how to write a report about this topic following the instructions in following pdf fileEASC 373 Exercise 3 Greenhouse Gases & IR radiation Due Date: Sunday Nov 15th – email to me ([email protected]) by midnight at latest (Late Assignments: –10% per day (or any part of a day) after deadline; Mark of zero if submitted more than 7 days late) Marks: This assignment counts 4% towards your final mark. Learning Objectives: o Working with simple climate models – testing ideas by holding some variables constant while changing one other. o The ground temperature effect of changing the concentrations of different GHGs and water vapor. o Improving diagram preparation skills o Working collaboratively with colleagues Instructions: o Got to the website http://climatemodels.uchicago.edu/modtran/ o You can find information about the model in this document (see p. 2) or read up on them on the following website: http://climatemodels.uchicago.edu/modtran/modtran.doc.html [click on the various tabs on the left hand side (“Overview” “How to” etc.)] o Do 4 model runs for CO2 concentrations (hold other variables constant) during the Subarctic Summer for: 1) no CO2 in the atmosphere; 2) pre--industrial CO2 levels (280 ppm); 3) current CO2 levels (398 ppm); and 4) potential future doubling of CO2 (560 ppm) o Open up a Word document and paste these four diagrams into your assignment answers document; label (caption) them carefully o Answer the following questions in your Word document: • What Ground Temperature offset would you have to apply to explain the difference between no CO2 and current levels of energy output? • Methane is also a powerful greenhouse gas. Try increasing CH4 from 1.7ppm to 17 ppm. How much ground temperature offset is needed to restore outgoing radiation to the 1.7ppm level? • Water vapor is a powerful GHG – change the water vapor scale from 1 to 10 and see what happens to the energy output to space. What ground temperature offset do you need to apply to explain this difference (or how much will the atmosphere need to heat up?). o Write a short conclusions paragraph that summarizes your experiments. o Complete your assignment and email the Word document to me before the deadline ([email protected]). You can run the model as a team but make sure the figure captions and the conclusions paragraph are your own work. About MODTRAN MODTRAN is a simple computer model that shows the intensity of infrared (IR) light that leaves planet Earth with changing GHG concentrations. GHGs are selective as to what IR light they absorb and emit. The model therefore shows how GHGs affect the energy balance and thus the temperature of planet Earth. 1) You can change various variables within the model including: GHG concentrations (CO2 CH4) localities (e.g. tropics subarctic) cloud cover. You can also change the temperature of the ground (“Ground T offset”) to balance out the outgoing IR energy. For a full explanation of each term go to http://climatemodels.uchicago.edu/modtran/modtran.doc.html (Under “How to”). The graphical output of the model shows: 2) various smooth (colour) curves (2a) which represent blackbody curves at different temperatures (see legend (2b) upper right corner of the graph) – remember the warmer an object the more intense its emission of IR light 3) jagged blue curve: this is the model output; it is the intensity of light that a sensor at an altitude of 70 km looking down would measure. Notice the various bends in the curve for example at 700 cycles/cm (3a) (this is due to CO2 absorbing and emitting light) and at 900--1 000 cycles/cm (3b) (due to the atmospheric window – the atmosphere is transparent to IR if there are no clouds). 4) The model output shows the rate of energy lost to space (W/m2) and is proportional to the area under the jagged blue curve (3) 5) you can chose to plot different variables against altitude for example temperature (as shown here) 6) you can compare two model runs by saving the 1st model run (click “Save this Run to Background”) and then perform the 2nd run – the output graph will contain two IR curves rather than one. You can also see the raw numerical data of the model output by clicking “Show Raw Model Output”
