Homework 5: 1. Effect of trace gases on the vertical temperature...

METEO 6030, Earth Climate System Spring 2006

Univ. of Utah Thomas Reichler

Homework 5: 1. Effect of trace gases on the vertical temperature structure In class I briefly explained what a radiative convective model (rcm) is, how this type of model works, and for what it is used for. In this homework, I would like you to perform some experiments with a relatively simple rcm which has 18 vertical layers and a mixed layer ocean of variable heat capacity at the bottom. I will put a description of this type of model at the end of this homework. Since the model has only one dimension it runs rather fast (seconds) to equilibrium. a. Use the rcm (see below) to investigate the influence of various trace gases on the vertical temperature structure of the atmosphere. Specifically, I want you to use the rcm to perform at least the following 4 experiments: # Experiment O3

(cm) CO2

(ppmv) CH4

(ppmv) N2O

(ppmv) CF11 (pptv)

CF12 (pptv)

a. H2O only .00001 0 0 0 0 0 b. H2O and CO2 only .00001 300 0 0 0 0 c. Present day control 0.4 300 1.6 0.3 275 468 d. 2x CO2 experiment 0.4 600 1.6 0.3 275 468 For the other parameters, use the following constant settings:

NDAYS=1200 (to make sure a new equilibrium profile has been reached) OCNHT=0.001 (small, so that equilibrium is reached fast) CLDLYR=11 (standard, 1=TOA, 19=surface) CLDFRC=0.5 (50% cloud fraction, standard) CLDTAU=8.5 (cloud optical depth, standard) ALBSFC=0.1 (albedo of the surface, standard)

Use the output file (“out6030”) of each experiment and your favorite plotting program to make plots of the four different temperature profiles (X: 150-300K, Y: 0-30 km) in different line styles or colors. For better comparison, plot all profiles into one single figure. b. What do these results tell you about the importance of the individual constituents? c. What is the change in surface temperature for the four experiments? If you want, you can perform additional experiments to come up with a better answers. The rcm The fortran-77 source code of the rcm can found at /home/reichler/rcm. Copy the content of this folder to your own Linux directory. To compile the model, use the following command:



f77 -ffixed-line-length-none rcm.f -o rcm.x

This should compile without any errors. Contact me if not. The datrcm-file The rcm is controlled through a data file (“datrcm”) which contains various parameters settings, and which are read during the run of the rcm. You only have to modify some of the parameters in “datrcm”, and you do not have to modify or understand rcm.f (unless you wish). datrcm is a regular text file which can be edited with any editor (e.g., vi). Open the file and look at it. The default datrcm file is for the present day control experiments (c. above). Each line of datrcm contains some numbers separated by commas, and further to the right the name of the parameters. You must change some of those numbers for the above experiments. Running the model Put the rcm file in the same directory from where you start the model. To run the model simply enter at the command line rcm.x

During the run, the model prints at the screen the date of some parameters in intervals of 64 days: dT (K) t (d) t19 (K) t18 (K) SW (Wm2) LW (Wm2) 20.52 2.00 293.74 292.85 237.44 246.52 0.65 64.00 290.92 290.04 236.80 240.25 0.25 126.00 289.91 289.04 236.58 237.84 0.09 188.00 289.54 288.67 236.50 236.96 0.03 250.00 289.41 288.54 236.47 236.64 0.01 312.00 289.36 288.49 236.46 236.52 0.00 374.00 289.34 288.47 236.45 236.48 0.01 436.00 289.33 288.46 236.45 236.46 0.00 498.00 289.33 288.46 236.45 236.45 0.00 560.00 289.33 288.46 236.45 236.45 0.01 622.00 289.33 288.46 236.45 236.45 0.00 684.00 289.33 288.46 236.45 236.45 0.00 746.00 289.33 288.46 236.45 236.45 0.01 808.00 289.33 288.46 236.45 236.45 0.00 870.00 289.33 288.46 236.45 236.45 0.00 932.00 289.33 288.46 236.45 236.45 0.02 994.00 289.33 288.46 236.45 236.45 0.00 1056.00 289.33 288.46 236.45 236.45 0.00 1118.00 289.33 288.46 236.45 236.45 0.00 1180.00 289.33 288.46 236.45 236.45

dT The total column integrated temperature change between individual time steps.

Small values indicate that the model has reached equilibrium. t Time step in days.



t19 The surface temperature in K. t18 The temperature of the lowest level (close to the surface). SW Total SW absorption (Sin minus Sout at TOA). LW OLR. The out6030 file I constructed a specific output file for this homework which is called out6030. This file gives you the state of some parameters of the model at the end of its run. It is the best to rename this file after each experiment so that you remember its meaning. The file is in ASCII format so that you can read it easily with any editor or any plotting program. The file contains the vertical profile for the 19 levels from the TOA (1) to the surface (19) of the following variables: p Pressure in sigma coordinates, sigma = p/ps z Height in km T Temperature in K SW Short wave radiation at some levels in Wm-2. LW Longwave radiation at some levels in Wm-2. LW-cool Cooling rate (K/d) due to longwave emission. SW-cool Heating rate (K/d) due to shortwave absorption. Running and controlling the model using a shell script It would be a good idea, in particular in preparation for the next homework, where you will be asked to run the model for very many times, to learn how to run the rcm (or any other model) completely from within a UNIX shell script. Using this technique, you can run the model automatically for as many times as you want and for many different parameter settings without need to explicitly edit the datrcm file. Here, I try to show you one way how this can be done: 1. Make a save copy of your datrcm file! cp datrcm save_datrcm

2. Copy datrcm into core_datrcm cp datrcm core_datrcm

3. Edit in core_datrcm the value of those parameters which you want to be changed by

the shell script, e.g., vi core_datrcm

%O3_A%,23.00,5.00 O3, boz, coz %O3_A%,20.00,3.00 O3, b1z, c1z

I change the values of the O3 concentration to the variable name %O3_A%.



4. Write a shell script (sh, csh, tcsh ...) which contains something like: vi myshell.csh #!/bin/csh ... set O3 = .4 # total ozone amount abive ground (cm, NTP) ... cat > sed_datrcm <<EOF s?%O3_A%?$O3?g EOF sed -f sed_datrcm core_datrcm > datrcm ./rcm.x mv out6030 OUT/myfile ... exit

5. Make the shell script executable: chmod +x myshell.csh

6. Create an output directory: mkdir OUT

7. Run the shell script: myshell.csh

You must feel somewhat comfortable with the shell language in order to understand the above lines. Consult a tutorial on how to program in shell or ask me if you have questions.



from: McGuffie and Henderson-Sellers ()2005: A climate modeling primer, Wiley.

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