Introduction to Geography
Chapter 2: Weather and Climate
Weather and
Climate
► Weather
 Day-to-day
variations in
temperature and
precipitation
► Climate
 Statistical summary
of weather
conditions through
time
Solar Energy
► Radiant
energy from sun
 Small amount intercepted by Earth
► Powers
circulation of atmosphere & oceans
► Supports life on Earth
► Varies across Earth’s
surface
Insolation
► Amount
of energy
intercepted by Earth
► 2 factors
 Intensity of solar
radiation
► Angle
of incidence
 Duration of sunlight
► Varies
by season
Intensity of Solar Radiation
► Varies
daily & seasonally
► Seasonal angle depends on latitude
► Tilt of Earth’s axis = 23.5 degrees
Total Insolation
►Total
amount of solar
radiation from seasonal
changes in:
 Length of daylight
 Distance from the Sun
►Tropical
areas
►High latitudes
World Temperatures—January
World Temperatures—July
Storage of Heat
► Variable
ability to store heat depends on
material
► Water absorbs and releases more heat than
land
► Therefore…
 Greater seasonal difference in temperatures in
mid-continent areas in high latitudes (Asia,
North America)
 Moderate climates near water
Heat Transfer
Responsible for movement of energy from place to
place on Earth
► Radiation (radiant energy): energy transmitted by
electromagnetic waves (heat, light, radio, TV)
► Wave length
►
 Shortwave:
► Insolation
► Passes
through
atmosphere
 Longwave:
► Energy
reradiated
from Earth
► Most blocked by
atmosphere
(greenhouse effect)
Greenhouse Effect
►
Greenhouse gases
 Transparent to shortwave but absorb longwave
 Water vapor, carbon dioxide, ozone, methane
Increased greenhouse gases = increased
global warming
► Additions by
human
activities,
probably 
global warming
►
Latent Heat Exchange
► Transfers
energy from low to high latitudes
► Causes precipitation
► Two types
 Sensible
►Detectable
by touch
 Latent
►“In
storage” in
water & water
vapor
►Latent heat
exchange
Heat Exchange & Atmospheric
Circulation
► Evaporation
of water from surface of the oceans
► Water vapor rises in the atmosphere
► Converted to water (rain) or ice (snow)
► Powered by convection:
movement of fluid
when heated
► Advection = horizontal
movements of air
 AKA wind
Condensation
► Conversion
of water from vapor to liquid
► Capacity of air to hold water vapor:
 Depends on temperature
► Condensation
► Cooling
= clouds
air
 Causes increase in
relative humidity
 Saturation point =
condensation
 Cooling beyond
saturation 
condensation (clouds)
Relative Humidity
►Relative
humidity: actual water content of
air, expressed as percentage of what air
could hold
► Fluctuates as
temperature
changes
Temperature
Relative Humidity
86 degrees F
50% if holds half water vapor possible
71 degrees F
75%
60 degrees F
100%
Convectional Precipitation
► Adiabatic
cooling:
cooling of warmed air
as it rises (1ºC per 100
meters; 5.5ºF. per
1000 feet)
► “Normal”
precipitation
► ALL air holds water
 Depends on
temperature
► Responsible
for large
portion of precipitation
Orographic Precipitation
►Air forced to rise
►Adiabatic cooling
► Rain
on windward
side
► Desert on leeward
side: Rain shadow
► Examples
 Cascades & Sierras
 Rockies
over mountains
from expansion
Frontal Precipitation
► Air
forced up boundary between cold & warm air
► Front:
boundary between two large air masses
► Cold air advancing
= cold front
► Warm air advancing
= warm front
Air Masses
► Air
mass
 Region of air with
similar characteristics
► Air
masses form if air
remains over a uniform
surface long enough
for it to acquire
uniform properties
► In
North America
 Continental polar air
(cold)
 Maritime tropical air
(warm)
Fronts
► Cold
front
 Cold air mass
moves towards
warm air mass
► Warm
front
 Warm air mass
moves towards
cooler air mass
Pressure and
Winds
► Dependent
on conditions
 Varies with altitude
► Measured
with barometer
► Pressure gradient
 Difference in pressure
between two places
 Air moves from high to low
pressure
Coriolis Effect
►Deflection
of wind above
rotating Earth
 N Hemisphere: to the right
 S Hemisphere:
to the left
►Cells
rotating
clockwise &
counterclockwise
Global Circulation
►
4 zones
 Intertropical convergence zone (ITCZ)
► Warm
air rising
► Convectional precipitation
► Trade winds
 Subtropical high-pressure
zones
► Descending
of air from ITCZ
► Areas of dry, bright
sunshine, little precipitation
 Midlatitude low-pressure
zones
► Converging
warm & cold air
► Polar
front
► Westerlies
 Polar high-pressure zones
► Dense
air, high pressure
► Little precipitation & cold
Worldwide Pressure and Winds (January)
Worldwide Pressure and Winds (July)
Ocean Circulation Patterns
► Wind
creates
waves and currents
► Gyres
 Wind-driven
circular flows
► El
Niño
 Occasional shifts in
ocean circulation
Storms
► Cyclones
 Large low pressure areas
 Winds
► Counterclockwise
► Clockwise
in S
Hemisphere
 Cyclone: low
pressure cell
► Air
converges &
ascends
 Anticyclone:
high pressure
cell
► Air
descends &
diverges
in N Hemisphere
Hurricanes
► Tropical
Cyclones
 Need warm, moist air
► Most
powerful over oceans
 Storm surge
► Elevated
sea level in center
of storm
 Regional Names
► Hurricanes
► Typhoons
► Tropical
cyclones
 Tropical Disturbances
► Tropical
depressions
 Winds 38 mph or less
► Tropical
storm
 Winds 39-73 mph
► Tropical
Cyclone (Hurricane)
 Winds 74 mph and above
Hurricane Katrina
August 28, 2005
Hurricane Names
► Cyclone
is named when winds hit 39mph
 Began in 1953
► Originally
just used female names
 Alternation began in 1979
► Use
a 6 year rotation list
 http://www.nhc.noaa.gov/aboutnames.shtml
 Retired names
►http://www.nhc.noaa.gov/retirednames.shtml
31
Hurricanes
►
Eye
 Non-stormy hurricane center
►
Eyewall
 Zone at edge of eye where
wind speeds are highest
►
Eyewall replacement
 Process where new wall of
storms surrounds wall of
storms circling the eye
►
Spiral rainbands
 Intense bands of T-storms
rotating counterclockwise
around storm
32
Storms
► Midlatitude
cyclones
 Large migratory lowpressure system in
the mid-latitudes,
moving in the
direction of the
westerlies
 Responsible for
majority of day-to-day
weather changes
 Bring precipitation to
much of world’s
population
Climate
► Summary
of weather conditions over long period
► Influences





Hours of daylight
Precipitation
Temperature
Winds
Pollution
► Changes
over time
► Humans and climate
► 2 primary measures
 Temperature
 Precipitation
Air Temperature
►Changes
with elevation (6.4ºC per 1000
meters; 3.5ºF. per 1000 feet)
►Affected by:
 Topography
 Proximity to
oceans
 Water
availability
Precipitation
►Variability
over time and space
 Worldwide variation = 0-120 inches
► Reliability
& regularity
Classifying Climate
► Include
temperature and precipitation, effects of
temperature on water availability to plants
► Wladimir Köppen, German geographer (1918)
 Used distribution of plants
 Advantage of effect on other environmental
factors
 5 basic climate
types with
subdivisions
 Most widely
used system
Classifying Climate
Climate Regions
► Horizontal
bands based on latitude
► Climate regions similar to
 Bioregions
 Temperature and precipitation maps
► Other
influences
 Continents
 Mountains
Humid Low-Latitude Tropical
Climates (A)
► Warm
& humid all year
► Humid tropical (Af, Am)
 +/- 10 degrees N/S of
equator
 Little seasonal temp.
variation
 High temps; rain
► Seasonally
humid
tropical climates (Aw)
 Concentrated rainfall
► Seasonal
shifts of ITCZ
Dry Climates (B)
►
Dry climates, BW & BS
 35% of Earth’s land area & 10% of
Earth’s population
 Border low-latitude humid climates
on North and South
►
Desert climates (BWh, BWk)
 Warm and dry
 Subtropics
►
Semi-arid climates (BSh, BSk)
 Transition areas between
deserts & humid areas
 Grasslands, steppes
 Seasonal temp. contrasts
Warm Midlatitude
Climates (C)
►
Seasonal temp variation & less precipitation
 Must be able to survive cold season
► Weather
►
related to fronts & temp.
Humid subtropical (Cfa, Cw)
 25-40°N/S on E side of continents
►
Marine west coast (Cfb, Cfc)
 Continental west coasts,
35-65°N/S
 Mild climates
►
Mediterranean climates (Cs)
 Dry summers with seasonal
precipitation
Cold Midlatitude
Climates (D)
►
Humid continental climates (Dfa,
Dwa, Dfb, Dwb)
 Strong contrasts
 Remote from oceans
 Interior & eastern side of Northern
Hemisphere Continents (35-60
degrees)
►
Subarctic climates (Dfc, Dwc, Dfd,
Dwd)
 Northern edge of humid
continental climates
 No agriculture
 Northern Hemisphere only
 Vegetation: Boreal forests
Polar Climates
(E)
► High-latitude
climates
► Low temps
► Extreme seasonal
variability
► Tundra climate (ET)
 Permafrost
 Tundra
► Ice-cap
climates (EF)
 Near poles & high
altitudes at low latitudes
Climate Change
►3
hypotheses
► Astronomical
 Variations of Earth’s orbit
 Sunspots
► Geologic
 Continental drift
 Volcanic eruptions
 Mountain ranges
► Human
 Atmosphere
 Vegetation
Climate Change
►Time
scale of observations determine what
patterns of change stand out in the record
►Determining Climates of the Past




Dendrochronology
Oxygen isotope analysis of oceanic sediments
Ice cores
Pollen analysis
46
47
Global Warming
► 20th c. warming: 1º C (1.8º F.)
 Link with increased carbon dioxide (CO2)
► Evidence of global warming
 Computer models & historic climate data
► Consequences of global warming
 Rise in sea level & increase in extreme weather
► Dealing with global warming
 Develop means to adapt & measures to counteract effects
End of Chapter 2