Low-cloud characteristics over the tropical western Pacific from ARM observations and CAM5 simulations

Arunchandra S. Chandra, Chidong Zhang, Stephen A. Klein, Hsi Yen Ma

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)8953-8970
Number of pages18
JournalJournal of Geophysical Research
Volume120
Issue number17
DOIs
StatePublished - Jan 1 2015

Keywords

  • CAM5 underestimates total low clouds, produces excessive low clouds near mixed-layer top
  • The excessive humidity at the mixedlayer top is suggested due to vertical transport errors
  • Themacrophysics scheme is responsible for the excessive low clouds near the mixed-layer top

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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