Temperature And Heat Exchange Processes Flashcards
Describe the temperature reference points of the centigrade scale used in NZ aviation.
- 0degrees Celsius = water freezing or ice melting
- 100degrees Celsius = waters boiling point
- These numbers only work at 1013.25hPa - SEA LEVEL
- If pressure is reduced water will boil at a lower temperature
Explain the factors that influence the amount of solar radiation received at the earth’s surface.
- Cloud cover
- Sun’s angle of incidence to the surface (season/latitude/time of day)
- Mountains
- Albedo
Explain the warming or cooling of the atmosphere with reference to solar and terrestrial radiation.
- Daytime = Earth receives more energy than it emits, heating the atmosphere
- Night time = Earth emits more energy than it receives, cooling the atmosphere.
Describe conduction.
- Transfer of heat by touch
- Occurs faster in solids and liquids than gas
- Will only heat the first 10cm of air
Describe convection.
- Requires the air too be heated by conduction first
- Warm air becomes less dense and rises
- Cool air above is more dense and sinks
- This cool air can then be heated by conduction and rise
Describe advection.
- Horizontal transfer of heat or matter
- Also requires conduction to heat the lower parts of air
- Wind then blows the warm air through cold air and mixes
Explain how the atmosphere is warmed or cooled by conduction.
- Heats the surface
- Transferred by convection, turbulence or wind into the atmosphere.
- Over ice the cooling can only be spread by turbulence and wind.
Explain how the atmosphere is warmed or cooled by convection.
- Transfers warm air from the surface to the upper troposphere
- As the warm air rises, cooling air sinks creating a convective current.
Explain how the atmosphere is warmed or cooled by advection.
- Warm advection = warm air moving to colder areas
- Cold advection = cold air moving to warmer areas
Define the term ‘specific heat’
- The amount of solar radiation (or energy) required to increase temperature by 1degree Celsius.
- If it requires large amounts of solar radiation= high specific heat
- If it requires low amounts of solar radiation = low specific heat.
What is the specific heat of water and land?
- Water = 1
- Land = 0.2
Define the term ‘albedo’
- How reflective something is to solar radiation
- Reflects large amounts/lighter colours = high albedo
- Reflects small amounts/darker colours = low albedo
Explain the significance of the heating at Earth’s surface, in terms of specific heat.
- Land has a low specific heat
- Ocean has a high specific heat
- Land heats/cools faster than the ocean
- Creates pressure differential which creates a sea breeze or land breeze.
Explain the significance of the heating at Earth’s surface, in terms of albedo.
- Mountains covered in snow reflect solar radiation keeping them cool
- Dark roads absorb solar radiation and heat up faster
- Dark sand beaches absorb more radiation than light sand beaches
- Ocean waves make heating harder as sun angle is always changing.
Explain the significance of the heating at Earth’s surface, in terms of insolation.
- Means amount of solar radiation which strikes the Earths surface.
- Depends on: the angle of incidence of the sun’s rays
- Duration of day and distance from sun
- Transparency of the atmosphere
Describe Celsius.
- 0degrees = freezing point of water
- 100degrees = boiling point of water
- Named after Swedish astronomer Anders Celsius.
Describe Fahrenheit.
- 0degrees = freezing point of a mixture of water ice and ammonium chloride
- 100degrees = best estimate of human body temperature
- Named after Daniel Gabriel Fahrenheit
- 32degrees = water freezing
- 212degrees = water boiling
Describe Absolute (Kelvin)
- SI unit for temperature
- Uses absolute zero as its starting point
- No molecular movement at absolute zero
- Not written as a degree
What is the formula to convert Fahrenheit to Celsius?
(F - 32) x 5/9 = C
What is the formula to convert Celsius to Fahrenheit?
(C x 9/5) + 32 = F
What is the formula to convert Kelvin to Celsius?
0 K = -273.15 °C
What is the formula to convert Celsius to Kelvin?
0degrees Celsius = 273 K
Explain solar radiation.
- Solar radiation = electromagnetic radiation emitted from the Sun
Radiation is not hot but produces heat on contact.
Net gain of insolation during the day and loss at night.
Explain terrestrial radiation.
- Terrestrial radiation = electromagnetic radiation emitted from Earth.
Radiation is not hot but produces heat on contact.
Net gain of insolation during the day and loss at night.
State the wave length of solar radiation.
- Solar radiation = 0.4 - 4 micrometres
State the wave length of terrestrial radiation.
- Terrestrial radiation = 4 - 80 micrometres
Describe the effect of the sun angle on the amount of solar radiation received at the surface of the Earth.
- Sun’s angle at 90degrees to the Earth’s surface = maximum radiation received.
- Occurs near the equator
- High latitudes the angle reduces, spreading the same amount of radiation over a larger area
- Higher latitudes = less heating
Describe the effect of the length of day on the amount of solar radiation received at the surface of the Earth.
- Longer days = more solar radiation received
- Due to the delay of heating air, hottest time of day is mid afternoon
- Longer days also mean shorter nights
Describe the effect of seasons on the amount of solar radiation received at the surface of the Earth.
- Summer = most solar radiation received
- Winter = lowest amounts of solar radiation received
- Due to Earth’s tilted rotational axis at 23.5degrees orbit around the sun
Define the term solstice.
- Sun reaches most northerly or southerly latitude for the year.
- Represent the longest and shortest day
- June 20th or 21st = shortest day in SH
- Dec 21st or 22nd = longest day in SH
OPPOSITE applies for NH
Define the term equinox.
- Centre of Sun directly over the equator
- Day will be equal length in NH and SH
- March 20th and September 22nd or 23rd
State the significance of a solstice.
- June = Sun at most northern latitude (no sunlight at the South Pole.
- December = Sun at most southern latitude (no sunlight at the North Pole)
- Solar radiation for SH largest in Sep - Mar
- Lowest from Mar - Sep
State the significance of an equinox
- Only time when NH and SH have equal day length.
- Occurs twice a year
