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

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 Dew Point
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?
-Warm air can hold much more moisture (water vapour) than cold air. For example, one kilogram of dry air at 30c can hold 30 grams of water vapour before it becomes saturated. One kg of dry air at 0c can hold only 5gms of water vapour before it is saturated. This is because one kg of warm air has a much greater volume than one kg of cold air, thus allowing it to hold a greater quantity of water vapour.
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
The ratio of water present in the air compared to the amount the same volume could hold if it were saturated
Temperature to which air must be cooled at constant pressure to become saturated

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?
Freezing
Sublimation
Condensation

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

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

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

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

15. Confirmation What are the three things required for cloud formation?
High relative humidity
condensation nuclei
cooling of the air

17. 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

18. Precipitation Above freezing = rain
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

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

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

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

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

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

24. Confirmation
What are the 8 different types or precipitation?

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

26. 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
Dry Adiabatic
3.0 °C / 1000 ft
Saturated Adiabatic
1.5° C / 1000 ft
Standard
2.0 °C / 1000 ft
ICAO
1.98 °C / 1000 ft

27. 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

28. 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

29. Confirmation 1. What is the dry adiabatic lapse rate? 2. What is hail?
_____ 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?
Hard transparent layer of ice covering soft white core

30. Rain on the Beach