atmosphere has an energy budget.
receives energy from sun and earth (inputs) and loses energy to space (outputs).
if it loses more energy than gains, atmosphere cools down.
if gains more than loses, heats up. budget figures vary depending on who made it.
Incoming radiation (short wave radiation)
100% incoming solar radiation (insolation) is short wave radiation that comes
straight from the sun.
19% reflected by clouds, 6% lost to scattering (radiation diverted by gas and
molecules) 17% absorbed by atmosphere gases (CO2 and ozone). 4% absorbed by
clouds. 7% reflected by earth’s surface (albedo). 47% reaches surface to be
absorbed.
Outgoing radiation (long wave radiation)
energy received by earth is converted into heat when reaches surface.
as ground warms, some is re-radiated as long wave.
8% re-radiated energy lost to space.
evaporation and condensation account for a loss of 25% of the
heat energy from earth because heat energy is used up when
liquid turned into vapour (latent heat transfer).
7% re-radiated energy is absorbed by clouds, water vapour and
CO2.
Local day time energy budget
global (macro-scale) energy budget is the whole plants energy
system.
local (micro-scale) exists for individual planet areas, different at day and
night.
Definitions
incoming solar radiation: atmosphere’s main energy input
which is strongly influenced by cloud cover and latitude.
Sun’s rays more concentrated at the equator than poles.
reflected solar radiation: proportion of it varies with
surface nature. degree of reflection is referred to as
the albedo of the surface, proportion of sunlight
reflected from a surface. Snow has the highest albedo
(reflecting 95% of sunlight). Ocean surfaces absorb
more sunlight, low albedos.
surface absorption: energy arriving at surface has
potential to heat that surface as heat is absorbed.
surface nature effects. if surface can conduct heat fast
into lower soil layers, temp will be low. if heat not
carried away fast, will be concentrated at surface and
result in high temps there
latent heat (evaporation): liquid into vapour,
consumes a lot of energy. when water is present at
surface, proportion of incoming solar radiation will be
used to evaporate it. that energy won’t be available
to raise local energy levels and temps.
sensible heat transfer: transfer of heat by conduction
or convection when an air mass is in contact with a
warmer or colder surface.
long-wave radiation: emitted by surface, passes into
atmosphere and into space. downward directed
stream of long-wave radiation from particles in
atmosphere. difference between 2 streams is the net
radiation balance. during the day, outgoing stream is greater than incoming, net
energy loss from surface.
Local night time energy budget
long wave radiation loss at night (terrestrial radiation) as nights are cloudless so
nothing to return radiation back to surface. cloudy nights, energy loss reduced.
night, vapour in air close to ground can condense to form dew as air cooled by cold
surface, heat released.
heat transferred by sun to surface during day, released back to surface at night
which off-sets night time cooling at surface.
sensible heat transfer occurs, cold air moving into area reduce temps, warm air
moving in raises temps.
Mist and fog
cloud at ground level. cloud is a collection of water droplets. mist occurs when
visibility is between 1000m and 5000m. fog occurs where visibility below 1000m.
fog is thicker cloud cover than mist.
clouds form at ground level as air can only hold certain moisture amount. colder air
hold less moisture than warmer. Once max moisture amount reached, air saturated
and vapour turns to liquid. when clouds form as condensation of
water vapour to water droplets occur.
for fog/mist to form close to ground level…
air must have been cooled close to ground: advection fog; as
warm, moist air passes over cold surface it’s chilled,
condensation happens as air temp reduced so reaches
dew (saturation) point. radiation fog; occurs when
ground loses heat at night by long wave radiation so air
above is cooled causing condensation and fog.
more water vapour added to atmosphere close to ground:
can occur over warm, wet surfaces (large lakes) where water evaporated from
warm surface of lake and condenses in cold air above to form fog. for mist/fog to
form, condensation nuclei needed (e.g. dust/salt particles in air). more common in
urban/coastal areas, so mist/fog more common.
Dew
name for condensation of water on surface.
means when water vapour in air has turned into water droplets on
surface (e.g. leaf, window).
occurs as surface is cold and caused air to cool so be
saturated (reach dew point) so condensation occurred.
Temperature inversions
normally, air temp decreases with altitude, higher up in
troposphere cooler air gets.
situations where temperature inversion occurs, means there’s an abnormal layer of
warmer air above colder air in troposphere.
happens at night in calm conditions (sometimes known as a nocturnal inversion).
happens during the day when ground is heated by sun’s short-wave radiation, then
after a short time, heats air above when it emits long wave radiation.
at night, ground surface and air lose heat energy they’ve absorbed during the day.
but ground loses heat energy faster than air as more efficient heat conductor.
at end of night, ground surface is very cold, air above cooled too due to close
proximity to surface.
but air layer above still warmer as has cooled slower than ground surface, causing
temperature inversion.
temp inversion will act as a lid on pollutants causing them to remain in lower
atmosphere next to earth’s surface.
Land and sea breezes
Land is heated quicker than the sea and so the air above the land is warmer than
the air above the sea during the day. Warm day along the coast, differential
heating (one area being heated faster than another) of land and sea leads to the
development of local winds called sea breezes. Descending cool air, high pressure,
(air pushing down onto sea, hit sea and spreads and goes to an area of low
pressure). Rising warm air, low pressure.
As air above land is heated by radiation from sun, it expands and begins to rise
because the air is less dense. To replace rising air, cooler air is drawn in from
above sea surface, sea breeze, offers pleasant cooling
influence.
Land breeze: at night when land cools faster than sea at night.
Opposite to day, at night air above sea is warmer,
air above warmer surface water that is heated and
rises, pulling in air from cooler land surface.
Latitudinal patterns of radiation excesses and
deficits (net radiation)
some areas get more of sun’s energy than others.
net radiation: amount of sun’s energy that is
received by an area. net radiation is what is left
after you look at how much radiation entered an
area and how much was lost. if its 0 then energy
budget is balanced and an area neither warms nor
cools.
high albedo at poles (snow), low at equator (trees
absorbing). sun rays spread out at poles,
concentrated at equator. areas closer to equator
receive more radiation than poles.
the net radiation balance: poles have a negative
energy budget so should be getting colder and
tropics have a positive energy budget so should
be getting warmer but they aren’t because of the net radiation balance. the
balance is achieved by the horizontal transfer of energy form the equator to the
poles by winds and ocean currents to compensate for differences in global
insolation.
reasons for equator area getting more radiation…
insolation (incoming solar radiation) concentrated near equator,
dispersed near poles
insolation near poles has the pass-through greater amount of
atmosphere and there’s more change of it being reflected back
to space. reason why poles are colder.
Air pressure
gases in atmosphere press down on earth’s surface, exerting force
called air pressure, it pushes down very hard. differences in air pressure
cause different weather.
changes in air pressure make winds blow, air moves from high
pressure to low pressure and produces winds