Download Ch. 25 Climate

Climate
• The average weather conditions for an area
over a long period of time.
Temperature and Precipitation
• Used to define climates
• Daily averages: to estimate the average daily
temperature/precipitation, add the high and low of
the day and divide by 2.
• Monthly averages: to estimate average monthly
temperature/precipitation add all the daily averages
and divide by the number of days in the month.
• Yearly averages: to estimate the average yearly
temperature/precipitation add up all 12 monthly
averages and divide 12.
• Yearly range: the difference between the highest and
lowest monthly averages.
Latitude
• Influences both temperature and precipitation
• Different latitudes receive different amounts of
solar energy.
• Solar energy determines the temperature and
wind patterns of an area.
• The higher the latitude of an area, the smaller
the amount of solar energy received by that
area.
Seasons
• Because the Earth’s axis is tilted, the angle at
which the sun’s rays hit the earth changes as
Earth orbits the sun.
• During winter, the northern hemisphere is
tilted away from the sun, and areas at the
higher northern latitudes face the sun for less
time than during the summer; the days are
shorter and the temperatures are lower
during the winter.
Seasons
The amount of precipitation generally
decreases as latitude increases.
Air rises, cools, condenses
Air sinks, warms, dries
Air rises, cools, condenses
Heat Absorption and Release
• Different areas absorb and release heat differently
• Land heats faster than water and can reach higher
temperatures in the same amount of time.
El Nino – Southern oscillation
“ENSO”
• A cycle of changing wind and water-current patterns in
the Pacific Ocean, every 3-10 years.
• El Nino is the warm water phase of ENSO, causes
surface water temperatures along the west coast of
South America to be warmer.
• During El Nino, typhoons, cyclones, and floods may
occur in Pacific regions and southeast United States.
Other areas may have droughts.
• The southeast U.S. experiences cooler and wetter
winters.
• La Nina is the cooler water phase of ENSO, causes
surface water temperatures along the west coast of
North America to be cooler.
Seasonal Winds
(Monsoons)
• Temperature differences between the land and the
oceans sometimes cause seasonal wind shifts.
• During the summer, the land warms more quickly than
the oceans; the warm air rises and is replaced by cool
air from the ocean.
• The wind moves toward the land, which leads heavy
rains and flooding.
• During the winter, the land loses heat more quickly
than the ocean; the cool air flows away from the land;
the wind moves seaward – dry winds and drought.
Topography
Surface features of the land influence the flow of air.
Elevation
• Temperature decreases with
elevation.
Rain shadows
• When a moving air mass
encounters a mountain,
the air mass rises, cools,
and loses most of its
moisture.
• As a result, it precipitates
on one side of the
mountain;
• And the other side is
usually warm and dry.
– Warm, dry winds that
flow down the mountain
• Foehn (Alps)
• Chinooks (Rockies)
Andes Mountains
Himalayan Mountains
3 Major Climatic Zones
Tropical
Middle-latitudes (temperate)
Polar
Microclimates
• The climate of a small area
Climate Change
• Climatologists study and
compare past and present
climates:
– 1000’s of weather stations
(past and current data)
– Fossils of plants and animals
(environmental clues)
– Ice cores from polar icecaps
(gas composition)
– Tree rings
(wet/dry years)
– Sea-floor sediments
(oxygen levels tell us about
temperature)
• Causes of climate change:
– Plate tectonics (movement of
continents)
– Orbital changes in shape/tilt
– Human activity (CO2 increase)
– Volcanic activity