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Evaluation of Cloud Properties in Major Reanalyses

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Evaluation of Cloud Properties in Major Reanalyses

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  1. Underestimation of surface cloud radiative forcing, cloud albedo and cloud fraction in major reanalyses.Reanalysis data have been widely used in various climate-related studies, for example, as “surrogate observations” where there are either no or only sparse observations, or as boundary conditions for regional climate modeling. Evaluation of cloud properties in reanalysis also directly shed light on the deficiencies of relevant parameterizations in climate models because cloud observations have been not assimilated in most reanalyses. However, observational evaluation of cloud-related properties are limited, especially in terms of using surface-based observations. In a recent study published in J of Geophysics Research, DOE scientists at the Brookhaven National Laboratory and their collaborators take advantage of the long-term surface-based observations collected by the ARM program at the Southern Great Plains site to evaluate three major Numerical-Weather-Prediction reanalyses (ERA-Interim, NCEP/NCAR Reanalysis I, and NCEP/DOE Reanalysis II) in modeling surface relative shortwave cloud forcing, cloud fraction, and cloud albedo. The results show that the reanalyses significantly underestimate the cloud properties. The model biases are positively related to one another and are somewhat related to cloud fraction magnitude. The cloud properties are shown strongly related to 2-m relative humidity, especially for the observations and ERA-Interim, suggesting that clouds are closely coupled to the Earth’s surface and boundary layer processes. Addressing the surface-boundary layer-cloud coupling poses thus presents a pressing need for improving further model development and evaluation. Reference: Wu, W., Y. Liu, and A. K. Betts, 2012: Observationally based evaluation of NWP reanalyses in modeling cloud properties over the Southern Great Plains, J. Geophys. Res., 117, D12202, doi:10.1029/2011JD016971.

  2. Evaluation of Cloud Properties in Major Reanalyses Using Long-Term Surface-Based ARM Measurements • Motivation: Reanalysis data have been widely used in climate-related studies; Reanalysis likely suffers from similar parameterization deficiencies as climate modelssince cloud observations have been rarely assimilated; evaluations of reanalysis using ARM surface-based cloud and radiation measurements are limited. • Approach: 12-year ARM measurements at SGP are used to evaluate three major reanalyses (ERA-Interim, NCEP/NCAR Reanalysis I: R1, and NCEP/DOE Reanalysis II: R2) in terms ofsurface shortwave cloud forcing, cloud fraction, and cloud albedo. • Result: The three reanalyses all significantly underestimate the cloud properties; model biases are positively related to one another and somewhat related to cloud fraction; cloud properties are related to 2-m relative humidity, esp.,in the observations and ERA-Interim, suggesting the need for addressing coupling between surface, boundary layer and clouds. These scatter plots show the relationship of the model biases in the cloud properties to the observed and modeled cloud fraction. Blue, green, and purple represent ERA-Interim, R1, and R2, respectively. The colored numbers represent correlation coefficients for the same colored data points. Wu, W., Y. Liu, and A. K. Betts, 2012: Observationally based evaluation of NWP reanalyses in modeling cloud properties over the Southern Great Plains, J. Geophys. Res., 117, D12202, doi:10.1029/2011JD016971.

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