Enduring Understanding

2. Enduring Understanding • Energy transfer between the Earth’s surface and the atmosphere creates the weather. • The atmosphere remains in balance until acted on by an outside force.

3. Weather • Weather is the current state and short term variations in the state of the atmosphere • Takes place over minutes, hours, days, weeks, months

4. Causes of Weather • Climate is the long term variations for a particular area • Averaged over 30 years or more of weather data

5. Redistribution of Wealth • Without the atmosphere this energy imbalance would continue and the tropics would be very hot and the poles very cold year round • The oceans store the majority of heat at Earth’s surface

6. Redistribution of Wealth • Temperature differences in the air result in differences in density which the cause upward and downward movement • The convection currents of the atmosphere redistribute the heat energy as air over the warmer regions rises, cools, then descends over cooler regions.

7. Redistribution of Wealth • This movement causes weather

8. Air Masses • An air mass is a large body of air that takes on the characteristics of the body over which it forms. They can form over either land or water and are classified according to their source regions

9. Air Masses • Continental Tropical (cT) air masses contain warm, dry air that forms over warm areas of land • Maritime Tropical (mT) air masses contain warm, humid air that forms over warm areas of the ocean • Continental Polar (cP) air masses contain cold, dry air that forms over cold areas of land • Maritime Polar (mP) air masses contain cold, humid air that forms over cold areas of the ocean • Arctic (A) air masses are basically the same as cP, but much colder and are associated with extreme cold

10. North American Source Regions • All five main air mass types can be found in North America because of our close proximity to the source regions associated with each type of air mass

11. North American Source Regions • Continental Tropical (cT) air forms over the desert of the southwest United States and Mexico

12. North American Source Regions • Maritime Tropical (mT) air forms over the southern Atlantic, Gulf of Mexico, and southern Pacific oceans

13. North American Source Regions • Continental Polar (cP) air forms over the interior of Canada and Alaska

14. North American Source Regions • Maritime Polar (mP) air forms in the northern Pacific and Atlantic oceans

15. North American Source Regions • Arctic (A) air develops over the extreme northern regions of the continent

16. Stability and Air Mass Movement • Air masses do not stay in one place indefinitely. They move and transfer their heat from one area to another establishing a balance of heat throughout the planet

17. Stability and Air Mass Movement • Air mass modification occurs when the moving air mass changes to become more like the surface over which it travels • Heat and moisture are exchanged with the surface as the air mass travels over it

18. Stability and Air Mass Movement • Eventually the air mass will become modified to the point it is indistinguishable from the new surface over which it is traveling and simply becomes part of the air over the new source region

19. Coriolis effect • The Coriolis Effect on Earth causes moving particles (air molecules ) to deflect to the right in the northern hemisphere and to the left in the southern hemisphere

20. Global Wind Patterns • Trade Winds occur at where the warm, rising air from the equator begins to cool and sink. They occur below 30 degrees latitude and blow in an east to west direction

21. Global Wind Patterns • Prevailing Westerlies flow between 30 and 60 degrees latitude and blow from west to east. This pattern is responsible for much of the weather in North America

22. Global Wind Patterns • Winds are named for the direction they blow from

23. Global Wind Patterns • Polar Easterlies blow from east to west between 60 deg and the poles and are characterized by very cold air

24. Global Wind Patterns

25. Jet Streams • Often the weather report will state that the jet stream is affecting today’s forecast in some way. Earth weather is strongly influenced by atmospheric conditions and events between the wind zones

26. Jet Streams • Jet Streams are narrow bands of fast, high-altitude, westerly winds and flow at speeds of 185 km/hr • Their position varies and drives large-scale weather systems

27. Fronts • Since air masses of different characteristics are constantly in motion some of them are bound to eventually collide

28. Fronts • Front is the narrow region separating two air masses of different densities • Density differences are caused by differences in temperature, pressure, and humidity

30. Fronts • There are four main types of fronts and the interaction of colliding air masses often causes dramatic changes in weather

31. Fronts • Cold Fronts occur where cold, dense air displaces warm air and we see clouds, showers, and thunderstorms

32. Fronts-Cold FrontGenerally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises. http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=visualization

33. Cold Front-crossing NYS - October 2008 (metars and satellite)

34. Fronts • Warm Fronts are where advancing warm air displaces cold air and we see extensive cloudiness and precipitation

35. Fronts-Warm Generally, with the passage of a warm front, the temperature and humidity increase, the pressure decreases. http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=visualization

36. Fronts • Stationary Fronts are where the two air masses meet but neither advances. Little cloudiness and precipitation is seen

37. Fronts • Occluded Fronts occur where a cold air mass overtakes a warm front and wedges it upward. It then collides with another cold front and causes precipitation on both sides

38. Fronts-Occluded Occluded front is formed when a cold front overtakes a warm front.

39. Pressure Systems • The vertical movement of air combined with the coriolis effect results in the formation of rotating low and high pressure systems

40. High Pressure System • High Pressure Systems are formed by dense, sinking air and move in a clockwise direction (in the northern hemisphere) • High pressure is associated with fair weather

41. Low Pressure Systems • Low Pressure Systems form by low density rising air moving in a counterclockwise direction • Low pressure is associated with stormy weather

42. Analyzing/Forecasting Weather • In order to accurately analyze and forecast weather meteorologists must be able to reliably gather the necessary data about the atmosphere. The quality and amount of data available for a certain location greatly affect the outcome of the forecast

43. The Instruments of Meteorology • Thermometer measures temperature. • They usually contain liquids such as mercury or alcohol that expand when heated

44. The Instruments of Meteorology • Barometer measures air pressure. The common types are mercury and aneroid

45. The Instruments of Meteorology • Psychrometer measures relative humidity. A wet and dry bulb thermometer is the most common type

46. The Instruments of Meteorology • Anemometer measures wind velocity. The simplest type has cupped arms that rotate as the wind blows

47. Technology in Meteorology • The accuracy of weather forecasting has greatly improved over the last 40 years. Many technological advances from other sciences have been found to have practical applications in Meteorology Mild Sunny Cloudy Rainy

48. Technology in Meteorology • Weather Radar allows us to track real-time movement of precipitation inside the coverage area. • Today most of the United States is covered by one or more weather radar sites

49. Technology in Meteorology

50. Technology in Meteorology • Weather Satellites take photographs and other images of the Earth’s surface at regular intervals.