Transcript Lecture 11: Climate and Weather Extremes

San Jose State University
Department of Meteorology
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Weather: Can be described as the CURRENT
state of the atmosphere at a given location.
 Changes occur by the minute.
 Examples: Current Temperature, wind speed, etc.
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Climate: Can be described as the state of the
atmosphere over a given time.
 Examples: Average Temperature, Annual Rainfall,
etc.
Meteorology studies Weather, Climatology studies Climate
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State Variable:
 Simply a variable describing the state of the
atmosphere.
 Examples: Temperature, Humidity, Wind Speed,
Rain-rate/Total Rainfall
 Used in both Meteorology and Climatology
▪ Meteorology: Current Temperature, Current Humidity
▪ Climatology: Average Temperature, Average Humidity
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A good definition of extreme weather:
 Weather that involves an exceptionally high/low
state variable. (Such as a heat wave, or downpour)
 A weather event that is an extreme of the
climatological history.
 In more laymen’s terms: Extreme Weather events
are rare weather events that cause damage or
involve some kind of major in climate state.
 These events are short term…
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May involve long periods of extreme weather
events or periods of above occurrence of
extreme weather events (like Tornado
outbreaks or Hurricane Seasons)
Longer-term events that involve a major
departure from the average state variable.
 Droughts: Long Periods of very little rainfall
 Deluges: The opposite
 Heat Waves: Long Periods of hot weather.
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Examples
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Tornados
Hurricanes
Severe Thunderstorms
Blizzards
Drought
Heat Waves
Or… any pattern that is
extremely above or below
average.
Weather Events
“Short Term”
Climate Events
“Long Term”
We’ll come back to the Weather vs. Climate events later
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Typically, long periods of below-average
occurrences of extreme weather wouldn’t be
considered “extreme” because they do not
involve higher levels of damage/destruction
or harm.
These are considered a relief! 
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Our Earth has an uneven distribution of heat
and moisture both vertically and horizontally.
A Fundamental Principle: When things are
unbalanced, they will attempt to achieve
balance. Therefore, heat and moisture are
constantly moving around in our atmosphere
in a feeble attempt to reach an equilibrium.
Much more complicated than this…
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Take Home Message: WEATHER IS CAUSED
BY UNEVEN HEATING OF THE EARTH
 We will return to this when asking “How does
climate change affect extreme weather?”
This distribution of heating/energy feeds extreme weather.
Form as warm, moist air
rises and then cools and
condenses, creating
Cumulus clouds.
 Not extreme in
themselves
 Happen all the time
(though not here in San
Jose… otherwise we
wouldn’t make such a big
deal about them)
 Provide much of the
summer rainfall in the US
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• As the air condenses, it
gives off “Latent Heat,”
causing air to continue to
rise.
• The cumulus cloud
becomes a “Cumulus
Congestus” cloud: A
towering Cumulus
• As the cloud grows, the
top begins to freeze and
spread out. Cloud droplets
grow larger. Eventually,
the cloud becomes a
Cumulonimbus cloud…
Where thunderstorms
come from
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Eventually, the weight of the
droplets becomes too large to be
supported by the updrafts, and
rain begins to fall.
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Additionally, cooler air from the
upper troposphere begins to
“entrain” the cloud, creating a
downdraft of rain and a “Gust
Front”
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Eventually, the cool air cuts off
the warm, moist updraft,
choking out the storm
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These ARE extreme weather!
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Caused when there is more fuel,
combined with some kind of vertical
wind shear (changes in wind speed
with height), which promotes
updrafts!
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Keeps precipitation downwind of the
storm. This allows for the updrafts,
which are the fuel to the storm, to
survive, strengthening the storm.
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These storms produce hail, high
winds, substantial lightning, and
TORNADOS!!!!
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Also produce some really awesome
clouds (Wall Clouds, Mammatus, etc)
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Caused by an uneven distribution of charged
particles.
Typically + at the top and – at the bottom of
the cloud.
+ Charges at the surface complete the
current.
The Updrafts of a severe
thunderstorm are so
strong, that rain
droplets are pushed up
into the top of the
cloud, freeze and fall to
the ground… only to be
picked back up by the
updraft, and frozen
again, adding another
layer.
 Eventually, the hail gets
too heavy, and falls to
the ground.
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Golf Ball sized hail! Imagine getting
hit by that!
But…
SOFTBALL SIZED HAIL!!!!!!!!
Golf ball size will hurt… Softball
size can destroy!!!!!
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Strong, rotating column of wind
around a low-pressure area that
reaches the ground.
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If the column does not reach the
ground, it is called a Funnel Cloud
Diameters can range from 3002000 ft
Wind speeds can exceed 200
mph!
Typically last only a few minutes,
and travel several miles… but
not always.
Highest frequency is in the
United States
Typically occur in the United
States in Mid-late Spring (April –
June), but can occur any time
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Created by Dr. Theodore
Fujita in the late 1960’s,
and was updated in 2007
as the Enhanced Fujita
Scale.
Rates tornadoes based off
of damage caused.
The Scale goes from EF0,
to EF5
The original scale went
from F0 to F6
Typically, the stronger
tornados are less frequent.
Tornado Alley:
Texas,
Colorado,
Oklahoma,
Kansas,
Nebraska and
South Dakota
Typically, tornado
occurrences are not
isolated, but instead are a
part of a tornado
outbreak.
 A tornado outbreak is
when multiple tornados
occur over a given region,
usually due to a storm
system.
 Most of the death and
destruction due to
tornados occurs during a
tornado outbreak.
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One of the deadliest
tornado outbreaks in
history, and was the
largest outbreak in
history.
 336 confirmed
tornados (11 EF4’s and
4 EF5’s)
 346 confirmed deaths.
 Alabama was
particularly hit hard.
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Dallas metropolitan
area.
21 confirmed
tornados (3 EF2’s and
1 EF3).
No confirmed deaths.
Proof that major cities
are not “Tornado
Proof.”
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April 14-16, 2011: From the Midwest to the
Carolina coast.
February 5-6, 2008 (Super Tuesday):
Arkansas, Tennessee, Kentucky and Alabama
May 3, 1999: Oklahoma, Kansas
April 3-4, 1974: Practically the entire eastern
US; Called the “Super Outbreak”
March 18, 1925: Missouri, Illinois, Indiana.
Deadliest US Outbreak in history.
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The largest-scale single extreme
weather event.
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Typically occur from June to
November in the Atlantic.
 Called “Hurricane Season”
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Form in the tropical regions,
where there is a lot of HEAT.
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Typically move from South/East
to North/West
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Fueled by warm ocean
temperatures and ideal
atmospheric conditions
 Low upper level wind shear, and
moist air
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Tropical Depression: A weak “warm cored”
center of low pressure with maximum wind
speeds below 39 mph
 All Hurricanes start out as tropical depressions
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Tropical Storm: A stronger center of low
pressure with maximum winds of 39-73 mph
Hurricane: A very strong tropical low pressure
center with maximum wind speeds above 74
mph!
Cooler waters kill
Hurricanes!!!!
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The most damaging
Hurricane in United
States History!
Struck the eastern
portion of Louisiana on
August 29, 2005
Maximum Strength: 175
mph winds (Cat 5)
Strength at Landfall: 125
mph winds (Cat 3)
Total Damage: $108
BILLION
Total Deaths: ~1700
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Hurricane Ivan (Cat 3 at landfall)
 $18.1 billion damage, 123 deaths
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Hurricane Charley (Cat 4 at landfall)
 $18.6 billion damage, 35 deaths
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Hurricane Andrew (Cat 5 at landfall)
 $40.7 billion damage, 65 deaths
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Hurricane Hugo (Cat 4 at landfall)
 $14.1 billion damage, 61 deaths
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Total for these four storms…
 $91.5 billon damage, 283 deaths… MUCH LESS THAN
KATRINA… WHY???
 Katrina wasn’t an exceptionally strong storm at landfall…
but it hit the worst possible place… New Orleans!
Climate events are long term (in weeks or
months) compared to single weather events.
 Examples: Droughts, Heat Waves,
Hurricane/Tornado seasons.
 Since no one weather event defines the climate,
climate events are inspected for evidence of
climate change.
 Examples: The occurrence/severity of heat
waves, the number of storms in a hurricane
season, etc.
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These events are a much greater sign of
climate change because they are large scale
events in which “chance” can be ruled out.
I.e. One bad hurricane or tornado outbreak or
any extreme weather event is not good
evidence for climate change, but a bad
hurricane season, or a bad tornado year can
be… especially if it seems that they are
becoming more common…
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2003 European heat wave
 One of the deadliest heat waves in European
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history.
Many regions were as much as 18 degrees F above
average!!!
Affected Western and Central Europe.
Over 40,000 Europeans died!!!!
Similar event in Russia, 2010
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2005 Atlantic Hurricane Season
 The Largest number of Named Storms in recorded
History: 27 Named Storms (and One unnamed!)
▪ Average Season is 10-12 named storms!!!
 Noteable Storms: Hurricanes Emily (Cat 5), Katrina
(Cat 5), Rita (Cat 5), and Wilma (Cat 5)… That’s FOUR
Category 5 storms in One Year!!!!!
 WE RAN OUT OF NAMES!!!!!!!
▪ Used Greek Letters for the remaining storms… and went
pretty well into that list (Tropical Storm Zeta)
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El Nino: A warmer than average body of
warm water in the eastern equatorial Pacific
La Nina: the opposite…
Explain two
reasons for the
major increase in
reported number of
natural disasters…
(Hint, compare
frequency of
Earthquakes to
other disasters…)
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The text I blocked out from the last slide…
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Recall the graph we saw in the first week of
class… Remember the sharp increase in
temperatures over the past century…
Now think about the graph we just saw…
Coincidence: I think not!
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What causes weather:
IMBALANCE…
 The sun heats the Earth
UNEVENLY… That’s why the
temperature in Fargo, ND is
different from the Temperature in
Long Beach, CA.
 A major scientific principle…
Balance is always being
attempted… So the energy from
the sun is distributed around the
earth… this happens through
weather systems such as fronts,
low pressure systems, and
Hurricanes… which is why
hurricanes typically travel from
the equator towards the poles…
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Greenhouse gasses trap in more heat, so
there is more energy being distributed.
 Sort of like pouring fuel into a fire… The increase
in heat means an increase in fuel… which means
two things:
▪ More Storms/events
▪ Stronger Storms/events
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Storms are in theory getting stronger… and
extreme events are getting more frequent
and more severe.
 Events like the 2004/2005 Hurricane Seasons, the
2003 European Heat Wave, and the 2010 Tornado
Outbreaks are becoming more frequent…
 Because this has only been happening over the
past few decades, rushing to conclusions is
unwise… but things are looking pretty grim.
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Many Movies/Documentaries have been
created to either address or sensationalize
the issue of Climate Change…
Some of these I highly recommend:
 Six Degrees can Change the World… a look at how
our Earth would change if the earth’s average
temperature warmed up by Six degrees.
 An Inconvenient Truth… We’ve already talked
about this one in class…
 Many Others
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Sensationalized Films
 The Day After Tomorrow: A shutdown of the
“Thermohaline Conveyor” would cause Hurricane-like
blizzards over New York and Tornado Outbreaks in Los
Angeles… While massive climate shifts could occur if
the Thermohaline Conveyor shut down… this is a little
dramatic… to say the least
 Category 6: Day of Destruction. Probably the worst
weather movie in history: In this movie, Hurricanes
are forming from Arctic low pressure systems over the
Great Lakes…
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The Thermohaline Conveyor…
 A complex current that relies heavily on the of
salinity water.
 Carries heat up to the North Atlantic
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What’s happening in the North Atlantic right
now?
As polar ice continues to melt, it dumps fresh
water into the ocean, which could eventually
slow down or even stop the current’s flow.
This might have caused the “Little Ice Age”
A shutdown would cause Abrupt Cooling
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http://www.youtube.com/watch?v=02NRKze
mXYE
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The Shutdown of the Thermohaline Conveyor
would cause abrupt cooling, especially in
Europe.
This change could occur in as little as ten
years after the shutdown (not a few days like
The Day After Tomorrow)
Suddenly, many northern countries would
almost become uninhabitable.
 Major political implications
 Wars
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Compare an extreme weather event to an
extreme climate event. Give one example of
each.
Other than Climate Change, why might the
frequency of reported natural disasters be
increasing?
Did you understand today’s lecture. Was it
too much material? Too little? Suggestions?
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Watch the Movie “Six Degrees Could Change
the World” and:
 List one impact for each degree-level increase…
(e.g. What would happen in the world +1 degree?
+2 degrees? etc…)
 Even though six degrees doesn’t seem like much.
Why would such a change bring about disaster?
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Can’t get the movie? Check out:
http://www.youtube.com/watch?v=TKo4TSq
40l0. It’s also available on Netflix.