Output Data Review

We are currently reviewing the MERRA File Specification Document, and considering new variables and diagnostics that should be incorporated into future experiments and reanalyses. This is directed toward information that needs to be captured during run time, as opposed to diagnostics that can be post processed from existing data. For example, to get Max/Min temperature from MERRA would be the maximum/minimum hourly averaged temperature, in the current configuration. We will implement for future analyses hourly maximum and hourly minimum temperatures, so that the instantaneous Max/Min T can be captured from the system.

Any suggestions would be welcome. Please include any computations that may be non standard, and reasons or applications of the suggested diagnostic.

Apologies for letting the blog become stagnant. While I have seen a lot of interesting work with reanalyses and MERRA, finding the time to work up a worthwhile post is remarkably challenging.

Ancillary Land and Ocean data

Two data sets for Ocean and Land have been released through the GES DISC, derived from MERRA, but not included in the original data collection. The ocean data has 1 hourly fluxes, meteorology and stresses over both open water and ice. the MERRA-Land data is an offline reprocessing using MERRA atmospheric forcing with bias corrected precipitation to produce a new set of surface fluxes and land states (Reichle et al. 2011).

See the release page for more information.

Pressure levels greater than surface pressure

Some questions have come in regarding differences between MERRA and other reanalysis at pressure 1000mb and 850mb pressure levels. It is very important to note that MERRA does not extrapolate pressure level data vertically greater than the surface pressure. The result is that there is undefined data points in much of the 1000mb fields. This will affect the representativeness of both time and area averages of MERRA data compared with reanalyses or other data that extrapolates gridpoints to pressure levels greater than the surface pressure. The GMAO provides a summary of the impact that this has on averaging. In addition, the FAQ will be updated to call out this difference with other data sets. The main GMAO www page also has other pages with useful practical information about the data and assimilation system.

Status and File Spec

Production of MERRA data has been progressing at 10 days per day on three streams, which is what is expected. Data monitoring is going on regularly, and the system seems to be moving along at the expected data quality. We have some time series routines being run, and will report on those when we achieve 8 full annual cycles. Currently, Streams 1 and 2 have more than 2.5 years each, and stream 3 has 22 months.

The MERRA File specification document has also been updated and reflects exactly the data files being produced. The document can be found at the bottom of the MERRA home page, and a link is provided here.

File Specification Document

The MERRA File Specification Document describes every aspect of the output data files that users will need to use the data. The file formats, grid structures, frequency and variables are all included. There are also some brief discussions on the physics and analysis.

The file can be found at: http://gmao.gsfc.nasa.gov/research/merra/MERRA_FileSpec_DRAFT_4-10-2007.doc

Full documentation of the GCM science and analysis methods are in development.