Download Lightning – (a) formation

2nd Exam
ERTH303 19 Nov.,
Nov 2009
Chap.6 Cloud formation
Chap.7 Precipitation processes
–
What processes drive precip. in
Bozeman?
Chap.8
p Atmospheric
p
circulation
Pressure distributions
–
El Nino/La Nina
Chap.9 Air masses and Fronts
Chap 10 Midlatitude cyclones
Chap.10
Chap.11 Lightning and thunderstorms
1
Lightning, Thunder, & Tornadoes
ERTH303 19 Nov.,
Nov 2009
Lightning:
a) Formation
b) Types
Thunderstorms:
a) Types
b)) Distribution
Tornadoes:
a) Formation
b) Distributions
2
Lightning
About 40,000 thunderstorms daily,
each producing lightning:
ƒ Discharge of electricity
ƒ 80% = cloud-to-cloud lightning [sheet
lightning]
ƒ 20% = cloud-to-ground lightning
3
Lightning – (a) formation
Charge separation
ƒ Positive
P iti charges
h
aloft,
l ft negative
ti in
i lower
l
areas
ƒ Ice crystals needed for charge separation
4
Textbook Fig. 11-2
Lightning – (a) formation
5
Textbook Fig. 11-1
Lightning – (a) formation
Runaway discharges
ƒ Lighting
Li hti iis different
diff
t from
f
a static
t ti electric
l ti
spark
ƒ Results from electrons accelerated to
high speeds
ƒ Collisions cause an avalanche of runaway
electrons
ƒ Runaway breakdown
ƒ Energy
gy is released when electrons accumulate in
a small volume
6
Lightning – (a) formation
Components:
ƒ Stepped-leader
St
dl d
ƒ Emanates from cloud base
ƒ When it connects with unlike charged area
ƒ Electron flow = return stroke
ƒ Illumination occurs and heating
ƒ Multiple strokes
ƒ Dart leader and return stroke
ƒ Lightning flash
ƒ Combination of all strokes
7
Lightning – (a) formation
8
http://www.noaanews.noaa.gov/stories2007/images/lightning.jpg
Lightning – (b) types
Positive lightning strokes:
ƒ Often
Oft stronger
t
than
th negative
ti strokes
t k
ƒ Can occur several miles ahead of storm
9
Textbook Fig. 11-4
Lightning – (a) formation
ƒ Forked
ƒ Sheet (heat)
ƒ Ball:
ƒ round, glowing mass of electrified air; rolls in
air or on surface
ƒ See “A Personal Account…” on p. 312!
ƒ http://www.youtube.com/watch?v=6ioN-3UWYrY
http://www youtube com/watch?v=6ioN 3UWYrY
10
Lightning – (a) formation
ƒ St. Elmo’s fire
ƒ Ionization of air,
air before formation of
cloud-to-ground lightning - glowing
ƒ Sprites
S it
ƒ Large,
g , short-lived electrical bursts above
cloud tops; occurs when lightning occurs
below
ƒ Blue jets
ƒ Upward-moving electrical ejections from
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the top of active thunderstorms
Lightning – (a) formation
Blue jet (textbook Fig. 11-6)
Sprite (http://home.netcom.com/~sbyers11/RedSprite2.jpg)
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Lightning, Thunder, & Tornadoes
ERTH 303 19 Nov.,
Nov 2009
Lightning:
a) Formation
b) Types
Thunderstorms:
a) Types
b)) Distribution
Tornadoes:
a) Formation
b) Distributions
13
Thunder Storms – (a) types
Air mass thunder storms:
ƒ Localized,
Localized short-lived storms that
dissipate in tens of minutes
ƒ Cumulus
C
l Stage:
St
ƒ Localized convection
ƒ Adiabatic cooling
ƒ Condensation
14
Textbook Fig. 11-7
Thunder Storms – (a) types
Air mass thunder storms:
ƒ Mature Stage:
ƒ Precipitation (rain or
graupel)
ƒ Creates downdrafts
ƒ Cloud top extends to
elevation of stability
ƒ Strong winds at cloud tops
create anvil
15
Textbook Fig. 11-7
Thunder Storms – (a) types
Air mass thunder storms:
ƒ Dissipative Stage:
ƒ Downdrafts occupy entire cloud
base
ƒ Water vapor cut off
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Textbook Fig. 11-7
Thunder Storms – (a) types
Severe Thunder Storms:
ƒ Winds > 93 km/hr (58 mph)
ƒ Hailstones > 1.9 cm (0.75 in) diam.
ƒ Spawn tornadoes
Mesoscale convective complexes
(MCC)
17
Thunder Storms – (a) types
Severe Thunder Storms:
[mesoscale = 10’s – 100’s of km]
ƒ Mesoscale convective
systems(MCSs):
ƒ Cluster of thunderstorms
ƒ When in a line = squall lines
ƒ Mesoscale
M
l convective
ti complexes
l
(MCCs)
ƒ Circular or oval systems
18
Thunder Storms – (a) types
Mesoscale convective complex (MCC)
19
Textbook Fig. 11-9
Thunder Storms – (a) types
Squall line thunderstorms (MCS):
ƒ Individual storms cells arranged in linear band
(around 500 km long)
ƒ Form in warm sector of a midlatitude cyclone,
ahead of cold front
20
Textbook Fig. 11-12
Thunder Storms – (a) types
Squall line thunderstorms (MCS):
ƒ Strong vertical wind movement
21
Textbook Fig. 11-14
Thunder Storms – (a) types
Squall line thunderstorms (MCS):
ƒ Shelf clouds
22
Textbook Fig. 11-16
Thunder Storms – (a) types
Squall line thunderstorms (MCS):
ƒ Shelf clouds
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http://www.extremeinstability.com/stormpics/svrdsc00783.jpg
Thunder Storms – (a) types
SUPERCELL STORMS
ƒ A single
single, extremely powerful single cell
thunderstorm (20-50 km)
ƒ Complex array of upup and downdraft
relationships
24
http://www.extremeinstability.com/stormpics/svrdsc00783.jpg
Thunder Storms – (a) types
Vault – inflow of
warm surface air
Hook – tornado
formation imminent
25
Textbook Fig. 11-19
Thunder Storms – (b) distribution
ƒ Thunderstorms develop where moist
air is forced aloft
26
Textbook Fig. 11-21
Thunder Storms – (b) distribution
27
Textbook Fig. 11-22
Thunder Storms – (b) distribution
28
Textbook Fig. 11-23
Lightning, Thunder, & Tornadoes
ERTH 303 19 Nov.,
Nov 2009
Lightning:
a) Formation
b) Types
Thunderstorms:
a) Types
b)) Distribution
Tornadoes:
a) Formation
b) Distributions
29
Tornadoes
Tornadoes
ƒ Strong
St
pressure gradients
di t (e.g., 100 mb)
ƒ Tornado characteristics and dimensions
ƒ 100-yard average diameter
p ) over 3-4 km ((2ƒ Movement = 50km/hr ((30 mph)
2.5 mi)
ƒ Winds = 65 km/hr (40 mph) to 450 km/hr (280
mph)
ƒ Tornado formation
ƒ Squall lines, MCCs, supercells, tropical
cyclones
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Tornadoes – (a) formation
Supercell tornadoes
ƒ Mesocyclone
M
l
development
d
l
t
31
Textbook Fig. 11-25
Tornadoes – (a) formation
Supercell tornadoes
32
Textbook Fig. 11-27
Tornadoes – (a) formation
Nonsupercell tornadoes:
ƒ Develop along convergent boundary
33
Textbook Fig. 11-29
Tornadoes – (b) distributions
Global tornado frequency:
34
Textbook Fig. 11-30
Tornadoes – (b) distributions
US tornado frequency:
35
Textbook Fig. 11-31
Tornadoes – (b) distributions
S
Seasonal
l patterns:
tt
36
Textbook Fig. 11-32, 11-33
Tornadoes – (b) distributions
Temporal patterns:
ƒ > 88% kill
no one
ƒ 2% cause >
67% of all
fatalities
37
http://www.nssl.noaa.gov/users/brooks/public_html/tornado/#alltorn
Tornadoes – intensity scale
weak
(69%)
Strong
(29%)
violent
(2%)
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Textbook Table 11-2