Diurnal energy budgets
Daytime:
- Insolation is main energy input and is affected by
latitude, season and cloud cover.
- Albedo (reflected solar radiation) varies with colour.
o Black road surface has albedo of 5-10%.
o Grass has avg. albedo of 20-30%.
o Fresh snow has albedo of 75-90%.
- Surface absorption as energy reaches Earth’s surface,
which heats up (will heat up less if it can conduct heat to
lower layers).
- Sensible heat transfer involves movement of parcels of
air into and out of area, usually by convective transfer
(air warmed by surface rises).
- LWR heat loss to atmosphere and further out to space,
but also downward movement of LWR from particles in
atmosphere.
- Latent heat transfer when heat energy used to turn
liquid water into water vapour (hence when water
present at surface, proportion of energy available is
used to evaporate it, so less energy available to raise
local temperature).
- Some of reradiated LWR is absorbed by greenhouse
gases in atmosphere, raising air temperature.
Night-time:
, - During cloudless night, lots of LWR heat loss from Earth,
while on cloudy night, clouds return some LWR to
surface, reducing overall energy loss.
- Latent heat released when water vapour in air close to
surface condenses as dew (air has been cooled by cold
surface).
- Sub-surface supply heat which was transferred to soil
and bedrock during day is released back to surface at
night (partly offsetting nightly cooling at surface).
- Sensible heat transfer may reduce or increase
temperatures.
Latitudinal variations in radiation:
Radiation excess in tropics (less distance of atmosphere
that sun’s rays have to travel through, so they are more
focused and insolation is intense).
Radiation deficit in temperate regions and towards poles
(greater distance of atmosphere to travel through, so
more of SWR is reflected/absorbed/scattered by dust
and particulates in atmosphere).
Horizontal transfer of energy from equator to poles
takes place by winds and ocean currents, in form of
sensible heat (warm air masses/ocean water) and latent
heat (atmospheric water vapour, e.g. in hurricanes).
Trade winds blow from subtropical high-pressure belts
towards equator. They are regular and predictable.
Daytime:
- Insolation is main energy input and is affected by
latitude, season and cloud cover.
- Albedo (reflected solar radiation) varies with colour.
o Black road surface has albedo of 5-10%.
o Grass has avg. albedo of 20-30%.
o Fresh snow has albedo of 75-90%.
- Surface absorption as energy reaches Earth’s surface,
which heats up (will heat up less if it can conduct heat to
lower layers).
- Sensible heat transfer involves movement of parcels of
air into and out of area, usually by convective transfer
(air warmed by surface rises).
- LWR heat loss to atmosphere and further out to space,
but also downward movement of LWR from particles in
atmosphere.
- Latent heat transfer when heat energy used to turn
liquid water into water vapour (hence when water
present at surface, proportion of energy available is
used to evaporate it, so less energy available to raise
local temperature).
- Some of reradiated LWR is absorbed by greenhouse
gases in atmosphere, raising air temperature.
Night-time:
, - During cloudless night, lots of LWR heat loss from Earth,
while on cloudy night, clouds return some LWR to
surface, reducing overall energy loss.
- Latent heat released when water vapour in air close to
surface condenses as dew (air has been cooled by cold
surface).
- Sub-surface supply heat which was transferred to soil
and bedrock during day is released back to surface at
night (partly offsetting nightly cooling at surface).
- Sensible heat transfer may reduce or increase
temperatures.
Latitudinal variations in radiation:
Radiation excess in tropics (less distance of atmosphere
that sun’s rays have to travel through, so they are more
focused and insolation is intense).
Radiation deficit in temperate regions and towards poles
(greater distance of atmosphere to travel through, so
more of SWR is reflected/absorbed/scattered by dust
and particulates in atmosphere).
Horizontal transfer of energy from equator to poles
takes place by winds and ocean currents, in form of
sensible heat (warm air masses/ocean water) and latent
heat (atmospheric water vapour, e.g. in hurricanes).
Trade winds blow from subtropical high-pressure belts
towards equator. They are regular and predictable.
