Course: Introduction to Atmospheric sciencesATOC210 by GyuWon LEE

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Chapter 15 Thunderstorms and Tornados 
Reading materials Chapters 15 of the text
book
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
2
Questions 1) How do thunderstorms form? 2)
What are their outcomes?
Objectives 1) Understand the formation of
thunderstorm. 2) Understand their structure and
outcomes.
Approach 1) General concept 2) Types of
thunderstorms 3) Structure 4) Outcomes
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
3
General concept Thunderstorm
Definition - a storm containing lightning and
thunder. - Convective storms that form with
rising air. Conditions - Conditionally unstable
environment - Trigger 1) unequal
heating at the surface 2) the effect of
terrain 3) lifting of air along shallow
boundaries of converging surface winds 4)
low pressure systems (diverging upper-level winds
and converging surface winds. 5) frontal
lifting. Outcomes Thunder, lightning, high
winds, flash floods, damaging hail,
tornadoes (severe TSTM)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
4
Types of thunderstorms
1) Ordinary thunderstorms (air-mass tstm) - A
thunderstorm produced by local convection within
a conditionally unstable air mass. - Isolated,
short-lived (less than 1 hr) and small (a few km
across) - Rarely produce strong winds or large
hails 2) Severe thunderstorms - Intense
thunderstorms capable of producing heavy showers,
flash floods, hail, strong and gusty surface
winds, and tornadoes - Hail at least
three-quarter of an inch in diameter and/or
surface wind gusts of 50 knots or greater
and/or produce a tornado.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
5
Types of thunderstorms
Life cycle of an ordinary thunderstorms (air-mass
tstm)
Cumulus stage
Growing cumulus, No precipitation, no lightning,
thunder Updraft only
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
6
Types of thunderstorms
Life cycle of an ordinary thunderstorms (air-mass
tstm)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
7
Types of thunderstorms
Severe thunderstorms (supercell storm)
Strong vertical wind shear If the winds aloft
increase, the precipitation is pushed downwind so
that downdrafts do not cut off the supply of
humid airs.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
8
Types of thunderstorms
Mesoscale convective system
Squall line
Mesoscale convective complex
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
9
Structure of thunderstorms
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
10
Outcomes
Flash flood floods that rises rapidly with
little or no advance warning
Des Moines, Iowa (1993)
Montreal (1997)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
11
Outcomes
Lightning a discharge of electricity which
occurs in thunderstorms Thunder sound due to
rapidly expanding gases along the channel of a
lightning discharge.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
12
Outcomes
Lightning
From Environment Canada
the number of flashes per square kilometer per
year -- for cloud-to-ground lightning and
cloud-to-cloud lightning combined, average data
from 1998 to 2002.)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
13
Outcomes
Lightning
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
14
Outcomes
Tornado - a rapidly rotating column of air that
blows around a small area of intense low
pressure with a circulation that reaches the
ground. - counterclockwise or clockwise
(rare) rotation
From the disaster center
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
15
Outcomes
Tornado
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
16
Outcomes
Tornado
Fujita scale rotational wind speed based on the
damage
F0 weak 35 62 (kts) Light tree branches
broken, sign board damaged F1 63
97 Moderate trees snapped, windows
broken F2 strong 98 136 Considerable large
trees uprooted, weak structures
destroyed. F3 137 179 Severe trees leveled,
cars overturned, walls removed from
buildings F4 Violent 180 226 Devastating frame
houses destroyed. F5 227 276 Incredible
structures the size of autos moved over 100
m, steel-reinforced structures highly
damaged.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
17
Outcomes
Tornado
Upper /state (25 yrs) Lower / yr /
10000miles2
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
18
Outcomes Tornado
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
19
Outcomes Tornado
Radar observations of tornados
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
20
Outcomes Tornado
Radar observations of tornados
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE