Data Description:


Data are ECMWF values of effective atmospheric angular momentum
functions (EAMF).  Data are given up to four times daily (there may be
gaps in the record), and each epoch consists of a header record giving
the date, time, (and--since April 30, 1997--surface pressure), as well
as three data records.

Prior to April, 1997 (filename: aam.ecmwf), the three lines after
the header contain 6 values of X1, X2 and X3, respectively.  The 6
values are those for wind-northern hemisphere to top of model (10 mb
for the ECMWF), pressure-northern hemisphere, and pressure + inverted
barometer-northern hemisphere and the same three terms for the
southern hemisphere.  All data values are true values multiplied by
10**7.  Presently, the ECMWF does not calculate the inverted barometer
term (see note below), and these are given a missing indicator of
-99.0.  Missing data are either given the missing indicator, or are
absent from the record.

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

      read(lunit,101) iyear, imonth, iday, ihour
      read(lunit,102)  x1wnh,    x1pnh,  x1pibnh,
     +                 x1wsh,    x1psh,  x1pibsh
      read(lunit,102)  x2wnh,    x2pnh,  x2pibnh,
     +                 x2wsh,    x2psh,  x2pibsh
      read(lunit,102)  x3wnh,    x3pnh,  x3pibnh,
     +                 x3wsh,    x3psh,  x3pibsh
 101  format(1x,4i4)
 102  format(6f10.5)


Beginning in April, 1997 (filename: aam.ecmwf.2), the header record
contains average global surface pressure, in hPa, as well as the date.
The three lines after the header contain the same AAM terms listed
above.

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

      read(lunit,101) iyear, imonth, iday, ihour, surfpres
      read(lunit,102)  xx1wnh,    x1pnh,  x1pibnh,
     +                 x1wsh,    x1psh,  x1pibsh
      read(lunit,102)  x2wnh,    x2pnh,  x2pibnh,
     +                 x2wsh,    x2psh,  x2pibsh
      read(lunit,102)  x3wnh,    x3pnh,  x3pibnh,
     +                 x3wsh,    x3psh,  x3pibsh
 101  format(1x,4i4,f10.3)
 102  format(6f10.5)


Information about atmospheric excitation for Earth rotation/polar
motion and related fields are supplied by Salstein, et al., (1993):

Salstein, D.A., D.M. Kann, A.J. Miller, R.D. Rosen, 1986: 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.


NOTE: For the period 1 Jan. 1991 through 31 July 1992, the ECMWF did
not provide EAMF data.  However, this period was filled in with terms
calculated from the ECMWF archive at the National Center for
Atmospheric Research in Boulder, Colorado (NCAR).  This data is
archived up to twice daily, and we took the opportunity to include an
inverted barometer calculation for this period.  Users should be
aware, however, that there is a slight discontinuity between the EAMF
terms calculauted at NCAR and those calculated by ECMWF.