Transcript Climate and Weather - Chadwick School | Haiku Learning

Climate and
Weather
The lower atmosphere - composition
 Historically
– H2, CH4, NH3, H20,
etc.
 Currently
– 78% N2, 21% O2, 1%
Ar, .038% CO2
– varying amounts of H2O
vapor (1-4%)
– Oxygen added by
action of organisms
(which?)
The Atmosphere – its layers
 Troposphere
– extends from surface to 17km
– 75% of total mass of
atmosphere
– where weather occurs, air
currents etc.
– highest atmospheric pressure
– temperature decreases with
altitude
 ends at tropopause
– Source of natural greenhouse
effect
The Atmosphere
 Stratosphere
– extends from 17km to 48km
– contains less matter than
troposphere
– ozone layer (1000x more than
trop.)
– very little water vapor (1000x less
than trop)
– very calm (good for flying), no
weather, suspended matter will
stay for many years,
Climate and Weather
 What is weather?
 What is climate?
Climate and Weather Topics
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Solar radiation
Convection Currents
Coriolis effect
Rain shadow effect
Jet streams
Frontal weather
Cyclonic storms
Seasonal winds
ENSO
Milankovich cycles
CLIMATE
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The two most important aspects of climate
are temperature and precipitation.
– These two factors determine what type of
species (biome) will be found in a given
location.
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The climate in an area is determined by
1. Latitude
2. Direction from which winds arrive
3. Proximity to large bodies of water and
mountains
Solar Radiation
 The same amount of
sunlight hits the equator
and poles.
 However, at the poles the
light is spread over a wider
area resulting in less
intense sunlight, and less
heating.
 So, the equator is warmer
than the poles.
Convection Cells
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Warm air rises; cold air falls
Warm air holds more moisture than cold air
When air rises, it cools; when air falls, it warms
SO, warm, moist air rises, cools, and loses moisture as
rain; cool, dry air falls, warms, and picks up moisture from
the ground.
Cool, dry
precipitation
warm, dry
Warm, moist
Global Convection Cells
 Wet areas (warm, moist air rising)
– 0o(equator) - TRF
– 60o (Seattle) - TempRF
 Dry areas (cold, dry air falling)
– 30o - desert
– 90o (poles) – tundra
Surface Wind Currents
 The air traveling between these points travels
primarily north or south over the Earth’s surface
to complete the cells.
 This gives rise to prevailing winds that are
predictable in all areas of the world. They have
been used by sailors for centuries.
Coriolis Effect - Cont
 As the earth spins, the air currents (which would ordinarily
travel mostly north-south) are deflected by the Coriolis
effect.
– Deflected to right in NH and left in SH
 Coriolis video
 This causes winds to form huge circular paths – clockwise
in the N. Hem and counter-clockwise in the S. Hem.
Effect of Oceans and Mountains
 Oceans
– Being near a large body of water tends to minimize
temperature fluctuations because of water’s high
specific heat capacity
 Ex. coastal areas in CA are warmer in winter and cooler in
summer than inland areas.
Rain-shadow effect
 In areas where there is a strong on-shore wind pattern
and coastal mountains, there is a pattern of wet coastal
sides and dry inland sides of the mountains.
 Mountains force warm, moist air upward;
– Air cools, decreasing moisture holding capacity
– windward side is rainy
 Dry, cool air at the top of the mountain descends the to
other (leeward) side
– the moisture-holding capacity  as air warms
– moisture is sucked from the ground, causing desert
Longterm Effects on Climate Milankovich Cycles
 The Earth’s tilt and orbit
tend to wobble over time
– Orbit stretches and shrinks
in a 100,000yr cycle
– Axis tilt changes in a
40,000yr cycle
– Axis wobbles in a 26,000yr
cycle
 These variations impact
solar radiation and result
in climatic fluctuations
 These also limit our ability
to know what is “natural”
variation and what is
“human-induced”
variation in temperatures
WEATHER: Jet Stream
 Giant rivers of air that
flow around the earth.
 Their location (north
and south) determine
which areas receive
storms
 Their speed dictates
how fast weather
systems move across
land masses.
Fronts
 A front is a boundary
between two air masses
of different temps (and
pressures).
– Warm front – approaching
air is warmer than local air
– Cold front- approaching air
is colder than local air
– Both can cause rain; cold
fronts are associated with
more severe weather
Cyclonic storms
 masses of rotating air
caused by pressure
differentials between
the ground and air.
 Tornadoes and form
over land are more
localized
– Form with
thunderstorms
Typhoon/Cyclones/Hurricanes
 Form in many areas
in the world near
tropics
– US hurricanes mostly
form off Africa north
of equator.
 Are fed by warm
water
 Decrease with
– Wind shear
– Moving over cold
H2O
– Moving over land
 Spin CC in NH and
C in SH
Seasonal Winds
 Many parts of the
world experience
seasonal winds, or
wind direction
reversals
– Ex. monsoons (rain
shadow effect)
– Sirocco
– Santa Anas
El Nino (ENSO)
 The winds in the
Pacific normally blow
across the surface of
the water in the
Westward direction
 This causes
– Rain in Indonesia, mild
winters in CA,
upwelling off the coast
of S.Am., cold surface
waters on Eastern Pac.
La Nina is an increased
flow in this direction.
El Nino (ENSO)
 In El Nino years, the
winds blow across the
surface in the Eastern
direction
 This causes
– Drought in Indonesia,
wet winter in CA, (due to
movement of jet stream)
– no upwelling (fish and
mammal die-offs),
– warm surface water in
Eastern Pac.