Data Description:

Data are ECMWF reanalysis-40 values of effective atmospheric angular 
momentum functions as calculated from ERA40 reanalyses archived on 
pressure surfaces. The reanalysis data has been obtained from archives
on the NCAR Mass Storage System (MSS).  The Transfer functions and 
Principal moments in Eubanks (1993) are employed to derive the 
atmospheric angular momentum functions.

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.
Northern hemisphere and Southern hemisphere values are given separately,
global values can be obtains by summing the two hemispheres.

The lines after the header contains the non-inverted barometer (NIB) 
pressure terms, the inverted barometer IB pressure terms, and the wind 
terms of X1, X2 and X3, respectively. The wind terms are computed by 
integrating winds from the Earth's surface to 100 hPa, or to 10 hPa, or 
to 1 hPa. 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)  X1_pnib_nh, X1_pib_nh, X1_w100_nh, X1_w10_nh, X1_w1_nh,
     +                 X1_pnib_sh, X1_pib_sh, X1_w100_sh, X1_w10_sh, X1_w1_sh
      read(lunit,102)  X2_pnib_nh, X2_pib_nh, X2_w100_nh, X2_w10_nh, X2_w1_nh,
     +                 X2_pnib_sh, X2_pib_sh, X2_w100_sh, X2_w10_sh, X2_w1_sh
      read(lunit,102)  X3_pnib_nh, X3_pib_nh, X3_w100_nh, X3_w10_nh, X3_w1_nh,
     +                 X3_pnib_sh, X3_pib_sh, X3_w100_sh, X3_w10_sh, X3_w1_sh
 101  format(4i4)
 102  format(10f15.7)

where pnib = non-IB pressure, pib = IB pressure, w100 = wind sfc-100 hPa,
w10 = wind sfc-10 hPa, w1 = wind sfc-1 hPa, nh = Northern hemisphere, 
sh = Southern hemisphere.

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.

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 about the calculations of atmospheric angular momentum
functions, 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.

Eubanks, T.M., 1993: Variations in the orientation of the Earth. In: Smith DE (ed) 
Contributions of space geodesy to geodynamics: Earth dynamics. Geodynamics 24, 
American Geophysical Union, Washington, DC pp 1-54

For more information about the ERA40 datset:
The ERA-40 ARCHIVE AT NCAR (http://dss.ucar.edu/pub/era40/)
ECMWF Re-Analysis ERA-40 (http://www.ecmwf.int/research/era/)