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Meteorology

Explore the fundamentals of moisture in meteorology, including humidity, changes of state, cloud formation, and precipitation. Learn about key concepts like relative humidity, dew point, and types of precipitation. Discover how air temperature affects water vapor capacity and cloud formation processes.

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Meteorology

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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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