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  1. Weather





  6. Properties of Gases • Compressibility – relative volume change as a response to pressure • Expandability – gases expand to fit the container • Volumes – V occupied by same amount of substance in gas form >>>> solid form

  7. Pressure= force area Amount of pressure felt is a function of both the amount of force and the area over which it is applied In SI, force is expressed in newtons (N) and area in square meters (m2).

  8. Atmospheric Pressure – pressure of the atmosphere pushing down on the earth Barometer Measured P at sea level on a sunny day using a column of Hg balances the pressure of the atmosphere pushing on the pool of Hg surrounding the column Evangelista Torricelli proposed atmosphere has weight & that it changes daily

  9. Units of Atmosphere 1 atm = 760 mm Hg (exactly) (memorize) 1 torr = 1 mm Hg (memorize) 1 atm = 101,325 Pa =101.325 kPa (SI is the pascal (Pa) with the units N/m2) 1 atm = 29.921 in Hg =1.01325 bar 1 atm = 14.696 lb/in2 =14.696 psi

  10. Pressure problem A TV weather person says the barometric pressure is “30.1 inches of mercury”. What is this pressure in a.) atm b.) mm Hg c.) torr

  11. Demo: Making a Barometer

  12. Temperature • tells the direction that heat will flow. • Always flows from hot to cold • We often use the Celsius scale (°C) for scientific work. • 0 °C is the freezing point of water and 100 °C is the boiling point. • The Fahrenheit scale (°F) is most commonly encountered in the U.S. • 32 °F is the freezing point of water and 212 °F is the boiling water are and, respectively. • TF = 1.8TC + 32 • TC = (TF – 32)/1.8

  13. Air Pressure Effects • Less air pressure at sea level than on a mountain top • An area of low pressure is air that is rising • Air cools and expands as it rises • Because cool air can hold less water than warm air, water condenses forming clouds • An area of high pressure is air that is sinking • As it sinks, air warms and can hold more water • Winds blow to counteract pressure differences • Flow from high to low pressure • But earth rotation and friction make them flow along regions of the same pressure known as isobars

  14. Wind Circulation • Horizontal movement of air across the earth’s surface • Warm, moist air along the equator rises, cools and forms huge cumulonimbus clouds • Starts water flowing to north and south • At the poles, cold air sinks forming cold, surface winds that flow toward the equator • As earth rotates, winds in north hemisphere are deflected right and left in southern hemisphere

  15. Wind Circulation • Rain results from southwesterly winds • Northeast winds blow toward equator • Doldrums is no or light, variable winds around the equator • Jet streams form the high and low pressure regions • Subtropical – ~30° north & south of equator blows westerly • Equatorial – about 10° blows easterly, seasonal (July & August) • Polar Night – about 60° north blows westerly in winter

  16. Movement of Air University of Illinois

  17. occluded front – when a cold front overtakes a warm front stationary front – front is not moving Types of Fronts dry line – when moist air separated from dry air cold front warm front University of Illinois

  18. PROCEDURE: • Fill the clear container with room temperature water. • Add a few drops of blue food coloring to the very cold ice water. • Slowly pour the cold blue water into the tub of clear water. Pour the water very slowly so that it doesn't stir. • Explain what happened. Draw a picture of what you observed. • Add a few drops of food coloring to the very hot tap water. • Very slowly pour the hot water into the tub of water. • Observe what happens and draw a picture to represent your results. Demo: Temperature effects on mixing

  19. Geographic Considerations • Oceans vs. land heating effects • Water absorbs heat during the day and emits it at night  moderating temperature • Water holds heat producing hurricanes/typhoons • Mountains vs. plains • Block wind movement or redirect it • Cools air rapidly resulting in rain effects • Deserts vs. forests • Jet streams result in areas of high & low rain

  20. Cloud Classification Latin Root Translation cumulus heap stratus layer cirrus curl of hairnimbus rain

  21. altocumulus altostratus cumulus stratus stratocumulus

  22. cirrus nimbostratus cirrocumulus cirrostratus cumulonimbus

  23. Demo: “A Cloud is Born”

  24. Temperature Effects on Weather Temperature is very important and can cause multiple effects • Hail • Fog • Lightning • Hurricanes • Etc……….

  25. Hail Formation Hailstones form when a particle (salt particle or other pollutant) is coated with water which condenses to ice The particle moves up and down a huge cloud gaining a layer of water on each trip which is super-cooled in the top turning to ice. Layers form until the stone is too heavy to be held aloft in the turbulent cloud. Largest measured 17.8 cm diameter (47.6 cm circumference) in Aurora, Nebraska on June 22, 2003.

  26. Fog and Mist • Tiny water droplets suspended in air • Cold air holds less water than hot air • Cold air sinks so fog can form on one side of a hill Dew point – the temperature at which air is 100% saturated with water • Fog forms when air temperature reaches dew point • Fog disappears with wind movement or temperature rises (burns off)

  27. Text: AIMS Education foundation 4th Georgia Earth Science