Chapter 13
Linking Spatial & Temporal Aspects of Climate Through Quantitative Methods
2. What is a “coupled” GCM?
Answer: A coupled atmosphere-ocean general circulation model (AOGCM) has the ability to simulate
the feedbacks and energy transfer between the atmosphere and ocean, land, and ice surface. Some crude
AOGCMs greatly simplify the ocean and atmospheric processes while other more sophisticated models
involve far more detailed calculations involving physical processes, feedbacks, and energy exchanges.
4. What is the main advantage of a spectral model over a grid point model?
Answer: The primary advantage of a spectral model is that it represents atmospheric motion in terms of a
series of waves. Any motion that occurs on one side of the earth will “connect” after that motion
propagates around the world back toward the original location. Spectral models are more effective than
grid point models at simulating atmospheric processes.
6. What two kinds of energy are represented as components of the thermodynamic energy equation?
Answer: Internal energy and kinetic energy are represented in the thermodynamic energy equation. The
thermodynamic energy equation expresses the sum of the internal energy of the individual molecules of
the atmosphere and the kinetic energy that drives the motion of the atmosphere. The internal energy is the
“thermo” part of the equation and kinetic energy represents the “dynamic” part of the equation.
8. What is the purpose of the continuity equation?
Answer: The continuity equation is a mathematical expression of the principle of conservation of mass.
This equation is a vital component of all GCMs and weather forecasting models. Total mass must be
conserved and accounted for in any model. Horizontal and vertical advection must be accounted for to
ensure that atmospheric mass is conserved.
10. Are initial conditions more important in weather forecasting models or in GCMs? Why?
Answer: Initial conditions are more important in weather forecasting models because they have a shorter
time step as compared to GCMs. Time steps of only a few minutes are common in weather forecasting
models, increasing the importance of accurate initial conditions in the model. Even small errors in the
initialization of a weather forecasting model will produce unrealistic results that magnify over time.
Interactions and feedbacks between the earth’s spheres are more important than accurate initial conditions
when simulating the atmosphere over longer time periods.
12. Why is principal components analysis generally preferred over common factor analysis in
climatological studies?
Answer: Principal components analysis (PCA) is generally preferred over common factor analysis in
climatological studies because the matrix transformations in PCA assume that there is no underlying
uniqueness among the variables. This states that there is nothing unique at one weather station to cause its
observations to be different from other stations. PCA has been used in synoptic climatology to relate
atmospheric circulation to a variety of other variables. Factor analysis allows for some “unique” element
to contribute to the data, making it useful in social science research applications.
14. What impact does the Pacific-North American teleconnection have on North American climate?
Answer: The Pacific-North American (PNA) teleconnection is known to exert a major impact on the
atmospheric variability of North America due to changes in Rossby wave flow. In its positive mode, the
southeastern United States tends to be colder than normal while temperatures are above average in the
northwestern United States. The northwest United States is colder than normal while the southeast United
States is relatively warm during the negative phase of the PNA. The Ohio Valley often experiences
wetter-than-normal conditions during negative PNA periods, particularly in winter and spring.