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Meteorology Humidity, Temperature Stability

Humidity. HumidityAmount of water vapour in airCondensationInvisible water vapour cools, turns to visible water dropletsSublimationWater vapour changes directly to ice crystalsEvapourationWater droplets heat, turn into water vapour. Relative Humidity. SaturationWhen mass of air holds maxi

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Meteorology Humidity, Temperature Stability

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    1. Meteorology Humidity, Temperature & Stability Pilot Ground School 2008 - Lesson 4.5

    2. Humidity Humidity Amount of water vapour in air Condensation Invisible water vapour cools, turns to visible water droplets Sublimation Water vapour changes directly to ice crystals Evapouration Water droplets heat, turn into water vapour

    3. Relative Humidity Saturation When mass of air holds maximum amount of water vapour Dew Point Temperature air must be cooled (at constant pressure) to become saturated Relative Humidity Ratio of water vapour in given air mass compared to amount it could hold if saturated If given air mass is heated, then relative humidity decreases If given air mass is cooled, then relative humidity increases If water vapour is added, then relative humidity increases If water vapour is lost, then relative humidity decreases

    4. Temperature Freezing point for water = 0°C Boiling point for water = 100°C Isotherm Lines on weather map joining places of equal temperature Temperature effect on air density Cold air = More dense (heavier) Warm air = Less dense (lighter)

    5. Atmospheric Heating Atmosphere is heated from below (ground) Radiation Heating Ground heats up from sun during day, releases heat into air above Conduction Heat gradually transfers from one air mass to another, from hot to cold Very minor role in weather, air not a good conductor

    6. Heat Distribution Aloft Convection Warm air rising, causes cold air to replace it. Vertical circulation distributes heat Advection Cooling Cold air moving over warm surface gets heated Turbulence Mechanical turbulence distributes heat through vertical air movement Compression (AKA Subsidence, AKA Adiabatic Heating) When air sinks, it compresses and heats

    7. Atmospheric Cooling Radiation Cooling Ground cools during night, cools air above Advection Cooling Warm air moving over cold surface gets heated Expansion (AKA Adiabatic Cooling) When air rises, it expands and cools

    8. Lapse Rate Lapse Rate Decrease of temperature with altitude Lapse Rates ICAO Standard = 1.98°C / 1000 ft Dry Adiabatic = 3°C / 1000 ft Saturated (Wet) Adiabatic = 1.5 °C / 1000 ft Inversion Increases of temperature with altitude

    9. Air Stability Stability Tendency of air to stay at its horizontal level when moving Air resists upward or downward movement Instability Tendency of air to continue to move away from original horizontal level when disturbed

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