Weather

1. Weather

2. Weather is....

3. What Starts It All? • The Sun Starts it All • There is one basic reason we have weather, and that is the sun.  Weather systems start because the sun's energy heats up some parts of Earth more than others.    Land heats up faster than water, setting up temperature differences between oceans and continents.  This unequal heating creates variations in temperature and air pressure, winds, and ocean currents. 

4. Main points to remember as we learn about weather: • The sun warms the earth’s surface and therefore all the air above the surface • The earth is warmed most at the equator and least at the poles---why? • The air above land is warmed more quickly than air above water. • Warm air expands and rises, creating an area of low pressure; cold air is dense and sinks, creating an area of high pressure

5. Convection Currents

6. Heat Transfer • Heat always moves from a warmer place to a cooler place. • Hot objects in a cooler room will cool to room temperature. • Cold objects in a warmer room will heat up to room temperature.

7. Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. A liquid or gas. This effects fluid movement. What is a fluid?

8. Fluid movement Cooler, more d____, fluids sink through w_____, less dense fluids. ense armer In effect, warmer liquids and gases r___ up. ise Cooler liquids and gases s___. ink

9. Water movement Cools at the surface Convection current Hot water rises Cooler water sinks

10. Air Pressure • Warm air= expanding or rising air= leaves behind L pressure • Cold Air=sinking air= leaves an area of H pressure

11. Wind Movement • Uneven heating of the earth’s surface causes some areas to be warmer than others. • As we know, warm always follows cold to share it’s warmth- when this happens in the atmosphere, wind happens!

12. What causes winds? • The Sun’s energy is more concentrated at the Equator and spread out more over the poles. • Air over the equator is warm and less dense and has lower pressure. • Air over the poles is cold and denser and has higher pressure. • As warm air at the equator rises, cooler air from the poles will move in and replace it. • Air pressure moves in a pattern from high to low.

13. Global Convection Currents • The density changes caused by temperature changes create convection cells. • These cause circular patterns of air that circulate over the whole planet.

14. Air Masses and Fronts • The winds move heat from the tropical regions toward the poles in a never-ending effort to reach a temperature balance.   In the process, fronts set up between warm and cold air masses and a stream of fast-moving air high up in the sky called the "jet stream" forms.

15. Jet Stream • Forms high in the upper Troposphere between two air masses of different temperatures • Higher temperature difference = faster speed • Due to the Coriolis Effect, it flows around air masses. • Polar Jet: • It dips southward when frigid polar air masses move south. • It tends to stay north in the summer months.

16. Jet Stream Animation http://www.pbs.org/wgbh/nova/vanished/jetstr_five.html

17. Global Wind Belts • The winds from the poles blow toward the equator. • The winds from the equator blow toward the poles.

18. The Coriolis Effect • As the Earth rotates counterclockwise, the winds bend and curve around the Earth. • Gustave-Gaspard Coriolis, an engineer and mathematician, described this effect as an inertial force in 1835.

19. The Coriolis Effect • In the Northern Hemisphere, winds bend to the right of their direction of travel. • In the Southern Hemisphere, winds bend to the left of their direction of travel.

20. The Coriolis Effect • Weather patterns and systems move in a circular motion due to the bending of the winds caused by the Earth’s rotation.

21. Ocean Currents

22. Global Circulation and Wind Systems • Solar energy is at its greatest around the equator---Why?

23. Ocean Currents • Warmcurrents flow away from the equator. • Cold currents flow toward the equator.

24. Factors Influencing Currents • Sun • Wind • Coriolis • Gravity

25. Sun • Energy from the Sun heats the water. • Warm water is less dense that cold water. • Warm water rises, and cold water sinks. • As warm water rises, cold water moves it to replace it.

26. Convection Cycle

27. Wind • Just as wind moves from high pressure to low pressure areas, so does the water. • Winds blow across the surface of the water, causing friction. • The water piles up because the surface currents flow slower than the winds.

28. Gravity • As water piles up and flows from high pressure to low pressure, gravity will pull down on the water. • This forms vertical columns or mounds of water. • The Coriolis Effect causes the water to curve.

29. The Coriolis Effect • Causes water to move to the right in the Northern Hemisphere • Causes water to move to the left in the Southern Hemisphere

30. Surface Currents • Make up 10% of oceans’ water • Up to maximum depth of 400 m • Surface ocean currents are caused by the surface wind patterns.

31. Surface Currents

32. Gyres • Vertical columns or mounds of water at the surface and flow around them • Produce enormous circular currents • Five major locations: • North Pacific - clockwise • South Pacific - counterclockwise • Indian Ocean - counterclockwise • South Atlantic - counterclockwise • North Atlantic - clockwise

33. Oceanic Gyres

34. Gulf Stream • A strong surface current • Begins at the tip of Florida • Flows up the eastern coastline of the U.S. • Crosses the Atlantic Ocean • Causes warmer climate in NW Europe

35. Deep Water Currents • Make up about 90% of oceans’ water • Differences in density cause them to move. • Differences in density are related to temperature and salinity. • At high latitudes, they sink deep into the ocean basins. • Temperatures are so cold, they cause the density to increase.

36. El Niño • Abnormally highsurface ocean temperatures off the coast of South America • Causes unusual weather patterns across the globe

37. El Niño • Starts because the easterly trade winds weaken and allow the warm waters in the Western Pacific to move east toward South America • This changes where the convection current occurs. • Causing rain where it usually doesn't occur and drought where it usually rains

38. El Niño El Niño Winter El Niño Summer

39. La Niña • Abnormally lowsurface ocean temperatures off the coast of SouthAmerica • Causes unusualweather patterns across the globe

40. La Niña La Niña Winter La Niña Summer

41. Ocean’s Effect on Climate • Ocean currents move more slowly than winds. • Oceans hold more heat than the atmosphere and land. • Cold currents will cause nearby coastlines to be cooler. • Warm currents will cause nearby coastlines to be warmer. Where do the cold currents come from? The warm currents?