REVIEW QUESTIONS

Explain which units of ozone measurement you would use in each of the following cases and why.

1a. Track air parcel motion.

1b. Determine changes in the ozone level per set number of particles.

 

2. How is the Dobson Unit defined?

 

Consider Figure 3.04 to answer the following questions.

3a. Are the plots of ozone number density as a function of altitude similar or not at varying latitudes? Explain.

3b How does the altitude of the ozone peak vary among the three regions?

3c. Why is the maximum number density for ozone lowest for the tropical latitudes and highest for high latitudes?

 

4. Compare Figures 3.06 and 3.08. Explain why there is a significant difference in the ozone distributions for these two figures.

 

Use Figure 3.11 or 3.12 to address the following questions.

5a. What do the gray areas represent?

5b. What latitude region shows the least seasonal change in ozone values?

5c. Which latitudes and seasons have the highest mean ozone levels recorded?

5d. Is there latitudinal symmetry between the northern and southern hemispheres in ozone distributions during the year? Explain.

5e. Would you say that there is an annual cycle in ozone distributions? Explain.

 

Refer to Figures 3.11, 3.12, and 3.13 to answer the following questions.

6a. What problem(s) might arise if you make conclusions about seasonal ozone levels using only data averaged over multiple years?

6b. What does analysis of TOMS ozone data over the south polar region for each October from 1979 to 1994 reveal?

 

Refer to Figures 3.14 and 3.15 to answer the following questions.

7a. What measurement of ozone values do we have prior to the advent of satellite sensors?

7b. Based on ground ozone measurements, what trend in ozone levels has been seen over Europe since the 1920s?

7c. What did Dobson's ground-based measurements (during the IGY) indicate about ozone levels during the polar spring in the northern and southern hemispheres?

 

Refer to Figures 3.16 and 3.17 to answer the following questions.

8a. What general pattern can be seen from the TOMS data as a function of time for the 60°N to 60°S region?

8b. Are there year-to-year variations in the data? Explain.

8c. Does the same pattern repeat over all latitude ranges? Explain.

 

Use the Fresno, CA daily ozone data (Figures 3.18 and 3.19) for 1992 to answer the following questions.

9a. How do the ground ozone measurements compare to the TOMS values?

9b. What is the importance of this comparison for interpreting TOMS ozone values?

9c. What season shows the most variation and why?

9d. What was the maximum amount of daily fluctuation in ozone levels over Fresno in 1992?

9e. Would you say that there is a significant daily change in ozone levels over Fresno during 1992? Explain your decision.

ANSWERS 

1a. Ozone mixing ratio is conserved following air parcel motion which makes it an excellent tool for diagnosing atmospheric motion.

1b. Mixing ratio would also be best for determining changes in ozone level per set number of particles since it is defined as the number of ozone molecules per given number of air molecules.

2. Dobson Unit (DU) is the height of a stack of ozone molecules at the surface of the Earth at 0°C and 760 mmHg collected from a column of air above the stack.

3a. The profiles are similar in shape but have peaks at different altitudes depending on the latitude.

3b. Ozone values (measured in number density) peak at 18 km for high latitudes, 22 km for midlatitudes, and at 27 km for tropics. The higher the latitude, the lower in the atmosphere is the ozone peak.

3c. Rising motion in the tropics elevates the height of the ozone peak (while poleward transport carries the newly created molecules away from the tropics). At high latitudes, sinking motion lowers the height of the ozone peak.

4. Figure 3.06 shows a map of ozone as measured by the Solar Backscatter Ultraviolet (SBUV) instrument for the 50 mb (about 21 km) level. This altitude is below the peak in ozone so few UV photons penetrate to this level to create or destroy ozone. Figure 3.08 shows a map of ozone from SBUV, at 0.5 mb (about 53 km). At this altitude few of the UV photons have been blocked out. Ozone molecules are, as a result, created and destroyed very rapidly.

5a. Gray regions are no-data regions caused by polar night. No backscatter measurements are possible when there is little or no incoming solar radiation.

5b. The tropics show least seasonal change in ozone distribution.

5c. Northern high latitudes in March and April (northern hemisphere spring) show highest ozone values.

5d. There appears to be symmetry in the fact that there is an increase in ozone values as you move from tropical to mid and higher latitudes. The degree of change is not the same.

5e. It appears that highest ozone values occur in "spring " months (i.e. March and April in the northern hemisphere and September and October in the southern hemisphere). There are correspondingly lower values in the fall months.

6a. An averaged plot of ozone data for several years can show hemispheric or seasonal differences within an average year. You may conclude that there are significant hemispheric or seasonal differences in ozone distribution, but you will miss a trend that is occurring over time., such as the dramatic drop in October monthly ozone over Antarctica that occurred during the 1980s.

6b. TOMS data displayed in Figure 3.13 shows that there has been a significant decrease in the southern hemisphere spring (October) ozone values during the period from 1979 to 1994.

7a. Ground-based ozone measurements have been made starting with G.M.B. Dobson (for whom the unit of column ozone was named) since the 1920s with instruments of Dobson's design. Additional instruments were deployed as part of the International Geophysical Year (1950s).

7b. Data from northern European indicate roughly level ozone values from the 1920s to the mid-1970s with a decreasing trend beginning in the mid 1970s.

7c. Dobson's values demonstrate that during the southern winter, high latitude ozone values are much lower than the corresponding period in the northern hemisphere. A clear difference in the behavior of ozone between the two hemispheres is thus evident from his data. The low levels of ozone Dobson measured over the Antarctic were still significantly higher than those found today over the same regions. The amount of ozone over the Antarctic in late southern hemisphere winter and early southern hemisphere spring has decreased dramatically over the latter half of the twentieth century.

8a. Values oscillate up and down each year and there appears to be an overall downward trend to the oscillations.

8b. Year-to-year variations are evident in the minima and maxima for each year which vary.

8c. Based on Figure 3.17, the same oscillating pattern exists in all latitude ranges, however, the downward trend is less obvious in the 20N to 20S range.

9a. The two measurements agree quite well with each other: TOMS and the ground base observations seem to observe high ozone events simultaneously and low ozone events simultaneously. The two instruments also report similar magnitudes for column ozone of about 300 DU. They both report day to day variations of a similar magnitude. The largest excursions seem to be about 25 percent from one day to the next, but more typically both instruments report a day to day variation of under 5 percent.

9b. The Dobson Spectrophotometer provide a ground-truthing for the TOMS satellite data, verifying the accuracy of the satellite instrument.

9c. Figure 3.18 suggests that variability is greater during the winter months ( December, January, February, March) than during the summer months. The difference in day to day changes in ozone can be attributed to more active weather patterns in winter than in summer.

9d. The maximum daily fluctuation in ozone values over Fresno in 1992 was +/- 25% although these occurrences were rare.

9e. Based on Figure 3.19, the variations in daily ozone levels are minor. The frequency distribution is sharply peaked around 0% change, which means that significant daily changes in ozone levels were rare for 1992.