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Lecture

ATOC 184 Lecture Notes - Physical Law, Hot Air Balloon, Ageostrophy


Department
Atmospheric & Oceanic Sciences
Course Code
ATOC 184
Professor
Imad Mansour

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EXAM REVIEW SHEET
PROPERTIES
Temperature
temp= average speed of molecule movement in a substance ( and dependent on property of
material you are dealing with) eg: stove (movement in vibrates for solid things)
temp of air= energy of all air molecules that surround us.
Movement= faster for higher temperatures
Absolute zero= zero kelvin where molecules stop moving
Celcius= linked with water (vs human comfort) 100 celcius= water boils
Where is warmest temperaturs on planet? At equator
Warmest and coldest temps= over land because water heats up and cools more slowly than
land does (so water= larger heat capacity because it takes more energy to heat up water)
If we had more land= rate of global warming would be higher
Energy source= the sun (tilt of earth). How much heat we get is related to amount of photons
that hit an area. When the sun is directly overhead, spot there receives more photons and is
thus hotter aka the equator.
Angle and tilt and distance(diming further away)= are the things that determine how warm or
how cold areas of the planet get
Seasons= axis of rotation. Season variations at equator= much less (more constant temps).
Canada= huge temp variations.
When air is warm= molecules become more energetic, move faster and collide more
Pressure
Fx=mx (mass times acceleration = force)
Pressure= force atmosphere is applying on ground
Atmospheric pressure: measuring force of air in column above us.
When pressure is higher= more mass above us
Pressure drops rather quickly when you go up in height (9km-> 66% drop of pressure)
Fewer oxygen molecules higher up you go(ex: mountain climbing)
The higher the pressure is, the more the molecules per square inch. Therefore, the molecules
get more sparse as you go aloft since pressure decreases.
Pressure change more vertically than horizontally ex: CN tower vs NYC and Boston
MAP: where values are high= pressure is high
Highs= rising up of air
Low= sinking down of air
Gravity pulls molecules towards surface( more molecules at surface than aloft)
Air molecules= in motion and colliding. Number of collisions= determines pressure (more
collisions= higher pressure).
As # of molecules decrease with height= pressure decreases. When we have a lot of molecules,
pressure= high.
If the pressure remains the same but temp increases, volume must increase (due to than
spacing out more because there is no boundary to collide to walls unlike containers). Cold
temp= molecules pack down.
Molecules travel from areas of high concentration to areas of low concentration.= pressure
gradient (change of pressure across distance)
Regions that are warm= thickness is larger
WIND= motion of air molecules from regions of high to low concentrations
When pressure isn’t uniform: air molecules try to balance out (from high to low pressure via
force). Atmosphere tends to exhibit a balance between vertical pressure gradient going
upwards and gravity . So wind doesn't blow much up or down due to this balance.
Layers of atmosphere:
o Troposphere (temp decreases as we go up) Ozone= reason why weather is confined to
troposphere. (stratosphere= lighter and hotter EX: OIL AND WATER)
o Stratosphere (temp goes up because ozone absorbs radiation of the sun)
o Mesosphere
o Thermosphere

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Tropopause: line between troposphere and stratosphere
o Takes up more place at equator than north pole because warm air takes up more space
than cold air.
Jet Stream
Wind= movement of air
Regions where wind is blowing faster than everywhere else (wind blows as result of diff. in
pressure from one location to the next)
Strong difference in temp= strong difference in pressure (warm air takes up more space than
cold air) which leads to creation of jet stream
Jet stream= demarcates where cold cold air masses and warm air masses will be
North of jet= cold & south of jet= hot (divider between relatively warm air and cool air)
Expect storms to follow stream. Jet stream moves due to temperature gradient.
Wind= direction FROM
PLOTTING WIND:
WATER
Water in all 3 forms: liquid, gas, ice
Water vapour on earth= concentrated in specific areas (usually where storms are occurring
and mostly located in clouds)
Water vapour= 0-6% of actual atmosphere
Force exerted by water vapour= vapour pressure. In cold atmosphere, pressure is near zero
and can go up to 60mb. [vapour pressure= can separate pressure for each gas in atmosphere]
IMAGE: areas that are bright= moist
GET Water vapour through the evaporation of water
Dewpoint= temp at which condensation starts to occur.
If dewpoint and temp is the same= then you are in a cloud
Dewpoint can’t be higher than air temp because liquid falls out from the sky and there is a
removal of moisture from atmosphere at that point
More water vapour in summer (cant hold water when really cold)
o because it is easier to evaporate water than ice and the sun is hotter so we have more
energy as well.
o The warmer the atmosphere= higher the capacity for water vapour is because warmer
temp increases speed of molecules and since they are more energetic it is harder for
than to bond together into liquid molecules
o Capacity for water vapour= saturation vapour pressure
Vapour pressure= amount of pressure associated with water molecules
When capacity for air to hold Water Vapour increases, the relative humidity drops
Saturation vapour pressure= largert amount of pressure that we have have in atmosphere at
given time (how much atmosphere can hold)
Relative humidity= vapour pressure/ saturation vapour pressure
Dewpoint gives actual vapour pressure
Actual temp gives saturation vapour pressure
Relative humidity goes up and night and down during day. Temp at night= cooler. Capacity for
air to hold WV decreases so RH rises.
MEASUREMENTS
Synoptic measurements=take measurements simultaneously across the globe in Greenwhich
meantime
Weather station: temp sensors, instruments to measure height of clouds etc, measurements
provided by instrument= recorded every hour (or every minute when weather is interesting)

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Stations across N.A= density of stations= where population is and near water bodies
5 centers in Canada, 300 approx in USA
How important is # of station? Weather can change a lot across short distance ex: jet stream
Meteogram: trace of temp, dewpoint and weather and recreates time traces of weather for any
station
READ CONIDTIONS
Weather buoys (reading over water and measure wave height)
Rawinsodes= weather balloons (with instrument package and launched 2 times a day. GPS =
get idea of wind. Also measures pressure. 75 stations
o Allows us to get readings from higher up in atmosphere and at surface as well
Radar: transmits microwave energy
o Sends a signal
o How heavy precip= how much is reflected back (large reflectivity= heavy precip)
Need targets for radar beam to hit
Once radar beam bounces off of something, can tell through frequency and if
thing is moving away or towards radar and how fast
Doppler Radar: (tells us about precip and wind through reflectivity
o Doppler effect= car goes by (at rate which sounds waves reach air, high pitch vs low
pitch) The rate at which sound wave is hiting ear as it gets closer gets quicker and
increases in pitch.
Satellite images
o A) Infrared
Brightest= high clouds aka colder clouds & cold surface
Darkest= low clouds= warm clouds & warm surface
Times wont be able to tell if there is cloud or not due to little diff. of temp of
cloud and ground.
As cloud grows= temp at top of cloud gets colder and colder
Water vapour= regions bight= moist and dark= dry
Hurricane= concentration of WV
o B) Visible satellite images (what you could see if you were looking at earth)
Cant use at night
Brightest= thick clouds and snow (hard to tell diff.)
Darkest= water and forests
What we see on visible satellite is dependant on albedo of thing (aka how
much sunlight something reflects). Snow and clouds don't have much of a
different in albedo)
o C) Satellites for NA= GOES W and GOES E= don't move
Aircraft reports, better when going up or down in altitude because then we can have a good
picture of atmosphere wheres if not, just measures at one point in altitude
Lightening Detection: crackling in radio signal due to energy wave wend out by lighteing that
causes interference EX: lightening, many stations close by will receive signal so sensors can
determine location and strength of lightening
TEMP AND THICKNESS
Temp is dropping, atmosphere takes up less space.
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