Atmosphere, Seasons & Circulation

1. Atmosphere, Seasons & Circulation Ms. Levensailor

2. Ocean and Atmosphere • Interact with each other. • Water evaporated from the ocean enters the atmosphere. • This impacts climates on land. • Atmosphere is composed of: • Nitrogen (78%) • Oxygen (21%) • Water vapor (1%)

3. Atmospheric Movement • Moves in response to: • Uneven solar heating • Earth’s rotation • Solar heating of Earth varies with latitude.

4. Solar Heating & Seasons • Solar heating varies with seasons

5. Large Scale Atmospheric Circulation • Warm air rises and cool air sinks. • Warm air expands and becomes less dense. • Cool air contracts and becomes more dense. • Convection currents: circular current of air.

6. Convection Currents • If uneven solar heating was the only factor in Earth’s air circulation it would look like this

7. Earth’s Rotation Plays a Role • Coriolis effect: eastward rotation of Earth on its axis deflects the moving air or water away from its initial course. • Coriolis effect: • Northern Hemisphere: curve is to the right (clockwise) • Southern Hemisphere: curve is to the left (counterclockwise)

8. Coriolis Effect • Influences the movement of air in atmospheric circulation cells. • Air rising from the equatorial region moves poleward and is gradually deflected eastward. • Turns right in the Northern Hemisphere. • Turns left in the Southern Hemisphere.

9. Coriolis Effect on Air Cells • Circulation cells are large circuits of air. • There are 3 cells in each hemisphere: • Hadley cells • Ferrel cells • Polar cells

10. Atmospheric Circulation • Cells generate large scale surface wind patterns. • Trade winds (easterlies) centered at 15° N and 15° S latitudes. • Surface winds of the Hadley cells. • Westerlies centered at 45° N and 45° S. • Surface winds of the Ferrel cells.

11. Circulation of the Ocean

12. Mass flow of Ocean Water • Known as ocean currents. • Driven by wind and gravity! • Surface currents: wind-driven movement of ocean water at or near the ocean’s surface. • Thermohaline currents: slow, deep currents that affect the bulk of seawater below the surface. • Depends on density differences as a result of temperature and salinity.

13. Surface Currents • 10% of the water in the ocean is involved in surface currents. • Water flowing horizontally in the upmost 400 meters. • Responsible force: WIND! • Surface winds form global patterns within latitude bands. • Northern Hemisphere surface currents flow to the right. • Southern Hemisphere surface currents flow to the left. • Continents block continuous flow and creates a circular pattern (GYRE).

14. Ocean Layers & Gyre

15. Ekman Spiral • A body of water can be thought of as a set of layers. • Top layer driven by wind. • Each layer below is moved by friction. • Moving at a slower speed and at an angle to the layer immediately above it. • Horizontal movements in a layered water column. • Each layer moving in a slightly different direction.

16. Seawater flows in 6 surface circuits • 2 in the Northern Hemisphere. • 4 in the Southern Hemisphere. • Antarctic Circumpolar is not a gyre.

17. Direction of currents

18. Boundary Currents • Western Boundary Currents: Gulf stream • Narrow, fast, deep currents. • Move warm water poleward. • Eastern Boundary Currents: California current • Carry cold water equatorward • Shallow and broad.