README_nc

[NOTE: The following description applies to the data at its original 
resolution (360x180). If you have asked for data on a different grid,
the string "360x180" will be replaced by a different resolution (e.g.,
"T42" or "96x48").]

The AMIP 2 boundary condition data are to be used in simulations as
described in the document on the web: 
http://www-pcmdi.llnl.gov/projects/amip/AMIP2EXPDSN/BCS/amip2bcs.html.  
This document has also been published as a PCMDI report:  Taylor, K.E., 
D. Williamson and F. Zwiers, 2000: "The sea surface temperature and sea
ice concentration boundary conditions for AMIP II simulations," PCMDI
Report No. 60, Program for Climate Model Diagnosis and Intercomparison,
Lawrence Livermore National Laboratory, 25 pp (available at
http://www-pcmdi.llnl.gov/publications/ab60.html). These boundary
condition data sets are based on, but not the same as, the monthly mean
data. 

There are a few uncompressed files and 8 compressed tar files:  half 
the compressed files contain boundary condition data (the "bcs" files --
YOU SHOULD USE THE "BCS" FILES IN DRIVING YOUR MODEL SIMULATIONS); 
the other half contain observed monthly mean data (the "obs" files,
which you can use after you run your model to see that you recover 
the observed values).  

First you should uncompress the files
(e.g., gunzip sst_bcs_nc_360x180_187001-189012.tar.gz).  Then you should
extract the individual files from the tar files (e.g., tar xvf
sst_bcs_nc_360x180_187001-189012.tar).  The following describes how to read
the SST boundary condition  files you have extracted (for the years 
1870-1890); a similar procedure applies for the later time-periods and 
also for the sea ice concentration files, as well as the observed monthly
mean data.

The SST and seaice data have been extrapolated to cover the entire globe, 
but note that you shouldn't trust it over land regions or inland seas and 
lakes.

Upon completing the "gunzip" and "tar" steps, you should have
access to the following files containing sea surface temperature (SST)
data:

  amipbc_sst_360x180_1870.nc   contains boundary condition data (mid-month
                                values) for January - December 1870.
  amipbc_sst_360x180_1871.nc   contains boundary condition data (mid-month
                                values) for January - December 1871.
         .
         .
         .

  amipbc_sst_360x180_1890.nc   contains boundary condition data (mid-month
                                values) for January - December 1890.

Along with the 8 tarred and zipped files, you will also find a few other
files similar to the following:


  amipbc_sst_360x180_1987-2006_clim.nc  contains boundary condition data 
                            based on the observed climatology computed for 
                            the period: January 1987 - December 2006.

  bcinfo_sst_360x180.nc   contains some statistical information concerning
                           the boundary condition data, which will not
                           be of general interest.
  
  amipbc_sst_360x180.out       contains the text output documenting the
                           conditions under which the boundary conditions
                           were generated, which will not be of general
                           interest.

***********
begin netCDF files
***********
The ncdump utility can be used to extract the header information from
each file.  For data on a 1x1 degree grid, for example, the result of
the command, "ncdump -h amipbc_sst_1x1_2001.nc", produces the following
listing:

netcdf amipbc_sst_360x180_2001 {
dimensions:
	time = UNLIMITED ; // (12 currently)
	longitude = 360 ;
	latitude = 180 ;
variables:
	double time(time) ;
		time:units = "days since 1979-1-1 0" ;
	double longitude(longitude) ;
		longitude:units = "degrees_east" ;
		longitude:long_name = "Longitude" ;
	double latitude(latitude) ;
		latitude:units = "degrees_north" ;
		latitude:long_name = "Latitude" ;
	float tosbcs(time, latitude, longitude) ;
		tosbcs:comment = "AMIP Boundary Condition Data: Mid-Month SST (K)" ;
		tosbcs:long_name = "AMIP II BCS Psuedo Sea Surface Temperature" ;
		tosbcs:units = "K" ;
		tosbcs:grid_name = "linear" ;
		tosbcs:grid_type = "uniform" ;
		tosbcs:level_description = "Earth surface" ;
		tosbcs:time_statistic = "instantaneous" ;
		tosbcs:missing_value = 1.e+20f ;

// global attributes:
		:Conventions = "COARDS" ;
		:calendar = "gregorian" ;
		:comments = "See: http://www-pcmdi.llnl.gov/amip2/AMIP2EXPDSN/BCS/amip2bcs.html" ;
		:model = "obs" ;
		:institution = "pcmdi" ;
}


netCDF files can be read using the netCDF software available from
http://www.unidata.ucar.edu/packages/netcdf/, or using a number of
other utilities, including cdunif and EzGet available from
 http://www-pcmdi.llnl.gov/old/software/ezget/index.html. For example, the
following FORTRAN code, which relies on EzGet, will retrieve the 1x1
degree data from any of the files:

      real dat(360,180,12)

      call initget

c       NOTE:  to read a different file or SIC instead of SST, replace 
c              the following strings as appropriate.

      call defvar(1, 'tosbcs', 'amipbc_sst_1x1_1971.nc')

      call defdim(1, 1, 'longitude', 'unit', 'as saved', 0.0, 0.0, 0.0)
      call defdim(1, 2, 'latitude', 'unit', 'as saved', 0.0, 0.0, 0.0)
      call defdim(1, 3, 'time', 'unit', 'as saved', 0.0, 0.0, 0.0)

      call getfield(1, dat)

      call closeget
     
      
Note that in this case the data will be retrieved in the same order
that they were saved: with longitude as the first dimension, latitude
the second, and month the last dimension.  The longitudes are stored
from west to east starting at longitude 0.5 degrees east.  The
latitudes are stored from south to north starting at 89.5 degrees
south.  The months are stored with time increasing.

Most files contain a full year of data (January through December).
For files with data only for part of the year, the above code
would not fully fill the array "dat". 

***********
end netCDF files
***********