Section 12.1: The Causes of Weather Section 12.2: Weather Systems

1. 12 Meteorology Section 12.1: The Causes of Weather Section 12.2: Weather Systems Section 12.3:Gathering Weather Data Section 12.4:Weather Analysis and Prediction

2. Section 12.1 The Causes of Weather Air masses have different temperatures and amounts of moisture because of the uneven heating of Earth’s surface. heat: transfer of thermal energy from a warmer material to a cooler material

3. Section 12.1 The Causes of Weather Meteorology is the study of atmospheric phenomena. The root word of meteorology is the Greek word meteoros, which means high in the air. What is meteorology?

4. Section 12.1 The Causes of Weather Weather versus climate Weather is the short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth. Climate is the long-term average (30+ years) of variations in weather for a particular area. What is meteorology?

5. Section 12.1 The Causes of Weather Imbalanced heating Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area. Heating Earth’s Surface

6. Section 12.1 The Causes of Weather An air mass is a large volume of air that has the same characteristics, such as humidity and temperature, as its source region. A source region is the area over which an air mass forms. Air Masses

7. Section 12.1 The Causes of Weather Air mass modification- When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification. Air Masses

8. Section 12.2 Weather Systems Weather results when air masses with different pressures and temperatures move, change, and collide. convection isthe transfer of thermal energy by the flow of a heated substance

9. Section 12.2 Weather Systems The directions of Earth’s winds are influenced by Earth’s rotation. This Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line. Global Wind Systems

10. Section 12.2 Weather Systems Please click the image above to view the video.

11. Section 12.2 Weather Systems The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur. Global Wind Systems

12. Section 12.2 Weather Systems Polar easterlies The polar easterlies are the wind zones between 60 N latitude and the north pole, and 60 S latitude and the south pole. Global Wind Systems

13. Section 12.2 Weather Systems Prevailing westerlies The prevailing westerlies are the wind systems on Earth located between latitudes 30 N and 60 N, and 30 S and 60 S. Global Wind Systems

14. Section 12.2 Weather Systems Trade winds Between latitudes 30 N and 30 S are two circulation belts of wind known as the trade winds. Global Wind Systems

15. Section 12.2 Weather Systems A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams. A jet stream is a narrow band of fast, high-altitude, westerly wind. Jet Streams

16. Section 12.2 Weather Systems Jet streams and weather systems Storms form along jet streams and can generate large-scale weather systems. Jet streams affect the intensity of weather systems by moving air of different temperatures from one region of Earth to another. Jet Streams

17. Section 12.2 Weather Systems A collision of two air masses forms a front—a narrow region between two air masses of different densities. Fronts

18. Section 12.2 Weather Systems Cold front When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. Fronts

19. Section 12.2 Weather Systems Warm front Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope. Fronts

20. Section 12.2 Weather Systems Stationary front When two air masses meet but neither advances, the boundary between them stalls. This stationary front frequently occurs between two modified air masses that have small temperature and pressure gradients between them. Fronts

21. Section 12.2 Weather Systems Occluded front Sometimes, a cold air mass moves so rapidly that it overtakes a warm front and forces the warm air upward. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front. Fronts

22. Section 12.2 Weather Systems Please click the image above to view the video.

23. Section 12.2 Weather Systems Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere. Pressure Systems

24. Section 12.2 Weather Systems Low-pressure systems In surface low-pressure systems, air rises. When air from outside the system replaces the rising air, this air spirals inward toward the center and then upward. Pressure Systems

25. Section 12.2 Weather Systems In the northern hemisphere, winds move counterclockwise around a low-pressure center, and clockwise around a high-pressure center. Pressure Systems Low-pressure center High-pressure center

26. Section 12.3 Gathering Weather Data Accurate measurements of atmospheric properties are a critical part of weather analysis and prediction. temperature: the average thermal energy of the particles that make up a substance

27. Section 12.3 Gathering Weather Data Two important factors in weather forecasting are the accuracy of the data and the amount of available data. Data from Earth’s Surface

28. Section 12.3 Gathering Weather Data A thermometer measures temperature using either the Fahrenheit or Celsius scale. A barometer measures air pressure. Temperature and air pressure Data from Earth’s Surface

29. Section 12.3 Gathering Weather Data An anemometer measures wind speed. A hygrometer measures relative humidity. Wind speed and relative humidity Data from Earth’s Surface

30. Section 12.3 Gathering Weather Data The Automated Surface Observing System (ASOS) gathers data in a consistent manner, 24 hours a day, every day. It provides essential weather data for aviation, weather forecasting, and weather-related research. Automated Surface Observing System Data from Earth’s Surface

31. Section 12.3 Gathering Weather Data The instrument used for gathering upper-atmosphere data is a radiosonde. A radiosonde’s sensors measure the air’s temperature, pressure, and humidity. Data from the Upper Atmosphere

32. Section 12.3 Gathering Weather Data A weather radar system detects specific locations of precipitation. The Doppler effect is the change in pitch or frequency that occurs due to the relative motion of a wave, such as sound or light, as it comes toward or goes away from an observer. Weather radar Weather Observation Systems

33. Section 12.3 Gathering Weather Data Analysis of Doppler radar data can be used to determine the speed at which precipitation moves toward or away from a radar station. Weather radar Weather Observation Systems

34. Section 12.3 Gathering Weather Data Some weather satellites use infrared imagery to make observations at night. Objects radiate thermal energy at slightly different frequencies. Infrared imagery detects these different frequencies, which enables meteorologists to map either cloud cover or surface temperatures. Weather satellites Weather Observation Systems

35. Section 12.3 Gathering Weather Data Some satellites use cameras that require visible light to photograph Earth. These digital photos are sent back to ground stations, and their data are plotted on maps. Unlike weather radar, which tracks precipitation but not clouds, satellites track clouds but not necessarily precipitation. Weather satellites Weather Observation Systems

36. Section 12.3 Gathering Weather Data Another type of satellite imagery that is useful in weather analysis and forecasting is called water-vapor imagery. Water-vapor imagery is a valuable tool for weather analysis and prediction because it shows moisture in the atmosphere, not just cloud patterns. Weather satellites Weather Observation Systems

37. Section 12.4 Weather Analysis and Prediction Several methods are used to develop short-term and long-term weather forecasts.

38. Section 12.4 Weather Analysis and Prediction Station models A station model is a record of weather data for a particular site at a particular time. Surface Weather Analysis

39. Section 12.4 Weather Analysis and Prediction Station models Meteorological symbols are used to represent weather data in a station model. Surface Weather Analysis

40. Section 12.4 Weather Analysis and Prediction Plotting station model data To plot data nationwide and globally, meteorologists use lines that connect points of equal or constant values. Surface Weather Analysis

41. Section 12.4 Weather Analysis and Prediction Plotting station model data Lines of equal pressure are called isobars. Lines of equal temperature are called isotherms. Surface Weather Analysis

42. Section 12.4 Weather Analysis and Prediction Digital forecasts A digital forecast is created by applying physical principles and mathematics to atmospheric variables and then making a prediction about how these variables will change over time. Types of Forecasts

43. Section 12.4 Weather Analysis and Prediction Analog forecasts An analog forecast is based on a comparison of current weather patterns to similar weather patterns from the past. Types of Forecasts

44. Section 12.4 Weather Analysis and Prediction The most accurate and detailed forecasts are short term because weather systems change directions, speeds, and intensities over time. Short-Term Forecasts

45. Section 12.4 Weather Analysis and Prediction Because it is impossible for computers to model every variable that affects the weather at a given time and place, all long-term forecasts are less reliable than short-term forecasts. Long-Term Forecasts

46. Table Of Contents CHAPTER13 Section 13.1 Thunderstorms Section 13.2 Severe Weather Section 13.3 Tropical Storms Section 13.4 Recurrent Weather Click a hyperlink to view the corresponding slides. Exit

47. SECTION13.1 Thunderstorms How thunderstorms form • For a thunderstorm to form, three conditions must exist: a source of moisture, lifting of the air mass, and an unstable atmosphere.

48. SECTION13.1 Thunderstorms • Thunderstorms are often classified according to the mechanism that causes the air mass that formed them to rise. • There are two main types of thunderstorms: air-mass and frontal. Types of Thunderstorms

49. SECTION13.1 Thunderstorms Air-mass thunderstorms • When air rises because of unequal heating of Earth’s surface beneath one air mass, the thunderstorm is called an air-mass thunderstorm. • There are two kinds of air-mass thunderstorms. Types of Thunderstorms

50. SECTION13.1 Thunderstorms Air-mass thunderstorms • Mountain thunderstorms occur when an air mass rises by orographic lifting, which involves air moving up the side of a mountain. Types of Thunderstorms