ATS 351, Spring 2010
Lab #12 - Answer Key
Hurricanes - 60 points
Hurricane Structure (14 points)
1. (4 points) On the plot below, label in the regions provided: the eye, eye wall, and spiral rain band. Also indicate the direction of rotation of the hurricane (at low levels – you may draw arrows if you wish).
Rotation is counterclockwise
2. (10 points) Why are skies often clear in a hurricane's eye?
The Coriolis force deflects the converging wind around the center of low pressure. Therefore, hte strong rising motion and convection are confined to the eye wall. The release of latent heat aloft causes the air to diverge, producing high pressure aloft. This initiates downward motion in the center of the storm. Through compressional warming the eye of a hurricane is characterized by warm air, clear skies, and low wind speeds.
Formation and Development (18 points)
3. (2 points) Why is a hurricane more likely to form in October than in May?
The oceans heat up during the summer and therefore the highest temperatures are found in the fall and not prior to the summer heating. Since hurricanes gain energy from latent and sensible heat fluxes from the warm ocean surface, the warmer the temperatures, the greater the fluxes and the more likely a hurricane will form. Therefore, formation is more favorable for hurricanes in October as opposed to May.
4. (4 points) Why do hurricanes form over the ocean and dissipate over the land?
As it was said above, hurricanes gain energy from latent and sensible heat fluxes from the warm ocean surface. When hurricanes move over land, this source of energy is gone and hurricanes will dissipate. Also, friction increases when hurricanes move over land, which decreases wind speeds. This also helps to weaken the storm.
5. (8 points) Please list the 4 stages of hurricane development and describe the characteristics of each stage.
Tropical disturbance: a group of thunderstorms with slight circulation
Tropical depression: when winds exceed 20 knots and the formation of the closed low begins; on satellite, it appears as a cluster of thunderstorms; it is given a number at this point
Tropical storm: winds exceed 35 knots and the central pressure drops; on satellite, there is a more organized, circular shape and the storm gets a name
Hurricane: winds exceed 64 knots and surface pressure continues to drop; on satellite imagery, clear cyclonic rotation around the center.
6. (4 points) What feature of a hurricane is responsible for the greatest percentage of human casualties and damage when the storm makes landfall? Where can this feature be found within the storm, relative to the storm’s direction of movement?
Storm surge; it is strongest where the storm motion and winds are in the same direction which is on the right side of the hurricane.
- Answer the following true/false questions based on the two satellite images provided below. (20 points – 2 each)
System ASystem B
a. System A's surface winds are clockwise.
F
b. The energy source for system B is warm ocean water.
F
c. System B would likely be found in the winter.
T
d. System A generally moves toward the west.
T
e. System A is a warm-core system.
T
f. System B has strongest winds at upper levels.
T
g. Rainfall rates are much larger in system B than in system A.
F
h. The horizontal temperature gradient is the main energy source for system B.
T
i. System A is a mid-latitude cyclone.
F
j. The pressure gradient force is stronger in system A than in system B at the surface.
T
- (8 points) Using the satellite image below of Hurricane Isabel, where would you expect the strongest surface winds to be located as Isabel makes landfall? Explain.
(Note: The arrow on the image indicates the direction of motion)
Winds around a hurricane blow counterclockwise at the surface. Therefore, the NE quadrant of the hurricane contains the strongest winds because in this case, the winds in this region are blowing in the same direction as the storm motion. For this reason, I would expect the strongest surface winds to be located at the coast near the VA/NC border.