TY - JOUR
T1 - Low-cloud characteristics over the tropical western Pacific from ARM observations and CAM5 simulations
AU - Chandra, Arunchandra S.
AU - Zhang, Chidong
AU - Klein, Stephen A.
AU - Ma, Hsi Yen
N1 - Funding Information:
The authors thank Louise Nuijens and two anonymous reviewers for their comments and suggestions on the earlier version of this manuscript. We would also like to thank Karen Johnson from Brookhaven National Laboratory and Connor Flynn from Pacific Northwest National Laboratory for sharing the details on ARSCL missing data at Manus site. This study was supported by the U.S. Department of Energy Atmospheric Science Research program through grant DE-SC0006808. The observational data are available from the U.S. Department of Energy SGP ARM Climate Research Facility (http:// www.archive.arm.gov). The CAM5 simu lations were performed under the Department of Energy Cloud-Associated Parameterizations Testbed (CAPT: http:// www-pcmdi.llnl.gov/projects/capt/index. php) protocol. Their data are available on request from CAPT coinvestigators Stephen A. Klein, klein21@llnl.gov, and Hsi-Yen Ma, ma21@llnl.gov.
PY - 2015
Y1 - 2015
N2 - This study evaluates the ability of the Community Atmospheric Model version 5 (CAM5) to reproduce low clouds observed by the Atmospheric Radiation Measurement (ARM) cloud radar at Manus Island of the tropical western Pacific during the Years of Tropical Convection. Here low clouds are defined as clouds with their tops below the freezing level and bases within the boundary layer. Low-cloud statistics in CAM5 simulations and ARM observations are compared in terms of their general occurrence, mean vertical profiles, fraction of precipitating versus nonprecipitating events, diurnal cycle, and monthly time series. Other types of clouds are included to put the comparison in a broader context. The comparison shows that the model overproduces total clouds and their precipitation fraction but underestimates low clouds in general. The model, however, produces excessive low clouds in a thin layer between 954 and 930 hPa, which coincides with excessive humidity near the top of the mixed layer. This suggests that the erroneously excessive low clouds stem from parameterization of both cloud and turbulence mixing. The model also fails to produce the observed diurnal cycle in low clouds, not exclusively due to the model coarse grid spacing that does not resolve Manus Island. This study demonstrates the utility of ARM long-term cloud observations in the tropical western Pacific in verifying low clouds simulated by global climate models, illustrates issues of using ARM observations in model validation, and provides an example of severe model biases in producing observed low clouds in the tropical western Pacific.
AB - This study evaluates the ability of the Community Atmospheric Model version 5 (CAM5) to reproduce low clouds observed by the Atmospheric Radiation Measurement (ARM) cloud radar at Manus Island of the tropical western Pacific during the Years of Tropical Convection. Here low clouds are defined as clouds with their tops below the freezing level and bases within the boundary layer. Low-cloud statistics in CAM5 simulations and ARM observations are compared in terms of their general occurrence, mean vertical profiles, fraction of precipitating versus nonprecipitating events, diurnal cycle, and monthly time series. Other types of clouds are included to put the comparison in a broader context. The comparison shows that the model overproduces total clouds and their precipitation fraction but underestimates low clouds in general. The model, however, produces excessive low clouds in a thin layer between 954 and 930 hPa, which coincides with excessive humidity near the top of the mixed layer. This suggests that the erroneously excessive low clouds stem from parameterization of both cloud and turbulence mixing. The model also fails to produce the observed diurnal cycle in low clouds, not exclusively due to the model coarse grid spacing that does not resolve Manus Island. This study demonstrates the utility of ARM long-term cloud observations in the tropical western Pacific in verifying low clouds simulated by global climate models, illustrates issues of using ARM observations in model validation, and provides an example of severe model biases in producing observed low clouds in the tropical western Pacific.
KW - CAM5 underestimates total low clouds, produces excessive low clouds near mixed-layer top
KW - The excessive humidity at the mixedlayer top is suggested due to vertical transport errors
KW - Themacrophysics scheme is responsible for the excessive low clouds near the mixed-layer top
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U2 - 10.1002/2015JD023369
DO - 10.1002/2015JD023369
M3 - Article
AN - SCOPUS:84943453997
VL - 120
SP - 8953
EP - 8970
JO - Journal of Geophysical Research: Atmospheres
JF - Journal of Geophysical Research: Atmospheres
SN - 2169-897X
IS - 17
ER -