Data Description:

Data are NCEP values of effective atmospheric angular momentum
functions as calculated from NCEP/NCAR reanalyses archived on pressure
surfaces.  Data are given four-times daily, and each epoch consists
of a header record giving the date and time, and three data records.

The three lines after the header contain 8 values of X1, X2 and X3,
respectively.  The 8 values are those for wind-northern hemisphere to
50 mb, wind-northern hemisphere to top of model [10 mb in the case of
NCEP/NCAR reanalyses], pressure-northern hemisphere, and pressure +
inverted barometer-northern hemisphere and the same four terms for the
southern hemisphere.  All data values are true values multiplied by
10**7.  Presently, the only component of wind to 50 mb which is
calculated is X3.  [The X1 and X2 values for wind to 50 mb are given
the missing indicator of -99.00000].  Note that the inverted barometer
correction involves applying the mean atmospheric surface pressure
over the whole world ocean to every point over the world ocean.

Each days data may be read with the following FORTRAN code:

      read(lunit,101) iyear, imonth, iday, ihour
      read(lunit,102) x1w50nh,  x1w10nh,    x1pnh, x1pibnh, x1w50sh,
     +                 x1w10sh,    x1psh,  x1pibsh
      read(lunit,102) x2w50nh,  x2w10nh,    x2pnh,  x2pibnh, x2w50sh,
     +                 x2w10sh,    x2psh,  x2pibsh
      read(lunit,102) x3w50nh,  x3w10nh,    x3pnh,  x3pibnh, x3w50sh,
     +                 x3w10sh,    x3psh,  x3pibsh
 101  format(1x,4i4)
 102  format(8f10.5)


For more information about this data set, consult the following
reference.  We ask that any use of this data in a published work refer
to this article.

Salstein, D.A., and R.D. Rosen, 1997: Global momentum and energy
signals from reanalysis systems.  Preprints, 7th Conf. on Climate
Variations, American Meteorological Society, Boston, MA, 344-348.


For more information abot the NCEP/NCAR reanalysis project, consult
the following:

Kalnay, E., et al., 1996: The NCEP/NCAR 40-year reanalysis
project. Bull. Amer. Meteor. Soc., 77, 437-471.


For more information about the momentum calculations, consult the
following:

Barnes, R. T. H., R. Hide, A. A. White, and C. A. Wilson, 1983:
Atmospheric angular momentum fluctuations, length-of-day changes and
polar motion.  Proc. R. Soc. London, Ser. A, 387, 31-73.