GMAO Core MERRA Research & Evaluation of Global Water Cycle in Reanalyses
M. G. Bosilovich
October 26, 2012 15:25:45
Description of Problem
The changes of observing system have significant impact on the temporal consistency of all reanalysis datasets. Especially when new observation types are introduced, the related discontinuities or jumps could be big obstacles for climate study.
MERRA is a global reanalysis dataset based on NASA GEOS5 data assimilation system. In 2011, we continued to investigate the impact of observing system changes on the MERRA dataset, especially the different characters of impact from individual observing system change events, namely the introduction of SSM/I in 1987 and NOAA15 ATOVS in 1998.
Scientific Objectives and Approach
Based on two observing system experiments (OSE) withholding SSM/I and NOAA-15 ATOVS and data, we systematically analyzed the impacts of the introduction of SSM/I data in 1987 and ATOVS data in late 1998, respectively. An OSE withholding a new kind of observation is a natural continuation of MERRA at the time before the new observation data is added in the MERRA stream, except that the new observation data that comes along will not be assimilated. By comparing the OSE output with the original MERRA data, the impact of the new observation could be isolated. Each OSE covers two year period, so to get clear seasonal cycle.
Based on the two OSEs, we found:
1. The impacts of both SSMI and NOAA15 ATOVS on cloud, precipitation, TOA and Surface fluxes are tightly related.
2. The change in precipitation drives significant change in overturning circulation.
3. The impact of SSM/I is mainly over the tropical region, while the impact of NOAA15 ATOVS has significant signal in middle and high latitudes.
4. Associated with SSM/I, the changes in moisture and moisture increment have same sign, but the changes in temperature and temperature increment have opposite sign. Associated with NOAA15 ATOVS, the changes in state variables and corresponding increments have same sign. These facts imply different cause and effect relationships between the changes in state parameter and corresponding increment in different observing system.
5. SSM/I observation causes more moisture injected in the tropical middle and low troposphere, the additional moisture is depleted through convective precipitation in the tropics. The released latent heat from moisture process (convective precipitation) heats the tropics, especially the equatorial region, and the associated intensification of Hadley Circulation make adiabatic cooling in equatorial region and warming in subtropical region, the net effect of the moisture, dynamic and radiative processes is positive warming, and the temperature observation from other observation kinds (SSM/I contents little temperature infor) passively adjust the temperature increment negatively, so to offset the extra warming caused by SSM/I data.
Refereed Journal Publications
Kennedy A.D., X. Dong, B. Xi, S. Xie, Y. Zhang, J. Chen, 2011: A comparison of MERRA and NARR Reanalysis Datasets with the DOE ARM SGP Continuous Forcing data, J. Clim., 24, 4541-4557
Bosilovich, M.G., F.R. Robertson and J. Chen, 2011: Global Energy and Water Budgets in MERRA, J. Clim., 24, 5721-5739.
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, 2011: MERRA – NASA’s Modern-Era Retrospective Analysis for Research and Applications, J. Clim., 24, 3624-3648.
Robertson, F.R., M.G. Bosilovich, J. Chen and T.L. Miller, 2011: The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes, J. Clim., 24, 5197–5217.
Other Publications and Conferences
“Improving the long-term homogeneity in MERRA reanalysis for climate study”, Chen J., M. Bosilovich, E. Kalnay, F. Robertson, Y. Zhou, WCRP Open Science Conference, Denver, CO, October 24-28, 2011.
“Evaluation of the observation influence on transport in reanalysis regional water cycles”, Bosilovich M., J. Chen, F. Robertson, WCRP Open Science Conference, Denver, CO, October 24-28, 2011.