Ground School: Meteorology 5.03 Moisture References: -Transport Canada Study and Reference Guide Pilot - -FTGU pages 135-138, 146-147 Instructor 40 Minutes

Ground School 5.03 Meteorology - Moisture MTPs: Relative Humidity and Dew Point Changes of State Cloud Formation Precipitation ICAO Lapse Rates

Ground School 5.03 Meteorology - 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

Ground School 5.03 Meteorology - 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

Ground School 5.03 Meteorology - 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?

Ground School 5.03 Meteorology - Humidity Questions: 1. Define Relative Humidity. The ratio of water present in the air compared to the amount the same volume could hold if it were saturated 2. Define Dew Point Temperature to which air must be cooled at constant pressure to become saturated

Ground School 5.03 Meteorology – Changes of State Freezing Evaporation Melting Sublimation Condensation

Freezing Melting Evaporation Sublimation WATER ICE Sublimation SOLID LIQUID Melting WATER ICE Evaporation Sublimation Sublimation Condensation GAS Review diagram. Some everyday examples of these processes are; Clouds forming = Condensation. Freezing = Ice. Sublimation = Hoar frost Sublimation = Hoar frost dissipates Melting = Ice/Snow to water Evaporation = Lakes, Rivers lowering etc. QTC: Can you think of any any other examples? WATER VAPOUR

Ground School 5.03 Meteorology – Changes of State Questions: 1. What do you call a change of state from liquid to solid? Freezing 2. From solid to gas? Sublimation 3. From vapour to liquid? Condensation

What kind of cloud? Cloud Formation

Ground School 5.03 Meteorology – Cloud Formation Invisible water vapour becomes visible as water droplets or ice Condensation of water vapour

Ground School 5.03 Meteorology – Cloud Formation What is required: High relative humidity Condensation nuclei Cooling of the air Cold surface Adiabatic cooling

Ground School 5.03 Meteorology – Cloud Formation Steps Air is heated and rises Air cools to point of saturation Air condenses onto condensation nuclei

Ground School 5.03 Meteorology – Cloud Formation Question What are the three things required for cloud formation? High relative humidity condensation nuclei cooling of the air http://www.physicalgeography.net/fundamentals/8c.html

Precipitation

Ground School 5.03 Meteorology – 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

Ground School 5.03 Meteorology – 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

Ground School 5.03 Meteorology – Precipitation Regions of a cloud Snow Rain and/or snow Rain Large drops and heavy rain = strong vertical motion

Ground School 5.03 Meteorology – Precipitation Types of precipitation Drizzle very small drops of water which appears to float Rain Large water droplets

Ground School 5.03 Meteorology – Precipitation Hail Hard transparent layer of ice covering soft white core Snow Grains Tiny snow crystals that have acquired a coating of rime

Ground School 5.03 Meteorology – Precipitation Snow Pellets Soft white ice (hail without hard transparent layer Snow Agglomeration of ice crystals hexagonal/star shaped

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

Online Ground School 5.03 Meteorology – Precipitation Question What are the 8 different types or precipitation?

Online Ground School 5.03 Meteorology – ICAO lapse rate Rate of decrease in temperature with altitude

Ground School 5.03 Meteorology – 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

Ground School 5.03 Meteorology – ICAO lapse rate Can determine base of clouds: Temperature on ground 10 degrees Dew point 7 degrees Lapse Rate Saturated adiabatic (1.5/1000 ft) Cloud base = 2000 feet

Ground School 5.03 Meteorology – ICAO lapse rate Inversion Increase in temperature with altitude Isothermal Layer Layer in which temperature remains the same

Ground School 5.03 Meteorology – Confirmation 1. What is the dry adiabatic lapse rate? _____ degrees per _________feet 2. What is hail? Hard transparent layer of ice covering soft white core 3. A parcel of air has a relative humidity of 50%. If the temperature were to decrease how would the relative humidity change?