Task 204

GMAO Core MERRA Research & Evaluation of Global Water Cycle in Reanalyses

Principal Investigator(s):

J. Chen


M. G. Bosilovich

Last Updated:

October 26, 2012 15:25:44

Description of Problem

MERRA is a new NASA reanalysis dataset which is listed as the core project of GMAO. In 2010, our research is to investigate the impact of observing system on the MERRA dataset, especially in the energy and water cycle parameters.

Scientific Objectives and Approach

In order to characterize the temporal variation of MERRA associated with observation system, we investigate the change of observation type and counts assimilated in MERRA, and global mean precipitation, evaporation and P-E time series.

We also conducted two observing system experiments (OSE) withholding NOAA-15 ATOVS and SSM/I data to address the impact of the introduction of ATOVS data in late 1998 and SSM/I data in 1987, respectively.


The sequential dramatic increase of observation types and counts is the major character of the evolution of the global observing system in the last 40 years (Figure 1). The global mean precipitation time series, which is heavily affected by the bias between simulated and observed moisture field, gives a visualized description of the inhomogeneity of a reanalysis dataset (Figure 2).

The OSE withholding NOAA-15 is a natural continuation of MERRA at the time before NOAA-15 ATOVS data is added in the MERRA stream, except that the new NOAA-15 data that comes along will not be assimilated. In general, the humidity in the lower free atmosphere increases, because the introduction of NOAA-15. At the same time, the moisture increment increases and results a increasing of precipitation. The additional precipitation releases latent heat, which is almost offset by the negative change of temperature increment, although not at the same location. This drives the large scale overturning circulation and changes the temperature field over high latitude and high altitude region. We also found the impacts of NOAA-15 ATOVS and SSM/I are largely different. Our results show that the impact of a new observation type can be systematic, although the distribution usually is not uniform. We also show that the impacts from different observation types can be very different, so the impacts from different observation types need to be treated individually.

Refereed Journal Publications

Kennedy A.D., X. Dong, B. Xi, S. Xie, Y. Zhang, J. Chen, 2010: A comparison of MERRA and NARR Reanalysis Datasets with the DOE ARM SGP Continuous Forcing data, J. Clim., submitted.

Bosilovich, M.G., F.R. Robertson and J. Chen, 2010: Global Energy and Water Budgets in MERRA, J. Clim., submitted.

Robertson, F.R., M.G. Bosilovich, J. Chen and T.L. Miller, 2010: The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes, J. Clim., submitted.

Rienecker, M.M., M. Suarez4, R. Gelaro, R. Todling, J. Bacmeister, E. Liu, M. Bosilovich, S. Schubert, L. Takacs, G. Kim, S. Bloom, J. Chen, D. Collins, A. Conaty, A. da Silva, W. Gu, J. Joiner, R Koster, R Lucchesi, A. Molod, T. Owens, S. Pawson, P. Pegion, C. Redder, R. Reichle, F. Robertson, A Ruddick, M. Sienkiewicz, J. Woollen, 2010: MERRA – NASA’s Modern-Era Retrospective Analysis for Research and Applications, J. Clim., submitted.

Other Publications and Conferences

“Temporal climate inhomogeneity in reanalyses and an ongoing effort on homogenization of MERRA reanalysis”, Chen J., M.G. Bosilovich, E. Kalnay, Y. Zhou, F.R. Robertson, AGU Fall Meeting 2010, San Francisco, CA, December 13-17, 2010

“The Inhomogeneity in MERRA reanalysis and a homogenization blueprint”, Chen J., M. Bosilovich, E. Kalnay, F. Robertson, Y. Zhou, C. Danforth, Evaluation of Reanalyses – Developing an Integrated Earth System Analysis (IESA) Capability, Baltimore, MD, November 1-3, 2010

“The Inhomogeneities caused by changes of the observing system in MERRA reanalysis”, Chen J., M. Bosilovich, F. Robertson, E. Liu, NOAA’s 35th Climate Diagnostics and Prediction Workshop, Raleigh, NC, October 4-7, 2010

“The impact of ATOVS radiance in MERRA reanalysis”, Chen J., M. Bosilovich, 17th Conference on Satellite Meteorology and Oceanography, Annapolis, MD, September 27 – October 1, 2010

“Reanalysis and the climate change study”, Chen J., COAA 2010 Workshop, College Park, MD, May 1, 2010

Task Figures

Fig. 1 – The global sum of used observation in MERRA (color) and total available observation (grey background).

Fig. 2 – The global mean precipitation time series from major reanalysis datasets (color) and GPCP and CMAP observation synthetics (black).