What is Pressure?

1. What is Pressure? To understand highs and lows, we first need to explore some basic science about air pressure. Pressure is defined by how much force per area.

2. The Collapsing Can Experiment We take air pressure for granted, but a change in air pressure is strong enough to collapse an aluminum can.

3. The can crushes from air pressure. When the water and air in the can is heated, the molecules speed up and bumping more into each other and the side of the container– creating higher pressure. When rapidly cooled, the opposite takes place. Because the pressure is so low inside the can, the outside air pressure crushes it.

4. Fun experiment – but what’s this got to do with the highs and lows? Pressure change is why the wind blows.

5. Baton Rouge or Chicago?

6. We don’t need many warm clothes because in Baton Rouge we live in a warm climate. Why is it usually warm in Baton Rouge and cold in Chicago?

7. - Winds Angle of the Sun’s Rays • The surface of the Earth is not heated equally. • Energy from the sun strikes Earth most directly near the equator. Near the poles, the same amount of energy is spread out over a larger area.

8. The unequal heating of the Earth causes different temperatures which cause different air pressures –Pressure differences cause the movement of global wind patterns. www.rise.org.au/info/Res/wind/index.html

9. Coriolis Effect • If the Earth were still – the global wind patterns would blow “straight” from high pressure to low pressure. • The rotation of the Earth creates an apparent curvature of wind patterns called the Coriolis Effect

10. - Winds Coriolis Effect • As Earth rotates, the Coriolis effect turns winds in the Northern Hemisphere toward the right.

11. Sea Breezes Pressure differences also explain sea breezes.

12. The unequal heating of land and water leads to sea breezes – wind blows from high pressure to low pressure. http://physics.uwstout.edu/wx/u7/U7_04.gif

13. www.winningwind.com/seabreeze.html

14. What makes Chicago the “windy city”? http://mydogaddison.com/db4/00389/mydogaddison.com/_uimages/thewindycity.JPG

15. Chicago is located on the shore of Lake Michigan – therefore due the heat differential between water and land – experiences many breezes

16. - Winds Global Wind Belts • A series of wind belts circles Earth. Between the wind belts are calm areas where air is rising or falling.

17. - Winds Jet Streams • The jet streams are high-speed bands of winds occurring at the top of the troposphere.

18. Earth’s winds include include Local winds two types three types Trade winds Winds Graphic Organizer Global winds Prevailing westerlies Polar easterlies Sea breeze Land breeze

19. - Air Masses and Fronts Classifying Air Masses • Four major types of air masses influence the weather in North America: maritime tropical, continental tropical, maritime polar, and continental polar.

20. - Air Masses and Fronts Types of Air Masses • Air masses can be warm or cold, and humid or dry. As an air mass moves into an area, the weather changes.

21. - Air Masses and Fronts How a Front Forms • The boundary where unlike air masses meet is called a front.

22. - Air Masses and Fronts Types of Fronts • Colliding air masses can form four types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

23. - Air Masses and Fronts Types of Fronts Types of Weather Front How It Forms A cold air mass overtakes a warm air mass. Clouds, possibly storms with heavy precipitation Cold front A warm air mass overtakes a cold air mass. Clouds, light precipitation Warm front Cold and warm air masses meet, but neither can move the other. Stationary front Clouds, precipitation Occluded front A warm air mass is caught between two cold air masses. Clouds, precipitation

24. Climate - the average weather in a location over a long period of time. Climatic Zones

25. 5 Factors That Affect Climate • Latitude: locations farther from the equator receive less sunlight • Altitude: temperature decreases with height. • Winds: winds blown from hot area will raise temperature while winds blown from cold area will lower temperatures

26. 5 Factors That Affect Climate cont’d • Distance from the sea: land heats and cools faster than sea; coastal areas have lower temperature ranges than inland areas • Aspect: slopes facing the sun are warmer than those not facing the sun

27. Louisiana Climate • Warm and wet • Year round rain showers • High temperatures and humidity during summer • Warm, sunny winter weather

28. Average January Temperature in Louisiana http://www.worldbookonline.com/wb/Students?content_spotlight/climates/north_american_climate_louisiana

29. Average July Temperatures in Louisiana http://www.worldbookonline.com/wb/Students?content_spotlight/climates/north_american_climate_louisiana

30. Average Yearly Precipitation in Louisiana http://www.worldbookonline.com/wb/Students?content_spotlight/climates/north_american_climate_louisiana

31. Locations next to water have milder climates. A mild climate means that there is not much temperature change between day and night and between summer and winter. The water stores the sun’s energy, and gradually releases it to the surrounding area.

32. For example: • The coastal city of Astoria, Oregon experiences warmer daily minimum temperatures and cooler maximum temperatures than Pendleton, Oregon which is about 400 kilometers (250 miles) inland.

33. Which area has the mildest climate? Why? Pendleton has a temperature range from 33 ° F to 72 ° F. Astoria has a temperature range from 41° F to 60° F

34. Proximity to Water & Climate The regions closer to large bodies of water have milder climates. The water takes in and releases heat slowly, which maintains a smaller ranges of temperature in the air around it.

35. How are weather and climate related?

36. Weather • The way the air (atmosphere) around us behaves • Includes short term changes • It changes when its hot or cold, wet or dry • Examples: a snow flurry, thunder, lightening, sunshine, rain showers

37. Computer Weather Forecasting • Scientists use computers to develop different models of how a front may move. These predictions are then used to make weather forecasts. As more data become available, some models are found to be incorrect, while others are found to closely fit the predicted conditions. The upper graph shows the predicted air pressure from two models. The lower graph shows actual data for air pressure.

38. What two variables are being graphed? How is air pressure predicted to change according to each model in the top graph? Which computer model most closely matches the actual air pressure data? What weather would you forecast for Monday and Tuesday? Explain. Computer Weather Forecasting

39. - Predicting the Weather Reading Weather Map Symbols • The figure below shows what various weather symbols mean.

40. - Predicting the Weather Reading Weather Maps • This is the type of weather map produced by the National Weather Service. It shows data collected from many weather stations.

41. - Predicting the Weather Reading Weather Maps • Weather maps in newspapers use symbols to show fronts, high- and low-pressure areas, and precipitation. Color bands indicate different temperature ranges.

42. Weather Maps cold front  warm front  stationary front 

43. A line connecting points of equal pressure is called an isobar. That means, that at every point along a given isobar, the values of pressure are the same.

44. A line connecting points of equal temperature is called an isotherm. Meaning, at every point along an isotherm, the values of temperature are the same.

45. El Niño & La Niña In normal years, water in the eastern Pacific is kept relatively cool by currents along the coast of North and South America. When El Niño occurs, warm surface water from the western Pacific moves east toward the coast of South America. La Niña occurs when surface waters in the eastern Pacific Ocean are colder than normal.

46. Hurricanes • Severe tropical storms that form in Southern Atlantic Ocean, Caribbean Sea, Eastern Pacific Ocean and Gulf of Mexico. • They gather heat and energy through contact with warm ocean waters.

47. - Storms Structure of a Hurricane • In a hurricane, air moves rapidly around a low-pressure area called the eye.

48. Begins as a low-pressure area over warm water,or a tropical disturbance. Warm, humid air rises and begins to spiral. As air rises, more warm, moist air is drawn into the system and the hurricane gains energy. - Storms Hurricane Formation As winds spiral inward, bands of high windsand heavy rains form.

49. Hurricane Paths • The path of the hurricane depends greatly upon the wind belt upon which it is located. • A hurricane originating in the eastern tropical Atlantic, for example, is driven westward by easterly trade winds in the tropics. • The Gulf of Mexico and East Coast of the United States are at risk to experience one or more hurricanes each year. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/mvmt.rxml

50. Hurricane Paths • Hurricanes can be steered by low pressure systems, high pressure systems, warm fronts or cold fronts.