New Results: High Latitude Fluxes

There are a number of presentations that include MERRA data at the Workshop: Surface Fluxes: Challenges for High Latitudes in Boulder CO this week. Given the scarcity of observations at high latitudes and uncertainty in satellite observations, reanalyses may be useful data sets.

Michael Brunke, Xubin Zeng,( Uncertainties in global surface flux datasets in high latitudes.) compare various reanalyses and remote sensing products with tower and ship data from various field experiments (CATCH, FASTEX and SHEBA). The results show MERRA is much more comparable to the station data than the previous generations reanalyses, and in range of the remotely sensed products (e.g. Figure 1). The poster is available online.


Figure 1 Comparison of 6-hourly mean wind stress from MERRA, ERA-40, NCEP-R1, and NCEP-R2. The solid lines are the one-to-one slope and the dashed lines are the straight-line regressions with the regression slopes indicated.

Richard Cullather. Evaluation of Arctic Energy and Moisture Budgets in the MERRA Reanalysis. has also compared MERRA Arctic data with long term station measurements and some field experiment sites. For example, Figure 2 shows the time series of MERRA precipitation compared to observations made at a drift camp site. While there are some discrepancies in the magnitude of a few events, the comparison (and correlations of 0.74) seems quite reasonable given the uncertainties at high latitudes.

Figure 2 Drift Camp observed precipitation compared to MERRA. The points are 7 day running means over the period late 1987 through 1990 (a total of 1200 days).

In addition, there is:
J. Brent Roberts, Franklin R. Robertson, Carol Anne Clayson, Analysis of atmosphere-ocean surface flux feedbacks in recent satellite and model reanalysis products.

More on that later.

Full presentations will be posted online at the workshop site shortly after the conclusion.

Update to Data Streams

We are updating MERRA data to permit longer spinup of streams 2 and 3. The announcement and how it affects data downloads follows. Data files formally available in the MERRA data streams are being renamed "SPINUP_*" and will also be available for download. Most research and applications for the data will only require use of the "Mainstream" MERRA data.

Updating of the MERRA data products site to contain only Mainstream data (http://disc.sci.gsfc.nasa.gov/mdisc/data-holdings/merra-mainstream-and-spinup-data) will begin Thursday, March 11, 2010. A two step procedure will be followed to achieve this. In step one, all current  products for the years 1989 through 1992 and 1998 through 2000 will be deleted. It is strongly advised that the MERRA data for the two aforementioned periods not be accessed until this data update is complete.  In step two,  
 products will be used to repopulate these data years. We anticipate that it will take about two weeks to complete the data update. The remaining year
s of the data and all the MERRA data services will still be available during this time period. Once the update activities are completed, a new notification will be sent out and posted on the web. We thank you for your patience during this period.  If you have any questions or concerns please send an email to the GES DISC User Services (help-disc@listserv.gsfc.nasa.gov).


So when the update is complete, Stream 1 will contain 1979 through 1992, Stream 2 will have 5 years spinup (4 available for download) containing 1993 through 2000, and stream 3 will have 4 years spinup (3 available for download) containing 2001 through present.

2009 data should become available during the week of March 15.

Update to Precipitation Validation

Precipitation is a reasonable metric for evaluating reanalyses, because it is coupled to both the water and energy cycles and will be affected by the heating and water vapor increments, as well as variations in the dynamic response of the system to the data assimilation. Bosilovich et al (2008) evaluated precipitation among reanalyses, and also included results from the MERRA validation experiments. Below is an update of some of the Taylor diagrams presented there, now including both MERRA and ERA Interim reanalyses. See Bosilovich et al. (2008) for more explanaiton and the original citations for Taylor diagrams. These are showing that both MERRA and Interim precipitation are close in skill, and ahead of the previous generations of reanalyses. NCEP CFSR will be included in the next version of this evaluation. This was presented in part at the last AMS Annual Meeting (presentation at AMS).