Transcript Weather 3

Violent Weather
Tornadoes (diameter 0.25 km/0.16 miles)
Thunderstorms: (diameter up to tens of km)
Tropical Cyclones (600 km/375miles in
diameter)
Thunderstorm
Definition: A storm that produces lightning and thunder. It frequently produces gusty
winds, heavy rain and hail, may be tornadoes.
Frequency: About 2000 thunderstorms are in progress at any given time, 45,000/day,
16,000,000/yr globally. ~100,000 T-storms/yr in the US.
Types:
(1) Air-mass thunderstorms:
(a) Occur in mT air mass
(b) unequal heating of Earth surface causing the warm/moist air to rise.
(c) They are often short-lived with a preference in midafternoon.
(2) Sever Thunderstorms:
(a) criteria: wind speed reach >58mph or produce hail > 0.75in in diameter or
generate a tornado.
(b) Formation: (i) unequal heating; (ii) other mechanisms upper lifting warm air
(3) Supercell Thunderstorm: A very powerful storm cell with clouds reaching 20 km in
height, and diameter 20-50 km. Less than half of supercell T-storms produce tornados,
but virtually all the strongest and most violent tornados are spowned by supercells.
(a) 2000~3000 in the US
(b) Cause most of the damage from T-storms.
Thunderstorms
Figure 8.19
Thunderstorms Mapped in Space
Figure 8.20
Hailstones
Figure 8.21
Tornado Damage
Storm track and damage left
behind on May 3, 1999 45
miles southwest of Oklahoma
City, killing 49 people!
A violent wind storm that takes the form of a
rotating column of air that extends down from a
cumulonimbus cloud.
It does not occur alone, but associated with
sever T-storms (< 1%) or supercell T-storms
(<50%).
Mesocyclone and
Tornado
Figure 8.22
Tornado
Figure 8.22
Tornado
Figure 8.22
Super Cell
Tornado
and
Eye
Wall
Figure 8.23
Tornadoes
Figure 8.24
Hurricane Isabel
Hurricanes
A whirling tropical cyclones with sustained wind
speed 74 mph (119 kph).
Size: 600 km (375 miles) in diameter
Similar storms are known as Typhoon in western
Pacific (China, Japan, Philippines etc), and as
Cyclones in the Bay of Bengal and Arabian Sean.
Figure 8.28
Hurricane
Formation
1. Tropical disturbance caused
by the Easterly wave of air
movement, the undulation of
trade wind from east to west.
2. Warm and moist air, thus sea
surface temp (SST) > 27oC or
80oF. Rising of warm and
moist air release tremendous
latent heat, causing the air to
rise more.
3. Stronger Coriolis force, thus
no hurricane below 5o
latitudes. No hurricane above
15o latitude due to low SST.
Figure 8.25
Profile of a Hurricane
Figure 8.27
Hurricanes Gilbert and Catarina
Figure 8.26
Tropical Cyclones
Figure 8.26