Modeling the oceanic thermohaline circulation with STELLA
Dept. of Geosciences, Penn State University
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This activity describes the construction of and then experimentation with a STELLA model of the thermohaline circulation in the north Atlantic. Based on a famous paper by Stommel (1961), this model exhibits two stable states or attractors. The dynamics of this system are relevant to understanding episodes of abrupt climate change such as the Younger Dryas.
At Penn State, we use this in an intermediate level undergraduate class called Earth 202: Modeling the Earth System. This is a required class in one of our majors.
Skills and concepts that students must have mastered
The students need to know some basic things about systems dynamics, including feedbacks, steady states, and the language of systems components used in STELLA. Our students will have spent a good deal of time learning about the workings of the climate system, including oceanic circulation.
How the activity is situated in the course
This is one of a set of about 7 modeling exercises the students undertake during this class. We treat class periods as mini-labs and extend these projects our over several class periods.
Content/concepts goals for this activity
The content/concept goals for this exercise are to understand some of the behaviors of systems with multiple stable states, including the importance of initial conditions and how perturbations can push the system over thresholds leading to an abrupt change of state.
Higher order thinking skills goals for this activity
The higher order thinking goals for this exercise involve analysis of the quantitative output of the model and experimentation with models in order to answer questions.
Other skills goals for this activity
Students work in small groups on these projects.
Description of the activity/assignment
The thermohaline circulation system of the North Atlantic Ocean is critically important to the climate system since it is involved with the transport of significant amount of heat to high latitudes of the northern hemisphere. In this exercise, students build a simple STELLA model of this system, which is surprisingly complex in its behavior. The students carry out a series of experiments designed to help them understand how the system responds to changes and how its state is sensitive to the initial conditions.
Determining whether students have met the goals
The students submit written answers to questions posed by the experiments.
More information about assessment tools and techniques.
Download teaching materials and tips
- Stommel, H., 1961, Thermohaline convection with two stable regimes of flow: Tellus, 8, 224-230.
- STELLA modeling software (free trial version is available)