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Air-Sea Interactions & Ocean Circulation Air-Sea interaction I. Intro A. The atmosphere and Ocean act as an interdependent system. 1. Ocean currents are created largely by wind patterns 2. Many weather patterns are caused by the ocean. 3. Extreme weather (drought, excessive precipitation) are related to periodic changes in oceanic conditions (like El Nino) 4. Oceans and land absorb about 50% of solar radiation (due to water’s high heat capacity this energy is maintained for long periods of time). 5. Atmosphere and clouds absorb about 25% of solar radiation B. Properties of the Atmosphere 1. composition – Air is mostly Nitrogen and Oxygen 2. Temperature a. Troposphere- from earth’s surface to about 7 miles above. i. All weather is produced here ii. There is a great deal of atmospheric mixing at this level. High altitudes are colder. 3. Density – Warm air is less dense than cold air (warm air rises and cold air sinks). i. A convection cell is caused by hot air rising and cold sinking. 4. Water vapor content a. Warm air can hold more water (clothes dry faster in a dry, warm breeze). i. increase in water vapor decreases air’s density (humid air less dense than dry). 5. Pressure – at sea level air has 1.0 atmospheres of pressure. i. the higher you go, the less air on top of you = lower pressure. ii. Column of cool, dense air (heavier) = high pressure = air sinks. Column of warm, less dense air = low pressure = air rises. iii. Sinking air begins to warm (compression) and rising cools (expansion). 6. Movement – Air ALWAYS moves from high pressure to low pressure. a. This is wind. C (capitol C). How the Coriolis Effect, effects moving objects. 1. An object set in motion will move in a straight line unless acted upon by another force. 2. The earth rotates towards the East. a. If you stood on the N. Pole you would be rotating counter-clockwise. b. If you stood on the S. Pole you would be rotating clockwise. 3. Moving objects (above the surface) in N. hemisphere will appear to curve to the right (from viewers perspective). a. in S. hemisphere they will appear to curve to the left. b. this is the Coriolis Effect. More Coriolis Effect. 4. Merry-go-round example. D. Global Atmospheric Circulation Patterns. 1. Circulation cells – caused by convection as the result of low pressure (near warmer climates) and high pressure (near colder climates. a. Hadley cells are located between 0 and 30 degrees north and south of the equator. 1. Responsible for creating the Trade Winds, the strongest winds on earth. b. Ferrel Cells – Between 30 and 60 degrees N. and S. of the equator. i. The driving force is the Hadley cells and Polar cells. Like interlocking gears. ii. This is the Temperate Zone and is the location of the Westerly Winds. c. Polar Cells – located between 60 and 90 degrees from the equator. 2. Pressure a. Cool, dense air column descending at 30 degrees is called Subtropical Highs. i Similar descending air at the poles are called Polar Highs. ii. Conditions = dry and clear skies. b. Subpolar Equatorial low – 60 degrees i. Warm rising air – lots of water ii. Conditions – Cloudy with lots of precipitation. 3. Wind Belts – Most wind is created by the lowermost portion of a circulation cell (ie. Near the ground). a. The major belts include Trade Winds, Westerlies, and Polar Easterly winds. (see fig 6.10) 4. Boundaries – area between wind belts are typically lacking in wind (look at your fig. 6.10) a. They include the Doldrums (0°), Horse Latitudes (30°) and Polar Fronts (60°). E. Weather and Climate Patterns of the ocean. 1. Winds – As air moves from high pressure to low pressure, the coriolis effect modifies it. a. In N. Hem, air moving away from High Pressure moves away to the right (Anticyclonic flow) b. Air moving toward Low pressure moves in and to the right. i. flow around low pressure system called Cyclonic Flow. c. Sea breeze- land heats up and cools down 5 times faster than ocean (lower heat capacity). i. Why does a sea breeze blow in to land at day and out to sea at night? You tell me. 2. Storms and fronts – Conditions near equator and poles fairly consistent and calm. a. Storms (strong winds, precipitation, thunder and lightning) common between 30° and 60° (temperate zone where we are). b. Storms are atmospheric disturbances caused by air masses meeting. 3. Tropical Cyclones – AKA hurricanes, typhoons and cyclones. a. Caused by a low pressure cell moving away from the equator, picking up energy as it moves. b. Hurricanes are an efficient way to redistribute heat from one area to another. F. Random Fact to memorize- When sea ice forms the remaining seawater becomes more salty….ie. More dense (remember cold seeps). The End of Air-sea interactions. Ocean Circulation I. Intro – A. Ocean Currents are masses of Ocean Water in motion. II. Forces driving ocean circulation. A. Wind is the primary force driving ocean surface circulation. B. The Coriolis effect modifies this movement. C. Near Equator – Trade winds drive currents D. Temperate current (30 -60 degrees) – Westerlies affect currents. E. Polar currents affected by Polar Easterlies F. Thermohaline circulation. 1. caused by water density (rising & sinking) 2. Cold water is denser than warm water. 3. Saltly water (higher salinity) is more dense than fresh or less-salty water. 4. Causes the Gulf stream to dive to the bottom of the Atlantic near Greenland (cold and Salty) G. Ekman spiral- Caused by wind that has been modified by the coriolis effect. 1. Wind moving surface water in spiral physically moves deeper water in similar motion. a. Sort of like a water hurricane, but totally different ;-) 2. So as one moves down the direction changes. a. at 100m the water flows at about 90 degrees to surface wind. H. Upwelling- Deep nutrient-rich water from ocean floor pulled to the surface at coastlines. 1. Caused by Wind, Coriolis Effect and Ekman Transport. I. Random Fact – During winter months in the Indian ocean, dry monsoon wind blows consistently from inland out to sea……Why? 1. Did you know Monsoons had a dry phase? End of Ocean Currents Weather documentary Waves (3hrs) I. Waves (surf) – moving energy traveling along the interface of ocean and atmosphere. •Wave stuff, or stuff that waves do. A. The highest parts of waves are called Crests, and the lowest are troughs. B. The time between two successive waves is called the Period. B. Water waves are Orbital. C. Wave Speed is equal to wavelength divided (length) by period time. Eg. 20 m in 10 sec = 2.0 m/s while 25 m in 10 sec = 2.5 m/s D. Deep vs. Shallow waves. 1. Shallow waves include tsunamis, tides and near-shore wind generated waves. a. speed of shallow wave is proportional to water depth (the ocean floor begins to slow it. 2. The speed of Deep water wave is proportional to wave period E. Wave height depends on Wind speed, Wind duration and fetch (distance wind blows in a single direction). F. Rogue waves tend to occur where storm waves move against strong currents. 1. large, spontaneous and dangerous to even very large ships. G. Typical order of wave formation – 1. Sea, 2. swell, 3. surf. 1. Wind blows across the Sea, pushing Swells, that break into Surf near the shore. H. Waves that are breaking along the shore and are forming in a curling crest over an air pocket are called Plunging waves. (into the mind) I. Tsunamis are created by earthquakes on the sea floor (particularly on convergent plate boundaries) Waves for Electricity • The Majority of earth’s captured energy is in the oceans. • Waves are an ultimate result of energy transfer from sun to ocean, to atmosphere and back to the ocean again. • We can harvest this energy. • !00% renewable and Carbon neutral. End of Waves