Atmospheric and Oceanic Movements What drives their motion? Heat transport from hot to cold There is an imbalance in heating of the Earth's surface (with > heating in the tropics), because
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- Thus the pole-to-equator temperature imbalance results from differential energy input that is not completely erased heat flow.
- Global Atmospheric Circulation Cells
- Easterlie winds at equator and 60° latitude, Westerlie winds at 30° latitude In Northern Hemisphere Clockwise-rotating, falling air, high pressure cells: no rain
- Monsoons
- Ocean Circulation: moves 50% of the excess heat from equator to pole
- Upwelling of deep ocean water
- Deep ocean circulation
| Atmospheric and Oceanic Movements
What drives their motion? Heat transport from hot to cold There is an imbalance in heating of the Earth's surface (with > heating in the tropics), because: 1) Albedo is higher at high latitudes (reflective snow and sea ice, low angle of incidence). 2) Albedo is lower at low latitude (absorbant sea water, high angle of incidence). 3) Per unit area, high latitudes receive a smaller flux of solar radiation than low latitudes, because the same amount of energy is spread over a greater area. 4) Emission rate of long wave radiation is a function of planetary temperature. With respect to the Stefan-Boltzman Law (Energy flux = T4), polar and equatorial regions are almost the same temperature. Therefore, they radiate energy back to space at about the same rate. There is some heat flow between equator and pole (i.e., the outgoing heat flux at each latitude is not the same as the incoming flux at that latitude). This heat is carrier by the oceans and atmosphere (more on this below). Yet there still is an equator-to-pole temperature gradient, so heat flow is not infinitely efficient. Indeed, the magnitude of the heat flux is proportional to the temperature gradient (i.e., heat flow is more vigorous when the gradient is large; less vigorous when the gradient is small). Thus the pole-to-equator temperature imbalance results from differential energy input that is not completely erased heat flow. Atmospheric Circulation: moves 50% of the excess heat from equator to pole Sensible heat transport: describes the movement of hot air Latent heat transport: describes heat moved by transport and phase changes of water Global Atmospheric Circulation Cells Air rises at equator and at polar front (~60° latitude) Rising air cools, moisture condenses - rain or snow Air sinks at 30° and 90° latitude Sinking air warms, holds more moisture - no precipitation Find deserts/dust/salty water where air falls, forests/swamps/brackish water where air rises Coriolis Effect A bit more complicate than just rising and falling, because the world turns on its axis. There is an apparent deflection of flowing air due to planetary rotation: Coriolis Effect Deflection is to the right in the Northern Hemisphere, to the left in Southern Hemisphere Easterlie winds at equator and 60° latitude, Westerlie winds at 30° latitude In Northern Hemisphere Clockwise-rotating, falling air, high pressure cells: no rain Counterclockwise-rotating, rising air, low pressure cells: lots of precipitation Land-sea air flow Water has a higher heat capacity than rock. Water can store more heat. Land cools/heats faster. This difference creates the large thermal contrasts between land and sea that shifts seasonally.
on to land; rain falls under the rising air. Dry high-pressure cell over the colder oceans. Get summer, continental monsoonal rains. Examples: Asia and central North America
cell develops on land, while a wet/low pressure cell forms at the coast. Get winter, coastal monsoonal rains. Examples: California, Peru
Over most of its surface area, the ocean can be divided into warmer, brackish, less dense surface ocean water and cooler, saltier, denser deep ocean water. Surface oceans: involves about 20% of the Earth's ocean volume Surface flow is driven by the winds. Surface ocean currents follow trends in the wind field.
Strong, warm, northward flowing current on east coasts of continents Broad cool, southward flowing currents on west coast of continents. If the winds fail, circulation does too. Ekman Spirals: Coriolis deflection of deeper layers of water drives offshore flow. At depth, net motion of water is perpendicular to the winds This surface water "volume deficit" is made up by Upwelling of deep ocean water. Because deep water if so full of nutrients (remember the biological C pump), upwelling sites are zones of spectacular biotic production. Important in western coastal regions and at Equator: Examples: California, Peru, SW Africa Deep ocean circulation: involves about 80% of the Earth's ocean volume Driven by density contrasts in water (due to temperature and salinity). Salty water at equator (lots of evaporation), fresher water at poles Today, most deep water formation takes place in the North Atlantic (some in Antarctic) Why is North Atlantic so salty? Equatorial Easteries blow freshwater (not salt) over the Isthmus of Panama into the Pacific. As it cools (loses heat to the atmosphere), Atlantic gets denser and denser until finally it sinks. Salt flows in deep water currents to make up this the Atlantic/Pacific imbalance. This sucks more warm, salty, surface water to the N. Atlantic. Release of heat from this water accounts for 30% of the heat delivered to Europe at present. Download 16.82 Kb. Share with your friends:
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