|DEPARTMENT OF GEOSCIENCES
San Francisco State University
This exercise has you working with a schematic cross-section of the troposphere on the day of the Winter Solstice. The tropopause (300 mb level) and the 500 mb levels are shown. You'll also have to remember the geostrophic wind relation, discussed in previous weeks, to answer question 2.
1. Draw in on the cross section the height contours for the other (900, 800, 700, 600, 400 mb ) levels in the troposphere. We'll assume that the 1000 mb level is at the ground.
2. Examine the pattern in the location indicated by the bracketed Polar Jet Stream. Describe why one characteristic of this pattern is that it implies (a) that there is a distinct polar jet stream: and (b) that the polar jet stream intensifies with height and is at maximum strength at the tropopause. [Hint: remember the equation for the magnitude of the geostrophic wind in natural coordinates.]
3. The "polar front" is the deep (through the whole troposphere) boundary between the polar air masses and the subtropical air masses (in the figure, the blue and the red colors, respectively). On surface weather maps, the convention is to draw a line (with symbols, as explained in class) on the warm air side of the boundary. Place a blue "X" where you would expect the polar front to be at the surface for this schematic pattern.
4. Describe how the three cell model of the General Circulation discussed in class at the latitude of the polar front generally corroborates your results in (2) and (3) above.