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THC_final

by Lisa Boehm, Petra Hutner (Submitted: 02/09/2010)

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WHAT IS IT?

This model is a simulation which should give a general idea about how the thermohaline circulation (THC) works.
Water-particles with higher density sink to the bottom of the ocean which causes an undertow which drives the circulation.
The intention is to show the effects of different climate scenarios on the thermohaline circulation.

HOW IT WORKS

After starting the simulation, the red water-molecules begin to move. In the model, the density of the water is only depending on the water temperature, reflected in the different shades of red.

While running the program, the water-particles behave on behalf of their temperature. Reaching a specific water-temperature and probability, molecules evaporate and create a cloud at the top of the scene. If there are enough water drops, it rains down and so the water joins the circulation again.
If the water is cooling down under a certain limit, it is going to freeze at the pole region and the iceberg grows. The iceberg is shrinking if the surrounding temperature is going up again and the water-molecules become part of the circulation afresh.

HOW TO USE IT

First, the user can chose to make use of different sliders to affect the model:
"Initial-moving-water" will adjust the number of water molecules. If it is to low, the model might stop.
If the "evaporation-probability" is high, more water will evaporate on its way to the pole (right side of window).
"Rain-intensity" influences how much rain will fall, and how swiftly.

The user has also the opportunity to select one out of four scenarios in the drop-down menu called “global-change”. The numbers to choose represent the average temperature change on earth.

With the setup-button the initial situation is set up.
With the go-button the simulation starts.

THINGS TO NOTICE

The simulation stops if an extreme situation occurs.
The reason for the thermohaline circulation to stop is shown in a pop-up-window.
The user should also notice that the circulation changes, depending on which global-change-szenario is chosen. The warmer it gets, the later the water sinks to the bottom, the shorter the circulation gets.
The plot on the left hand side shows the temperature of the remaining observed water-molecules in subject to time.

EXTENDING THE MODEL

As an extension to this model you could add the variable “salinity” to both turtles and patches. The water density should then be calculated out of “temperature” and “salinity”, which will make the model more accurate.
Furthermore, the turtles could set their temperature (and salinity) not only by asking the patch they’re on, but also by taking in account the surrounding patches and turtles and calculating an average.

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