ESSAY: Model interpretation of climate signals: an application to the Asian monsoon climate - The Global Climate System: Patterns, Processes, and Teleconnections - page 289

Chapter 9
ESSAY: Model interpretation of climate
signals: an application to the Asian
monsoon climate
William Lau, NASA Goddard Space Flight Center
9.1 Introduction
Numerical modeling is a powerful tool to provide better understanding of
the modus operandi, and the prediction of the Earth's climate system.
However, a climate model's usefulness is limited by its crude representations
of physical processes, most of which we do not understand very well. Since
models are only crude approximations of the real system, model results must
be validated against observations to ensure reliability. The scarcity of
detailed observations for climate processes with the high spatial and temporal
resolutions needed for model validation and improvement has been a major
impediment for advancement in climate model simulation capability and
model predictions.
Climate modeling is an attempt to mimic the evolution of the real climate
states, which are described by a vast set of long-term global and regional
observations in the atmosphere, ocean and land, from both in situ and satellite
observations. Given that there are large uncertainties both in observations and
in models, and that even the best model is simply a crude approximation of
the real world, models and observations should be used in a synergistic
manner for better understanding and for improved prediction. The relation-
ship between observations, climate models, data assimilation, process stu-
dies, and climate predictions is shown schematically in Figure 9.1 . A climate
model consists of a dynamical core represented by governing equations of
climate state variables, and physics modules of varying complexity (see next
section for further discussion). The physics modules, which appeared in
the form of numerical sub-models or parameterizations, are the drivers of a
climate model. The modules are developed and continuously improved from
knowledge gained from field measurements and related process studies.
Long-term monitoring refers to observations that are made repeatedly for
sustained periods to track the evolution of key parameters of the Earth system.
Because models are imperfect, and observations have inherent errors and
inadequate coverage, neither model nor observations alone will provide a
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