Earth Science

1. Earth Science Chapter 7 Study of the Atmosphere

2. Introduction • The atmosphere was most likely created by the process of volcanic outgassing. • Weather is the state or condition of the atmosphere at a particular location for a short period of time. • The study of weather is called meteorology.

3. Electromagnetic Energy • Electromagnetic energy is energy that has the properties of transverse waves.

4. Electromagnetic Energy • All stars, including the sun constantly produce and emit electromagnetic energy. • Solar energy is the major source of energy for Earth. • Most of the energy from the Sun is in the form of invisible waves (ultraviolet and infrared). • The sun also gives off visible light that can be separated into different wavelengths. • The entire range of wavelengths is known as the electromagnetic spectrum.

6. Electromagnetic Energy • When electromagnetic energy comes in contact with a material, it can be: • refracted, or bent • reflected to a new direction • scattered (refracted and reflected) into several directions • absorbed by the material

7. Electromagnetic Energy • Half of the energy absorbed by Earth is long-wave (infrared) and half is short-wave (visible and ultraviolet). • Almost all of the energy released by Earth or re-radiated is long-wave radiation.

8. Energy Transfer in the Atmosphere • There are 3 methods of energy transfer: convection, conduction, and radiation. • Convection is the transfer of heat energy by movements of fluids (liquids and gasses). • Conduction is the transfer of heat energy by the collision of atoms with adjoining atoms. • Radiation is the transfer of electromagnetic energy through space in the form of waves.

10. Heat Energy and Phase Changes • Normally when heat is added to a substance the temperature will rise. • The exception is during a change in phase. • Latent heat is energy taken in or given off by a substance during a change in phase. • These transfers of energy DO NOT result in a change in temperature.

11. Atmospheric Relationships • Temperature • Temperature is greatly affected by intensity and duration of insolation • INcoming SOLar radiATION. • The atmosphere receives most of its heat energy by conduction through direct contact with Earth’s surface. • The amount of reradiated energy absorbed is directly related to the amount of water vapor, carbon dioxide and various other pollutants.

12. Atmospheric Relationships • Factors affecting local temperature • Latitude • Higher latitude = lower intensity of insolation = lower temperatures • Altitude • Higher altitude = lower temperatures • Closeness to large bodies of water • Water heats and cools slower than land, so large bodies of water regulate temp.

13. Atmospheric Relationships • Moisture • The warmer the air the more moisture it can hold • When the air contains all the moisture it can hold at a particular temperature it is saturated. • The air is not usually saturated. • To become saturated more water vapor must be added or the air must be cooled. • The temperature at which condensation occurs is called the dewpoint temperature.

14. Atmospheric Relationships • Absolute humidity is the actual amount of water vapor in the air. • Relative humidity is a comparison between the amount of water in the air and the amount the air can actually hold at that temperature. • Example: If the air is holding half as much water as it could, the relative humidity is 50%. • An instrument called a psychrometer is used to find dewpoint and relative humidity.

15. Atmospheric Relationships • Air pressure (atmospheric pressure) • The force, or weight, of the air pushing down on a unit area of a surface. • Air pressure is inversely proportional to temperature changes. • Air pressure is directly proportional to density changes. • The instrument used to measure air pressure is called a barometer.

16. Atmospheric Relationships • Air pressure is inversely proportional to the amount of moisture in the air. • When moist air moves into a region, air pressure decreases and the barometer “falls”. • A “falling” barometer is an indication that rainy weather is on the way. • As altitude increases, the number of air molecules decreases and, thus, pressure decreases.

17. Atmospheric Relationships • Factors affecting rate of evaporation: • Amount of energy available • More heat energy = more evaporation • Surface area • More surface area = more evaporation • Amount of moisture in the air • More moisture = less evaporation

18. Atmospheric Relationships • Large horizontal movements of air near Earth’s surface are called winds. • Smaller, local horizontal movements are called breezes. • Winds are named from the direction they come from.

19. Atmospheric Relationships • The primary causes of winds are differences in air temperature, which causes differences in air pressure. • Air always moves from areas of high pressure to areas of low pressure. • The rate of change in pressure between two locations is called the pressure gradient. • Close isobars = steep gradient

20. Atmospheric Relationships Local Breezes Sea Breeze Land Breeze

22. Atmospheric Relationships Planetary Winds

23. Atmospheric Relationships • Jet streams are winds at high altitudes that exert a controlling influence over the direction traveled by air-masses at Earth’s surface. • 7 to 8 miles above Earth’s surface • Avg. speed in summer 35 mph; in winter 75 mph • Atmospheric transparency is how much or little the Sun’s radiation is scattered or reflected. • Varies inversely with the amount of aerosols (dust and vapor) in the air.

24. Clouds and Precipitation • Clouds - collections of tiny water droplets or ice crystals suspended in the atmosphere. • Form when moist air expands and cools as it rises vertically in the atmosphere. • When air cools to the dewpoint temperature, it becomes saturated & condensation occurs. • When the water droplets or ice crystals in a cloud grow large enough to fall, precipitation results.

25. Moisture and Energy Transfer • Adiabatic temperature change – any change in temperature of a system without heat being added or removed from that system. • In the atmosphere, when air descends, it is compressed by the air around and its temperature increases. • When air rises, it expands and its temperature decreases.

26. Moisture and Energy Transfer

27. Forecasting the Weather • Measurements of atmospheric variables, when combined with similar measurements taken earlier, can provide the information needed to predict the weather. • Since relationships between variables are often complex, predictions are not always accurate. • These relationships are expressed as the probability of occurrence. • Example: 40% chance of snow

28. Weather Maps and Forecasting • A station model is a recording of weather observations for a particular location

29. Weather Maps and Forecasting • An air-mass is a huge body of air in the troposphere (diameter up to 2000 km) having similar pressure, moisture, wind, and temperature characteristics throughout. • Air-masses have definite characteristics that depend on their source region. • On a weather map air-masses are usually labeled with two letters indicating the moisture and temperature characteristics

30. Weather Maps and Forecasting • Maritime air-masses (m) • Develop over water and are moist • Continental air-masses (c) • Develop over land and are dry • Polar air-masses (P) • Develop in high latitudes and are cool • Tropical air-masses (T) • Develop in lower latitudes and are warm • Arctic air-masses (A) • Develop in very high latitudes & are very cold and dry

32. Weather Maps and Forecasting • Cyclone - low-pressure air mass with winds moving counterclockwise toward its center. • When the moving air converges at the center of a low, it rises vertically, often producing rain. • Anticyclone - high-pressure air mass with winds moving clockwise away from its center. • The air descending in their center is often dry and they usually bring cool, clear weather.

33. Weather Maps and Forecasting

34. Weather Maps and Forecasting • The boundary between two air-masses is called a front. • Atmospheric conditions at fronts: • Unstable air • Clouds • Strong winds • Precipitation • Other weather changes

35. Weather Maps and Forecasting • Warm fronts • Occur when warm air meets and rises over cold air on the ground. • Have long gentle slopes. • can be over 1000 km • Bring predictable sequence weather and clouds. • Precipitation may occur ahead of the front

36. Weather Maps and Forecasting

37. Weather Maps and Forecasting • Cold Fronts • Occur when cold air meets and pushes out warmer air. • Have short, steep slopes. • Move faster than warm fronts. • No sequence of clouds warning approach. • Precipitation occurs all around the front

38. Weather Maps and Forecasting

39. Weather Maps and Forecasting • Occluded front • When a faster moving cold front overtakes a slower moving warm front and lifts the warmer air between the two fronts above the ground. • Weather is characteristic of both fronts without any gap in the sequence. • Stationary front • When a warm air-mass and a cold air-mass are side-by-side, with neither one moving. • Weather is similar to a warm front.

42. Weather Maps and Forecasting • Mid-latitude cyclones • Mix polar and tropical air-masses. • First develop in areas of low pressure. • The greater the pressure gradient, the faster the winds move into the low, and the greater the impact of the Coriolis Effect. • The counterclockwise flow circulates the warm air northward and the cold air southward. • Fronts occur at the interfaces of air-masses.

46. Weather Maps and Forecasting • Making predictions • Decreasing air pressure often brings warm unsettled air and rainy weather • Increasing air pressure brings cool, clear weather. • Weather systems in the United States generally move from west to east. • Look at pressure and rate of movement of air-masses to the west to predict local weather.

47. Hurricanes and Tornadoes • A hurricane is a doughnut shaped ring of counterclockwise winds exceeding 75 mph around an area of extremely low pressure. • As the air moves closer to the center of the storm, its velocity increases. • The eye of the hurricane is a relatively calm area of clear skies in the middle of the hurricane.

48. Hurricanes and Tornadoes

49. Hurricanes and Tornadoes • A hurricane is fueled by heat stored in water vapor. • The released heat warms the air and provides lift for its upward flight. • This reduces the pressure near the surface and encourages a more rapid inflow of air. • Hurricanes develop in late summer when high temperatures provide the heat and moisture. • Energy produced in 1 day is equal to US electrical energy production for 1 year.

50. Hurricanes and Tornadoes • Tornadoes are local storms of short duration that are among nature’s most destructive forces. • Violent windstorms that take the form of a rotating funnel of air that extends downward from a cumulonimbus cloud. • Winds can exceed 300 mph. • Pressure drop is usually around 25 mb, but drops of up to 200 mb have been observed.