SIO 217C: Climate
Spring 2014
Thermal and Height Structure Discussion Questions
1. Does closer vertical spacing of isotherms below 10 km in ACC Fig. 4.5 correspond to a
stronger lapse rate or a weaker lapse rate? Is a stronger lapse rate more statically stable or
less statically stable? Does closer vertical spacing of isotherms above 20 km in the tropics
and summer hemisphere of ACC Fig. 4.5 correspond to more or less static stability?
2. Explain how the magnitude and direction of horizontal temperature gradient is related to
isotherm slope in CD Fig. 2.9 and ACC Fig. 4.5. At what locations and seasons are
horizontal temperature gradients strongest, and why?
3. Note that isotherms are flat at tropical latitudes in CD Fig. 2.9 and ACC Fig. 4.5. Why is
this? Note that isotherms are vertical in the lower troposphere around 70°S in CD Fig. 2.9b
and in the stratosphere around 60°S in ACC Fig. 4.5b. What does this mean?
4. Why does zonal wind at 30° latitude increase with height to around 200 hPa or 12 km and
then decrease with height above that?
5. What is the approximate height of the tropopause at low latitudes in ACC Fig. 4.5a? What is
the approximate height of the tropopause at northern high latitudes in ACC Fig. 4.5a?
Explain how the locations of the westerly jets around 12 km are related to tropopause height
at low and high latitudes.
6. Compare ACC Fig. 4.3 and ACC Fig. 4.5. Is the location in latitude and height of each zonal
wind maximum consistent with the temperature structure of the atmosphere? Why or why
not?
7. Looking at ACC Fig. 4.5, what is the approximate tropospheric temperature gradient between
0 and 60° latitude for a particular hemisphere and season? Looking at ACC Fig. 4.3, what is
the approximate change in zonal wind between the surface and the zonal wind maximum
around 12 km for the same hemisphere and season? Are they approximately quantitatively
consistent?
8. Why is the jet at 30°N stronger and closer to the equator than the jet at 45°S in CD Fig. 2.10a
and ACC Fig. 4.3a? Why is the jet at 30°S stronger and closer to the equator than the jet at
45°N in CD Fig. 2.10b and ACC Fig. 4.3b? Why is there greater seasonal difference in the
northern hemisphere than the southern hemisphere?
9. Explain why areas of low/high pressure on the surface of constant height (sea level) in ACC
Fig. 4.4 match areas of low/high height on the surface of constant pressure (900 hPa) in CD
Fig. 2.4. Sketching a simple picture may provide the easiest demonstration. Would you
expect such correspondence if the two surfaces were widely separated in elevation? Why or
why not?
10. Note that the height of the 200 hPa surface in CD Fig. 2.3b decreases from equator to poles.
What is the physical reason for this?
11. Note that the height of the 900 hPa surface in CD Fig. 2.3a decreases from Hawaii to the
equator? Is this expected considering your answer to #10? What could explain this behavior?
12. Does the amount of column air mass between the 900 hPa surface and the 200 hPa surface in
CD Fig. 2.3 vary geographically? Why or why not?
13. CD Fig 2.5 indicates that for both hemispheres, the height of the 200 hPa surface is more
than 400 m lower at high latitudes during winter than during summer. What does this imply
about seasonal differences in atmospheric density below 200 hPa?
14. CD Fig 2.4 indicates that the height of the 900 hPa surface is more than 100 m lower during
winter than during summer over the North Pacific and more than 100 m higher during winter
than during summer over East Asia. Is column atmospheric mass over the North Pacific
greater during winter or summer? Is column atmospheric mass over East Asia greater during
winter or summer? Why? Sketching a simple picture may provide the easiest demonstration.
15. CD Fig. 2.7 shows seasonal temperature variations at 900 hPa. Why are northern midlatitude
continents colder than oceans in winter and warmer than oceans during summer? Why do
continents experience larger seasonal temperature variations than do oceans? Why is there
much more overall seasonal variation in temperature over the northern hemisphere than the
southern hemisphere?
16. Note how the contours in CD Figs. 2.3, 2.4, 2.5, 2.6 and 2.7 are much less closely spaced in
the tropics than at higher latitudes. Why is this?
Difficult Question
17. In terms of the equations governing the atmosphere, is it mathematically possible for the
zonal mean wind at 200 hPa or 12 km to be easterly instead of westerly at middle latitudes?
(Assume the Earth still rotates in the same direction and temperature decreases towards the
poles in the troposphere.) If mathematically possible, sketch what the distribution of zonal
mean wind would look like. Is such a distribution physically plausible? Why or why not?