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
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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
HIGH 90 Arctic Circle 66 1/2 MIDDLE Tropic of Cancer 23 1/2 LOW Equator 0 MIDDLE HIGH Graphic created by EJoyce Tropic of Capricorn Antarctic Circle 90 66 1/2 23 1/2
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 midlatitude 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