1. Ocean Currents Ocean Density

2. Energy in = energy out Half of solar radiation reaches Earth The atmosphere is transparent to shortwave but absorbs longwave radiation (greenhouse effect) The atmosphere is heated from the bottom by longwave radiation and convection

3. I.Uneven heating of Earth’s surface causes predictable latitudinal variation in climate. Why? - Angle of incidence… equator vs. poles Climatic Variation & Seasons on Earth Thus, radiation is more intense near the equator compared to the poles. For this reason, it’s warmer near the equator than at the poles. North Pole Earth Equator South Pole

4. Uneven heating of Earth’s surface causes atmospheric circulation Greater heating at equator than poles 1. sun’s rays hit more directly 2. less atmosphere to penetrate Therefore 1. Net gain of energy at equator 2. Net loss of energy at poles

5. II. What about seasons? Why do we have them? Tilt! Because of the tilt of Earth’s axis, the amount of radiation received by Northern and Southern Hemispheres varies seasonally A. Northern Hemisphere has summer when it tilts toward the sun, winter when it tilts away B. Southern Hemisphere has summer when it tilts toward the sun, winter when it tilts away Earth’s distance from the sun varies throughout the year – doesn’t that cause the seasons?

6. I.Tilt of the Earth’s axis towards or away from the sun creates the seasons Earth’s Seasons North Pole Earth When the north pole tilts toward the sun, it gets more radiation – more warmth during the summer SUMMER (Northern Hemisphere) South Pole WINTER (Southern Hemisphere) When the north pole tilts toward the sun, the south pole tilts away So when it’s summer in the north, it’s winter in the south Equator

7. I.Tilt of the Earth’s axis towards or away from the sun creates the seasons Earth’s Seasons When the north pole tilts away from the sun, it gets less radiation – So it’s colder during the winter North Pole Earth WINTER (Northern Hemisphere) South Pole SUMMER (Southern Hemisphere) When the north pole tilts away from the sun, the south pole tilts toward it… When it’s winter in the north, it’s summer in the south Equator

8. Air rises and falls in Hadley, Ferrel, and Polar cells (vertical circulation) Circulation cells explain global distribution of rainfall Earth’s rotation determines wind direction (horizontal circulation, Coriolis force)

9. High heat capacity of water and ocean currents buffer ocean temperatures Land temperatures fluctuate more, especially in higher latitudes These differences in surface energy balance influence air movements, and create prevailing winds

10. Salinity – The difference in the salinity of hot and cold water drives the currents. The higher the salinity of the water, the more dense the water is. Density - the state or quality of compactness; closely set or crowded condition. Water Mass – Area of different salinity density in the ocean.

11. At 30º N & S, air descends more strongly over cold ocean than over land In January… These pressure gradients create geographic variation in prevailing winds At 60 º N & S, air descends more strongly over cold land than over ocean

12. In summer at 60 º N & S, air descends over cold ocean (high pressure) and rises over warm land (low pressure) Cool equator-ward flow of air on W coast of continents Warm poleward flow of air on E coasts of continents

13. Ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds

14. Ocean currents move 40% of “excess heat” from equator to poles Driven by circulation of deep ocean waters Deepwater formation occurs near Greenland and in Antarctic 60% of heat transport is carried by atmosphere through storms that move along pressure gradients

15. The Pacific Ocean strongly influences the climate system because It is the largest ocean basin Normal ocean current and wind direction in central Pacific is easterly

16. Winds and surface water Wind blowing over the ocean can move it due to frictional drag. Waves create necessary roughness for wind to couple with water. One “rule of thumb” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)

17. Top-down drag Wind acts only on the surface water layer. This layer will also drag the underlying water, but with less force. Consequently, there is a diminution of speed downward. Direction of movement is also influenced by the Coriolis Effect and Ekman Spiral

18. Geostrophic Flow Surface currents generally mirror average planetary atmospheric circulation patterns