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TRANSCRIPT
Weather
Atmospheric condition in one place during a limited period of time
Climate
Weather patterns that an area typically experiences over a long period of time
Many factors influence weather & climate
No factor is more influential than the earth’s position in relation to the sun
Let’s review with a quick video
Axis
An imaginary line running from pole to pole at an angle of 23.5 degrees
Because of the angle, not all places receive the same amount of direct sunlight at same time
Rotation
One complete west-to-east spin on the axis
Takes 24 hours
While rotations take place, the earth is traveling in an orbital path around the sun
This is called a revolution
Takes 365.25 days
Combination of tilt & revolution creates distinct seasons for most places in the world
Seasons are reversed for areas north & south of the Equator
We call March 21 & September 23 “equinoxes”
Marks the beginning of spring/fall
These lines represent the northernmost and southernmost places where direct rays hit the earth…this happens on “solstice” days
June 21: rays hit Tropic of Cancer
December 22: rays hit Tropic of Capricorn
These dates represent the start of summer/winter
Length of daylight for a place varies year-round based on how much direct & indirect sunlight the place receives
Amount of sunlight at the poles varies more dramatically than in any other place on earth
At North Pole, the sun never sets from March 20-September 23
At South Pole, sun never sets from September 23-March 20
Therefore, if one goes to northern Alaska in the summertime, the sun rarely sets
Conversely, in the wintertime the sun rarely appears
Remember: at the equinox, the sun is directly above the equator
Let’s review with a quick video
Earth’s atmosphere traps much of the warmth from the sun
Without this “greenhouse effect” the earth would be too cold for most living things
Levels of carbon dioxide in the atmosphere have risen rapidly in recent decades as a result of human interaction with the environment
Scientists call the coinciding rise in global temperatures “global warming”
This is controversial
Worst case scenario: melting of ice caps & mountain glaciers that could cause a rise in sea levels that would submerge coastal lands
There are four major factors that affect climate
LATITUDE
ELEVATION
WIND & OCEAN CURRENTS
NEARBY LANDFORMS
There are three latitude zones Within each zone, climates follow patterns
Low Latitudes (Tropics) Runs from tropic line to tropic line Area is warm or hot almost year-round
Rainfall varies from place to place High Latitudes (Polar)
Includes areas north of Arctic Circle & south of Antarctic Circle
Cool to cold almost year-round Low and High Latitude zones have less
temperature change through the year because the amount of solar energy remains relatively constant
Mid-Latitudes (Temperate)
Includes everything else Has dramatic seasonal weather changes
Equator
Tropic of Cancer
Tropic of Capricorn
Antarctic Circle
Arctic Circle HIGH
LOW
HIGH
MIDDLE
MIDDLE
90
90
0
23 1/2
23 1/2
66 1/2
66 1/2
Graphic created by EJoyce
What causes the temperature differences?
Air gets thinner as altitude increases
Thinner air retains less heat
Despite fact that sunlight is brighter in higher places
As elevation increases, temperatures decrease
For example, Mt. Kilimanjaro, near the equator in Africa, has snow year round
Wind occurs because the sun heats up the Earth’s atmosphere & surface unevenly
Interaction of warm air & cool air as well as pressure systems
All areas have prevailing wind patterns
They tend to be horizontal
They have names based on their locations
Trade winds are north & south of equator
Westerlies are in mid-latitude areas
Polar easterlies are in polar areas
Area near equator is called the “doldrums”---least amount of wind
Ocean currents are caused by many of the same factors that cause winds
Cold water tends to flow from poles to the equator
Warm water tends to flow from equator to the poles
Wind patterns & ocean currents have one major thing in common
They either cool or warm up areas they pass or hit
North Atlantic Drift, a warm-water ocean current, keeps Europe mild despite its northern latitude
Coastal lands tend to have less dramatic changeable weather
Less variance in rainfall & temperatures
Another important landform impact is the “orographic cycle” also known as the “rain shadow effect”
Winds that come in from the ocean are pushed upward when the meet a mountain range
The coastal or “windward” side is typically cooler and wet
As the winds reach the interior or “leeward” side of the mountain, the air is drier and warmer
Many times deserts develop in leeward regions
Windward side of
the Mountain
Leeward side of
the Mountain
Rain
Shadow
Graphic created by EJoyce
While the text and other references discuss numerous categories of climates, we will focus on just four
Tropical
Mid-Latitude
High Latitude
Highlands
Different climate types exist within each category
Different vegetation types also exist within each climate category
Between equator and poles
Experiences more seasonal changes in climate than tropical or high-latitude regions
Near the equator
High year-round temperatures
Can be wet (rain forest) or arid (dry, desert)
Near the poles
Low year-round temperatures
High mountainous areas
Usually maintain low year-round temperatures, regardless of their location
For example, the Himalaya Mountains show cold on this temperature map despite the latitude zone.
El Nino is a periodic reversal of the pattern of ocean currents & water temperatures in the Pacific
Causes precipitation to increase along the western coasts of North & South America
Causes drought in Southeast Asia & Australia
La Nina does the direct opposite
No one really knows why either of these two climatic events take place
Mid-latitudes are regions most prone to violent storms
Why? Wind patterns tend to cross over in the mid-latitude region
U.S. experiences more tornadoes than any other country
Most massive storms develop in the tropics, but can end up being most destructive in the mid-latitudes
Hurricanes in the Atlantic
Typhoons in the Pacific
Cyclones in the Indian
Definition of a front
Two air masses of widely different temperatures or moisture levels meet
Rainfall tends to happen along these fronts
Once again, the mid-latitudes are the regions that are most prone to frontal systems
High pressure system
Contains a region of sinking air
Usually creates clear skies and fair weather
Low pressure system
Contains a region of rising air
Usually creates clouds, rain and strong winds
Hurricanes are extremely low pressure systems