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Weather and climate
 Weather
 Weather is over a short
period of time
 Constantly changing
 Climate
 Climate is over a long
period of time
 Generalized composite
of weather
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Weather and climate
 Elements of weather and climate
 Temperature
 Humidity
 Cloudiness
 Precipitation
 Air Pressure
 Winds speed and direction
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Earth’s
Atmosphere
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Atmosphere: Temperature Profile
 Temperatures vary you
move from the earth’s
surface out into space
Ozone formation
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Atmosphere: Temperature Profile
 The stratosphere
 Chlorofluorocarbons in the ozone layer
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Reduce ozone concentrations
Have created a recurring ozone hole
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Changes of State
 Water uniquely occurs
naturally as solid, liquid
and gas in the
atmosphere
 Energy is absorbed or
liberated as water
changes state
 The amount of heat per
gram absorbed or
liberated is known as
latent heat
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Water Phase Changes
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Humidity
 Humidity: the amount
of water vapor in the air
 Saturation: the
condition when air
cannot hold any more
water vapor
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Humidity
 Relative humidity
 Water vapor content of
air compared to
saturation level
 Specific humidity
 The actual mass of
water vapor in the air
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Atmospheric heating
 Incoming solar radiation
 Reflection – albedo
(percent reflected)
 Scattering
 Absorption
 Most visible radiation
reaches the surface
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Atmospheric heating
 Outgoing Radiation
 Earth re-radiates radiation (terrestrial radiation) at the
longer wavelengths
 Terrestrial radiation is absorbed by
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Carbon dioxide and
Water vapor in the atmosphere
Lower atmosphere is heated from Earth's surface
 The greenhouse effect
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Atmospheric Energy Balance
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Solar Heating and Atmospheric
Circulation
 Air at high elevations is:
 Cooler
 Expands
 Water vapor tends to
condense
 Air at sea level is:
 Warmer
 More compressed
 Can hold more water
vapor
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Solar Heating & Latitude
Indirect – less sun, less heat, spread over wide area,
most energy is reflected, amount varies with season
Direct – more sun, more heat, concentrated in
small area; most energy absorbed; constant
year-round
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Air Circulation & Convection
Currents
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Coriolis Force
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Atmospheric Circulation &
Convection Cells
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Temperature measurement
 Daily maximum and minimum
 Other measurements
 Daily mean temperature
 Daily range
 Monthly mean
 Annual mean
 Annual temperature range
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Temperatures & Location
Mean monthly temperatures
for Vancouver, British
Columbia and Winnipeg,
Manitoba
Mean monthly temperatures
for Eureka, California and
New York City
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Temperature measurement
 Human perception of temperature
 Important factors are
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Air temperature
Relative humidity
Wind speed
Sunshine
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Controls of temperature
 Temperature variations
 Receipt of solar radiation is the most important
control
 Other important controls
 Differential heating of land and water
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Land heats more rapidly than water
Land gets hotter than water
Land cools faster than water
Land gets cooler than water
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Controls of temperature
 Other important controls
 Altitude
 Geographic position
 Cloud cover
 Albedo
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World mean sea-level
temperatures in January
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World mean sea-level
temperatures in July
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Hydrologic Cycle
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Adiabatic cooling of rising air
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Cloud Formation
 Condensation
 Ground: Grass, car windows, etc.
 Atmosphere: tiny bits of particulate matter

Condensation nuclei, dust, smoke, ocean salt crystals which
serve as hygroscopic ("water seeking") nuclei
 Formation
 Made of millions and millions of
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Minute water droplets, or
Tiny crystals of ice
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Cloud Formation
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Precipitation
 Cloud droplets
 Less than 20
micrometers (0.02
millimeter) in diameter
 Fall incredibly slow
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Precipitation
 Formation of precipitation
 Collision-coalescence process
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Warm clouds
Large hygroscopic condensation
nuclei
Large droplets form
Droplets collide with other droplets
during their descent
Common in the tropics
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Precipitation
 Types of upward
movement of air
 Orographic,
 Convectional,
 Thunderstorms and
Unstable Air
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Orographic precipitation
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Convectional Precipitation
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Thunderstorms and Unstable Air
 When the environmental
temperature lapse rate
exceeds the dry (and wet)
adiabatic rate
 Rising air remains warmer
than its surrounding air
 Leads to strong, persistent
convection
 Clouds with intense
vertical development
 Cumulonimbus clouds
and thunderstorms
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Precipitation
 Forms of precipitation
 Rain – droplets have at least a 0.5 mm diameter
 Drizzle – droplets have less than a 0.5 mm diameter
 Snow – ice crystals, or aggregates of ice crystals
 Sleet – Small particles of ice
 Glaze, or freezing rain – impact with a solid causes
freezing
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Atmospheric Pressure
 Pressure exerted by Earth’s
atmosphere because of the
weight of overlying air
 Standard sea level pressure
1013.2mb
 Measuring device: barometer
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Works by measuring how
much weight can be
supported by air pressure
Air pressure decreases with increasing altitude
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Pressure and Wind
 Wind – horizontal motion of air
 Caused by differences in atmospheric pressure
 Air moves in response to differences in pressure
 Maximum pressure change is perpendicular to these
lines (pressure gradient)
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Local / Regional Winds
 Sea & Land Breezes
 Valley & Mountain Breezes
 Foehn winds
 Katabatic winds
 Monsoons
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Sea Breeze
In the morning, the air over land warms
quicker than that of the ocean
Air moves off the ocean and onto the
land
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Land Breeze
The air over the land cools faster than
that over the sea
Warmer air over the sea rises, and the
cooler air over the land moves in to take
its place
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Valley Breezes
Mountain Breezes
 During the day, the mountain
 During the evening, the
heats up faster than the valley.
 The air above the mountain
heats up, rises, expands, and
creates a mini low pressure
system.
 The cooler air in the valley is updrafted along the mountain
slopes
mountain cools down faster than
the valley.
 The air above the mountain
cools, sinks, becomes more
dense, and creates a mini high
pressure system.
 The cooler air is down-drafted
along the mountain slopes
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Foehn winds
A type of dry down-slope
wind which occurs in the lee
(downwind side) of a
mountain range.
“Rain-shadow” wind
Source: 1, 2,
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Katabatic winds
A wind that carries
high density air from
a higher elevation
down a slope under
the force of gravity
Santa Ana winds
Source: 1, 2
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Circulation Cells
Hadley Cells
 Air rises at equator (forms low
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pressure / ITCZ)
Goes across the upper atmosphere to
30° N/S
Meets air in Ferrel Cell moving
towards 30° N/S
Air sinks at 30° N/S (forms high
pressure / horse latitudes)
Goes across the surface of the earth
towards the equator (trade winds)
Meets air in other Hadley Cell
moving towards the equator, where
the . .
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Circulation Cells
Ferrel Cells
 Air sinks at 30° N/S (forms high
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pressure / horse latitudes)
Goes across the surface of the earth
towards 30° N/S (westerlies)
Meets air in Polar Cell moving
towards 90° N/S
Air rises up at 90° N/S (forms low
pressure / supolar low)
Goes across the upper atmosphere
towards 30° N/S
Meets air in Ferrel Cell moving
towards 30° N/S, where the . . .
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Circulation Cells
Polar Cells
 Air rises at 90° N/S (forms low
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pressure / supolar low)
Goes across the upper atmosphere to
the poles
Meets air in the other Polar Cell
moving towards the poles
Air sinks at the poles (forms high
pressure / polar high)
Goes across the surface of the earth
towards 90° N/S (polar easterlies)
Meets air in Ferrel Cell moving
towards 90° N/S, where the . . .
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Pressure Systems
 Doldrums (Equatorial Low)
 aka (ITCZ)
 Horse Latitudes
(Subtropical High)
 Subpolar Low
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Wind Belts
 Trades – 15ºN & 15ºS latitude
 Westerlies – 45ºN & 45ºS latitude
 Polar Easterlies – 75ºN & 75ºS
latitude
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Winds High Above the Surface
 The Coriolis effect modifies
the wind due to the pressure
gradient
 In the northern hemisphere,
winds are pulled to the right until
the pressure gradient and the
Coriolis force balance
 The wind consequently blows
with a steady speed and direction
 This is the geostrophic wind
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Winds in the Upper Atmosphere
Rossby Waves
 The geostrophic wind deflected to the west constitutes
the upper air westerlies
 The warm tropical air interacts with the cold polar air
 Causing wave like undulations in the circulation
patterns
 Pockets of warm and cold air form high and lows
 Create variable weather in the mid-latitudes
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Rotating Air Masses
Bends in the polar jet create troughs and ridges
Forms cyclones and anticyclones
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Cyclones
Low pressure zone in polar jet
trough
Winds at surface flow
counterclockwise towards the
core
Air is updrafted and cooled
Forms clouds, rain and upper
level outflow of air
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Anticyclones
High pressure zone at ridge of
polar jet
Air converges in upper
atmosphere
Descends towards the ground
Flows outward at surface
Dry, windy conditions
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Air masses are classified on the basis of their
source region
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Fronts
 Types of fronts
 Warm front
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Warm air replaces cooler air
Shown on a map by a line with semicircles
Small slope (1:200)
Clouds become lower as the front nears
Slow rate of advance
Light-to-moderate precipitation
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Fronts
 Types of fronts
 Cold front
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Cold air replaces warm air
Shown on a map by a line with triangles
Twice as steep (1:100) as warm fronts
Advances faster than a warm front
Associated weather is more violent than a warm front
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Cold Fronts and Warm Fronts
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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.
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Stages in the development of a
thunderstorm
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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)
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Lightning Varieties
Volcanic Lightning
Nuclear Lightning
Triggered Lightning
(NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)
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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
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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
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Tornado Wind Patterns
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Hurricane Origins
Cannot form at the equator (Coriolis effect = 0)
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Hurricanes
 How a Hurricane Works
 Tropical disturbance
 Tropical depression
 Tropical Storm
 Hurricane
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The Eye
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Hurricane Wind Patterns
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