Chapter 2: Weather and Climate

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Introduction to GeographyPeople, Places, and
Environment, 6eCarl DahlmanWilliam H. Renwick

• Chapter 2 Weather and Climate
• Holly Barcus
• Morehead State University
• And Joe Naumann
• UMSL

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Weather Climate affect us in many ways
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Major Factor in Habitability of Areas

• Affects human comfort levels
• Affects the costs of living and working in an
  area extremely high cost of mineral extraction
  in mineral-rich Siberia
• Affects the agricultural products that can be
  produced

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Weather and Climate

• Weather
• Day-to-day variations in temperature and
  precipitation
• Climate
• Statistical summary of weather conditions through
  time
• Definition The average yearly pattern of
  precipitation and temperature.

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Weather Conditions

• Examples storms, temperature
• Movement of energy
• Fundamental features of Earths surface
• Regulate natural systems
• Limit human use of environment

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Weather Climate

• Whereas climate is the average annual pattern of
  precipitation and temperatures for an area,
  weather is the momentary, and very temporary,
  condition of the atmosphere.
• Weather is experienced moment by moment
• To experience the climate of an area, one must
  live there for many years. To truly experience
  climate, one must experience the extremes as well
  as the averages.

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Solar Energy

• Radiant energy from sun (insolation)
• Powers circulation of atmosphere and oceans and
  supports life on Earth
• Varies across Earths surface

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Insolation

• Amount of energy intercepted by Earth
• 2 factors
• Intensity of solar radiation
• Duration of sunlight

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Intensity of Solar Radiation

• Angle of incidence
• Varies daily seasonally
• Axial tilt 23.5 degrees
• Lower angle larger area lesser intensity
• Higher angle smaller area greater intensity

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Earth-Sun Relationships Click the Stonehenge
picture below to see video

• Even in ancient times, humans were able to
  observe that the relationship differed from day
  to day in a cycle.

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Air Temperature

• Earth Inclination (23.5º tilt of the axis is
  responsible for the seasons and redistributing
  the heat energy received)
• Reflection and Reradiation human actions can
  affect this
• The Lapse Rate 3.5 per 1000 feet
• Decrease with ascent
• Increase with descent

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Latitude

• Sun is directly overhead at the equator
• March Equinox March 20 or 21
• September Equinox Sept. 20 or 21
• June Solstice June 20 or 21
• Tropic of Cancer
• December Solstice
• Tropic of Capricorn
• Hemispherically Correct Terminology used above

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Earth Inclination (tilt of axis)

• 23½ tilt from the vertical.
• Check Tropics of Cancer Capricorn
• Check Arctic Antarctic Circles
• Relationship or coincidence?

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Length of Day

• Total heat received by a place is dependent upon
  the number of hours of sunlight and its intensity
  (angle of inclination)
• Equator
• Higher latitudes

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Seasonal change in insolation in the middle
latitudes

• The angle at which the suns rays strike the
  earth change from day to day as a result of the
  tilt of the earths axis, not because the sun
  moves.

North of the Tropic of Cancer and south of the
Tropic of Capricorn, the rays never strike at a
right angle (perpendicular)
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What if the axis were perpendicular?
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Seasonal Variation in Radiation

• Varies because of angle of incidence, day length,
  distance from sun
• Equator
• High latitudes
• Temperature

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Tilt of the Earths Axis --

• Responsible for changing lengths of days
  throughout the year
• Responsible for seasons
• Responsible for variability of insolation

Helps redistribute and moderate temperatures
keeping the tropics from being even hotter and
the poles colder.
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Energy Balance
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Solar Heat Storage

• Heat is absorbed by and released from objects
• Water absorbs and releases more heat than land
• Land heats and cools more quickly and to a
  greater extent than water
• Water is a moderating influence on temperatures

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Differential Heating of Land and Water
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Adiabatic Process

• Water vapor in the atmosphere affects the
  heating/cooling rate of air
• Latent heat (stored in water vapor) affects
  temperatures
• Latent heat exchange (transfer of heat from lower
  altitudes to higher ones) is very important in
  causing precipitation.

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The Three States of Water
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Adiabatic Process Video click the thermometer to
see the video

• For our purposes, we will only consider the dry
  lapse rate.
• 3.5F increase per 1000 foot decrease.
• 3.5F decrease per 1000 foot increase

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Heat Transfer

• Responsible for movement of energy from place to
  place on Earth
• Radiation (radiant energy)
• Electromagnetic waves
• Heat (short waves converted to long waves)
• 2 wavelengths Short (sun - light) and long
  (Earth - heat)

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Greenhouse Effect

• Short vs. long waves
• Greenhouse gases
• Critical to heat exchange
• Water vapor, carbon dioxide, ozone, methane
• Increased greenhouse gases increased global
  warming

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Greenhouse Effect

• Click the greenhouse to see the video

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Greenhouse effect Global Warming

• Click the greenhouse to see the video

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Latent Heat Exchange

• Transfers energy from low to high latitudes
• Causes precipitation
• Two types
• Sensible
• Detectable by touch
• Latent
• In storage in water and water vapor
• Latent heat exchange (adiabatic process)

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Heat Exchange Atmospheric Circulation

• Convection
• Upward movement of fluids caused by heating
• Boiling water
• Atmosphere
• Advection
• Horizontal
• movement of air
• Monsoons

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Wind Definition

• Wind is the horizontal movement of air from a
  high pressure area to a low pressure area.

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Sea Breeze

1. Warm air over land rises (low)
2. Sea Breeze moves inland
3. Cumuli develop aloft and move seaward
4. Upper level return land breeze
5. Cool air aloft sinks over water (high)
6. Sea Breeze (meso-cold) Front

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Land Breeze

1. Cool air over land sinks (high)
2. Land Breeze moves out over water
3. Relatively warmer water heats air which then
   rises (low)
4. Upper level return sea breeze
5. Cool air over land sinks

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Radiation, Heat Migrating Tropical Low (ITC)

• Notice that the more intense radiation zones move
  from north of the equator to south of the equator
  and back caused by the axis tilt

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The Tropical Low (ITCZ) Driving Engine of the
Wind System

• There is a seasonal lag in the shifting of the
  wind belts.

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Apparent shifting of direct radiation from the
sun and the resulting wind belts
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Hydrologic Cycle Temperature/ Precipitation
Relationship
Water vapor is continually changing from a gas to
a liquid and from a liquid to a gas. Where it is
cold enough, the change also involves ice.
Click this diagram to see a video
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Precipitation

• Normal precipitation
• Condensation
• Conversion of water from vapor to liquid state
• ALL air holds water
• Dependent on temperature
• Saturation vapor pressure
• Maximum water vapor air can hold at a particular
  temperature

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Relative Humidity

• Water content of air
• Percent of water air could hold at a given
  temperature
• Fluctuates hourly as temperature changes
• Saturation point condensation
• Condensation clouds

Temperature Relative Humidity
86 degrees F 50 if holds half water vapor possible
71 degrees F 75
60 degrees F 100
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Precipitation 3 Types

• (1) Convectional precipitation
• Warm, humid rises, expanding and cooling
• Saturation point is reached
• Clouds form
• Adiabatic cooling
• Decrease in temperature that results from
  expansion of rising air
• Convectional storms

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(2) Orographic Precipitation

• Wind forces air up and over mountains
• Rain on windward side
• Desert on leeward side Rain shadow
• Examples
• Cascades Sierras
• Rockies
• Exception Appalachians

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(3) Frontal Precipitation

• Air forced up a boundary between cold and warm
  air masses
• Air mass
• Region of air with similar characteristics
• Cold front
• Cold air mass moves towards warm air mass
• Typical weather
• Warm front
• Warm air mass moves towards cooler air mass
• Typical weather

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Frontal (Cyclonic) Precipitation curving
rotation come from the Coriolis effect.
Normally, a mass of warm air rises above a mass
of cooler air when the two masses meet. As the
warmer mass cools, there is condensation and
possibly precipitation.
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Cold front closes the gap
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Circulation Patterns

• Air mass 14.7 lbs per square inch
• Atmospheric pressure
• Varies with altitude
• Higher altitude less atmospheric pressure
• Barometer
• Maps use isobars

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Jet Streams

• Fluctuations in the jet streams affect the
  behavior of various air masses.
• Their immediate effect is on weather.

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Air Masses Affecting N. America

• St. Louis winter cyclonic (frontal)
  precipitation
• St. Louis summer convectional precipitation

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Pressure and Winds

• Air density
• Warm air less dense
• Pressure gradient
• Difference in pressure between two places
• Coriolis Effect
• Indirect, curving path of wind caused by rotation
  of the Earth
• Strongest in polar regions

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Click the picture to see the Flash animation
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Global Circulation

• 4 zones
• Intertropical convergence zone (ITCZ)
• Convectional precipitation
• Trade winds
• Subtropical high-pressure zones
• Areas of dry, bright sunshine, little
  precipitation
• Midlatitude low-pressure zones
• Polar front
• Westerlies
• Polar high-pressure zones
• Dense air, high pressure
• Little precipitation
• Seasonal variations

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Wind Belts

• In April, the belts start shifting to the north.

• In October, the belts start shifting to the south.

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Monsoon a seasonal shifting of wind direction.

• Wind horizontal movement of air from a high to a
  low pressure area
• Where? -- South, Southeast, East Asia
• Southeastern U.S. (not as pronounced in the U.S.)

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Our Water World

• Surface 70 water
• Water moves horizontally, vertically, and
  obliquely
• Some movement results in heat transfers
• Polar waters to equatorial areas visa versa
• Upwelling of water from depths of 200 ft. plus
• Slow descent of surface waters
• Some movement doesnt transfer heat
• Storm activity, tidal movements, seismic waves
• Ocean currents are those movements that transfer
  heat

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Ocean Circulation Patterns

• Wind creates waves and currents
• Gyres
• Wind-driven circular flows
• El Niño
• Occasional shifts in ocean circulation

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North Atlantic Drift Moderates European
Temperatures
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Characteristics of Ocean Currents in the
three-dimensional oceans

• Cold a relative term
• Warm a relative term
• High salinity a relative term
• Weakly saline a relative term
• Occurring at great depth
• Occurring at intermediate depths
• Occurring at the surface

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Prevailing Winds Influence Ocean Currents

• Between tropics greatest volume of water flows to
  the west
• Influenced by the northeasterly trade wind belt
  and the southeasterly trade wind belt solar
  power?
• Small countercurrent between them
• When the westerly currents reach continental
  shores are deflected poleward (Coriolis force)
• In the midlatitudes, the prevailing westerlies
  propel the ocean currents to the east
• Result circulating systems (gyres)
• Clockwise circulation in northern hemisphere
  counterclockwise circulation in southern one.

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El Nino Click the CD to see the video

• La Nina produces the opposite effects

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The Oceans Role in the Ecosystem

• Redistributes heat preventing greater extremes at
  the tropics and the poles
• Poles less cold
• Tropics less hot
• Source of atmospheric humidity (evaporation)
• Home of abundant plant and animal life valuable
  food sources
• Phytoplankton produce much oxygen

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Precipitable Water Vapor
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Storms

• Cyclones
• Large low-pressure areas
• Winds
• Counterclockwise in Northern Hemisphere
• Clockwise in Southern Hemisphere
• Hurricanes and typhoons
• Tropical cyclones
• Need warm, moist air
• Most powerful over oceans
• Storm surge
• Elevated sea level in center of storm
• Midlatitude cyclones

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Severe Storms Click the picture of a warm front
to see the video
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Climate

• Summary of weather conditions over several
  decades or more
• Influences
• Changes over time
• Humans and climate
• 2 primary measures
• Temperature
• Precipitation

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Air Temperature
Frequently encountered terms Tierra
Caliente Tierra Templada Tierra Fria

• Variation
• Latitude
• Seasonal solar energy input
• Elevation
• Topography

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Precipitation

• Variable between places and through time
• Worldwide variation 0-120 inches
• Global circulation patterns
• Amount of precipitation
• Reliability
• Regularity
• Soil saturation
• Human adjustments

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Classifying Climate

• Allows analysis and planning
• Communication
• Köppen System
• Wladimir Köppen, 1918
• Distribution of plants
• 5 basic climate types with subdivisions
• Most widely used system

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Climate Regions

• Horizontal bands based on latitude
• Climate regions similar to
• Bioregions/Vegetation Retions
• Temperature and precipitation maps
• Other influences (see next slide)

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CLIMATE VARIABLES Lamppost!

• Latitude
• Altitude
• Maritime Influence
• Pressure Systems
• Prevailing Winds
• Ocean Currents
• Storms
• Topography

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Climate System Model
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Humid Low-Latitude Tropical Climates (A)

• Warm all year
• Humid tropical (Af, Am)
• /- 10 degrees N/S of equator
• Warm humid Little seasonal temp. variation
• High temps Rain
• Amazon River Basin, Equatorial Africa, Islands of
  South East Asia
• Seasonally humid tropical climates (Aw)
• Concentrated rainfall
• Seasonal shifts of ITCZ
• Central South America

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Dry Climates (B)

• Dry climates, BW BS
• 35 of Earths land area
• Border low latitude humid climates on North and
  South
• North Africa, Central Asia
• Desert climates (BWh, BWk)
• Warm and dry
• Subtropics
• New Mexico (BWh), China (BWk)
• Semi-arid climates (BSh, BSk)
• Transitional areas between deserts and humid
  areas
• Grasslands, steppes
• Seasonal temperature contrasts

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Warm Mid-latitude Climates (C)

• Seasonal temp variation (4 seasons)
• Reversed seasons in the southern hemisphere
• Less precipitation
• Humid subtropical (Cfa, Cw)
• Latitude 25-40 degrees on east side of
  continents
• Eastern China, SE US, Brazil, Argentina
• Marine west coast (Cfb, Cfc)
• Continental west coasts, 35-65 degrees
• Mild climates
• California to coastal Alaska, Southern Chile
• Mediterranean climates (Cs)
• Dry summers with seasonal precipitation

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Cold Mid-latitude Climates (D) Only found in
the northern hemisphere

• Humid continental climates (Dfa, Dwa, Dfb, Dwb)
• Strong contrasts
• Remote from oceans little moisture
• 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

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None in southern hemisphere

• St. Louis on border between Dfa Cfa to the south

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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

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USA Climatically Blessed

• Within the 50 states and Puerto Rico, the USA has
  some of every type of climate in most
  classification systems (variations of Kopen
• The US can produce at least some of every type of
  food and industrial crop in the world
• No other country has this distinction
• The USA has relatively large areas of climate
  that have the potential to be highly productive
  agriculturally

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Climate Change 3 hypotheses or a combination of
them

• Astronomical
• Geometry of Earths orbit
• Sunspots
• Geologic
• Continental drift
• Volcanic eruptions
• Human (human actions may accelerate or exacerbate
  changes in the other two)
• Atmosphere pollution global warming
• Vegetation massive destruction of biomes

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Climate change is very complex.

• Inconstant Climates historical evidence of
  significant changes dynamic, not static
• Cyclical Change cycle of wet and dry years in
  the Midwest around St. Louis
• Have we identified all the various cycles?
• More frequent El Niño years? Linked to human
  actions?
• Human Actions
• Global Warming
• Great reduction of the rainforests
• Major humidity pumps for the atmosphere
• Major oxygen producers (often overlooked feature)

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More about climate cycles

• El Niño La Niña period between them may be
  shortening
• The Dust Bowl was the result of a cycle of wet
  and dry years in the Great Plains that humans did
  not understand

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Human Impact on the Arctic Click the map to see
the video

• Global warming
• Ozone depletion
• Resource extraction
• Settlement

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Solar powered world
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Solar-Powered World

• So many things on earth depend on the sun that it
  may not be an understatement to say that we live
  on a solar-powered world.
• Without the sun the earth would be frozen and
  lifeless
• Sun warms the earth to a range of temperatures
  where a variety of chemical compounds exist as
  solids, liquids, or gases in some places H2O
  can exist in all three.

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More solar-powered world

• H2O, particularly in liquid state is vital to
  practically every form of life on earth
• Sunlight provides the energy for photosynthesis
  which produces plant food
• Basis of food chain
• Uses CO2 and produces O2
• Solar energy results in variable heating and
  cooling of the earth surface, thereby causing
  wind and driving the wind belts.
• Ocean currents are partly solar-powered because
  the wind belts influence them.

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More solar-powered world

1. Tilt of the earths axis helps distribute the
   insolation over a larger parts of the earths
   surface and causes the seasons.
2. Burning fossil fuels is merely releasing energy
   that plants received from the sun and locked into
   their cells long, long ago.
3. Burning wood (hasnt had time to become a fossil
   fuel) is also merely releasing energy that plants
   received from the sun and locked into their cells

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Solar Powered World fossil fuels
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Interactions With Climate

• Soil
• Decomposer activity
• Moisture content
• Vegetation food chain base
• Succession of plants climax vegetation
• Available water
• Streams ground water

Everything is interconnected in the biosphere.
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Natural Vegetation

• Develops in response to soil and climate
• Influences soil by providing the organic matter
  or humus i.e. rainforest feed itself
• Influences climate
• Evapotranspiration provides much of the humidity
  the cutting down of tropical rainforests may
  result in decreased precipitation and prevent the
  reestablishment of rainforests
• Reaches and maintains a climax vegetation
  condition as long as climate remains constant and
  human actions dont interfere.

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Tropical Rainforest Exists on Extremely Poor Soil
Very poor, lateritic soil
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How Physical are the Physical Factors in the
Biosphere?

• The human impact on climate and other physical
  systems is a serious problem!

The end of Chapter 2