Thermal Energy Transfer

Recall: Energy and Climate Driving force is solar heat energy (most concentrated at equator and least concentrated at the poles) When warm air rises, it expands and becomes less dense. As altitude ↑, temperature ↓. Air will cool, become denser and sinks. Rising and sinking masses of air in convection currents causes changes in atmospheric pressure, which causes wind (movement of air from high pressure to low pressure)

Global Wind Patterns Polar cell Warm air rises at the equator and cold air sinks at the poles. Rotation of Earth causes the air to form bends of smaller convection currents (cells). Rotation of Earth also causes the wind to appear to turn instead of flowing straight from the Equator to the poles. This is the Coriolis Effect and explains the surface winds (eg. Trade winds). Ferrell cell Hadley cell Hadley cell Thunderstorms form when warm moist unstable air rises into the atmosphere. This air will cool, become more dense and condense to form clouds (and latent heat energy will be released). In the tropic zones, evaporation occurs quickly (esp. in the afternoons when surface heating produces the max number of convection currents in the atmosphere). Ferrell cell Polar cell Research is being done to see if expansion of Hadley cells can be linked to global warming

Jet Streams Band of fast-moving air formed in the upper troposphere between two air masses of different temperatures. Thousands of km long and can be a few km thick Continually curve and meander to the north and south Can carry warm moist air (which can produce localized precipitation further downstream) Can carry cool dry air (which can cause localized dry weather to form) http://www.weatherquestions.com/What_causes_the_jet_stream.htm But how does the temperature difference between two air masses cause the jet stream? Since colder air is more dense than warmer air, there is an air pressure difference between them at any altitude. And if the warm and cold air masses are quite deep, higher altitudes in the atmosphere experience progressively larger air pressure differences.  Since it is horizontal air pressure differences that cause wind, this leads to very strong winds. But at some altitude high in the troposphere, the temperature difference reverses, and as you progress higher the winds then decrease. The altitude at which the winds were strongest is considered to be the jet stream level.  So, the strongest jet stream winds then occur between air masses having the largest temperature differences over the deepest layer of the troposphere.  Even though the wind "tries" to flow from high pressure to low pressure, the turning of the Earth causes the air flow to turn to the right (in the Northern Hemisphere), so the jet stream flows around the air masses, rather than directly from one to the other. 

Ocean Currents Oceans make up a large component of the hydrosphere. They are important because it stores and transports large amounts of heat energy (Recall: H2O has a high specific heat capacity!)

Oceans & Density Two factors affect the density of water: 1) Salinity and 2) Temperature Tropics are warmer. Water evaporates quicker, leaving salt behind, which accumulates and sink. Colder water (eg. Arctic ocean) more dense because of temperature (less evaporation) AND salt. When sea ice forms, the salt does not freeze and is left behind in the water As cold water sinks, it is replaced by the warm water which rises to the surface, creating a current. In this manner, energy is transferred throughout the oceans Ocean currents created by thermohaline circulation http://marinebio.org/oceans/temperature/ http://oceanservice.noaa.gov/education/kits/currents/06conveyor2.html Temperature and density share an inverse relationship. As temperature increases, the space between water molecules increases—also known as density, which therefore decreases. If the temperature of water decreases its density increases, but only to a point. At a temperature of 4°C pure water reaches its maximum or peak density, cooled further it expands and becomes less dense than the surrounding water which is why when water freezes at 0°C it floats. Salinity and density share a positive relationship. As density increases, the amount of salts in the water—also known as salinity, increases. Salinity can decrease from the melting of polar ice or increase from the freezing of polar ice. Evaporation increases salinity and density while the addition of freshwater decreases salinity and density.

Great Ocean Conveyor Belt The ocean water is always churning underneath. The difference in density of cold water versus density of warmer water is responsible for ocean currents. Global wind patterns also push the surface currents in the ocean as well!

Warm water from the Caribbean, Gulf of Mexico and equatorial Atlantic flow northward in the Gulf Stream As it travels to the North, it evaporates, giving up heat to the atmosphere, leaving cold salty dense water that sinks to the ocean floor. Water then flows southward, beneath the Gulf Stream, to the South and begins to warm up and becomes less dense. It makes its way through the Indian and Pacific Oceans and mixes with the warmer water and returns to the Gulf Stream to complete its circulation, which takes 1000 years!

Global Warming and Thermohaline Circulation Global warming causes an increase in the overall temperature of Earth. Leads to melted ice at the poles = less saline water (due to ↑ freshwater) = less dense water = does not sink Leads to ↑ evaporation at the tropics = more saline water = more dense = sinking ↑ in freshwater would slow or reverse the thermohaline circulation or stop it entirely resulting in uneven distribution of energy in the ocean Other things impacted: coastal communities (↑ infrastructure cost), coral reefs (bleaching), fisheries, polar species, etc