AAM data file format

The BADC holds AAM data in ASCII files. These files are supplied by the European Centre for Medium-range Weather Forecasting (ECMWF) and the Met Office. File names are detailed in the Help file.

Temporal coverage

ECMWF data spans 1979 to 1993, with data at 24 hourly intervals.
Met Office data are available from 1983 to the present. The Met Office data consists of three subsets:
1. Data prior to 1st November 1986 in Met Office format (24-hourly intervals).
2. Data after 1st November 1986 in Met Office format (12-hourly intervals).
3. Washington-coded data for dates after 1st November 1986 (12-hourly intervals).

Parameters stored

The parameters stored in the ECMWF and most recent (after 1st November 1986) Met Office files are the same, namely (for each time interval stored):

 
   X1PN, X1PS, X1WN, X1WS
   X2PN, X2PS, X2WN, X2WS
   X3PN, X3PS, X3WN, X3WS

where:

X - to be read as chi
1/2/3 represent the AAM component:
1. component with rotation axis aligned with greenwich meridian;
2. " " " " " " 90°East;
3. " " " " " " principal axis of earth's inertia tensor. n.b. X3 has the opposite sign to X3 as defined in BHWW (1983) (5.3) and Hide (1984) (a3) (see references);
P/W indicates pressure (also called matter) or wind term. This is calculated using only the part of the atmosphere between 1000 mb and 50 mb.
N/S represents Northern or Southern hemisphere.

The early Met Office data contains global wind and pressure terms rather than separate components for each hemisphere and includes an additional "total" term (P+W). The situation can be summarised as follows:

|---------------------------------------------------------------------------|
|     Dataset           |      Pressure       |      Wind           |  P+W  |
|                       |---------------------|---------------------|       |
|                       | North | South | N+S | North | South | N+S |       |
|---------------------------------------------------------------------------|
|Met Office pre Nov. 86 |   -   |   -   |  Y  |   -   |   -   |  Y  |   Y   |
|---------------------------------------------------------------------------|
|Met Office post Nov. 86|   Y   |   Y   |  -  |   Y   |   Y   |  -  |   -   |
|---------------------------------------------------------------------------|
|     ECMWF             |   Y   |   Y   |  -  |   Y   |   Y   |  -  |   -   |
|---------------------------------------------------------------------------|

where "Y" denotes that a term is present and "-" denotes that term is absent (for all three components X1, X2, X3).

In addition, Met Office data post-Nov. 1986 is stored at 12-hourly intervals (earlier data and ECMWF data are 24-hourly).