This is a very brief description of GHCN version 2 temperature data and metadata (inventory) files, providing details, such as formats, not available in www.ncdc.noaa.gov/ghcn/ghcn.html.
New monthly data are added to GHCN a few days after the end of the month. Please note that sometimes these new data are later replaced with data with different values due to, for example, occasional corrections to the transmitted data that countries will send over the Global Telecommunications System.
All files except this one were compressed with a standard UNIX compression. To uncompress the files, most operating systems will respond to: "uncompress filename.Z", after which, the file is larger and the .Z ending is removed. Because the compressed files are binary, the file transfer protocol may have to be set to binary prior to downloading (in ftp, type bin).
The three raw data files are:
The versions of these data sets that have data which we adjusted to account for various non-climatic inhomogeneities are:
Each line of the data file has:
station number which has three parts:
one digit (0-9). The duplicate order is based on length of data. Maximum and minimum temperature files have duplicate numbers but only one time series (because there is only one way to calculate the mean monthly maximum temperature). The duplicate numbers in max/min refer back to the mean temperature duplicate time series created by (Max+Min)/2.
If there are no data available for that station for a year, that year is not included in the data base.
A short FORTRAN program that can read and subset GHCN v2 data has been provided (read.data.f).
Station inventory and metadata:
All stations with data in max/min OR mean temperature data files are listed in the inventory file: v2.inv. The available metadata are too involved to describe here. To understand them, please refer to: www.ncdc.noaa.gov/ghcn/ghcn.html and to the simple FORTRAN program read.inv.f. The comments in this program describe the various metadata fields. There are no flags in the inventory file to indicate whether the available data are mean only or mean and max/min.
Data that have failed Quality Control:
We've run a Quality Control system on GHCN data and removed data points that we determined are probably erroneous. However, there are some cases where additional knowledge provides adequate justification for classifying some of these data as valid. For example, if an isolated station in 1880 was extremely cold in the month of March, we may have to classify it as suspect. However, a researcher with an 1880 newspaper article describing the first ever March snowfall in that area may use that special information to reclassify the extremely cold data point as good. Therefore, we are providing a file of the data points that our QC flagged as probably bad. We do not recommend that they be used without special scrutiny. And we ask that if you have corroborating evidence that any of the "bad" data points should be reclassified as good, please send us that information so we can make the appropriate changes in the GHCN data files. The data points that failed QC are in the files v2.m*.failed.qc. Each line in these files contains station number, duplicate number, year, month, and the value (again the value needs to be divided by 10 to get degrees C). A detailed description of GHCN's Quality Control can be found through www.ncdc.noaa.gov/ghcn/ghcn.html.
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