SIO 217C: Climate
Spring 2014
Zonal Mean Circulation Discussion Questions
1. In CD Fig. 7.1, why is upper tropospheric pressure higher above the warmer surface than the
cooler surface? Why is lower tropospheric pressure lower above the warmer surface than the
cooler surface?
2. In ACC Fig. 4.1, why does the mean meridional circulation not extend above about 15 km?
3. Why is pressure vertical velocity positive when it is downward?
4. Describe how locations of convergence and divergence in the lower troposphere and upper
troposphere in CD Fig. 2.11 are related to locations of upward and downward motion in the
middle troposphere in CD Fig. 2.12. Physically, why must there be a relationship between
locations of convergence and divergence and vertical motion?
5. CD Fig. 2.11 indicates that for a particular latitude, zonal mean northward flow at one level
always occurs with zonal mean southward flow at a different level. Why is this?
6. Using ACC Eq. 4.1, calculate the zonal angular momentum of an air parcel 12 km above the
equator that has zero zonal speed with respect to Earth’s surface. Assuming zonal angular
momentum is conserved when the air parcel moves poleward, what is the direction and zonal
speed of the air parcel with respect to Earth’s surface at 10°, 20°, 30°, 60°, and 90° latitude?
7. Using ACC Eq. 4.1, calculate the zonal angular momentum of an air parcel 1 km above 30°
latitude that has a zero zonal speed with respect to Earth’s surface. Assuming zonal angular
momentum is conserved when the air parcel moves poleward, what is the direction and zonal
speed of the air parcel with respect to Earth’s surface at 20°, 10°, and 0° latitude?
8. Provide a physical explanation for why zonal wind in the upper troposphere is westerly at
30° latitude and why zonal wind in the lower troposphere is easterly near the equator. What
are the shortcomings of your explanation?
Difficult Question
9. Does easterly zonal mean wind in the upper troposphere at the equator rotate faster or slower
than the earth in the absolute reference frame? Do you think it is physically possible that
zonal mean wind could be westerly in the upper troposphere at the equator? Why or why not?