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Water in the Atmosphere

Water in the Atmosphere. I. Atmospheric Moisture. Water exists on Earth in 3 forms: Liquid Solid (ice) Gas. In our atmosphere, water exists mainly in its gaseous form: water vapor What is the principal source of water vapor in Earth’s atmosphere?. The oceans!. A. Humidity.

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Water in the Atmosphere

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  1. Water in the Atmosphere

  2. I. Atmospheric Moisture Water exists on Earth in 3 forms: • Liquid • Solid (ice) • Gas

  3. In our atmosphere, water exists mainly in its gaseous form: water vapor What is the principal source of water vapor in Earth’s atmosphere?

  4. The oceans!

  5. A. Humidity • Humidity: the amount of water vapor in the atmosphere • Saturated: when the air is holding all the water vapor it can at a given temperature

  6. As the air temperature increases, what happens to the amount of water vapor that volume of air can hold?

  7. Warmer air can hold more water vapor than cold air

  8. 1. Relative Humidity: ratio of the amount of water vapor in the air to the amount it can hold when saturated. • Psychrometer: instrument used to measure relative humidity. Sling Electronic

  9. What does it mean to say the air is saturated?

  10. It cannot hold any more water!

  11. What happens when the air becomes saturated?

  12. Fill in the blank… The higher the relative humidity, the _______________ the chance that water vapor will condense into rain or snow.

  13. When a certain volume of air is saturated, what is its relative humidity?

  14. 100%

  15. As outside temperatures increase during the day, what happens to relative humidity? Hygrometer

  16. RH decreases (with increasing temperatures)

  17. If outside temperatures stay the same or decrease, what happens to relative humidity?

  18. RH increases (greater chance of precipitation) with decreasing temperatures

  19. 2. Specific Humidity • The actual amount of moisture in the air. High Low

  20. B. Dew Point • The temperature to which air must be cooled to reach saturation • At any temperature lower than the dew point, water vapor begins to condense

  21. What happens during condensation?

  22. Water vapor changes to liquid water

  23. Dew: air contacts a cool surface and loses heat until it reaches saturation

  24. Frost: if dew point falls below freezing, water vapor changes directly to solid ice crystals, or frost

  25. II. Clouds • Clouds are visible masses of liquid water droplets suspended in the atmosphere

  26. A. Cloud Formation • Clouds form when water vapor condenses into liquid water droplets in the air • In order for condensation to occur: • air must be saturated (cooled to dew point) • must have a solid surface to condense on (condensation nuclei)

  27. Condensation Nuclei: small particles in the air created by: dust volcanoes factory smoke forest fires ocean salt

  28. Several processes may bring about the cooling necessary for clouds to form:

  29. 1. Convective Cooling • Most clouds form this way • Air temperatures decrease as air rises and expands

  30. Adiabatic Temperature Changes: • temperature changes without the addition or removal of heat • temperature changes due to rising or sinking air

  31. Warm air rises, expands and cools What happens to cool air?

  32. Cool air sinks, compresses and warms

  33. 2. Forceful Lifting Air cools as it is forced over a topographical feature (like a mountain range).

  34. 3. Temperature Changes Cold Air Warm Air Two masses of moist air with different temperatures mix

  35. 4. Advective Cooling • Wind carries warm moist air over cold oceans or cold land • The cold water or land absorbs heat from the air and the air cools

  36. B. Classifications of Clouds

  37. 1. Stratus Clouds • low level clouds • sheet-like or layered • cover a large area • Nimbostratus= stratus cloud with rain • Altostratus = stratus formation at higher altitude

  38. 2. Cumulus Clouds • puffy, piled, popcorn, or heaped • form when warm moist air rises and cools • flat base • Cumulonimbus: cloud of great vertical development (“thunderhead”) • middle altitude clouds

  39. 3. Cirrus Clouds • cirrus means “curly” • wispy, stringy • high altitude clouds • made up of ice crystals due to the low temperature and high altitude • seen prior to a snowfall or rainfall

  40. Any moisture that falls from the air to Earth’s surface May be liquid or solid Four main types: rain snow sleet hail III. Precipitation

  41. 1. RAIN: forms when separate drops of water fall to the Earth from clouds

  42. 2. SNOW: forms when water vapor condenses directly into ice crystals

  43. 3. SLEET: a mixture of snow and rain; forms when rain passes through a cold layer of air and freezes into ice pellets

  44. 4. HAIL: balls or irregular lumps of ice (hailstones); usually form in cumulonimbus clouds

  45. Big Hail!

  46. Bad Hail!

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