Identification

Title

Improved techniques for evaluating GCM cloudiness applied to the NCAR CCM3

Abstract

Evaluations of GCM cloudiness typically compare climatological output with observations, but averaging over time can obscure the presence of compensating errors. A more informative and stringent evaluation can be obtained by averaging cloud properties according to meteorological process (i.e., compositing). The present study illustrates this by comparing simulated and observed cloudiness composited on 500-mb pressure vertical velocity over the summertime midlatitude North Pacific. Observed cloud properties are daily ERBE cloud radiative forcing, daily NVAP liquid water path, and 3-hourly ISCCP cloud optical thickness and cloud-top pressure. ECMWF and NCEP—NCAR reanalyses provide vertical velocity. The GCM evaluated is the NCAR CCM3 with Rasch and Kristjánsson (1998) predicted cloud condensate. Results show that CCM3 overproduces cloud optical thickness, cloud-top height, and cloud radiative forcing under conditions of synoptic ascent and underproduces cloud cover, cloud-top height, and cloud radiative forcing under conditions of synoptic subsidence. The underproduction of cloudiness in the subsidence regime creates an unrealistic sensitivity of CCM3 low-level cloud cover to changes in circulation. As a result interannual variability of summertime midlatitude North Pacific cloudiness in CCM3 is much more closely coupled to sea level pressure variability than SST variability, opposite the case for observed cloudiness. This demonstrates small-scale cloud parameterization errors directly and dominantly impact large-scale cloud variability despite the existence of a reasonable climatology.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7833tb6

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2001-06-01T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

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Use constraints

Copyright 2001 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statement, requires written permission or a license form the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/AMS) or from the AMS at 617-227-2425 or copyright@ametsoc.org.

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact