Understanding Humidity, Temperature & Stability in Meteorology

1. 4 0 3 . 0 6 Humidity, Temperature & Stability

2. Humidity • Amount of water vapour present in the air. Relative Humidity • The ratio of water vapour present in the air compared to the amount the same volume could hold if it were saturated. • If a given mass of air is heated and no new water vapour is added, the relative humidity decreases.

3. Dew Point • The temperature to which air must be cooled, at a constant pressure, to become saturated. Saturation • When a mass of air is holding the maximum amount of water vapour it can hold, at a given temperature, it is saturated.

4. Condensation • When invisible water vapour cools, it condenses to the form of visible water droplets. Sublimation • The water vapour changes directly into ice crystals without passing through the visible water droplet stage.

5. Evaporation • When water droplets heat and form water vapour. Isotherm • Lines joining places of equal temperature

6. Freezing Point • Point at which water freezes (0°C). Boiling Point • The point at which water boils (100°C).

7. Temperature has an effect on air density. Cold air is more dense (heavier) Warm air is less dense (lighter)

8. Confirmation Stage NOTE: You must use the buttons in the Confirmation Stage

9. Meteorology Humidity, Temperature, & Stability Let's try a few review questions on Meteorology: Question #1 - What name is given to the ratio of water vapour present in the air compared to the amount the same volume could hold if it were saturated. A Dew Point B Sublimation ratio C Relative humidity Isotherm D

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12. Meteorology Humidity, Temperature, & Stability Let's try a few review questions on Meteorology: Question #2 - What are lines joining places of equal temperature? A Isobars B Isotherms C Dew Point Saturation D

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15. Atmospheric Heating The Atmosphere is heated from below. Radiation short wave radiation from the sun is absorbed by the earth’s surface and re-radiated to the atmosphere in long waves. This long wave radiation heats the troposphere from below. Advection as colder air moves over a warmer surface, it is heated by contact with this surface.

16. Atmospheric Heating The Atmosphere is heated from below. Compression as air sinks, it moves into an area of higher pressure and is compressed. As it compresses it heats up.

17. Heat Distribution Aloft Conduction heat gradually diffuses through an object, moving from hot to cold. Plays a very minor role in weather. Convection when warm air rises, colder air moves in to replace it causing a vertical circulation resulting in heat distribution. Turbulence friction between the earth’s surface and the moving air causes mechanical turbulence which results in heat distribution.

18. Atmospheric Cooling Advection warm air moves over a cooler surface and cools down by contact with this surface. Expansion As air is forced to rise, it expands and cools. Radiation After sunset, the earth continues to radiate its heat thus becoming cooler. Air in contact with this cooler surface becomes cooler.

19. Vertical Distribution of Temperature Decrease of temperature with altitude is know as lapse rate. Increase in temperature with altitude is know as an inversion. Types of lapse rates Dry Adiabatic 3.0 °C / 1000’ Wet Adiabatic 1.5 °C / 1000’ ICAO 1.98°C / 1000’

20. Stability and Instability Stability The tendency of air to remain at its horizontal level when distributed. It resists upward or downward displacement. Instability The tendency of air to continue to move away from its original horizontal level when disturbed.

21. Relationship between Lapse Rate and Stability Unstable air is indicated by a steep lapse rate Stable air is indicated by a shallow lapse rate Heating from below causes instability Cooling from below causes stability

22. Weather Characteristics

23. Confirmation Stage NOTE: You must use the buttons in the Confirmation Stage

24. Meteorology Humidity, Temperature, & Stability Let's try a few review questions on Meteorology: Question #3 - Earth absorbs the suns short wave radiation then re-radiates this heat to the atmosphere in long waves. A Radiation B Convection C Turbulence Expansion D

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27. Meteorology Humidity, Temperature, & Stability Let's try a few review questions on Meteorology: Question #4 - What is the dry lapse rate? A 1.98°C/1000ft B 2.0°C/1000ft C 3.0°C/1000ft 1.5°C/1000ft D

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30. Meteorology Humidity, Temperature, & Stability Congratulations!! You have now completed the Humidity, Temperature & Stability lesson of the Meteorology Module. Of course, this lesson is always available to you for future reference if required. You are now ready to move along to the next Meteorology lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam. Good Luck!