Meteorology

5.01 Heating and Cooling of the AtmosphereReferences:

FTGU pages 123, 124, 136 and 137

5.01 Heating and Coolingof the Atmosphere

• MTPs:– Vertical Structure– Composition– ICAO Standard Atmosphere– Temperature Scales– Atmospheric Properties– Atmospheric Density– Temperature Differences– Heating and Cooling

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

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

Vertical Structure

Vertical Structure

• Label the layers of the atmosphere!

• Choose from these:– Stratosphere– Thermosphere– Exosphere– Troposphere– Mesosphere

Composition

• The atmosphere is made up of a mixture of gases– Nitrogen (78%)– Oxygen (21%)

– Other (~1%) (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

Nitrogen

Oxygen

Other

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

Temperature

• Sun heats earth, earth heats atmosphere• Celsius (nearly worldwide):

– Freezing point of water: 0°C– Boiling point of water: 100°C

Atmospheric Properties

• 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

Atmospheric Properties

• 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!

– www.youtube.com/watch?v=Li9eyds1Y_g

Atmospheric Properties

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

Atmospheric Density

• Density Relationships:–Density vs. Temperature:

• Indirectly proportional

–Density vs. Humidity:• Indirectly proportional

–Density vs. Pressure:• Directly proportional

Confirmation

• Questions • 1. What is the most important property of the

atmosphere?

• 2. If the density of the air increases, what happens to the pressure?

• 3. What gas makes up the majority of the atmosphere?– Nitrogen 78%

Temperature Differences

• Horizontal Temperature Differences– Diurnal Variation– Seasonal Variation – earth’s tilt– Latitude- north pole versus equator– Topography

• Land and water differences– Clouds

• Clouds reflect large amounts of solar radiation

• At night, clouds trap the heat radiated off the earth

Atmosphere Heating

• Types of Atmospheric Heating:

– Radiation (heating)• Earth absorbs

sun’s short wave radiation

• The lower atmosphere is then heated by the earth

66

LONG & SHORT WAVELONG & SHORT WAVE’’SS

SHORT WAVEINSOLATION

LONG WAVETERRESTRIALRADIATION

Atmospheric Heating

– Conduction• If two substances are

in contact, heat will flow from the warmer to the colder substance

• Air is a poor conductor, so this usually only occurs in small layers

• Same as the heat transferred when roasting marshmallows

Air warmed by conductionAir warmed by conduction

Cool airCool air

Cold airCold air

Solar radiationSolar radiation

warm surfacewarm surface

Atmospheric Heating

– Convection• Air heated

through conduction becomes buoyant and rises

• This air then heats the air in the upper atmosphere

99

COLD AIR

COLD AIR

COLD AIR

mixing

occurs

warmwarmairair

risesrises

heat is carriedheat is carriedverticallyvertically

by convectionby convection

WARM SURFACEWARM SURFACE

Convection

Atmospheric Heating

– Advection (heating)

• Occurs when cold air moves over a warm surface and its lower layer is heated by conduction

advectiveadvectivewarmingwarming

COLDCOLD WARMWARM

WARM SURFACEWARM SURFACE

Advection

Atmospheric Heating

– Turbulent Mixing• Turbulent air

mixes a warmer surface layer of air with an unheated air aloft, spreading the heat upward

1111

TURBULENT MIXINGTURBULENT MIXING

WIND CAUSES WIND CAUSES TURBULENCE TURBULENCE

MIXES LOW MIXES LOW LEVEL HEAT TO LEVEL HEAT TO UPPER LEVELSUPPER LEVELS

Cool air

warm surface

warm air

Turbulentmixing

Atmospheric Heating

–Compression• As air descends it compresses due to increased pressure and therefore heats up

CompressionSinking Air iscompressed byhigher pressure and its temperature will increase

Atmospheric Cooling

– 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

Advection CoolingAdvection Cooling

cool surface

COLDCOLD

WARMWARM

advective cooling

Warm Air moving Over a cooler surface

Atmospheric Cooling

– 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

WARMWARM

Lower pressure Lower pressureCOOL

AIREXPANDS

&COOLS

Expansion Cooling

Confirmation

Questions1. Name 2 types of atmospheric heating

2. Name 2 types of atmospheric cooling

3. Describe how the earth is heated and cooled through radiation.

4. Which layer of the atmosphere contains all weather?

Soaring