Status Sept 27

Just a quick post on current jobs and activities.

The validation runs for Jan-Jul and Jul-Oct 2004, Jan and Jul 2006, Jul and Aug 1987 are complete. Jan and Jul 2001 are going, and should wrap up next week. For the next two weeks a summary of the results will be pulled together.

For production, the system will run in three data streams. Each stream will be spun up for two years at a coarse (2 degrees resolution) then the native MERRA resolution for 1 year. The streams will each start at January of 1979, 1989 and 1998.


Presently, the coarse (2 degree) runs are complete and the native (1/2 degree) spin up runs have started. They are all either completed January or into February. Each stream is producing around 10 days/day when the computers are up. With reasonable up time, they should reach the nominal beginning of production by early November.

Incremental Analysis Update

GEOS5 uses an Incremental Analysis Update (IAU) to constrain the atmospheric numerical model by observations. The following figure shows the schematic of the procedure. Starting at 09Z, a 6 hour forecast is run, and forecast data from 09Z, 12Z and 15Z are used to create the analysis (blue diamond). From the analysis and the forecast, a tendency is calculated. This tendency is applied to another model forecast cycle in the prognostic equations (green arrow and light blue box). This is called the corrector segment, so that the tendencies are nudging the model forecast in the direction of the observations at every time step.

MERRA will have two primary products. First, the analyses will consist of the model state variables written instantaneously after the analysis every 6 hours (00Z, 06Z, 12Z and 18Z). There will be model level (72 eta levels) and pressure interpolated (42 pressure levels) for each analysis time. Second, the diagnostic fields are written from the model corrector segment. These include 1 hourly average 2 dimensional (1/2 deg latitude by 2/3 degree longitude) surface, single level (e.g. H500), radiation, land specific and vertically integrated fields. In addition, 3 hourly average 3 dimensional coarse resolution 1.25 deg x 1.25 degree) atmospheric diagnostics are produced from the corrector segment. These include all the tendencies for the state variables, as well as fluxes and budget terms.



One advantage of IAU is that it allows the corrector segment data to be written. This data is exposed to the observational forcing spread out in time, rather than a large change in the initial conditions. The spin up spin down problems in the forecast, associated with initializing a forecast system with an analysis data, are much smaller. Essentially, this allows the production of 1 hourly precipitation and other physics fields. The figure below shows a global average precipitation time series (data is written at every model time step, ~30 min) using the synoptic analysis as initial conditions, IAU and a pure model forecast. Reinitializing the forecasts with the analysis causes jumps in the time series. The free running model tries to have a global precipitation rate of ~3 mm/day. The analysis tried to reduce that, but after the initial time the forecast starts to drift back to it's preferred climate state. The IAU provides forcing at every time step, constraining the system with the observations.

Ocean Surface Winds and Fluxes

The ocean atmosphere interactions are one of the crucial elements in climate variability. The MERRA system does not have a coupled ocean model and data assimilation, but future reanalyses will likely go in this direction. In MERRA, seas surface temperatures are prescribed and ocean surface wind observations (from buoys and satellites) are analyzed. Downward components of the radiation would be related to the parameterized clouds and radiation calculations, as well as the input observations (radiances, temperature and moisture). The following figures prepared for validation compare some winds and fluxes with GEOS5 experiments and other reanalyses.

This following figure shows the daily time-series for Jan 2004 and 2006 U10M and V10M winds at the TAO mooring location of 165E on the equator. GEOS-5 shows good agreement with TAO and matches the minimum and maximum values everywhere. In Jan 2004 and 2006, GEOS-5 is more highly correlated with QSCAT than NCEP CDAS or JRA-25. The NCEP-CDAS analysis shows several periods of larger bias against the observations.

The next figure shows maps of monthly latent heat flux for GEOS5, JRA-25 and NCEP CDAS. GEOS-5 has much less evaporation out of the ocean than JRA-25 and NCEP CDAS, especially in the western boundary currents: Gulf Stream and Kuroshio. Mean and RMS differences between GEOS-5 and JRA-25 and GEOS-5 and NCEP CDAS are much larger than that of NCEP CDAS and JRA-25 in the above region. Similar patterns are seen in January 2004.

In three validation periods investigated so far (Jan/Jul2004 and Jan 2006), GEOS-5 net radiation is more highly correlated with TAO in the Eastern Pacific that other reanalyses.
NCEP-CDAS generally is biased low in most time-periods and TAO locations. GEOS5 also correlates well with the TAO incoming shortwave radiation observations.


The three reanalyses are fairly different in their net heat fluxes. GEOS-5 has less heat loss than both NCEP and JRA in the Kuroshio and Gulfstream areas, and more heat gain off Western Australia. In the 45S-45N band, GEOS5 and JRA have substantial differences.