The Ocean-Land-Atmosphere-Model: Optimization and Evaluation of Simulated Radiative Fluxes and Precipitation
Abstract
This work continues the presentation and evaluation of the Ocean Land Atmosphere Model
(OLAM), focusing on the model's ability to represent radiation and precipitation.
OLAM is a new, state-of-the-art earth system model, capable of user-specified grid
resolution and local mesh refinement. An objective optimization of the microphysics
parameterization is carried out. Data products from the Clouds and the Earth's Radiant
Energy System (CERES) and the Global Precipitation Climatology Project (GPCP) are
used to construct a maximum likelihood function, and thousands of simulations using
different values for key parameters are carried out. Shortwave fluxes are found to
be highly sensitive to both the density of cloud droplets and the assumed shape of
the cloud droplet diameter distribution function. Because there is considerable uncertainty
in which values for these parameters to use in climate models, they are targeted as
the tunable parameters of the objective optimization procedure, which identified high-likelihood
volumes of parameter space as well as parameter uncertainties and covariances. Once
optimized, the model closely matches observed large-scale radiative fluxes and precipitation.
The impact of model resolution is also tested. At finer characteristic length scales
(CLS), smaller-scale features such as the ITCZ are better resolved. It is also found
that the Amazon was much better simulated at 100- than 200-km CLS. Furthermore, a
simulation using OLAM's variable resolution functionality to cover South America with
100-km CLS and the rest of the world with 200-km CLS generates a precipitation pattern
in the Amazon similar to the global 100-km CLS run.
Type
Other articleSubject
cloud microphysics parameterizationpart ii
numerical-simulation
global precipitation
boundary-layers
arctic stratus
climate
system
rams
shallow
meteorology & atmospheric sciences
Permalink
https://hdl.handle.net/10161/4277Published Version (Please cite this version)
10.1175/2009MWR3131.1Citation
Medvigy,David;Walko,Robert L.;Otte,Martin J.;Avissar,Roni. 2010. The Ocean-Land-Atmosphere-Model:
Optimization and Evaluation of Simulated Radiative Fluxes and Precipitation. Monthly
Weather Review 138(5): 1923-1939.
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