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  1. Weather

  2. What is weather? The condition of the air (or atmosphere) at a given location at a given time

  3. Climate “Typical” weather in region; the average weather or the regular variations in weather in a region over a period of years • includes temperature, air pressure, humidity, days of sunshine, etc... • drastically affected by water & mountains • coastlines have cooler summers and warmer winters • mountains greatly slow down winds and weather

  4. Atmosphere Blanket of air surrounding the earth Air – the mixture of gases, mainly nitrogen and oxygen, that forms the Earth’s atmosphere • 78% Nitrogen • 21% Oxygen • 1% Argon • 1% Other stuff : Carbon dioxide, water vapor, ozone, dust, ash, smoke, etc.

  5. Structure of the Atmosphere

  6. Lower Layers Troposphere – the layer of the atmosphere that is closest to the earth’s surface, where all weather phenomenon occurs. 8 km thick at the poles 16 km thick at the equator; (air temperature normally decreases with height) Stratosphere - upper layer of air 8 - 16 km to about 50 km and top of the stratosphere contains the ozone layer; almost completely free of clouds.

  7. Middle and Upper layers Mesosphere – the layer of air, 50km to 80km where temperature begins to decrease with height, mainly because ozone in the stratosphere absorbs energy from the sun, principally ultraviolet radiation Thermosphere - where air temperatures can exceed 1000° C (1800° F), 80km to 9600 km, primarily due to oxygen absorbing the sun’s energetic rays

  8. Upper-Upper layers Ionosphere – the region within the atmosphere containing ionized molecules, layers of ionized air in the atmosphere extending from almost 60 km above the surface of the earth to altitudes of 1000 km and more. Exosphere - The region beyond the thermosphere, which extends to about 9,600 km, the outer limit of the atmosphere.

  9. Conditions of the Air • Temperature – amount of hotness or coldness relative to something else • Thermometer – an instrument that measures relative hotness or coldness • Dew Point temperature – The temperature at which air becomes saturated • Temperature scales: • 1°C = 1.8°F or 1°F = 5/9 ° C

  10. Heat transfer • Conduction – the movement of heat from molecule to molecule • Convection – the movement of heat by warm and cold currents • Radiation – the release and transfer of energy in wavelengths of heat and light

  11. How is the atmosphere is heated? Draw

  12. Draw on back of notes

  13. Pressure Air pressure - the downward pressure exerted by the weight of the overlying atmosphere or the “weight” of the atmosphere per unit AREA. • Barometer – an instrument used to measure air pressure Measured in inches of mercury in a column • Or millibars (metric conversion) • Average air pressure at sea level is 1013 millibars

  14. Water in the atmosphereWater Vapor • Humidity – the amount of water vapor in the air • Relative humidity – the actual amount of water vapor in the air compared to the greatest amount the air can hold

  15. Precipitation water or ice that condenses in the air and falls to the ground as: • Rain- liquid water that falls to the ground • Snow - ice crystal flakes;water vapor in the atmosphere that froze into ice crystals and falls to the ground in the form of flakes • Sleet -partially melted grains of ice • Hail - pellets made of layers of ice and snow • Freezing rain –rain that freezes into ice as it hits the ground

  16. Evaporation the process of changing from liquid to gas; molecules in a liquid state GAIN energy to change into a gaseous state (latent heat energy is the stored in molecules through evaporation) Evaporation DRIVES the water cycle

  17. Condensation • the process of changing from gas to liquid; molecules in a gaseous state that LOSE energy to change into a liquid state.

  18. Clouds • a visible mass of dense water vapor or ice suspended in the atmosphere; formed by surface heating & convection and/or warm air lifted by rising over mountains

  19. Wind Air moving at a speed fast enough to be noticed… • Low pressure – air is de-compressed (allowed to expand) and sucks air toward. • High pressure – air is compressed (contracted) and flows away. high pressure moves to low pressure Winds are named by the direction they come FROM Instruments: • WeatherVane – measures wind direction • Anemometer – measures wind speed

  20. LOCAL WINDS: Sea breeze

  21. Sea breeze wind blowing from sea to land during the day when the sun warms the land faster and cool air from above the water forces the warm air above the land to rise Draw diagrams

  22. LOCAL WINDS: Land Breeze

  23. LOCAL WINDS: Land Breeze wind blowing from land to sea at night because the land cools faster than the sea Draw diagrams

  24. Draw diagrams

  25. High pressure – air is compressed (contracted) and flows away. • Low pressure – air is de-compressed (allowed to expand) and sucks air toward. • Add the Coriolis Effect and you get ‘cyclonic’ and ‘anticyclonic’ flow.

  26. Coriolis Effect the effect of Earth’s rotation on movement of air masses

  27. (people on turn table) • • • • • – hadley cells (belts) • - belts

  28. Coriolis Effect on a Synoptic Scale • Low pressure… air moves: • Up • In • Counter clockwise • High pressure … air moves: • Down • Out • Clockwise

  29. Global Winds Draw next page

  30. Air Mass A large region of air with similar properties throughout (ie. temperature, humidity)

  31. Major Air Masses • cA – Continental Artic – dry, very cold • cP – Continental Polar – dry and cold • cT – Continental Tropical – dry and warm • mP – Maritime Polar – moist and cold • mT – Maritime Tropical – moist and warm • Draw next page


  33. Relative Humidity Comparison of the specific humidity and the maximum amount of water vapor that the air can hold at a given temperature and pressure • Unit is in percentage = % Relative humidity = specific humidity X 100% maximum capacity 100% Rel. Hum. – saturated air 0% Rel. Hum. – dry air

  34. Psychrometer Dry air - greater evaporation - greater cooling - greater the difference in the 2 temperatures High humidity – no evaporation (saturated air) - temperatures of the 2 bulbs will be the same or very close

  35. Psychrometer • Instrument to measure humidity • Dry bulb – measures air temp. • Wet bulb – has a water soak wick around the bulb – water evaporates – cools the air