Download 15.3 answer key

Section 15.3 Severe Weather ANSWERS
1. Summarize the three stages of development of a thunderstorm.
a. A large amount of warm, moist air rises to create a cumulus cloud
(can occur on sunny days or due to a cold front “pushing” warm air
upward)
b. Condensation within the cloud warms the air and creates vertical
updraft. The cloud rises high enough for freezing to occur, and the
ice crystals increase coalescence (forming raindrops). The falling
rain cools the air and creates the downdraft. Lightning may occur.
c. The rain and the downdraft cut off the updraft and the storm loses
energy. Rain continues until the moisture supply runs out.
2. Explain how updrafts are formed in cumulonimbus clouds.
When the moisture condenses to form the cloud, it releases a great deal
of heat (heat of vaporization – 2260Joules/gram). The heat that is
released warms the air, causing it to rise quickly.
3. Explain how downdrafts are formed in cumulonimbus clouds.
Since rain drops form by coalescence, they have already lost heat by
condensing, and are coldest at the top of the cloud (due to the altitude),
they cool the air as they fall, creating dense air that sinks.
4. Explain how lightning is formed in thunderstorms.
The strong vertical motion in the cloud causes snow, ice and water
droplets to collide, resulting in transfer of charges. The top of the
clouds become positively charges and the bottoms negatively charged.
When the attraction becomes very great, an electric discharge occurs
through a thin path of air, causing the heat and light of lightning.
5. Why are tornados difficult to study?
Tornadoes are difficult to study because they destroy instruments used
to take measurements.
6. What technology allows meteorologists to study tornadoes today?
Today, Doppler radar allows meteorologists to study winds within the
funnel cloud.
7. What is wind shear?
Wind shear means the wind is blowing at different directions at different
altitudes. It causes rotation in an updraft. (And is really dangerous for
airplanes, as you may have heard on tv or in movies.)
8. Summarize the three stages in the development of a tornado.
a. An updraft in a thunderstorm begins to rotate due to wind shear,
creating a cyclone.
b. Low pressure at the center causes the cyclone to become narrower
and stretch downward. The narrower center spins faster and forms a
wall cloud (at the bottom of the cumulonimbus).
c. The cyclones stretches and narrows further, forming the funnel cloud
which touches ground to form a tornado.
9. What information is used to classify tornadoes?
Tornadoes are classified on the Fujita scale according to the wind speed
and damage caused.
10. What are the conditions in the central plains of the US that allow tornadoes to
form?
Three distinct air masses meet here (cold arctic air, dry desert air and moist
tropical air). Strong thunderstorms form where air masses that are very
different meet up.
11. Why are hurricanes more dangerous than tornadoes?
Hurricanes are much larger and last much longer.
12. Explain why most hurricanes that affect us tend to form in the Caribbean Sea?
The warmest waters in the Atlantic are found on the Western side (in the
Caribbean) due to the Trade winds “pushing the warm water.
13. What are hurricanes called in West Pacific and in the Indian Ocean?
They are known as typhoons in the Pacific and tropical cyclones in the
Indian Ocean.
14. Why don’t hurricanes form directly over the equator?
The Coriolis effect is not strong enough directly over the equator.
(Remember that winds must move far enough N or S so that there is a
difference in Earth’s rotational speed to create Coriolis Effect.)
15. Why do the thunderstorms need a period with little wind shear to form
hurricanes?
This allows the storms to build vertical height (and strong updrafts).
16. Explain the difference between a tropical depression, tropical storm and a
hurricane.
Depression – winds up to 37 km/h
Storm – winds above 65km/h
Hurricane – winds above 120 km/h
17. Define a storm surge and relate it to low pressure at the centre of the hurricane.
A storm surge is a rise in sea water lever due to low pressure. (Imagine a
vacuum hose sucking air up above water – the water is pulled upward.)
18. Where are the winds most and least intense in a hurricane?
Winds are calm in the center of the storm (the eye) but strongest at the
edges of the eye (called the eye wall).
19. Explain why hurricanes lose intensity over land.
Hurricanes lose intensity over land due to landforms and structures that
provide friction to slow the winds and the lack of water vapour that drives
the storm (creates the updrafts)