Metr 503 Spring 2005

Quiz #1: Snap -- Part I--Metr 201 Quiz Key

1. Draw in height contours for the 900, 800, 700, 600, 500, 400 mb levels. (See below)

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.

Conceptual Structure of Answer to Part I (b)

(1) V₃₀₀ = V_t + V₁₀₀₀

(2) V_t ~ Meridional Temperature Gradient ~ Meridional Gradient of 1000-300 mb Thickness

(3) V₁₀₀₀ ~ 0

(4) V₃₀₀ = V_t

Apply (4) at the latitude of the Polar Jet (and at 30N and, say, 70N).

(But, you could have also used the geostrophic wind relation, which basically says that the wind speed is directly proportional to ∆z/∆n where z represents the height of the given isobaric surface and ∆z/∆n is its slope.)

According to equation (4), the 300 mb wind speed would be greatest at the tropopause in the polar front region because the thermal wind would return its largest value there. The reason for that is that is where the greatest packing of the 1000-300 mb thickness contours would be found.

Alternatively, since the wind speed is directly proportional to the gradient of heights (all other things being equal) the wind speed would be greatest at the 300 mb level at the latitude of the polar front, since that is where the height surfaces have their greatest slope and greatest increase of slope with depth.

Assuming that the surface winds are negligible, both approaches (the last two pargraphs) imply that there is a distinct polar jet stream, that has its greatest value at the tropopause.

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. (See below)