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"WEATHER” TOPIC 8

"WEATHER” TOPIC 8. weather -. condition of the atmosphere at any given location for a short period of time. Weather variable are used to describe the condition of the atmosphere (the weather). On a weather map, weather variables are shown with a station model. Examples of weather variables;.

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"WEATHER” TOPIC 8

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  1. "WEATHER”TOPIC 8

  2. weather - • condition of the atmosphere at any given location for a short period of time.

  3. Weather variable are used to describe the condition of the atmosphere (the weather). • On a weather map, weather variables are shown with a station model.

  4. Examples of weather variables; temperature, air pressure, wind, moisture conditions, cloud cover, precipitation, and storms. 4

  5. Most of the weather changes occur in the troposphere. The troposphere is the part of the atmosphere immediately above Earth's surface. (ESRT pg14!)

  6. Max. Airspace altitude from 40,000 feet (7.6 miles) Mount Everest 29035 feet (5.5 miles)

  7. Weather is caused by variations in insolation. (land vs water, angle of insolation, etc.) • Variations in insolation cause unequal heating of Earth’s surface. • Heat energy tends to move, high concentration to low concentration. • The movement of heat energy causes change within the atmosphere = weather.

  8. 7.1) ATMOSPHERIC TEMPERATURE Temperature conversions; Celsius, Fahrenheit, Kelvin scales (see Earth Science Reference Tables). Examples;

  9. Air temperature is usually measured using a thermometer.

  10. Temperature is modeled on maps and charts by the use of lines called isotherms.

  11. Heating of the Atmosphere. The sun is the original source of almost all the heat in the atmosphere.

  12. 5 ways in which the atmosphere is heated 1 -Absorption of insolation by gases and aerosols. 2 -Conduction between Earth's surface and the atmosphere. 3 - Absorption of long-wave radiation from earth by green house gases. 4 - Condensation releases latent heat into the atmosphere. 5 - Friction from the Coriolis effect.

  13. Convectional Transfer of Heat in the Atmosphere. Heat energy is transferred within the atmosphere by convection.

  14. Differences in air pressure cause air to move in circular patterns called convection currents. • Wind isthe part of the convection current that is parallel to Earth's surface (or the horizontal movement of air at Earth’s surface).

  15. Heating of Air by Compression &Cooling of Air by Expansion. When a gas expands… • its temperature decreases. example ; spray can, car tire. When a gas is compressed…. • its temperature increases.

  16. Within the troposphere….. As air rises • atmospheric pressure decreases… • the air expands and • its temperature decreases. As air descends… • atmospheric pressure increases… • the air is compressed and • its temperature increases.

  17. Sinking air becomes warmer Rising air becomes cooler mountain (side view)

  18. Under average conditions air temperature in the troposphere decreases with increasing altitude.

  19. See Earth Science Reference Tables; "Selected Properties of Earth's Atmosphere"

  20. 7.2) ATMOSPHERIC PRESSURE & DENSITY

  21. The denser the atmosphere… • the greater its weight, and • the greater its air pressure.

  22. atmospheric pressure - • a.k.a.; barometric pressure or air pressure. • the pressure due to the weight of the overlying atmosphere. diagram

  23. Measurement of and Changes in Air Pressure • The instrument that is used to measure air pressure is a… barometer. Mercury barometer

  24. Air pressure is measure in either • Millibars • Inches

  25. To convert from millibars to inches of mercury use the Earth Science Reference Tables, page 13. Examples. • 976.0 mb = • 1001.0 mb = • 30.00 inches = • 29.09 inches = 28.82 inches 29.56 inches 1016.0 mb 985.0 mb

  26. Lines drawn on a weather map that connect locations that have the same barometric pressure are called… isobars

  27. The Effect of Temperature on Air Pressure. As the temperature of the air increases, the air expands and its density and pressure decrease. • example; Hot Air Balloon

  28. The Effect of Water Vapor on Air Pressure. The greater the amount of water vapor in the air, the lower the air density and pressure. molecular weight water (H20) 1(2) + 16 = 18 molecular weight air Nitrogen (N2) Oxygen (O2) 14 (2) = 28 16 (2) = 32 one molecule of water weighs less than one molecule of air.

  29. The Effect of Altitude on Atmospheric Pressure. As altitude or elevation increases, atmospheric density and pressure decrease. diagram

  30. less pressure more pressure

  31. SUMMARY; As either altitude, temperature or moisture content increases, air pressure decreases.

  32. 7.3) WIND wind • the horizontal movement of air parallel to Earth's surface.

  33. Wind Speed Winds are caused by differences in air pressure. • air moves from High pressure towards Low pressure. Differences in air pressure are caused by… • differences in temperature. • differences in water vapor content.

  34. air pressure gradient • the difference in air pressure for a specific distance. • The closer together the isobars on a weather map are, the greater (steeper) the pressure gradient. • The greater the pressure gradient, the faster the wind. • diagram: steep gradient strong wind low gradient weak winds

  35. anemometer • an instrument that measures wind speed.

  36. Land Breeze vs. Sea Breeze (diagrams)

  37. Land breeze LOW HIGH air sinks air rises cool warm LAND WATER

  38. Sea breeze LOW HIGH air rises air sinks warm cool LAND WATER

  39. Wind Direction. • Wind moves from areas of high pressure to areas of low pressure.

  40. Coriolis effect • (caused by Earth rotation) • deflects winds to the right in the Northern Hemisphere. • deflects winds to the left in the Southern Hemisphere.

  41. A wind is named for the direction from which it comes.

  42. wind vane(weather vane) • measures the direction of the wind.

  43. 7-4)CIRCULATION OF AIR IN THE TROPOSPHERE.

  44. Convection Cells. Unequal distribution of insolation on Earth results in… unequal heating and differences in air pressure. Mean January prevailing surface winds and centers of atmospheric pressure, 1959-1997. The distribution of solar radiation at the earth's surface. (Source: NASA)

  45. Cooler air, is more dense, and sinks. Warm air, is less dense, and rises.

  46. Complete Activity on Earth Pressure Belts Air rises at 0o latitude (the equator) and 60o North and South Latitudes. Air sinks near 30o and 90o North and South Latitudes. Regions where air comes together are called regions of convergence. Regions where air spreads out are regions of divergence.

  47. 90oN H L 60oN H 30oN 0o L H 30oS L 60oS H 90oS

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