The topics discussed include the following: an overview of radiation and mesoscale flows and lessons learned from the intercomparison of GCM radiative codes

Cess, Robert D.

Churchill, Dean

Flatau, P. J.

English

NASA Technical Reports Server

3.8
N94-24389
The role of radiation in mesoscale flows: physics, parameterizations, codes
P. j. Flatau: Review of radiation parameterization for mesoscale models
Dean Churchill:
Robert D. Cess:
An overview of radiation and mesoscale flows
Lessons learned from the intercomparison of GCM radiative codes
Piotr Flatau discussed three issues in his keynote talk on radiative transfer
parameterizations for mesoscale models:
How mesoscale processes influence climate by interaction of extensive stratiform cloudiness,
cirrus debris, and increased moisture with the radiative field
The importance of cloud microphysical/radiation processes (such as changes in particle shape and
size, varying refractive index, and changes in albedo) in mesoscalc dynamics
Which local processes (e.g., convection, turbulence, entrainment fluxes, and evaporation) are
most influenced by radiative fluxes, and what time scales are involved
He suggested that, knowing what the issues are, one is faced with several technical
problems, including what optical properties to measure and observe, and whether we can
transform our knowledge about the radiative properties of MCSs and mesoscale
phenomena into consistent radiative transfer parameterization. It is also essential to
consider how to convincingly present results from mesoscale models and field studies in
their more global climate context, and how experiences in other radiation and climate
related projects (ARM, FIRE (Starr 1990), etc.) could contribute to the design of the CME
field project. Flatau then discussed several topics related to radiative parameterizations and
cloud microphysics, including assumptions needed to develop a two-stream approximation
to the radiative transfer equation, assumptions needed to get single scattering properties
such as single scattering albedo and asymmetry parameter, and coupling of radiative
transfer with particle size distributions through averaged single scattering properties. It is
possible, he concluded, to tie properties such as irregular cirrus particles, inhomogeneous
particles, and particles with refractive index other than that of water or ice (aerosols,
chemistry) to radiative transfer schemes but only at a cost comparable to that of explicit
microphysical schemes. Current theoretical approaches of single scattering
parameterizations consist of anomalous diffraction theory, power law fits to Mie
calculations, and table look-ups. Theoretical approaches for scattering calculations on non-
spherical particles presently consist of discrete dipole approximation, ray-tracing, and
multipole methods. These are costly calculations not suitable for parameterizations in their
current form. Flatau also discussed the unified approach to radiative transfer solvers
showing that all existing schemes reduce to the banded (blocked) type linear problem. As
42
https://ntrs.nasa.gov/search.jsp?R=19940019916 2020-06-16T16:55:36+00:00Z
for the infrared emissivity approach, the mesoscale radiative transfer differs from solvers
employed in GCMs because more details are available in mesoscale models. This
presentation concluded with the presentation of several current radiative transfer schemes
in use.
Dean Churchill's presentation concentrated on the phenomenology of mesoscale
flows as influenced by radiation. He gave a short summary of interactions between
radiation and cloud physics, radiation and dynamics, and radiation and convection. He
discussed Houze's (1989) paper stressing the differences between convective and stratified
parts of mesoscale convective systems and their implications for large-scale heating. He
then reviewed the work of Churchill (1992) discussing the role of solar and infrared
radiation in stratified regions of tropical cloud clusters (an EMEX casestudy), and that of
Churchill and Houze (1991) concerning the interaction between turbulence and radiation.
Finally, he mentioned some implications of mesoscale circulations in tropical cloud clusters
for large-scale dynamics and climate (Hartman et al. 1984).
Robert Cess discussed lessons learned from the intercomparisons of GCM radiative
transfer codes. He discussed an international project to isolate and understand interactive
processes in general circulation models as well as in observational data. To date 12 GCMs
have been used to produce 24 simulations of global warming caused by a doubling of
atmospheric carbon dioxide. Cess enumerated possible reasons for model disagreement,
namely differences in radiation codes, differences in atmospheric temperature structure,
differences in radiative overlap by atmospheric water vapor, differences in the radiative
impact of clouds, and coding errors. He warned to "never adjust more than one thing at a
time or it will be impossible to tell which adjustment produced what result".
N94-24390
3.9 Chemistry on the mesoscale: modeling and measurement issues
Anne Thompson
John Pleim:
Christopher Walcek:
Jason Ching:
Frank Binkowski:
Wei-Kuo Tao:
Russell Dickerson:
Kenneth Pickering:
RADM - A cotq_led chemistry/mesoscale model
Convection in RADM (Regional Acid Deposition Model)
Unresolved issues for mesoscale modeling with chemisto':
preco_itating clouds
Unresoh'ed issues for mesoscale modeling with chemisto': aerosols
Tracer Studies with GCEM (Goddard Cumulus Ensemble Model)
Fiehl obsepa, ations of trace gas transport in convection
Photochemical consequences qfl convection
!1011 -
43


The role of radiation in mesoscale flows: Physics, parameterizations, codes

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server