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Ch. 7 and
Supplement 7
Weather and Climate
Adapted from Ms. Sealy’s ppt
Weather
– The short-term day-today changes in
temperature, air
pressure, humidity,
precipitation, sunshine,
cloud cover and wind
direction and speed.
– Most weather is
predicted using:
weather balloons,
aircraft, radar, and
satellites
Climate
– is the long term average
precipitation and temperature of an
area
– is determined by air pressure,
albedo, angle of sunlight, clouds,
distance to oceans, fronts, heat
(convection), land changes, latitude,
location, humidity, mountain ranges,
pollution, rotation, wind patterns and
human
– Climate is what you expect,
weather is what you get!
Climate
is
the average weather patterns for an area over
a long period of time (30 - 1,000,000 years).
It is determined by
Average Precipitation
and
Average Temperature
which are influenced by
latitude
altitude
ocean currents
and affects
where people live
how people live
what they
grow and eat
Fig. 6.3, p. 123
Climatograms
• Shows the precipitation and
temperature on one graph. Easy
to compare biomes
ATMOSPHERIC
CIRCULATION PATTERNS
• KEY PROPERTIES OF AIR
– Cold air is more dense than warm
air
– Cold air sinks and warms
– Warm air rises and cools
– Warm air can hold more water vapor
than cold air
– As air cools, it cannot hold as much
water vapor, so it may precipitate
Weather Changes
• Air Mass: a large body of air that has
similar temperature and moisture
level throughout.
• Air Masses that affect the US are cA,
cP, mP, mT and cT
When air masses meet, the
boundary between them is
called a front and it causes
changes in weather
•
Cold front: when a cold air mass
collides with a stationary warm air
mass. The result is:
thunderstorms, short bursts of
heavy rain
Warm Front:
•
when a warm air mass collides
with a stationary cold air mass.
The result is: warm steady rain
Air Pressure
Atmospheric pressure is highest near
Earth’s surface due to weight of air
above.
Plotting areas of same pressure (isobars,
usually measured in mm Hg) shows
high and low pressure areas.
High and Low Pressure
High pressure = cold,
dense air, descends
toward surface; usually
means fair weather.
Low pressure = warm,
less dense air; rises,
expands then cools; often
cloudy, stormy. If there’s
enough water and
condensation nuclei
present, rain results.
Weather is also affected by
changes in atmospheric
pressure
•
High pressure has descending air that
moves outward from the center of the
high-pressure system. Descending air
is warm and dry. The result is: nice
dry weather
•
Low pressure
has ascending air that flows
towards the center of the lowpressure area. Ascending aircools and condenses as it rises.
The result is: clouds, rain
Energy Transfer by Convection
in the Atmosphere
Convection Cell
Global Air currents affect
regional climates
•
•
•
Uneven heating of the Earth’s surface
causes the equator to receive more
sunlight making it hotter
The poles receive less light making
them cooler.
This causes areas of high and low
pressure and global circulation of
winds as air moves from high to low
pressure
Cold
Cool Temperate
Warm Temperate
Tropical
(equator)
Tropical
Warm Temperate
Cool Temperate
Cold
Fig. 6.6a, p. 125
Climate type
Easterlies
(from the east)
60°N
Westerlies
(from the west)
Northeast
tradewinds
30°N
(Doldrums)
equator
30°S
60°S
Initial pattern of
air circulation
Southeast
tradewinds
Westerlies
Easterlies
Deflections in the
paths of air flow
near the earth’s surface
Fig. 6.6b, p. 125
Seasons
•
•
Seasonal changes in temp and
precipitation affect climate
because the earth is tilted on its
axis. It is colder in the winter and
warmer in the summer because:
The earth is tilted 23.5° on its
axis
Spring
(sun aims directly
at equator)
Winter
(northern hemisphere
tilts away from sun)
23.5°
Solar
radiation
Summer
(northern hemisphere
tilts toward sun)
Fall
(sun aims directly at equator)
Fig. 6.5, p. 124
Coriolis Effect
•
Rotation of
the Earth on
its axis
prevents air
currents from
moving
directly north
or south
causing the
winds to
curve
• http://www.classzone.com/books/
earth_science/terc/content/visuali
zations/es1904/es1904page01.cf
m
http://www.sciencehouse.org/nesdis/upwelling/bac
kground.html
Albedo
• Is the reflectivity of a surface to
solar radiation.
• Snow= high albedo (0.8)
• Water= low (0.07)
• Forest = .05-0.1
• Average albedo of the earth is
0.37
Altitude
• For every 1000 feet, there is a 3°F
drop in temperature.
• Every 300 feet in elevation is
equivalent to a shift of 62 miles
north in latitude and biome
similarity.
CLOUDS
Ocean currents
• Surface currents
– Driven by wind (10%)
• Deep water currents
– Driven by density and gravity
Influenced by
•
•
•
•
Solar heatingWinds
Gravity
Coriolis
• http://www.montereyinstitute.org/n
oaa/lesson08.html
• http://www.montereyinstitute.org/n
oaa/lesson08/l8la1.htm view at
home
Polar (ice)
Warm temperate
Highland
Warm ocean current
Subarctic (snow)
Dry
Major upwelling zones
Cold ocean current
Cool temperate
Tropical
River
Fig. 6.4, p. 124
– Ocean Currents Affect climate
•
•
Differences in water temp, winds and
the rotation of the earth create
currents.
Currents redistribute heat. For
example the Gulf Stream brings
heat to Europe and moderates the
climate
OCEAN CIRCULATION
PATTERNS
• Water holds a lot of heat – has
a high heat capacity.
• This means water takes a long
time to heat up and a long time
to cool off
• Oceans moderate climates
– Coastal areas have warmer winters
and cooler summers
Water also changes climate by causing land
breezes and sea breezes
Cool air
descends
Warm air ascends
Land warmer than
sea; breeze flows
onshore
Fig. 6.15a, p. 130
Cool air
descends
Warm air
ascends
Land cooler than
sea; breeze flows
offshore
Fig. 6.15b, p. 130
Upwelling
•
Upwelling is created when the
trade winds blow offshore
pushing surface water away
from land. The outgoing
surface water is replaced by
nutrient bottom water
Wind
Movement of
surface water
Diving birds
Fish
Upwelling
Zooplankton
Phytoplankton
Nutrients
Fig. 6.9, p. 126
The El Nino Southern
Oscillation occurs every few
years in the Pacific Ocean
– In an ENSO, prevailing westerly winds
weaken or stop
– Surface waters along the coast of
North America and South America
(west) become warmer
– Normal upwelling stops
– This reduces the population of some
fish species
– Also causes severe weather, storms in
the US especially CA, and drought in
southeast Asia
Surface winds
blow westward
EQUATOR
AUSTRALIA
Warm waters
pushed westward
SOUTH
AMERICA
Warm water
Thermocline
Cold water
Normal Conditions
Fig. 6.10a, p. 127
Winds weaken,
causing updrafts
and storms
Drought in
Australia and
Southeast Asia
EQUATOR
AUSTRALIA
Warm water
flow stopped
or reversed
SOUTH
AMERICA
Warm water deepens off
South America
Warm water
Thermocline
Cold water
El Niño Conditions
Fig. 6.10b, p. 127
El Niño
Drought
Unusually high rainfall
Unusually warm periods
Fig. 6.11, p. 127
La Nina
•
•
La Ninas follow an El Nino and
are characterized by cooling
trends. La Nina brings more
Atlantic hurricanes, colder
winters in the north and warmer
winters in the south.
Can lead to wetter winters in the
Pacific NW, torrential rains in SE
Asia, lower wheat yields in
Argentina and more wildfires in
Fla.
The chemical makeup of the
atmosphere affects the
weather.
Small amounts of water vapor, carbon
dioxide, ozone, methane, nitrous oxide
and chlorofluorocarbons trap heat in
the atmosphere warming the planet.
These gases are called: greenhouse
gases
The greenhouse effect is when greenhouse
gases allow light, infrared radiation and UV
radiation through to the surface of the earth
where it is reflected back into space. The
greenhouse gases trap some reflected infrared
radiation
(a) Rays of sunlight penetrate
the lower atmosphere and
warm the earth's surface.
(b) The earth's surface absorbs much of (c) As concentrations of greenhouse
the incoming solar radiation and
gases rise, their molecules absorb
degrades it to longer-wavelength
and emit more infrared radiation,
infrared radiation (heat), which rises
which adds more heat to the
into the lower atmosphere. Some of
lower atmosphere.
this heat escapes into space and some
is absorbed by molecules of
greenhouse gases and emitted as
infrared radiation, which warms the
lower atmosphere.
Fig. 6.13, p. 128
Topography of the earth also
creates microclimates
A microclimate is small area that has a
different climate than the general
climate of an area.
– Vegetation in an area influences climate:
forests stay warmer in the winter and
cooler in the summer because of the trees
–
Cities create heat
islands that trap heat
and decrease wind
speeds
LOCAL GEOGRAPHY
• Mountains Affect Precipitation
• Air rises, cool and rains
• Air descends, warms and draws up moisture
• This creates a
rain shadow effect
where one side
of the mountain
receives most of
the rain and the
other side is very
dry
a Winds carry
moisture inland
from Pacific Ocean
b Clouds, rain on
windward side of
mountain range
Moist habitats
c Rain shadow on
leeward side of
mountain range
4,000/75
3,000/85 2,000/25
1,800/125
1,000/25
1,000/85
15/25
The rain shadow effect changes climate
Mojave Desert is in the rain shadow of the
Sierra Nevada Mts.
Fig. 6.14, p. 129
Weather Extremes
– Hurricanes: most severe of all
•
•
•
What is it? Tropical storm with
winds greater than 75 mph
The bad: loss of life and property
The good: flushes out coastline
• Hurricane Katrina- August 2005
• The most destructive hurricane
(economically ) ever. Landed in
Louisiana as a category 3
• $75 billion and 1,830 deaths
• 1900 Galveston Hurricane
6,000-12,000 died
Tornadoes:
• Form when cold dry air collides
with warm moist air, which
causes the warm air to rise
quickly making a funnel cloud
•
•
•
•
Winds up to 300 mph
Classified as F1-F6 (Fujita)
Most common in US
Usually occur between April-July
and often in the center of the
country (Tornado Alley)
Prince Williams
Sound
Gulf of Alaska
Risk of Tornadoes
Highest
High
Medium
Low
CANADA
UNITED STATES
Grand Banks
Hurricane Frequency
High
Moderately
high
MEXICO
Atlantic
Ocean
Fig. 6.2, p. 122
HOW DO HUMANS AFFECT
CLIMATE?
•
•
•
•
Deforestation
Urbanization
Release of pollutants
Burning of fossil fuels