An Evaluation of Marine Boundary Layer Cloud Property Simulations in Community Atmosphere Model Using Satellite Observations: Conventional Sub-grid Parameterization vs. CLUBB

TitleAn Evaluation of Marine Boundary Layer Cloud Property Simulations in Community Atmosphere Model Using Satellite Observations: Conventional Sub-grid Parameterization vs. CLUBB
Publication TypeJournal Article
Year of Publication2017
JournalJournal of Climate
Date Published12/2017
Abstract / Summary

This paper presents a satellite observation based evaluation of the marine boundary layer (MBL) cloud properties from two Community Atmospheric Model Version 5 (CAM5) simulations, one with the standard parameterization schemes (CAM5-Base), and the other with the Cloud Layer Unified By Binormals scheme (CAM5-CLUBB). When comparing the direct model outputs, we find that CAM5-CLUBB produces more MBL clouds, a smoother transition from stratocumulus to cumulus and a tighter correlation between in-cloud water and cloud fraction than CAM5-Base. In the model-to-observation comparison using the COSP satellite simulators, we find that both simulations capture the main features and spatial patterns of the observed cloud fraction from MODIS and shortwave cloud radiative forcing (SWCF) from CERES. However, CAM5-CLUBB suffers more than CAM5-Base from a problem that can be best summarized as “undetectable” clouds, i.e., a significant fraction of simulated MBL clouds are thinner than MODIS detection threshold. This issue leads to a smaller COSP-MODIS cloud fraction and a weaker SWCF in CAM5-CLUBB than the observations and also CAM5-Base in the tropical descending regions. Finally, we compare modeled radar reflectivity with CloudSat observations, and find that both simulations, especially CAM5-CLUBB, suffer from excessive drizzle problem. Further analysis reveals that the sub-grid precipitation enhancement factors in CAM5-CLUBB are unrealistically large, which makes MBL clouds precipitate too excessively, and in turn results in too many “undetectable” thin clouds.

URLhttp://dx.doi.org/10.1175/jcli-d-17-0277.1
DOI10.1175/jcli-d-17-0277.1
Journal: Journal of Climate
Year of Publication: 2017
Date Published: 12/2017

This paper presents a satellite observation based evaluation of the marine boundary layer (MBL) cloud properties from two Community Atmospheric Model Version 5 (CAM5) simulations, one with the standard parameterization schemes (CAM5-Base), and the other with the Cloud Layer Unified By Binormals scheme (CAM5-CLUBB). When comparing the direct model outputs, we find that CAM5-CLUBB produces more MBL clouds, a smoother transition from stratocumulus to cumulus and a tighter correlation between in-cloud water and cloud fraction than CAM5-Base. In the model-to-observation comparison using the COSP satellite simulators, we find that both simulations capture the main features and spatial patterns of the observed cloud fraction from MODIS and shortwave cloud radiative forcing (SWCF) from CERES. However, CAM5-CLUBB suffers more than CAM5-Base from a problem that can be best summarized as “undetectable” clouds, i.e., a significant fraction of simulated MBL clouds are thinner than MODIS detection threshold. This issue leads to a smaller COSP-MODIS cloud fraction and a weaker SWCF in CAM5-CLUBB than the observations and also CAM5-Base in the tropical descending regions. Finally, we compare modeled radar reflectivity with CloudSat observations, and find that both simulations, especially CAM5-CLUBB, suffer from excessive drizzle problem. Further analysis reveals that the sub-grid precipitation enhancement factors in CAM5-CLUBB are unrealistically large, which makes MBL clouds precipitate too excessively, and in turn results in too many “undetectable” thin clouds.

DOI: 10.1175/jcli-d-17-0277.1
Citation:
Song, H.  2017.  "An Evaluation of Marine Boundary Layer Cloud Property Simulations in Community Atmosphere Model Using Satellite Observations: Conventional Sub-grid Parameterization vs. CLUBB."  Journal of Climate.  https://doi.org/10.1175/jcli-d-17-0277.1.