2.1 Atmosphere and weather: diurnal energy budgets Flashcards
Define evaporation
Evaporation is the physical process by which moisture is lost directly into the atmosphere from water surfaces and the soil due to the effects of air movement and sun’s heat. This involves a change of state (liquid to gas). Rates vary depending upon humidity, wind velocity, insolation and nature of ground surface.
Define condensation
Condensation is the process by which the state of water vapour (gas) in the atmosphere is changed into a liquid (1), or if temperatures fall below 0 °C, a solid. It results from air being cooled until it is saturated at the dew point. (1)
Define sublimation
Sublimation is the change of state from a solid, usually ice or snow, directly into a gas, usually water vapour.
Define relative humidity
Relative humidity is the amount (percentage) of water vapour in the air compared to that which can be held at a particular temperature, with 100% relative humidity being saturated.
Define absolute humidity
Absolute humidity is the mass of water vapour which is present in the air at any one time.
Define humidity
Humidity is the water content of the atmosphere and can either be absolute or relative humidity.
Define stability
Stability is when the rising parcel of air is cooling more quickly than the surrounding air (i.e. the parcel of air has a higher lapse rate).
Define instability
Instability is when the rising air is cooling more slowly than the surrounding air (i.e. the parcel of air has a slower lapse rate than the surrounding air).
Define convection
Convection is when air is warmed during the daytime and rises in pockets as thermals. (1) As air expands, it uses energy and loses heat and the temperature drops. (1) Air is cooled by reduction of pressure with height. (1)
Define orographic uplift
Orographic uplift is when warm, moist air is forced to rise as it crosses a mountain barrier (orographic ascent).
Define fog
Fog is the suspended water droplets producing Fog of visibility less than 1 km.
Define dew
Dew is water in the form of droplets (1), caused by condensation or cooling on exposed surfaces (1).
Define latent heat transfer
Latent heat is the amount of heat energy needed (1 mark) to change the substance from say a liquid to a gas (1 mark) or the heat released (1 mark) when a gas condenses into a liquid (1 mark).
Define sensible heat transfer
Sensible heat is heat absorbed or given off by a substance, transfer is usually by conduction.
Define high pressure
High pressure is an area of descending air (high level convergence) that increases pressure (isobars) at the surface
Define low pressure
Low pressure is an area of ascending air (1) (often associated with convectional heating (1)) and hence low pressure (isobars) at the surface.
Define terrestrial radiation
Terrestrial radiation is outgoing long wave radiation (1) consequent upon the heating of the earth’s surface by solar radiation. (1)
Define incoming solar radiation
The energy emitted from the sun (1 mark) that reaches the earth as short wave radiation (1 mark).
Define solar radiation
Solar radiation is incoming short wave radiation from the sun.
Define reflected solar radiation
Radiation which is reflected (bounced off) the Earth’s surface (1 mark). Any elaboration i.e. shortwave radiation / albedo etc. (1 mark)
Define temperature inversion
Temperature inversion is the state of the atmosphere where temperature increases with altitude rather than decreasing. Opposite state to usual
Define albedo
The amount / percentage / fraction of short wave radiation (1) reflected back (1) depending on the surface (1)
Define radiation cooling
Loss of heat (1) by thermal radiation (1) results from outgoing radiation being greater than incoming radiation (1)
What factors affection incoming solar radiation
1) The solar constant – the energy released by the sun. This does vary in amount as it is linked to the amount of sunspot activity on the Sun.
2) The distance of the Earth from the Sun – our distance is not constant due to orbital rotation; this can cause a 6% variance in the amount of solar energy being received.
3) The altitude of the Sun in the sky – as the Earth is a sphere, the amount of incoming solar radiation being received varies greatly depending on the angle of the Earth’s surface that is falling on. The same amount of solar radiation above 60° north and south of the Equator has to cover twice the land surface compared to the Equator.
4) The length of night and day experienced – as the Earth is tilted at an angle of 23.5° there is a long period of time during the year when areas north of the Artic Circle (66.5° north of the Equator) and south of the Antarctic Circle (66.5° south of the Equator) do not receive any incoming solar radiation; the areas between the two Tropics of Cancer and Capricorn (at 23.5° north and south of the Equator, respectively) receive high amounts all year round.