Download Thunderstorms and Tornadoes

Week 13 Notes
TONIGHT
• Midterm #2 Corrections (HW#11)
• Thunderstorms and Tornadoes (Chp 10)
• Homework #12 – “Perfect Climate”
Next Week (Apr 28)
• Hurricanes (Chp 11)
• Air Pollution (chp 12)
• Climate Classifications
May 5
• Climate Change
• TERM PAPERS DUE
May 12
• FINAL EXAM
• Extra Credit Papers Due
Midterm #2
• Class Average = 71 points
– Scores adjusted by +4 points
• pre-Midterm Review
– w/ review: 77%
– wo/ review: 61%
• Changing answers
– About 2/3 of changed answers were wrong
Midterm #2 Corrections
• Homework #11
• Same as before
• TYPED (no exceptions)
• Correct Your Missed Questions
• Must be 3 part answer
• Correct answer
• 1 paragraph (2 or 3 sentences) explaining the
correct answer
• Source of correct answer
• DUE AT BEGINNING OF CLASS NEXT WEEK (Apr 28)
•Well-done complete corrections = 10 points
• Points deducted for incomplete or not following directions
Example Correction
Example:
# 39. C, Scattering
– The sky is blue because of Rayleigh scattering.
The size of oxygen and nitrogen molecules
selectively scatter the shorter blue wavelengths.
It is this prominent scattered blue light that our
eyes see.
– Ahrens text: pg 405 (or Atmospheric Optics
PowerPoint, slide # 62)
Term Papers
(and Extra Credit Term Papers)
• 6-10 Pages, typed, double-spaced (exclusive of figures, bibliography)
• Scientific Style –
• ABSOLUTELY NO 1ST PERSON. This is a science paper.
• Well-organized
• Properly documented
• At least 4 CREDIBLE reference sources
(only half may be Internet only source).
• ABSOLUTELY NO WIKIPEDIA.COM
• References Format: APA
http://www.wisc.edu/writetest/Handbook/DocAPA.html
• Grading: Maximum 200 points
Content, Accuracy - 150 points
Organization, Format - 30 points
Grammar, Style - 20 points
Thunderstorms and
Tornadoes
Thunderstorms
• Not Rare
• 40,000 Times Each Day Over the World
• Frequency Is Different but Every Place in the World
has T-storms
• T-storm Hazards
• Lightning
• Flash Floods
• Hail
• Winds (Downbursts, Microbursts)
• Tornadoes
• Hurricanes
Thunderstorm Formation
• Warm Humid Rises into an Unstable Atmosphere
• Trigger needed to Start Lift
• Unequal heating
• Frontal Lift
• Terrain
• Enhanced by Strong Diverging Winds Aloft
• Cumulonimbus
• Types
• Ordinary (Air Mass) Thunderstorms
• Severe Thunderstorms
Air Mass Thunderstorms
• Most Common
• Least Destructive
• Limited Life of Less Than an Hour
• Localized
• Life Cycle
•Cumulus Stage
•Mature Stage
•Dissipative Stage
Cumulus Stage
• Unstable Air Rises by Localized
Convection
• Vertical Motion 10 to 45 mph
• Cloud Extends Above Freezing
Level
• Ice Crystals Form and Grow by
Bergeron Process
• Precipitation Begins to Fall
Mature Stage
• Heavy Rain Drags Air forming
Downdrafts
• Downdrafts Strengthened By
Cooling From Evaporation
• Most Vigorous Rain along edges of
cloud
• Updrafts Dominate Inner Part of
Cloud
Mature Thunderstorm
Dissipating Stage
• As Precipitation and downdrafts
dominate then updrafts cut off
• Only 20% of Moisture Falls as
Rain – the Rest Evaporates
Severe Thunderstorms
• Defined as
•Wind Speeds Exceed 58 mph
• Hailstones Greater Than ¾” diameter
• Can Spawn Tornadoes
• Extreme Downdrafts and Updrafts Intensify Storm
• Scale: 6 to 60 mi Across
Mesoscale
Severe Thunderstorms
• Large Area Allows Several Storms to Cluster (Multi
Cell Storms)
• Mesoscale Convective Systems (MCSs)
• Oval Clusters Are Mesoscale Convective
Complexes (MCCs)
• Linear Bands Are Squall Lines
• Supercells Contain a Single Updraft Zone
• Appear in Isolation or as Part of MCCs
• Individual But Storms Develop From A
Common Origin
Mesoscale Convective Systems (MCSs)
• Cover Large Parts of States
• Life Span: up to 12 Hours or more
• Accounts for 60% of All Rain in Middle of US and
Canada
• Surrounding Air and Inflow Supports Stronger Winds
and Heavier Precipitation
Mesoscale Convective Systems (MCSs)
Mesoscale Convective Complexes (MCCs)
• Oval or Roughly Circular
• Organized Systems Containing Numerous ral Tstorms
• Not All Produce Severe Storms But They Are SelfPropagating
• Create Downdrafts That Produce Other Cells
• Consider Large Cluster of Thunderstorms
• Warm Humid Air at Surface (mT, Wind S)
• Dry Air Above (CT, Mexico, Wind SW)
• Wind Shear
• Downdraft From Other Storms
• Outflow Boundary
Mesoscale Convective Complexes (MCCs)
Squall Lines
• Large Number of Individual Storm Cells
• Linear Band ~ 300 mi in Length
• Form 60 to 180 mi ahead of Cold Front
Squall Lines
Gusts Fronts
Gusts Front
Supercell Thunderstorms
Supercell Thunderstorms
Supercell Thunderstorms
• Diameter 12 to 30 mi
• Smaller than Squall
Line or MCCs
• Most Violent
• Life Span:
2 to 4 Hours
Supercell Structure
Thunderstorm Moisture
Thunderstorm Distribution
Avg. Number of Thunderstorm Days per year
Lightning Formation
• Excess negative and
excess positive charges
• Lightning: attempt to
equalize electrical
differences
• Air is a poor conductor,
thus electrical potential
(charge differences) must
be very high before
lightning will occur
Lightning Formation
• Stepped leader: advancing,
branching shaft of negative
charges
• As stepped leader approaches
ground, a spark of positive
charges surges upward from the
ground
• Stepped leader and upward
surge create a path for
current flow
Lightning Formation
• Negative current flows
downward from cloud
Lightning Formation
• Return stroke: positive current
flow upward
• Lightning is a sequence of
strokes and return strokes
• Usually 2-3 strokes; sometimes
up to 20 strokes
Lightning Causes
• Most Common Theory
• Collusion of Hail stone
and Ice Crystal
• Ice Crystal is Positive
Charged – Colder
Lighter - Carried to Top
of Cloud
• Hailstone - Negative
Charged - Heavier
Stays More in Bottom
of Cloud
Types of Lightning
Cloud-to-Air
Within Cloud
Cloud-to-Cloud
Cloud-to-Ground
Cloud-to-Ground Lightning
Cloud-to-Ground Lightning
Cloud-to-Ground Lightning
Thunder
• Air in Column is Heated to 50,000° F
• Heated Air Expands Explosively
• Shockwave heard as a Loud Noise
• Speed Difference Flash and Sound
• Sounds Travels at 1100 feet per second
• Light Travels at 186,000 miles per second
• Each 5 seconds between flash and sound is a mile.
• Nearby Thunder Is Sharp
• Distant Thunder Echoes and “Rumbles”
Types of Lightning
• Cloud-to-Cloud
• 80% of All Lightning
• Sheet Lightning
• Flash is Obscured by Clouds
• Sky Lights Up Uniformly
• Cloud-to-Ground (Water)
• 20%
• Negative Charges at Base of Cloud
Other Lightning Types
• Ball Lightning
• Appears as a Round, Glowing Mass, Basketball Size
• One Form Avoids Electric Conductors and Another is
Attracted
• Saint Elmo’s Fire
• Ionization of Air Just Before Cloud-to-ground Strike
• Causes Church Steeples and Ship’s Mast to Glow
Green-blue, Giving Out Sparks That Hiss
Other Lightning Types
Lightning Statistics
• 12,000 fires/yr in US are started by lightning
• 5.2 million acres
• $50 million worth of timber destroyed
• Total Lightning Losses/ Year: $5 billion
• Deaths:
• Avg =
62/year
• 2008
• 27 killed
• 302 injured
Lightning
• Electrical Charge Builds in Air Before Lightning Strikes
• If Nothing Else Can be Done Flatten Out on Ground
Get Away From High Points (Trees)
Lightning Safety
• Lightning can strike up to 15 miles from where it’s
raining
• Take cover in a building
• Stay away from electrical appliances
• Get Out of the Water
• Stay in the Car Unless It Is a Convertible
Downbursts
• Downbursts
•Strong Downdrafts up to 165 mph
• Spread in All Directions to Form Intense Horizontal
Winds
• Damage Sometimes Mistaken for Tornado
• Microburst
• Downburst Less Than 4 km (2.5 mi) in Diameter
• Airport Danger due to Strong Wind Shear
• Headwind for Lift Followed by Tailwind Causing
Negative Lift
Downbursts
Worst Tornado Movies
• Twister
• Revenge of the Twisters
• Category 7
• Any other movie with a tornado in it …
Except
• The Wizard of Oz
Tornadoes
•Extremely Rapid, Rotating Winds
Beneath the Base of Cumulonimbus
Clouds
•Most Rotate Cyclonically (CCW NH)
• Shapes
• Some Very Thin rope-shaped
Columns
• Others Characteristic Funnel Shape
Smallest at Surface
• Result From an Extraordinarily Large
Pressure Difference Over a Few Tenths of
a mile (100 mb)
Tornado Characteristics
• Wide Variety of Shapes and Sizes
• Majority Have Diameters = 100 to
2000 feet
• Time Span a Few Minutes to Several
Hours
• Forward Speed 30mph
• Path of Destruction 2-2.5 mi
• Wind Speed 40 mph to 280 mph
Tornado Path
Tornado Formation
• Development Situations
• Frontal Boundaries
• Squall Lines
• Mesoscale Convective Complexes (MCCs)
• Supercells
• Tropical Cyclones
• Not Very Well Understood
• Most Intense and Destructive Are From
Supercells
Tornado Development
Supercell Tornado Development
• Formation of a Slow Horizontal Rotation of a Large
Segment of the Cloud
• Up to 12 mi in Diameter
• Deep in Cloud Several thousand feet in air
• Results in Large Vortices
• Mesocyclone Precedes Tornado by ~30 min
• Depends on Wind Shear
• A Rapid Change in Direction Rolling Motion About
Horizontal Axis
• Updraft Tilts to Form Mesocyclone
Supercell Tornado Development
Supercell Tornado Development
Tornado Damage
• Most Damage Is From the High Winds
• Most Injuries Caused by Flying Debris
• Most Violent Tornadoes Have Small Zones of Intense
Rotation
• Small High Intensity Vortices
• No suction
• Can Destroy One Home Leave Next Door OK
Fujita Scale
Fujita Scale
F#Wind Speed
Damage
F0
40-72 mph
Minor, branches broken
F1
72-112
Peels roofs, cars moved
F2
113-157
Roofs torn, boxcars, trees
F3
158-206
Roofs & walls, trains
F4
207-260
Houses destroyed
F5
261-318
Houses lifted, debark trees
Tornado Damage
F1
72-112 mph
Peels roofs, cars moved
F2
113- 157 mph
Roofs torn, boxcars, trees
Tornado Damage
F3
158-206 mph
Roofs & walls removed, trains
moved
F4
207 - 260 mph
Houses destroyed
Tornado Damage
F5
261- 318 mph
Houses lifted, debark trees
F5 Path of Destruction
LaPlata, MD
2002
Enhanced Fujita Scale
• Based on Consistent Assessment of Damage
• Enhance description of damage with examples and photos
that include not only structures, but also vegetation
• Base damage assignment on more than one structure, if
available
Fujita Scale
F Number
Enhanced Fujita Scale
3 Second Gust
3 Second Gust
(mph)
EF Number
(mph)
0
45-78
0
65-85
1
79-117
1
86-110
2
118-161
2
111-135
3
162-209
3
136-165
4
210-261
4
166-200
5
262-317
5
Over 200
Tornado Frequency
TORNADO
ALLEY
Number of tornadoes
Avg. Number per 10,000 mi.2
Worldwide Tornadoes
Waterspouts
• Waterspouts
• Tornadoes Over Water
• Typically Smaller Diameters and Weaker
• Some Form Initially Over Water but
• Majority Form Over Water
• Fair Weather
• Unstable when Warm Water Heats Air From Below
• Rope-like Structure
• Water Not Sucked Up
Waterspouts
Waterspouts
HAIL FORMATION
• Particle forms in area of
weak updrafts to about 1
mm
• Begins to fall
• Swept back up by strong
updrafts
• Particles collides with
supercooled particles that
freeze to it
• Lifting and falling occur
many times (layers)
• Large enough to fall or
get into downdraft
(entrainment)
HAIL
• Spherical or irregular
chunks of ice greater
than 5 mm diameter
• Cross-section shows
many layers
• Lethal missiles
•Injure or kill
•Damage in US alone is
hundreds of millions of
dollars
Diameter: 140mm (5.5in)
Weight 0.75kg(1.7lbs)
Speed: 45m/s (100mph)
HAIL CLIMATOLOGY
Avg. Number of Hailstorms per year
Weather Hazards
Homework #12 - Your Perfect Climate
• In a brief paragraph, describe your “perfect” climate
and why?
– Hot sunny days? Cool and foggy”
– Rain, Snow?
– Different seasons?
– Weather related activities you enjoy?
• Then find a location (NOT in California) that best fits
your idea of a perfect climate
– Provide details of its average temperatures, rainfall,
snow, etc.
– A good source will be “Climate Charts” in the Week
#1 Additonal Resources.