Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network

  Advanced Search  

1 JULY 2003 1621J E F F E R Y A N D A U S T I N 2003 American Meteorological Society

Summary: 1 JULY 2003 1621J E F F E R Y A N D A U S T I N
2003 American Meteorological Society
Unified Treatment of Thermodynamic and Optical Variability in a Simple Model of
Unresolved Low Clouds
Atmospheric Sciences Programme, University of British Columbia, Vancouver, British Columbia, Canada
(Manuscript received 16 May 2001, in final form 6 January 2003)
Comparative studies of global climate models have long shown a marked sensitivity to the parameterization
of cloud properties. Early attempts to quantify this sensitivity were hampered by diagnostic schemes that were
inherently biased toward the contemporary climate. Recently, prognostic cloud schemes based on an assumed
statistical distribution of subgrid variability replaced the older diagnostic schemes in some models. Although
the relationship between unresolved variability and mean cloud amount is known in principle, a corresponding
relationship between ice-free low cloud thermodynamic and optical properties is lacking. The authors present
a simple, analytically tractable statistical optical depth parameterization for boundary layer clouds that links
mean reflectivity and emissivity to the underlying distribution of unresolved fluctuations in model thermodynamic
variables. To characterize possible impacts of this parameterization on the radiative budget of a large-scale
model, they apply it to a zonally averaged climatology, illustrating the importance of a coupled treatment of
subgrid-scale condensation and optical variability. They derive analytic expressions for two response functions
that characterize two potential low cloud feedback scenarios in a warming climate.


Source: Austin, Philip H. - Department of Earth and Ocean Sciences, University of British Columbia


Collections: Geosciences