Transcript Earth sciences: diffusion Day 4 COLQ 201 Multiagent modeling Harry Howard Tulane University Course organization  http://www.tulane.edu/~howard/Multiagent/  Photos? 20-Jan-2010 COLQ 201, Prof.

Earth sciences: diffusion
Day 4
COLQ 201
Multiagent modeling
Harry Howard
Tulane University
Course organization
 http://www.tulane.edu/~howard/Multiagent/
 Photos?
20-Jan-2010
COLQ 201, Prof. Howard, Tulane University
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NetLogoGreenHouse or
Climate_change
Community model
The two models
 What is the difference between them?
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COLQ 201, Prof. Howard, Tulane University
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A first look at the interface
 What controls do you see in the interface?
 Do you see anything that is not consistent with the
'standard' interface that we looked at last time?
 Stop button.
 What is albedo?
 The albedo of an object is the extent to which it
diffusely reflects light from light sources such as the
Sun.
 It is therefore more specific than the term reflectivity.
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COLQ 201, Prof. Howard, Tulane University
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The information tab
 What is it?
 What do the colors mean?
 The earth is rose colored.
 On the earth surface is a green strip.
 Above it is a blue atmosphere, with black space at the top.
 Yellow arrowheads stream downward representing sunlight energy.
 Each red dot represents the energy of one yellow sunlight
arrowhead. The temperature of the earth is related to the total
number of red dots.
 Infrared energy is represented by a magenta arrowhead.
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What happens
 Some of the sunlight reflects off clouds and more can reflect off the
earth surface.
 If sunlight is absorbed by the earth, it turns into a red dot, representing
heat energy.
 The red dots randomly move around the earth. The temperature of the
earth is related to the total number of red dots.
 Sometimes the red dots transform into infrared (IR) light that heads
toward space, carrying off energy.
 The probability of a red dot becoming IR light depends on the earth
temperature. When the earth is cold, few red dots cause IR light; when it is
hot, most do.
 Each IR arrowhead carries the same energy as a yellow arrowhead and as
a red dot. The IR light goes through clouds but can bounce off CO2
molecules.
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COLQ 201, Prof. Howard, Tulane University
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The controls
 The "reset" button
 If "Use-My-Start-Values" is switched off, "reset" sets the model to
a reasonable approximation of the situation in the year 2000.
 If "Use-My-Start-Values" is switched on, "reset" uses the values in
the "year," and "temp" sliders.
 The "sun-brightness" slider
 controls how much sun energy enters the earth atmosphere. A
value of 1.0 corresponds to our sun.
 Higher values allow you to see what would happen if the earth was
closer to the sun, or if the sun got brighter.
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Controls, cont.
 The "albedo" slider
 controls how much of the sun energy hitting the earth is absorbed. The earth's
albedo is about 0.6.
 If albedo is 1, the earth reflects all sunlight. This could happen if the earth froze
and is indicated by a white surface.
 If albedo is 0, the earth absorbs all sunlight. This is indicated as a black surface.
 You can add and remove clouds with the FORM CLOUDS and REMOVE
CLOUDS buttons.
 Clouds block sunlight but not IR.
 You can add and remove greenhouse gasses, represented as CO2 molecules.
 CO2 blocks IR light but not sunlight.
 The buttons add and subtract molecules in groups of 25 up to 150.
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COLQ 201, Prof. Howard, Tulane University
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Another control
 Follow a single sunlight arrowhead using the
WATCH SUNRAY button.
 This is easier if you slow down the model using the
slider at the top.
 What happens to the arrowhead when it hits the earth?
 Describe its later path.
 Does it escape the earth?
 What happens then?
 Do all arrowheads follow similar paths?
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COLQ 201, Prof. Howard, Tulane University
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Exercises
 Explore the effect of albedo: change it while keeping everything else
constant (sun = 1, no clouds, no CO2). Be sure to run the model long
enough for the temperature to settle down.
 Does increasing the albedo increase or decrease the earth's temperature?
 Explore the effect of sun brightness: change it while keeping
everything else constant (albedo = 0.6, no clouds, no CO2).
 What happens to the temperature?
 It should rise quickly and then settle down around 50 degrees.
 Why does it stop rising?
 Why does the temperature continue to bounce around?
 When the temperature is constant, there about as many incoming yellow
arrowheads as outgoing IR ones. Why?
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COLQ 201, Prof. Howard, Tulane University
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Exercises, cont.
 Explore the effect of clouds: change it while keeping
everything else constant (sun = 1, albedo = 0.6, no CO2).
 Explore the effect of adding CO2: change it while keeping
everything else constant (sun = 1, albedo = 0.6, no clouds).
 What is the cause of the change you observe. Follow one sunlight
arrowhead.
 Add clouds and CO2 to the model and then watch a single
sunlight arrowhead.
 What is the highest temperature you can produce?
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With your neighbor …
 What are the agents?
 What rules do they follow?
 What are the patches?
 What rules do they follow?
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COLQ 201, Prof. Howard, Tulane University
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Programming NetLogo
The NetLogo world
 … is a two dimensional world that is made
up of turtles, patches and an observer.
 The patches create the ground in which the
turtles can move around on and
 the observer is a being that oversees
everything that is going on in the world.
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COLQ 201, Prof. Howard, Tulane University
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Next time
 Biology: flocking, herding & schooling:
Boids, MyFlocking
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COLQ 201, Prof. Howard, Tulane University
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