The original plan for MERRA production was to run in three streams, optimizing the computers processes. The original three streams were 1) 1979-1988, 2) 1989-1997 and 3) 1998-present. These were initialized with 2 years of coarse resolution analysis, followed by 1 year at the native (1/2 degree) resolution. Streams 1 and 2 were continued providing overlapping data with the beginning of the next streams, in order to test the variance of the system and the viability of the initialization. The first overlapping period is 4 years from 1989-1992 and the second overlap period is 3 years from 1998-2000.
At present we are documenting scientific differences and will provide a report on the overlapping period. On 03/12/2010, the transition times of the streams were changed to utilize the additional data produced at the ends of stream 1 and 2. This does not invalidate the data currently available, but is considered only a minor scientific revision. The streams are now as follows:
Stream 1 1979-1992
Stream 2 1993-2000
Stream 3 2001-present
The connected streams from 1979-present will be refered to as the "mainstream" data. Access to Stream 2 1989-1991 and Stream 3 1998-2000 data is still provided, but the data are considered secondary and called “spinup” data. This effectively increases the spinup period for Streams 2 and stream 3 to 4 years of native resolution analysis.
For the reasons outlined above, there may be small differences between data downloaded before and after this date for the periods Jan 1989-Dec 1992 and Jan 1998 - Dec 2991. Other times in the 30+ year record are not affected.