This is the readme file for the Africa Rainfall Climatology version2 (ARC2) 
available on the Climate Prediction Center's ftp server.


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OVERVIEW:
This data is a result of a project to create a satellite-estimated precipitation
climatology over the Africa domain.  This climatology has been created to 
compliment the daily operational rainfall estimate product (RFE) in order to generate
anomaly fields over Africa over various timescales.  

In contrast to the operational daily rainfall estimate (RFE), where inputs include
SSMI, AMSUB, half-hourly GPI, and GTS data, the climatology method (ARC)
uses only 3-hourly GPI and GTS data, exclusively.  This is due to the absence of
microwave-derved estimates over a long-term historical record, and the large amount of data 
which makes up the operational half-hourly GPI input.  As such, the ARC algorithm itself 
has been slightly modified in order to maintain a homogeneous and stable climate data record. 

GTS rain gauge data used in both static and daily-updating climatology products
is of the same source, though inputs used to create GPI estimates differ slightly
in source.  For creation of the climatological GPI, 3-hourly Meteosat data was
obtained directly from Eumetsat's archived data group, while daily-updating products
use 3-hourly data pulled from NOAA's Meteosat data feed.

Data resolution and specifications of the ARC dataset are identical to that of the RFE.
Files consist of binary-formated grids at a 0.1 degree resolution and one day's temporal domain 
is from 0600 GMT through 0600 GMT.  Spatial extent of all estimates spans 20.0W-55.0E and 40.0S-40.0N.

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FILE FORMAT FOR DATA ACCESS:
Daily data files are written in compressed binary data format (big endian) and consist of 
one record (one array) of floating point rainfall estimates in mm.  For decompression, please use
the gzip (gunzip) utility.  Each daily array equals 751*801 elements, corresponding to 751 pixels 
in the x direction, and 801 pixels in the y direction.  After reshaping to a 0.1 degree grid, 
this will yield a spatial domain of -40S to 40N in latitude, and -20W to 55E in longitude 
encompassing the Africa continent.  Missing data is denoted as -999.0.  A .txt file list of missing 
days may be found in this ftp directory. 


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NOTE TO USERS:
The ARC2 dataset is a quite extensize, and as such, it is only available in binary
format.  Sample fortran programs are also provided in the ARC2 ftp directories to
convert binary data to ascii (.txt) format.  The format of the ascii output will be a three
column text file listing all 0.1 gridpoint coordinates (lat,lon) and the respective rainfall 
esimate in (mm). 


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