1. Earth sciences: diffusion Day 4 COLQ 201 Multiagent modeling Harry Howard Tulane University

2. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University2 Course organization  http://www.tulane.edu/~howard/Multiagent/ http://www.tulane.edu/~howard/Multiagent/  Photos?

3. NetLogoGreenHouse or Climate_change Community model

4. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University4 The two models  What is the difference between them?

5. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University5 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.

6. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University6 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.

7. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University7 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.

8. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University8 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.

9. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University9 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 CO 2 molecules.  CO 2 blocks IR light but not sunlight.  The buttons add and subtract molecules in groups of 25 up to 150.

10. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University10 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?

11. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University11 Exercises  Explore the effect of albedo: change it while keeping everything else constant (sun = 1, no clouds, no CO 2 ). 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 CO 2 ).  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?

12. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University12 Exercises, cont.  Explore the effect of clouds: change it while keeping everything else constant (sun = 1, albedo = 0.6, no CO 2 ).  Explore the effect of adding CO 2 : 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 CO 2 to the model and then watch a single sunlight arrowhead.  What is the highest temperature you can produce?

13. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University13 With your neighbor …  What are the agents?  What rules do they follow?  What are the patches?  What rules do they follow?

14. Programming NetLogo

15. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University15 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.

16. 20-Jan-2010COLQ 201, Prof. Howard, Tulane University16 Next time  Biology: flocking, herding & schooling:  Boids, MyFlocking