Studied by 1 person1999 Oklahoma Tornado Outbreak
152 tornadoes over 7 days the U.S. Great Plains
On average 1,300 tornadoes/year in the U.S.
Number of Tornadoes State in the U.s.
1999 and 2013 Tornadoes Moore, Oklahoma
City struck by two extremely powerful tornadoes
1999 oklahoma tornado
Highest-ever recorded wind speed of 484 km/hour
Killed 36, injured 295, and damaged/destroyed ~ 10,000 homes
2013 oklahoma tornado of comparable destructiveness
Followed remarkably similar path
Energy
a quantifiable physical property describing the state of a system
Ability of something to do work
Stored in many forms
Force
Push or a pull
Magnitude measured by how much a body is accelerated
Measured in Newtons (N) - Force necessary to accelerate 1 kg mass
Work
Done when energy is expended
Physics: force applied to an object and it moves a certain distance in the direction of the applied force
Work = force x distance over which it is applied
Measured in Joules (J)
Power
Atmospheric processes are concerned with large amounts of energy in atmospheric processes
Measured in exajoules (EJ) 1018 to describe global energy
Rate at which work is done = energy/time
Measured in joules/second = Watts (W)
Potential energy
Stored energy
Example: water held behind a dam
Kinetic energy
Energy of motion
Example: water flowing from the dam
Heat energy
Energy of random motion of atoms & molecules
Sensible heat
heat sensed or measured by thermometer
Latent heat:
amount of heat absorbed or released when a substance changes phase
Latent Heat
Amount of heat absorbed or release when a substance changes phase
No change in temperature
Liquid – gas – latent heat of vaporization
Conduction
Transfer through atomic/molecular interactions
Two bodies in contact with one another
Convection
Transfer through mass movement of a fluid
Hot air rises displaces cool air which falls
Creates a convection cell
Radiation
Transfer through electromagnetic waves
Emitted by any substance that possesses heat
Earth’s Energy Balance
energy received from the Sun balances the energy lost by the Earth back into space
Electromagnetic Energy
Everything above absolute zero (0˚ Kelvin = -273˚C ) emits electromagnetic energy
Electromagnetic Energy
form of energy that propagates as both electric and magnetic waves (𝜆)
travel in packets of energy called photons
aka light, radiation, electromagnetic waves/radiation
Electromagnetic Energy
Wavelength
Frequency
Energy
Sun
Nuclear fusion (H ⇢ He) creates electromagnetic (solar) radiation
Temperature
150 million km from Earth
Speed of light 300,000 km/s
~ 8 min to reach Earth
Earth intercepts a very small amount of all solar radiation
Surface
6,000 oC
Internal
16 million oC
Electromagnetic Energy
Most of the sun’s energy is electromagnetic
Described by the wavelength
Distance from one crest to the next
All wavelengths are part of electromagnetic spectrum
Only a small part of this is visible
Infrared radiation
Earth radiation is entirely (thermal) infrared (long wave)
~45% of the solar energy infrared (short wave)
Visible Light
(0.4 to 0.7 µm)
47% of the solar energy
~ short Wave
Ultraviolet (UV)
0.01 to 0.4 µm
~8% of solar energy
Most filtered by ozone layer
Sort Wave
Absorption
gases & particulates interrupt the flow of radiation by absorbing specific wavelengths and gain heat
Reflection
redirected radiation returning to space and has no heating effect
Scattering
solar radiation bounces of an object in a variety of directions and has no heating effect
Energy Behavior
Temperature depends on amount of energy absorbed or reflected
Reflection depends on albedo
Describes the reflectivity of surfaces
Dark woodlands reflect 5 - 15%
Light grasslands reflect 25%
Absorption
Energy that is not reflected is absorbed
Different objects absorb different wavelengths
Hotter objects radiate energy more rapidly and at shorter wavelengths
The Atmosphere
Thin gaseous envelope that surrounds Earth
Gas molecules
Suspended particles of solid and liquid
Falling precipitation
Atmosphere
Causes weather experienced every day
Responsible for trapping heat that keeps the Earth warm
Knowledge of structure and dynamics critical to understand severe weather
Permanent (Constant) Gases
Nitrogen (N2) - 78%
Oxygen (O2) - 21 %
Argon (Ar) – 0.93%
Neon (Ne), Helium (He), Hydrogen (H2)
Variable (trace) Gases
Water (H2O) - 1 – 4 %
Carbon dioxide (CO2) - 0.04%
Methane (CH4)
Nitrous Oxide (N20)
Ozone (O3)
CFCs and HFCs (anthropogenic)
Thermal layers of the Atmosphere
distinguished by temperature changes and gases
differs in density & composition
“sphere” vs “pause”
Troposphere
Stratosphere
Mesosphere
Thermosphere
The Troposphere
Most active zone
Majority of nonmarine living organisms
Weather occurs in this layer
Vertical mixing is common
Temperature decreases with increasing altitude
Environmental lapse rate (ELR)
Temperature decreases at an average rate of 6.5oC per 1000m
Humidity
Amount of water vapour in the atmosphere
Varies spatially and temporall
Warm air can hold much more than cold air
Cold dry air can have close to 0%
Warm tropical air may have 4-5%
Measures of humidity
Vapour Pressure
Specific humidity
Dew-Point Temperature
Relative humidity
Clouds
composed of tiny water or ice droplets that have condensed/frozen onto condensation nuclei
four Weather Processes
Atmospheric pressure and circulation patterns
Vertical stability of the atmosphere
Coriolis effect
Interaction of different air masses
Atmospheric Air Pressure Changes
Atmospheric pressure (barometric pressure)
Weight of a column of air above a given point
Force exerted by molecules on surface
Relationship
Pressure decreases with increasing altitude
Thermal Pressure
Results from changes in temp.
Equatorial low, polar high
Dynamic Pressure
Caused by air movement
Subtropical High Pressure, polar lows
Warm air is associated with
low pressure
Cold air is associated with
high pressure
Relationship between air temp. and air pressure
not constant
dynamic pressure can override thermal pressure
How a pressure gradient creates wind
Any fluid under the influence of gravity will move until the pressure is uniform
Differential Heating
Changes in air temperature and air movement are responsible for horizontal changes in pressure
pressure belts
\n
A region on the earth that is dominated by either high pressure cells or low pressure cells
Low- and High-Pressure Centers
Surface, air moves from surface high pressures (H) to low pressures (L)
Atmospheric Stability
Tendency of air is to remain in place
Atmospheric stability describes what happens to a vertically rising parcel of air
Air parcels resist movement or return to original spot after they move
Atmospheric Stability 2
The stability of the atmosphere depends on
Relative temperature
Density
Temperature of a parcel of air compared with surrounding atmosphere2
n unstable air, parcels are rising until they reach air of similar temperature and density
Air is unstable when lighter, warm or moist air is overlain by denser cold or dry air
Some air sinks and some air rises
Fronts
Boundary between cooler and warmer air masses
Air masses do not mix
Warmer air will always be lifted by the colder, denser air mass
Air masses also have different humidity levels, densities, wind patterns, and stability
Stationary front
boundary shows little movement
Occluded front
rapidly moving cooler air overtakes another cold air mass wedging warm air in between
Severe weather refers to
Thunderstorms
Tornadoes
Hurricanes (Chapter 10)
Blizzards
Ice storms
Mountain windstorms
Heat waves
Dust storms
Hazardous due to the energy they release and damage they are capable of causing
Thunderstorm Occurrence
Most occur in equatorial regions
Most common in the afternoon or evening hours in spring or summer
Thunderstorms
Three conditions necessary
Moisture
Instability
Lifting Mechanism
Moisture
Warm & humid air available in lower atmosphere
Instability
Steep vertical temperature gradient such that the rising air is warmer than the air above it
Colder air over warmer, moist air
Updraft must force air up to the
upper atmosphere
Lifting Mechanism
Formation of a thunderstorm
Moist air is forced upwards, cools and water vapor condenses to form cumulus clouds
Air-mass-thunderstorms (Single Cell)
Most individual thunderstorms Last less than 1 hour and do little damage
Severe Thunderstorms
Classified as severe by National Weather Service
Winds > 93 km per hour, or
Hailstones > 1.9 cm , or
Generates a tornado
Formation conditions
Large changes in vertical wind shear
Greater the wind shear, the more severe the storm
High water vapor content in lower atmosphere
Updraft of air
Dry air mass above a moist air mass
Mesoscale convective systems (MCS)
circular clusters of storms
Squall lines
linear belts of thunderstorms
Supercells
large cells with single updrafts
Mesoscale convective systems (MCS)
Most common type of thunderstorm
Large clusters of self-propagating storms
downdrafts from one cell leads to formation of another
Continued growth - storms can last for 12 hours or more
Squall lines thunderstorm
Long lines of individual storm cells common along cold fronts
Updrafts form anvil-shaped clouds extending ahead of the line
Downdrafts surge forward as gust front in advance of precipitation
Can also develop along drylines
Fronts with differing moisture content
Damaging Winds
Begins with downdrafts
Can generate strong, straight-line windstorms
Down Bursts
Strong winds produced by a downdraft over horizonatl area up to 10 km
Classified as
Micro Bursts
Macroburts
Derechos
Microbursts
small downburst <4 km horizontal dimeter
Last for 2-4 minutes up to 270 km/h
Hazard for aviation
Macroburst
Wind gusts can be tornado strength
Cause fallen trees, power outages, injuries, fatalities
dozen strike North America /year
Most in eastern two-thirds of U.S. & Canada
Derechos
family of downburst clusters
At least 400 km in length
Lightning flash per year 1995-2002
More lightning occurs over land
More lightning occurs near the Equator
Lightning
Flashes of light produced by discharge of millions of joules of electricity
Common occurrence during thunderstorms
Extreme heat from discharge causes air to rapidly expand
Produces thunder
Most is lighting is cloud-to-cloud
Cloud-to-ground is less common
us lighnight
us Kills ~ 100 and injures m > 300 each year
Canada lighitng kills
10 injured an estimated 120 - 190 each year (Red Cross)
Development of Cloud-to-Ground Lightning
25 million ground strikes in U.S./year
Complex process (simplified here)
Difference in electrical charges between cloud & earth
Narrow column of high-speed electrons toward Earth
+ve stepped leader & –ve streamers join by a spark creating a return stroke
Additional leaders & return strokes follow path creating lightning flash
Types of Lightning
Males are five times more likely than females to be struck by lightning; around 85% of lightning fatalities are men (CDC)
People aged 15-34 years account for almost half of all lightning strike victims (41%). The majority (89%) of lightning deaths occur among whites (CDC)
~ 1/3 (32%) of lightning injuries occur indoors (CDC)
Staying Safe in Lightning
To determine distance of a lightning bolt - count number of seconds till thunder occurs:
divide by 3 to get distance in kilometers
30/30 rule
During a thunderstorm
Always shelter indoors if possible.
Outdoors - do not be the highest object or stand under highest trees.
Crouch low, with as little of your body touching the ground as possible
Cars are safe.
Wait 30 minutes after storm has passed
Hail
Hard, round, irregular pieces of ice originating from thunderstorms
Contain rings due to adding coatings during updrafts
Hail moves up and down in lower part of the storm adding layers of liquid water which then freezes
Hail
Cause mostly property damage
Averages $41 billion per year in the United States
Most common locations
North America: Great Plains in United States, Calgary region of Alberta, Canada
Other regions: North-central India, Bangladesh, Kenya, and Australia
Deaths not uncommon in Bangladesh and India because of poorly constructed dwellings
Tornadoes
Usually spawned by severe thunderstorms
One of nature’s most violent natural processes
1992 to 2002, killed average of 62 people per year
Variety of shapes
Rope
Funnel
Cylinder
Wedge
Defined by vortex extending downward from the cloud and touching the ground
Called funnel clouds when it does not touch ground
Form where there are large differences in atmospheric pressure over short distances
Organizational stage
Vertical wind shear causes rotation to develop within the storm
Strong updrafts in advance of the front tilt the horizontally rotating air vertically
Known as a mesocyclone
Updrafts at rear of the storm lower part of the cloud
Wall cloud
Wall cloud rotates and funnel descends
Tornadoes mature stage
Visible condensation funnel extends to ground
Moist air drawn upward
In stronger tornadoes, smaller whirls may develop within tornado
Suction vortices
Responsible for the greatest damage
Shrinking stage
supply of warm air is reduced and tornado begins to thin
More dangerous because wind speeds increase as diameter decreases
Rope stage
Downdrafts cause tornado to move erratically and disappear
Classification of tornadoes
Classified according to most intense damage that they produce
Assigned value on Enhanced Fujita (EF) Scale
Survey determines levels of damage experienced by 26 types of buildings, towers, and poles and hardwood and softwood trees
Estimate the maximum 3-second wind gusts
Waterspouts
Tornadoes that form over water
Develop beneath fair weather cumulus clouds as a result of wind shear
Occurrence of tornadoes
Found throughout the world, but much more common in the United States
Has the just the right combination of weather, topography, and geographic location
Most U.S. tornadoes occur in midwestern states between Rocky Mountains and Appalachians
Spring and summer in late afternoon and evening are most common times
Highest risk is in “Tornado Alley” – stretches from north to south through the Great Plains states
Note
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