Our oceans are affected by everything from the wind to the moon. Because of this, we will discuss wind currents, major climate events, watersheds and tidal pull in this unit.
Latitude What is Latitude? • Lines of Latitude run horizontally • Latitude is measured in degrees. • The Equator is 0 degrees Latitude. • Lines of Latitude locate places North or South of the Equator. • The North Pole is 90 degrees N Latitude, and the South Pole is 90 degrees S Latitude.
Air generally moves from the poles to the equator, this is because air flows from high pressure to low pressure • High pressure forms when cold air sinks (at the poles) • Low pressure forms when warm air rises (at the equator) • But the air doesn’t flow in a straight line
Coriolis Effect • The Earth spins fastest at the equator, and slowest near the poles • This causes air to move in a curved path • Air curves to the East in the Northern Hemisphere and to the West in the Southern Hemisphere.
Click here for a demo:http://video.mit.edu/watch/the-coriolis-effect-4407/
Planetary Wind • blow across the entire planet • blow at the same speed and direction • Some are high in the atmosphere and you cannot feel them on the ground • Each hemisphere contains 3 wind belts that divide up the planetary winds • Trade winds, Westerlies, and Easterlies
Warm, moist air creates a zone of low pressure along the equator. • As that warm air rises, it cools and sinks …all the while moving with the Coriolis Effect. This “Cell” creates a Planetary Wind known as the Trade Winds between 0-30°N or S Many European sailor used these winds for trade. The area near the Equator where the winds die out are known as the Doldrums.
The cool, calm air sinks from the top of the “cell” around 30 - 35°creating very calm conditions. • These latitudes are known as the Horse Latitudes. Sailors to the New World would get caught for days or weeks in the calm water. Unable to sail, they would throw their horses overboard to conserve fresh water.
From 30 – 60°lie the Westerlies. The wind flows from the West. • The higher into the atmosphere you travel, the stronger the winds blow. At the Westerlies strongest point, a Jet Stream is created.
High pressure (cold air) from the poles moves south toward lower pressure (warmer air) from 90 - 60°to form the Polar Easterlies. • The air flows from the East to the West. Due to the Coriolis Effect . . . • At north pole, they are Northeast winds since the wind comes from the Northeast. • At the south pole, they are Southeast winds since the wind comes from the Southeast.
Planetary Wind Shift • Because the Earth goes through seasons throughout the year, the wind belts can shift slightly • But the average shift is only about 10º
Local Winds • These winds blow over small areas • Unlike planetary winds, local winds can change speed and direction frequently • These are the winds we feel on the ground • They are influenced by local conditions and local temperature variations and geography.
El Niño and La Niña
The Trade Winds push warm water from East to West. Warm water accumulates toward the West while cold water accumulates to the East. Eventually, there is an overturn and an El Nino or La Nina event occur to balance the temperatures. These changes affect the equatorial band. Wind affects water, both affect air masses and air masses affect climate and human life.
ENSO- El Nino Southern Oscillation: describes the oceanic and atmospheric temperature changes in the Pacific El Niño- Unusually warm surface water temperatures in the Pacific ocean caused by weak or reversed direction trade winds. La Niña - Unusually cold surface water temperatures in the Pacific ocean caused by strong easterly trade winds. These occur in oscillation every 2-7 years on average, but El Nino tends to occur more frequently (we are currently experiencing one)
Shared Characteristics: El Niñoand La Niña are • Pacific Ocean-Atmospheric systems • The most powerful phenomenon on earth • Alters more than half the planet’s climate
La Nina Weather Characteristics • Coolingof the water in the Pacific Ocean • Less Snow and rain on the west coast • Decreased Humidity • Unusually cold weather in Alaska • Unusually warm, but dry weather in the rest of the USA (the Jet Streams are affected) • Drought in the southwest: often triggering forest fires • Higher than normal number of hurricanes in the Atlantic (velocity of Trade Winds increases) • Flooding in Australia
Increased number of Hurricanes (La Niña) Strong trade winds!
Causing devastating floods in Australia (2010-2011 La Niña) Australia has the opposite weather of Texas!!
More tornadoes through tornado alley? NO!!! Scientists have found no significant correlation between El Niño and La Niña weather patterns and increased tornadoes.
El Nino Weather Characteristics • Warmingof water in the Pacific Ocean • Rain and Flooding on the Pacific coast • Increased Humidity • Warm weather disrupts food chains of fish, birds and sea mammals • Increase of thunderstorms in the southern United States. • Fewer than normal number of hurricanes in the Atlantic (velocity of Trade Winds decreases) • Occurs every 2-12 years (more often than La Nina)
Fish populations decline off the coast of S. America (El Niño) Many fish do not like warm water (El Nino = bad fishing)
El Nino is expected to hang around through Spring or early Summer. • NOAA just issued a La Nina watch. Conditions are favorable for La Nina to emerge within 6 months. • NOAA’s next ENSO update will be released May 12th. They use drifting buoys to measure and transmit data on temperature, current and winds. This help predict the events.
Currents • Currents exist in every ocean, both at the surface and deep below the surface.
Surface Ocean Currents About 10% of the ocean (the top ¼ mile) is affected by wind.
Deep Ocean Currents Currents are controlled by water density. Water density is affected by temperature and salinity. Deep ocean currents provide oxygen to the deep seas and affect marine life. 90% of the ocean water moves in deep ocean currents
Does warm water sink or rise? • Does water with a high percentage of salt sink or rise?
Upwelling Upwelling brings up cold, nutrient rich water from the bottom of the ocean. Fish like cold water! More food (La Nina = good fishing)
Ekman Transport • https://youtu.be/zYms4lHpgLc • Surface currents move at an angle to the wind • Ekman Transport is the net motion of fluid as the result of a balance between Coriolis, friction between the layers of water and wind. • Each successive layer moves increasingly to the right.
But What About the Rest of the Ocean outside of the Equatorial Band? Since oceans cover about 70% of the earth’s surface, our ships, buoys and land data can’t possibly cover that much area. This is where satellites come in. . .
Satellites Contain instruments to measure wind, waves, temperature of the sea surface, ocean color, ocean surface currents, and tides.
Satellites . Satellites have revolutionized the ocean sciences. They have advanced our knowledge about the weather and ocean processes more than any other tool. Oceanographers can use these satellite measurements to predict what is happening in the deep ocean.
Videos • http://www.youtube.com/watch?v=SR5VPAqVQBw El Nino explanation video 3min • http://www.youtube.com/watch?v=jEAv-9TZktY La Nina explanation video 3.5min • http://www.youtube.com/watch?v=iWTucpsClLc Austin newscast in January talking about Australia flooding 2min • http://www.youtube.com/watch?v=l5x8dJ57xkk Texas weatherman predictions for this year from July 2010. about 3min • http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html All three animations
Major Ocean Currents • An Ocean Current is a large volume of water flowing in a certain direction. • Wind-driven currents are called surface currents. • Surface currents carry warm or cold water horizontally across the ocean’s surface
Major Ocean Currents • Surface currents extend to about 400 m below the surface, and they move as fast as 100 km/day. • Earth’s major wind belts, called prevailing winds, influence the formation of ocean currents and the direction they move.
Density Currents • Density Currents are a type of vertical current that carries water from the surface to deeper parts of the ocean. • Density Currents are caused by changes in density rather than wind. • Density currents circulate thermal energy, nutrients and gases.
Impacts of Weather and Climate • Warm-water currents and cold-water currents affect weather and climate in different ways • Regions near warm-water currents are often warmer and wetter than regions near cold-water currents
Impacts on Weather and Climate • The Gulf Stream is a warm-water current that affects coastal areas of the southwestern United States by transferring lots of thermal energy and moisture to the surrounding air. • The cold California Current affects coastal areas of the southwestern United States.
Ocean Currents and Climate • Warm Ocean Currents warm air at the coast • Warm/humid climate on land • Cool ocean currents cool air at coast (dry climate on land) • Cool/dry climate on land
Great Ocean Conveyor Belt • The Great Ocean conveyor Belt is the name for a model of the large system of ocean currents that affects weather and climate by circulating thermal energy around Earth. Scientists estimate that it takes about 1,000 years to complete one cycle. • In this model, high salinity water cools and sinks in the North Atlantic, and deep water returns to the surface in the Indian and Pacific Oceans through upwelling