Geoscience Reference
In-Depth Information
8
CHAPTER EIGHT
Numerical models of the
general circulation,
climate and weather
prediction
LEARNING OBJECTIVES
When you have read this chapter you will:
n
know the basic features of atmospheric general circulation circulation models (GCMs)
n
understand how simulations of the atmospheric circulation and its characteristics are performed
n
be familiar with the basic approaches to weather forecasting on different timescales.
Fundamental changes in our understanding of the
complex behavior of the atmosphere and climate
processes have been obtained over the past four
decades through the development and applica-
tion of numerical climate and weather models.
Numerical models simply use mathematical
relationships to describe physical processes.
There are many forms of climate and weather
models ranging from simple point energy
balance approaches to three-dimensional general
circulation models (GCM) which attempt to
model all the complexities of the earth climate
system. We discuss in more detail the GCM in its
various forms which is used to simulate both
climate and weather for day-to-day forecasting.
modeled using five basic sets of equations. The
basic equations describing the atmosphere are:
1
The three-dimensional equations of motion
(i.e., conservation of momentum; see Chapter
6A, B).
2
The equation of continuity (i.e., conservation
of mass or the hydrodynamic equation, p. 152).
3
The equation of continuity for atmospheric
water vapor (i.e., conservation of water vapor,
Chapter 4).
4
The equation of energy conservation (i.e., the
thermodynamic equation derived from the
first law of thermodynamics, Chapter 7F).
5
The equation of state for the atmosphere
(p. 30).
6
In addition, conservation equations for other
atmospheric constituents such as sulfur aero-
sols may be applied in more complex models.
A FUNDAMENTALS OF THE
GCM
In the GCM, all dynamic and thermodynamic
processes and the radiative and mass exchanges
that have been treated in Chapters 2-6 are
Model simulations of present-day and future
climate conditions involve iterating the model
