CLOUDS, CLOUD PHYSICS, AND CLOUD-RADIATION
INTERACTIONS: NEW DATA AND MODELS
Richard C. J. Somerville
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, CA
Abstract:
New observations and theoretical developments have recently led to
significant advances in parameterizations of cloud processes for both
climate and numerical weather prediction models. When a single-column
model (SCM), which consists of one isolated column of a global
atmospheric model, is forced with sufficiently accurate observational
estimates of horizontal advection terms, the parameterizations within the
SCM produce time-dependent fields which can be compared directly with
measurements. Within the limitations of SCMs, this comparison provides a
straightforward evaluation of the realism of the parameterizations. In the
case of cloud microphysical schemes, the fields available from the SCM
include cloud altitude, cloud amount, liquid and ice content, particle size
spectra, and radiative fluxes at both the surface and the top of the
atmosphere. Comparisons of these SCM products with data from the
Atmospheric Radiation Measurement (ARM) Program show conclusively
that prognostic cloud algorithms with detailed microphysics can be made
far more realistic than simpler diagnostic approaches. Using ARM
measurements, long-term comparisons of quantities strongly modulated by
clouds, such as downwelling surface shortwave radiation, clearly
demonstrate the potential superiority of parameterizations based on
comprehensive treatments of cloud microphysics and cloud-radiative
interactions. A necessary next step is to test these new parameterization
concepts thoroughly in state-of-the-art operational numerical weather
prediction models and climate models.