5.01 Heating and Cooling of the Atmosphere Ground School: Meteorology 5.01 Heating and Cooling of the Atmosphere References: -Transport Canada Study and Reference Guide Pilot - FTGU pages 123,124, 136 and 137 Instructor 40 Minutes

Ground School 5.01 Heating and Cooling of the Atmosphere MTPs: Vertical Structure Composition ICAO Standard Atmosphere Temperature Scales Atmospheric Properties Atmospheric Density Temperature Differences, Heating and Cooling

Ground School 5.01 Vertical Structure Troposphere Weather happens here To 25,000 – 30,000 feet over poles To 55,000 – 65,000 feet over equator Temperature decreases with height Stratosphere Troposphere to 170,000’ Temperature increases with height

Ground School 5.01 Vertical Structure Mesosphere Stratosphere to 270,000’ Temperature decreases with height, to -85°C Thermosphere Tops at 1.1 million to 2.6 million feet (350-800 kilometres) Temperature increases with height, up to 1,500°C Exosphere Mainly comprised of hydrogen and helium Extends into space

Ground School 5.01 Vertical Structure Label the layers of the atmosphere! Choose from these: Stratosphere Thermosphere Exosphere Troposphere Mesosphere

Ground School 5.01 Composition The atmosphere is made up of what main gases? Answer: Nitrogen Oxygen Other (Argon, CO2, water vapour, etc) *Although water vapour is less than 1% of the atmosphere, it remains the most important component from the standpoint of weather, based especially on its ability to change state.

Ground School 5.01 ICAO Standard Atmosphere The International Civil Aviation Organization (ICAO) Standard Atmosphere: Sea Level for North America Based on summer and winter averages at 40°N latitude The Standard: MSL pressure of 29.92” Hg (1013.25 hpa) MSL temperature of 15°C Air is a “perfectly dry gas” Lapse rate of 1.98°C per 1000 feet

Ground School 5.01 Temperature Scales Sun heats earth, earth heats atmosphere Celsius (nearly worldwide): Freezing point: 0°C Boiling point: 100°C Fahrenheit (USA): Freezing point: 32°F Boiling point: 212°F Conversion  °C x (9/5) + 32 = °F ****Does anybody know of a third temperature scale??? --Kelvin 273.15°K = 0°C

Ground School 5.01 Properties of the Atmosphere Mobility The ability for air to move Atmosphere like an “ocean of air” Wind like “streams of water” (Much more freedom of movement with air than water) Compression Air is compressed as it descends into greater pressure Occupies less space

Ground School 5.01 Properties of the Atmosphere Expansion As air rises, it reaches areas of lower pressure, causing it expand and cool This cooling can be enough to condense water vapour in the air, forming cloud This is why clouds and precipitation are common in areas of rising air From a meteorological standpoint, the most important property of the air!

Ground School 5.01 Atmospheric Density Density - mass per unit volume Cold air is dense: Molecules are move slowly and are packed close together Heavier and tends to sink Warm is less dense: Molecules are moving rapidly taking up more space (or less molecules in the same space) Warm air is lighter and is pushed up by the cold air

Ground School 5.01 Atmospheric Density Density Relationships: Density vs. Temperature: Indirectly proportional As temperature increases, density decreases Density vs. Humidity: As water vapour increases, density of the air decreases Density vs. Pressure: Directly proportional As pressure decreases, density decreases

Ground School 5.01 Temperature Differences Horizontal Temperature Differences Diurnal Variation Atmosphere warms during day, cools at night Seasonal Variation Amount of solar radiation changes seasonally due to Earth’s tilt Latitude Sun is more directly overhead near equator

Ground School 5.01 Temperature Differences Horizontal Temperature Differences: Topography Land and water differences Clouds Clouds reflect large amounts of solar radiation At night, clouds trap the heat radiated off the earth i.e. earth cools more rapidly on a clear night vs. cloudy night

Ground School 5.01 Temperature Differences Types of Atmospheric Heating: Radiation (heating) Earth absorbs sun’s short wave radiation The lower atmosphere is then heated by the earth

Ground School 5.01 Temperature Differences Conduction If two substances are in contact, heat will flow from the warmer to the colder substance ie. Layers of air of different temperatures being in contact Air is a poor conductor, so this usually only occurs in small layers Unless heat is distributed through vertical motion

Ground School 5.01 Temperature Differences Convection Air heated through conduction becomes buoyant and rises This air then heats the air in the upper atmosphere

Ground School 5.01 Temperature Differences Advection (heating) Occurs when cold air moves over a warm surface and its lower layer is heated by conduction

Ground School 5.01 Temperature Differences Turbulent Mixing Turbulent air mixes a warmer surface layer of air with an unheated air aloft, spreading the heat upward

Ground School 5.01 Temperature Differences Compression As air descends it compresses due to increased pressure and therefore heats up

Ground School 5.01 Temperature Differences Types of Atmospheric Cooling: Radiation cooling Occurs at night Surface layer of air touching earth cools as earth cools Most commonly only affects first 4000 feet of the atmosphere

Ground School 5.01 Temperature Differences Advection cooling Lower levels only When air is cooled by moving over a colder surface Cooling occurs as a result of conduction between air and surface Some mechanical turbulence can aid in spreading cooling effect

Ground School 5.01 Temperature Differences Expansion cooling The most important cooling process of the air Air forced to rise experiences lower pressure and is allowed to expand This expansion causes decrease in temperature

Ground School 5.01 Temperature Differences End