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Chapter 8

Study Guide For EESA05, Chapter 8

by OC2

Department
Environmental Science
Course Code
EESB18H3
Professor
Ingrid L.Stefanovic
Chapter
8

Page:
of 7
Chapter 8: Severe Weather
! tornado: violently rotating column of air carrying extreme winds
! worst tornado: longer contact with ground; larger width; straight path; fast speed
8.1 Energy
! E=mv2/2! energy of the moving body= mass (velocity)2/ 2
! Force: experience it when we push or pull an object; strength or magnitude of force can be measured by
how much the force accelerates the motion of the box or car
o F=ma ! force=mass of moving body x acceleration or change in velocity of the object per unit time
! Newton (N) is defined as the force required to accelerate 1 kg mass 1 m/s each sec that it is in motion
! Work is done when energy is expended; work is the energy expended in applying a force to move an
object a specific distance
o Work= f x distance over which it is applied! measured in joules, defined as a force of 1 N applied over
a distance of 1 m
! Rate at which work is done is powerenergy divided by time! expressed as j/s or watts
! Atmospheric processes involve huge amts of energy and power! expressed in terawatts (tW)
o 1 tW=1 trillion W=1 million MG (megawatts)
Types of Energy
! potential energy is stored energy
! kinetic energy: energy of motion
o a book on a shelf contains potential energy based on its height above the ground. If it falls from the
shelf to the ground, it loses potential energy and gains kinetic energy
! heat energy: energy of random motion of atoms and molecules that can be defined as the kinetic energy
of atoms or molecules within a substance
! heat can also be thought of as energy transferred from one body to another because of the temperature
difference b/w the two bodies
! two types of heat that are imp in atmospheric processes are sensible heat and latent heat
! sensible heat is heat that can be sensed or measured by a thermometer
! latent heat is heat that is either absorbed or released when a substance changes phase; in atmosphere
related to 3 phases of water
o energy released from transformation of liquid water to water vapor is latent heat of vaporization
Heat Transfer
! 3 processes of atmospheric heat: conduction, convection and radiation
! conduction is the transfer of heat thru a substance by means of atomic or molecular interactions. Requires
a difference in temp within the substance; heat will move from an area of greater temp to one of less temp
! convection is the transfer of heat by the movement of a fluid; convection cell is circulation loop;
convection imp in transferring heat in thunderstorms
! radiation is wave-like energy emitted by a substance that possess heat; transfer of energy by radiation
occurs by oscillations in electric and magnetic fields; thus the waves are called electromagnetic waves
8.2 Earth’s energy balance
! energy that reaches the earth from the sun affects the atm, ocean, land, and living things before being
radiated back into space
! earth’s energy balance is the eq’m b/w incoming and outgoing energy
! energy changes form repeatedly and in a complex manner from the time it reaches Earth to the time it
leaves, but it is neither created nor destroyed
! earth intercepts only a tiny fraction of the total energy emitted by the sun, but the intercepted energy is
adequate to sustain life
! solar energy also drives the hydrologic cycle, ocean waves and currents and global atmospheric
circulation
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! geothermal heat, derived from the interior of the planet, accts for only a fraction of 1 % of earth’s total
energy budge, although it is this internal heat that moves earth’s litospheric plates which in turn generates
EQ and volcanic eruptions
Electromagnetic energy
! much of the energy emitted by the sun is EM energy
! it has a wave form and travels thru space at or near the speed of light
! wavelength: distance b/w the crests and troughs of two successive waves
! various types of EM radiation are distinguished by their WL and the collection of all possible WL is
called EM spectrum
! EM waves with long WL include radio waves and microwaves
! Waves with short WL of less than 0.01 um are x-rays and gamma rays
! IR radiation imp for maintaining temperatures in earth’s atm that allow the planet to support life
! Levels of UV radiation at earth’s surface influenced by planet’s magnetic field and by ozone in the upper
atm
Radiation, Absorption and Temperature
! radiation and absorption of EM energy are affected by temperature and reflectivity
! object’s temp influence the amt and type of EM radiation it emits
o hot objects emit more EM energy than cool objects
! amt of energy radiated from an object each second is proportional to the 4th power of the object’s surface
absolute temp (Kelvin’s)
o if surface temperature of the object doubles, the radiated energy increases 16 times
! object’s temperature also affects the WL of the EM radiation it emits
o hot objects radiate energy more rapidly and at shorter WL than do cool objects
! absorption of energy is similarly affected by surface temperature
o cold object on earth’s surface will initially absorb a large amt of incoming solar energy and therefore
warm up
o as it warms, object begins to radiate more energy
o with constant input of energy, object will eventually reach an eq’m temp that allows it to absorb and
radiate energy at the same rate
Reflectivity
! color of an object plays a role in absorbing and radiating energy
! albedo is an object’s ability to reflect EM energy
! dark surfaces absorb and radiate EM energy readily and thus have low albedos
! light-coloured surfaces reflect EM energy rather than absorb it and have relatively high albedos
8.3 The Atmosphere
! atm is the thin envelope of gases that surrounds earth
! made up of gas molecules, suspended soil and liquid particles and falling rain and snow
! it is responsible for the weather we experience and it keeps earth warm enough to be habitable
Composition of the Atms
! mainly made up of N and O2 but it contains smaller amts of argon, H2O vapor and CO2
! water vapour plays an imp role in cloud formation and atmospheric circulation
! humidity: amt of water vapor, or moisture in the atms at a specific temp
o commonly changes with temp, because warm air can hold more moisture than cold air
o amt of moisture in the air is expressed by relative humidity, the ratio, or percentage, of the water vapor
present in the atms to the maximum amt of water vapor that could be there
! almost all water vapor in atms is evaporated from water on earth’s surface
! snow and rain remove water from atms and deposit it on earth where it may enter groundwater, rivers,
lakes and glaciers
! eventually this water evaporates and returns to the atms to begin the cycle again
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Structure of the Atms
! it lies below an altitude of 100 km
! it consists of 4 layers or spheres
! troposphere is the lowest level and it extends about 8 km to 16 km above the surface of the planet
! upper boundary of troposphere is called tropopause
! defining characteristic of troposphere is the rapid decrease in temp upward, but the most visible feature is
abundant condensed water vapor in the form of clouds
! most water vapor condenses in the troposphere, leaving very little water in the higher layers of the atms
! it contains the most of atmospheric CO2 and methane
! only ozone is less abundant here than it is in upper atms
! clouds comprise small water droplets or ice crystals
! puffy fair-weather cumulus clouds and towering cumulonimbus clouds (release a lot of energy during
thunderstorms thru condensation of water vapor)
8.4 Weather Processes
Atmospheric Pressure
! aka barometric pressure: weight of a column of air at a point on or above earth’s surface
! also thought of as the force exerted by gas molecules on a surface
! greater at sea level than at the top of a mountain, where there is less air above the surface
! all weight, pressure of atms is below an altitude of 50 km
! it differs over distances of 10s to 100s of km across earth’s surface and these differences strongly affect
weather
! air rises and cools in areas of low atmospheric pressure; as the air cools, water vapor condenses to form
clouds and precipitation
! areas of high pressure, drier air slowly descended producing clear skies
! air in high pressure areas may be cold or hot depending on such factors as the time of year
! changes in temperature, water vapor content, and movement of air are responsible for horizontal
variations in atmospheric pressure
! air flows horizontally from areas of high pressure to areas of low pressure; thus, atmospheric pressure
differences are a major driving force for wind
Unstable Air
! air can also move because of vertical heterogeneity of the troposphere
! tendency of a parcel of air to remain in place or to change its vertical position is referred to as
atmospheric stability
! air mass is stable if its parcel resist vertical movement or return to their original position after they have
moved
! air mass is said to be unstable if its parcel rises until they reach air of similar temperature and density
! atmosphere becomes unstable when lighter warm air is overlain by denser cold air; under these conditions
the instability causes some parcels of air to sink and others to rise like hot air balloons
! air turbulence and severe weather area associated with unstable atmospheric conditions
Coriolis Effect
! air moving from high pressure area to low pressure area tends to flow along a straight path
! our frame of reference rotates beneath the flowing air masses causing winds to take a curved path
! changes in motion or deflection is known as the Coriolis Effect
! winds deflected to the right in the N. Hemisphere and to the left in the left in S. Hemisphere
! winds along the equator not affected by CE
Fronts
! boundary b/w a cool air mass and warm air mass
! cold front forms when cool air moves into a mass of warm air
! stationary front is one with a boundary that does not move much
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