Goal:

Learn to use MOGUNTIA, to manipulate the input file, and to use the analysis program.

Exercise 1: Source over the oceans

First, a tracer will be emitted over the oceans. The lifetime of the tracer will be set to one year, and its global distribution will be analyzed. Also, it will be analyzed how fast a steady state distribution is obtained.

1. Open the precooked input file Exercise1.in in the folder moguntia on the Desktop.
2. Try to understand its contents
3. Run MOGUNTIA with this input file (takes 10 seconds).

Analyze the output:

1. Click on: inspect most recent output .
2. Enter a multiplication factor (e.g. 1e15).
3. Switch symbols off.
4. View the station output one by one.
5. Change the label of the y-axis (e.g. to oneyear 10^-3 ppt).
6. Analyze the file ll.1987_01.
7. Try a "movie-like" output by moving down the filelist with the cursor.
8. Change the output height to 500 hPa.
9. Fix the contours (e.g. 20: 0.0, 0.1, 0.2,.....).
10. Analyze the zonally averaged output.
11. Try to print.

Questions and additional exercises

• Can you roughly explain the tracer distribution?
• Use the wind-fields (inspect monthly-averaged wind data from main menu) to analyze the movement of the Inter Tropical Convergence Zone (ITCZ) over the Indian Ocean. The role of the ITCZ will be further analysed in the exercise on Interhemispheric Transport

Exercise 2: The lifetime concept

• From the output of exercise 1 it is clear that after 14 months, the tracer distribution is still not in steady state. Create a new input file in which the lifetime of the tracer is changed to a value that ensures steady state after 14 months.
• Run for at least 2 years to check if steady state in reached.
• Check steady state by comparing the zonally averaged tracer distribution of two subsequent years with fixed contour intervals.
• Make an educated guess of the global mean concentration. From this guess, determine the emission by using the (global) steady state formula:

  d C/ d t = 0 = Emission - Loss . C

Emission = global mean emission (molecules cm^-2 s^-1)

Loss = Loss rate (s^-1)

C = concentration converted to molecules cm^-2

• Check if the global mean concentration corresponds to the global mean emission rate (1000 molecules cm^-2 s^-1 over sea with about 2/3 sea).

Hint: the model air pressure is 900 hPa (1000-100 hPa is the model domain). Convert 900 hPa to the number of air molecules per square centimeter.

1 mol of air molecules = 6.022e23 molecules of air = 28.5 grams of air.

1 Pa = 1 N/m² = 1/9.8 kg/m² = 0.1/9.8 g/cm².

'number of tracer molecules' = 'mixing ratio' times 'number of air molecules'.