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Meteorology. 5.03 Moisture References: FTGU pages 135-138, 146-147. 5.03 Moisture. MTPs: Humidity Changes of State Dew and Frost Cloud Formation Precipitation ICAO Lapse Rates Inversion and Isothermals. Humidity. Relative Humidity

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  1. Meteorology 5.03 Moisture References: FTGU pages 135-138, 146-147

  2. 5.03 Moisture • MTPs: • Humidity • Changes of State • Dew and Frost • Cloud Formation • Precipitation • ICAO Lapse Rates • Inversion and Isothermals

  3. Humidity • Relative Humidity • Ratio of water present in air compared to the amount the same volume could hold if it were saturated • Dew Point • Temperature to which air must be cooled at constant pressure to become saturated

  4. Humidity • The warmer the air, the more water vapour it can hold...Why? 1 kg air at 0 degrees = 5g water 1 kg air at30 degrees = 30g water

  5. Humidity • Example • If we took a parcel of air at 10oC at 100% relative humidity and warmed it up, how would the relative humidity change?

  6. Confirmation • Define Relative Humidity • Define Dew Point

  7. Changes of State • Freezing • Evaporation • Melting • Sublimation • Condensation

  8. Changes of State

  9. Confirmation • What do you call a change of state from liquid to solid? • From solid to gas? • From vapour to liquid?

  10. Dew and Frost • Dew and Frost form on clear, still nights • Vegetation and other objects cool by radiation below the dewpoint • If the dewpoint is above freezing, dew will form by condensation • If the dewpoint is below freezing, frost will form by sublimation

  11. Cloud Formation • Invisible water vapour becomes visible as water droplets or ice • Condensation of water vapour

  12. Cloud Formation • What is required: • High relative humidity • Condensation nuclei • Cooling of the air • Cold surface • Adiabatic cooling

  13. Cloud Formation • Steps • Air is heated and rises • Air cools to point of saturation • Air condenses onto condensation nuclei

  14. Confirmation • What are the three things required for cloud formation?

  15. Precipitation • Water droplets grow in size and weight and fall due to gravity • Can also occur below freezing (water vapour and ice crystals) The average rain drop is a million times larger than a cloud water droplet

  16. Precipitation If the cloud is….. • Below freezing – joining of ice crystals • Above freezing = rain • If temp below is cold enough to allow crystals to fall to ground = snow

  17. Precipitation • Regions of a cloud • Snow • Rain and/or snow • Rain • Large drops and heavy rain = strong vertical motion

  18. Precipitation Types of precipitation • Drizzle • very small drops of water which appears to float • Rain • Large water droplets

  19. Precipitation • Hail • Hard transparent layer of ice covering soft white core • Snow Grains • Tiny snow crystals that have acquired a coating of rime

  20. Precipitation • Snow Pellets • Soft white ice (hail without hard transparent layer • Snow • Agglomeration of ice crystals hexagonal/star shaped

  21. Precipitation • Ice Prisms • Tiny ice crystals in the form of needles • Ice Pellets • Formed by freezing of raindrops

  22. Confirmation • What are the 8 different types or precipitation?

  23. ICAO Lapse Rates • Lapse rate • Rate of decrease in temperature with altitude

  24. ICAO Lapse Rate • Lapse rates: • Recall ICAO Standard Atmosphere: • Air is perfectly dry gas • Mean sea level pressure of 29.92 • Mean sea level temp of 15°C

  25. ICAO Lapse Rates • Can determine base of clouds: • Temperature on ground 10 degrees • Dew point 7 degrees • Lapse Rate Dry Adiabatic (3°C/1000 ft) • Cloud base = 1000 feet

  26. Inversion and Isothermals • There are exceptions to standard lapse rates • Inversion • Increase in temperature with altitude • Isothermal Layer • Layer in which temperature remains the same • Both these conditions produce stability. More on this in 5.05

  27. Confirmation 1. What is the dry adiabatic lapse rate? • _____ degrees per _________feet 2. What is hail? 3. A parcel of air has a relative humidity of 50%. If the temperature were to decrease how would the relative humidity change?

  28. Rain on the Beach

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