More Climatic Interactions
What is wind? The movement of air in a horizontal direction
What causes wind? The uneven heating of the Earth causes differences in air pressure.
Why does this happen? The Sun’s energy is more concentrated at the Equator and spread out more over the poles. Air over the equator is warm and less dense and has lower pressure. Air over the poles is cold and denser and has higher pressure.
Why does this happen? As warm air at the equator rises, cooler air from the poles will move in and replace it. Air pressure moves in a pattern from high to low.
Convection As warm air at the equator rises, cooler air from the poles will move in and replace it.
Global Convection Currents
The density changes caused by temperature changes create convection cells. These cause circular patterns of air that circulate over the whole planet.
Global Wind Belts Where the convections cells meet, prevailing winds and jet streams form. They blow from one direction over a certain area of the Earth’s surface.
Jet Stream Forms high in the upper Troposphere between two air masses of different temperatures Higher temperature difference = faster speed Due to the Coriolis Effect, it flows around air masses. Polar Jet: It dips southward when frigid polar air masses move south. It tends to stay north in the summer months.
Jet Stream Animation
Prevailing Winds Named for the direction from which they blow:
Polar Easterlies – High latitudes blow east to west toward the equator Westerlies – Mid latitudes blow west to east toward the poles Easterlies (Trade Winds) – Low latitudes blow east to west toward the Equator
Prevailing Winds Pressure belts form in between the wind belts.
MoreDirect Sun Hot 0 o Equator 30 o S 60 o S 90 o S 30 o N 60 o N
Global Wind Belts The winds from the poles blow toward the equator.
The winds from the equator blow toward the poles.
If wind is moving north and south, …
…then why is it defined as the horizontal movement of air? *Reflection Question* Does the Earth stand still?
The Coriolis Effect As the Earth rotates counterclockwise, the winds bend and curve around the Earth. Gustave-Gaspard Coriolis, an engineer and mathematician, described this effect as an inertial force in 1835.
The Coriolis Effect In the Northern Hemisphere, winds bend to the right of their direction of travel. In the Southern Hemisphere, winds bend to the left of their direction of travel. Let’s try a little investigation to see how this works.
The Coriolis Effect Weather patterns and systems move in a circular motion due to the bending of the winds caused by the Earth’s rotation.
Equilibrium Our Earth is always seeking balance.
In an effort to find balance, there is a continuous cycle of patterns. Reflection Question* What is the driving force behind the changes that create these patterns?
Reflection Question How are winds produced?
Ocean Currents Warm currents flow away from the equator.
Cold currents flow toward the equator.
Factors Influencing Currents
Sun Wind Coriolis Gravity
Sun Energy from the Sun heats the water.
Warm water is less dense that cold water. Warm water rises, and cold water sinks. As warm water rises, cold water moves it to replace it.
Wind Just as wind moves from high pressure to low pressure areas, so does the water. Winds blow across the surface of the water, causing friction. The water piles up because the surface currents flow slower than the winds.
Gravity As water piles up and flows from high pressure to low pressure, gravity will pull down on the water. This forms vertical columns or mounds of water. The Coriolis Effect causes the water to curve.
The Coriolis Effect Causes water to move to the right in the Northern Hemisphere Causes water to move to the left in the Southern Hemisphere
The Coriolis Effect
Surface Currents Make up 10% of oceans’ water
Up to maximum depth of 400 m Surface ocean currents are caused by the surface wind patterns.
Gyres Vertical columns or mounds of water at the surface and flow around them Produce enormous circular currents Five major locations: North Pacific - clockwise South Pacific - counterclockwise Indian Ocean - counterclockwise South Atlantic - counterclockwise North Atlantic - clockwise
Gulf Stream A strong surface current Begins at the tip of Florida
Flows up the eastern coastline of the U.S. Crosses the Atlantic Ocean Causes warmer climate in NW Europe
Upwelling Surface waters blow to the right of the wind.
As less dense, surface water moves off shore, cold, deep, denser waters come to the surface to replace them.
The Great Ocean Conveyor: Helps maintain Earth’s Balance
Deep Water Currents Make up about 90% of oceans’ water
Differences in density cause them to move. Differences in density are related to temperature and salinity. At high latitudes, they sink deep into the ocean basins. Temperatures are so cold, they cause the density to increase.
Reflective Question How are ocean currents produced?
El Nino Abnormally high surface ocean temperatures off the coast of South America Causes unusual weather patterns across the globe
El Nino Starts because the easterly trade winds weaken and allow the warm waters in the Western Pacific to move east toward South America This changes where the convection current occurs. Causing rain where it usually doesn't occur and drought where it usually rains
El Nino Winter
El Nino Summer
La Nina Abnormally low surface ocean temperatures off the coast of South America Causes unusual weather patterns across the globe
Ocean’s Effect on Climate
Ocean currents move more slowly than winds. Oceans hold more heat than the atmosphere and land. Cold currents will cause nearby coastlines to be cooler. Warm currents will cause nearby coastlines to be warmer. Where do the cold currents come from? The warm currents?
Predictable Patterns How do these currents affect the climate of the coastline?
Reflection Questions How do our oceans impact climate?
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