Meteorology and Climatology, 47(6), 1785-1791.

Easterling, D.R., and T.C. Peterson, 1995: A new method for detecting undocumented discontinuities in climatological time series. International Journal of Climatology, 15 (4), 369-377.

Menne, M.J., and C.N. Williams Jr., 2009: Homogenization of temperature series via pairwise comparisons. Journal of Climate, 22(7), 1700-1717.

Peterson, T.C., and D.R. Easterling, 1994: Creation of homogeneous composite climatological reference series. International Journal of Climatology, 14(6), 671-679.

Peterson, T.C., and R.S. Vose, 1997: An overview of the Global Historical Climatology Network temperature database. Bulletin of the American Meteorological Society, 78 (12), 2837-2849.