Data Description:

Data are NCEP values of global atmospheric angular momentum (unit in kg-m**2/s)
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 (year,month, day, hour), 
and data records.

The line after the header contains 9 values of inverted barometer (IB) pressure 
(or, mass) terms, Non-IB pressure terms, wind (or, motion) terms of X1, X2 and X3,
respectively. The wind terms are computed by integrating winds from the Earth 
surface to 10 hPa, the top of atmospheric model. 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 loaded into MATLAB directly, or may be read with the following 
FORTRAN code:

      read(lunit,100) iyear, imonth, iday, ihour,
     +                AAM_mass_IB_X, AAM_mass_IB_Y, AAM_mass_IB_Z,
     +                AAM_mass_NonIB_X, AAM_mass_NonIB_Y, AAM_mass_NonIB_Z,
     +                AAM_motion_X, AAM_motion_Y, AAM_motion_Z
 100  format(13E16.7)

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

Salstein, D.A., D.M. Kann, A.J. Miller, R.D. Rosen, 1993: The
Sub-bureau for Atmospheric Angular Momentum of the International Earth
Rotation Service: A Meteorological Data Center with Geodetic
Applications. Bull. Amer. Meteor. Soc., 74, 67-80.

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.

Salstein, D.A., Y.H. Zhou, and J.L. Chen, 2005: Revised angular momentum 
datasets for atmospheric angular momentum studies, European Geophysical Union 
(EGU) Spring Meeting, Vienna, Austria.

Zhou YH, Salstein DA, Chen JL, 2006: Revised atmospheric excitation function series 
related to Earth variable rotation under consideration of surface topography, 
J. Geophys. Res., 111, D12108, doi:10.1029/2005JD006608.

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.