MERRA turns 11, Global Energy Budget

Last week, MERRA had produced 11 years of data across all 3 streams (79-82, 89-92 and 98-00). Here is a quick evaluation of the global energy budget so far. The reference values are a recent update from Trenberth et al. (2009, BAMS accepted DOI: 10.1175/2008BAMS2634.1). There is a difference between MERRA and this reference, where MERRA is averaging all 11 years, while the reference data was developed from theory as well as observations and reanalyses from March 2000 - May 2004. MERRA is presently in 2001, so it will be a couple months before we can reproduce the global energy budget for this exact time.

(In the figure, MERRA data includes 130 months written in red)

At the surface, too much shortwave, and not enough longwave reach the surface, while at the top of the atmosphere, too little shortwave is reflected and too much longwave is emitted. This suggests that the cloud fraction is too low or cloud optical properties too thin (or both). It is interesting to note that the values tend toward improving in time toward the 2000s. A discussion on the trends in the global energy budget is being prepared.

Some other interesting features occur. The overestimate of the shortwave energy (primarily over the ocean) into the surface is not translating into increased sensible, latent or upward longwave fluxes. Instead, it contributes to the imbalance at the surface, and since the SSTs are prescribed the surface is not warming. Also, the difference of precipitation and evaporation reflect the influence of hte analysis increments on the water budget (globally taking water out of the system).

Trenberth et al (linked above) provide more discussion on the global budget, as well as comparisons to the NCEP and JRA reanalyses.