Transcript ES-Weather_II

Weather
Thunderstorms
Snow / Rain storms
Mid-latitude cyclones
Tropical cyclones
Types of Severe Weather
• Thunderstorms
• Snow / Rain storms
• Mid-latitude cyclones
– Blizzards
– Tornadoes
• Tropical cyclones
– Typhoons in the western Pacific
– Cyclones in the Indian Ocean
– Hurricanes in the U.S.
Stages in the development
of a thunderstorm
Thunderstorms
• How Lightning Works
Thunderstorms
Lightning Varieties
cloud-to-ground
Blue jets
Cloud discharge
Red sprites
Ball lightning
Elves
(NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)
Lightning Varieties
Volcanic Lightning
Nuclear Lightning
Triggered Lightning
(NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)
Severe weather types
• Tornadoes
– How a Tornado Forms
• Moist air from Gulf of
Mexico
• Fast moving cold, dry
air mass from Canada
• Jet stream moving east
at 150 mph
• Sets up shearing
conditions
Severe weather types
• Tornadoes
– How a Tornado Forms
• Warm moist Gulf air
releases latent heat,
creates strong updraft
• Updraft sheared by
polar air, then twisted
in a different direction
by jet stream
Tornado Wind Patterns
Severe weather types
• Tornadoes
– Why do some thunderstorms spawn
tornadoes while others do not?
– Super Cell Thunderstorms
Severe weather types
• Tornadoes
– The Fujita-Pearson Scale
• The size of a
tornado is not
necessarily an
indication of its
intensity!
Tornadoes
• “Tornado Capitol of the World”
– CNN’s “10 deadliest U.S. tornadoes”
Source: cnn.com
Tornadoes
• Why don’t tornadoes strike large cities?
– Occur over large regions
– Cities are relatively small targets
– Oklahoma City Tornado (1999)
Mid-latitude Cyclones
• Idealized weather
– Middle-latitude cyclones move eastward
across the United States
• First signs of their approach are in the western sky
• Require two to four days to pass over a region
– Largest weather contrasts occur in the spring
Mid-latitude Cyclones
Mid-latitude Cyclones
• Blizzards
– Form when a long cyclone brings
• Cold 60 km/hr winds
• Freezing temperatures
• Lots of snow
– Can travel very slowly
– Storm itself usually doesn’t kill
• Shoveling snow, auto accidents, etc.
Mid-latitude Cyclones
• Ice Storms
– Formation:
• Falling snow and ice melt, change to rain, then
freeze again as they reach the ground
• Sleet
• Freezing rain
Hurricanes
• Only natural disaster that is given a
human name
• Actually large tropical cyclones
• Convert heat in the ocean into winds
• Exports excess heat from the tropics to
the midlatitudes
Hurricanes
• How a Hurricane Works
– Tropical disturbance
• Low pressure zone develops and draws in clusters
of thunderstorms and winds
Hurricanes
• How a Hurricane Works
– Tropical disturbance
– Tropical depression
• Surface winds strengthen, move about the center
of the storm
• Central core funnels warm moist air up towards
stratosphere
• Air cools, vapor condenses, latent heat released
• Fuels more updrafts, cycle repeats, storm grows
Hurricanes
• How a Hurricane Works
– Tropical disturbance
– Tropical depression
– Tropical Storm
• Storm has sustained surface wind speeds of +39
mph
Hurricanes
• How a Hurricane Works
– Tropical disturbance
– Tropical depression
– Tropical Storm
– Hurricane
• Surface winds consistently over 74 mph
Hurricanes
• How a Hurricane Works
– Tropical disturbance
– Tropical depression
– Tropical Storm
– Hurricane
– The Eye
• As wind speed increases, winds are spiraled upwards
prior to reaching the center
• A distinctive clear “eye” is formed
• Strongest winds are located on the walls of the eye
Hurricane Wind Patterns
Hurricane Origins
• Form in the tropics ~ 5° and 20 ° latitude
• Cannot form at the equator
(Coriolis effect = 0)
Hurricanes
• Hurricane Damages
– Storm Surges
• Large mound of water builds up beneath the eye
• Reaches land as a surge of water
Hurricanes
• Hurricane Damages
– Storm Surges
• Wind speed varies
depending upon which
side of the hurricane
you’re on
• Amount of damage on the
coastline will vary
accordingly
Hurricanes
• Hurricane Damages
– Heavy Rains
– Mudflows and Debris Avalanches
– Flooding
Hurricanes
• Hurricane paths
– Curves due to
Coriolis affect
– Storms must go
around high
• Strong and large –
storms to Atlantic
seaboard
• Small and to the
north – storms may
miss the U.S.
Hurricane Paths
Forecasting the Hurricane
Season
• Frequency of hurricanes in the North
Atlantic is affected by climate
– Wet Sahel region in Africa = more
thunderstorms
– Warm SST = more energy for tropical
depressions
– Low atmospheric pressure in Caribbean =
more cyclones
Forecasting the Hurricane
Season
• The La Nina / El Nino Connection
– La Nina present in Pacific = more winds to
move storms
– El Nino present in the Pacific = less winds,
disrupts storms
El Niño
Normal conditions in the tropical
Pacific Ocean
• Surface winds move from east to west
• From high pressure in S. America to low
pressure in Australia
• Drags water westward
• Warm water pools in the western Pacific
Every 3 – 8 years, system
reverses
• Called the Southern Oscillation
• Trade winds weaken or reverse
• Warm water migrates from Australia to S.
America
• Arrives in time for Christmas – Corriente
del Niño
El Niño and La Niña
What is El Niño?
• Basically, it's a giant puddle (or pod) of
heated water that sloshes across the
Pacific Ocean
• Similar to an iceberg
– Bulge on the surface
– Most of “pod” beneath the surface
– Due to difference in density
• National Geographic’s Model
ENSO - El Niño-Southern
Oscillation
• Typically lasts 1 year
• May last up to 3
• In multi-year events, first year not as
affected
• Affects both hemispheres
Recognizing an El Niño
• Sea Surface Temperatures (SST)
• Normal: 6-8° C warmer in the western
tropical Pacific than in the eastern tropical
Pacific
• Check SST to see if in “normal” range
La Niña
• Return to “normal” conditions from an El Niño
•
strong
Produces:
– Strong currents
– Powerful upwelling
– Chilly and stormy conditions along S. American coast
• Eastern Pacific cools rapidly, Western Pacific
•
warms rapidly
Renewed Trade Wind activity spreads the cooler
eastern Pacific waters westward