Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Improvements in Cloud and Water Vapor Simulations Over the Tropical Oceans in CMIP6 Compared to CMIP5

TitleImprovements in Cloud and Water Vapor Simulations Over the Tropical Oceans in CMIP6 Compared to CMIP5
Publication TypeJournal Article
Year of Publication2021
AuthorsJiang, Jonathan H., Su Hui, Wu Longtao, Zhai Chengxing, and Schiro Kathleen A.
JournalEarth and Space Science
Volume8
Number5
Abstract / Summary

Clouds and water vapor are among the most difficult quantities for global climate models to simulate because they are affected by physical processes that operate over scales unresolved by current climate models. We use NASA satellite data to assess the representation of clouds and water vapor structures in 28 climate models that participate in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Each model is assigned numerical scores based on its performance in simulating spatial mean, variance and pattern correlation of multi-year mean clouds and water vapor structures in lower, middle, upper troposphere, and near the tropopause over tropical oceans. We find measurable improvements in CMIP6 models relative to CMIP5 models for both clouds and water vapor. The differences between models and satellite observations and the spread across the models are reduced. In addition, we find that the models' equilibrium climate sensitivity (ECS) is correlated with overall performance scores for both CMIP5 and CMIP6 models, with a weaker correlation in CMIP6, suggesting that the models that capture better tropical clouds and water vapor distributions tend to have higher ECS. The physical processes responsible for the apparent correlation between ECS and model performance score warrant further study.

URLhttp://dx.doi.org/10.1029/2020ea001520
DOI10.1029/2020ea001520
Journal: Earth and Space Science
Year of Publication: 2021
Volume: 8
Number: 5
Publication Date: 05/2021

Clouds and water vapor are among the most difficult quantities for global climate models to simulate because they are affected by physical processes that operate over scales unresolved by current climate models. We use NASA satellite data to assess the representation of clouds and water vapor structures in 28 climate models that participate in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Each model is assigned numerical scores based on its performance in simulating spatial mean, variance and pattern correlation of multi-year mean clouds and water vapor structures in lower, middle, upper troposphere, and near the tropopause over tropical oceans. We find measurable improvements in CMIP6 models relative to CMIP5 models for both clouds and water vapor. The differences between models and satellite observations and the spread across the models are reduced. In addition, we find that the models' equilibrium climate sensitivity (ECS) is correlated with overall performance scores for both CMIP5 and CMIP6 models, with a weaker correlation in CMIP6, suggesting that the models that capture better tropical clouds and water vapor distributions tend to have higher ECS. The physical processes responsible for the apparent correlation between ECS and model performance score warrant further study.

DOI: 10.1029/2020ea001520
Citation:
Jiang, J, H Su, L Wu, C Zhai, and K Schiro.  2021.  "Improvements in Cloud and Water Vapor Simulations Over the Tropical Oceans in CMIP6 Compared to CMIP5."  Earth and Space Science 8(5).  https://doi.org/10.1029/2020ea001520.