Robust effects of cloud superparameterization on simulated daily rainfall intensity statistics across multiple versions of the Community Earth System Model

This study evaluates several important statistics of daily rainfall based on frequency and amount distributions as simulated by a global climate model whose precipitation does not depend on convective parameterization—Super‐Parameterized Community Atmosphere Model (SPCAM). Three superparameterized a...

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Bibliographic Details
Published in:Journal of advances in modeling earth systems 2016-03, Vol.8 (1), p.140-165
Main Authors: Kooperman, Gabriel J., Pritchard, Michael S., Burt, Melissa A., Branson, Mark D., Randall, David A.
Format: Article
Language:English
Subjects:
Annual rainfall
Atmospheric models
Bias
Climate
Climate change
Climate models
Community Atmosphere Model
Daily precipitation
Earth
extreme precipitation
Global climate
Global Precipitation Climatology Project
Laboratories
Low clouds
Parameterization
Precipitation
Rain
Rainfall intensity
Rainfall rate
Rainfall simulators
Resolution
Scholarships & fellowships
Simulation
Statistical methods
Statistics
superparameterization
Tropical climate
Tropical Rainfall Measuring Mission
Tropical Rainfall Measuring Mission (TRMM)
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Summary:This study evaluates several important statistics of daily rainfall based on frequency and amount distributions as simulated by a global climate model whose precipitation does not depend on convective parameterization—Super‐Parameterized Community Atmosphere Model (SPCAM). Three superparameterized and conventional versions of CAM, coupled within the Community Earth System Model (CESM1 and CCSM4), are compared against two modern rainfall products (GPCP 1DD and TRMM 3B42) to discriminate robust effects of superparameterization that emerge across multiple versions. The geographic pattern of annual‐mean rainfall is mostly insensitive to superparameterization, with only slight improvements in the double‐ITCZ bias. However, unfolding intensity distributions reveal several improvements in the character of rainfall simulated by SPCAM. The rainfall rate that delivers the most accumulated rain (i.e., amount mode) is systematically too weak in all versions of CAM relative to TRMM 3B42 and does not improve with horizontal resolution. It is improved by superparameterization though, with higher modes in regions of tropical wave, Madden‐Julian Oscillation, and monsoon activity. Superparameterization produces better representations of extreme rates compared to TRMM 3B42, without sensitivity to horizontal resolution seen in CAM. SPCAM produces more dry days over land and fewer over the ocean. Updates to CAM's low cloud parameterizations have narrowed the frequency peak of light rain, converging toward SPCAM. Poleward of 50°, where more rainfall is produced by resolved‐scale processes in CAM, few differences discriminate the rainfall properties of the two models. These results are discussed in light of their implication for future rainfall changes in response to climate forcing. Key Points: Superparameterization improves the rainfall amount mode and extreme rates relative to TRMM 3B42 Mean rainfall and dry day frequency biases do not improve much with superparameterization Conventional and superparameterized rainfall intensity statistics are similar poleward of 50°
ISSN:1942-2466
1942-2466
DOI:10.1002/2015MS000574