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Convection Currents. SNC2D0. Convection. Convection A method of heat transfer in fluids (liquids and gases) Liquid/gas particles move in a circular pattern as they go through a cycle of heating and cooling Convection is the cause of all the wind and ocean currents on Earth

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convection
Convection
  • Convection
    • A method of heat transfer in fluids (liquids and gases)
    • Liquid/gas particles move in a circular pattern as they go through a cycle of heating and cooling
  • Convection is the cause of all the wind and ocean currents on Earth
  • It is driven by the fact that substances undergo thermal expansion
    • Substances get larger when heated
convection1
Convection
  • Thermal expansion
    • As temperature increases, volume increases
    • This decreases the density (D = m/V)
  • Low density fluids float on top of higher density fluids
    • This is why helium balloons float into the air, He is less dense than air
convection2
Convection
  • Therefore, if a fluid is heated, it expands and rises up
    • This leaves a low pressure region behind, and the surrounding cool fluid rushes in
    • This cool fluid is then heated
    • The hot fluid rises to the top and is cooled down
air currents
Air Currents
  • Convection occurs in the atmosphere
    • The sun heats up the land/water
    • The land/water in turn heats the air above it
    • This sets up a convection current in the air
  • The equator gets heated up the most
    • Hot air rises from the equator, leaving low pressure
    • Cool air from the North/South rushes in
    • The hot air that has risen travels towards the poles
    • This sets up a circular convection cell
coriolis effect
Coriolis Effect
  • Since the Earth is spinning, wind that would move in a Northern direction ends up moving East/West as well
  • This effect is called the Coriolis effect
    • If an object is spinning, and something rises off of that object, it has a curved motion
  • Coriolis Free Throw
prevailing winds
Prevailing Winds
  • The Coriolis effect and the convection currents combine to produce prevailing winds
  • Prevailing winds
    • Winds that always move in the same direction
    • Determine climate by moving air (and water) to different places
  • Trade winds
    • NE and SE from equator to 30º
    • Westerlies from 30º to 60º
    • Polar Easterlies 60º to the poles
local winds
Local Winds
  • Wind is also created locally
    • Often by the uneven heating of air due to land and water
    • Land heats/cools quicker than water
  • During the day the land is heated quickly, and heats up the air around it
    • This air rises and pulls the cool air from above the water towards the land
  • At night, the land is cool but the water is still warm
    • The water heats the air, which starts a convection current
    • Pulls air from the land towards the water
ocean currents
Ocean Currents
  • Convection currents occur in water in a similar way to how they occur in air
    • The flow of the water is not identical to the flow of air
  • Water is heated up near the equator
    • This water flows on top of the cooler water below it
    • The heated water flows towards the poles, where it cools
    • The cool water sinks and flows towards the equator
  • As water cools near the poles, it gets saltier
    • Since some of the water freezes, leaving the salt behind
    • This increases the density of the cold water
thermohaline circulation
Thermohaline Circulation
  • Thermohaline circulation
    • The circulation of water on the Earth
    • Driven by heat (thermo) and salinity (haline)
  • Ocean currents have a huge effect on climate
    • Warm water heats the air above it
    • Warm air brings a lot of precipitation with it
    • Cold water cools the air above it, this also dries it out
    • The cold air leads to dry climates when it moves onto land
  • BC and UK vs. Africa and California
homework
Homework
  • Pg 347 # 1 – 7