May 1997

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:
v2.mean
v2.max
v2.min

The versions of these data sets that have data which we adjusted
to account for various non-climatic inhomogeneities are:
v2.mean.adj
v2.max.adj
v2.min.adj

Each line of the data file has:

station number which has three parts:
	country code (3 digits)
	nearest WMO station number (5 digits)
	modifier (3 digits) (this is usually 000 if it is that WMO station)

Duplicate number:
	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.

Year:
	four digit year

Data:
	12 monthly values each as a 5 digit integer.  To convert to
degrees Celsius they must be divided by 10.
	Missing monthly values are given as -9999.

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.

Country codes:
	The file v2.country.codes lists the countries of the world and
GHCN's numerical country code.

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.