3 Temperature Flashcards
4 Variation types in net radiation
• latitudinal variations: no single place on Earth is in perfect radiation
or energy balance
• seasonal variations: Earth’s tilt affects annual patterns of net
radiation at a given place
• geographical variations: Earth surface characteristics (eg, albedo,
slope…) change from place to place
• solar variations: the output of energy from the Sun varies (eg, sun
spot cycles)
Latitudinal Variations in Radiation
• on an annual basis, Earth receives more radiation than it loses between
38 °N and 38 °S -thus there is an energy surplus
• towards the poles from these latitudes, more energy is lost than
received, resulting in an energy deficit
• albedo plays a large role in controlling the amount of absorbed solar
radiation, while latent and sensible heat transfers keep the outgoing
longwave radiation more stable
Latitudinal Variations in Radiation
• on an annual basis, Earth receives more radiation than it loses between
38 °N and 38 °S -thus there is an energy surplus
• towards the poles from these latitudes, more energy is lost than
received, resulting in an energy deficit
• albedo plays a large role in controlling the amount of absorbed solar radiation, while latent and sensible heat transfers keep the outgoing
longwave radiation more stable
Horizontal movement of energy
• the energy deficit at the poles is offset by horizontal movement of energy, known
as advection
• this keeps the poles from freezing too much, and the
tropics from overheating
• ¾ of all advected heat is through the wind system, the rest is through ocean currents
• thus, global radiation is
balanced, despite these
latitudinal differences
-. wind is more affective then ocean currents because they are faster, atmospheric movement is a much faster system then ocean
Seasonal Variaitons in radiaiton
• obviously, the tilt of earths axis effects the angle of incidence for radiation
• steeper angles spread the radiation over a larger area, and the
radiation has to pass through more atmosphere, so the amount
absorbed by the surface is less
• however, seasonal snow cover also controls the radiation balance, by
reflecting more radiation in winter and less in summer – but also by
cooling the surface, and reducing outgoing radiation in winter and
increasing it in the summer
• again, this contributes to a balance – summers are cooled by
increased amounts of outgoing radiation while winters are warmed
by reduced outgoing radiation
surface area=1/(sin(sun angle))
Geographical variaitons in radiation
• the geographical distribution of snow and ice play a key role in affecting net radiation • other “bright” (eg, deserts) and “dark” (eg, urban areas) regions have strong influences on net radiation as wel
Diurnal Cycle and variations in net radiation
• K↓ is incoming solar radiation, which only occurs when the Sun is above
the horizon
• therefore, Q* is also controlled by the diurnal cycle
• during the night, K↓ = 0 and emitted longwave radiation dominates
the equation, leading to nightly energy deficits
• during the day, K↓ > 0 and increases until the Sun reaches its
maximum height above the horizon
• at the poles, the Sun is up for 6 months and down for 6 months straight
•however, the sun angle is always low so Q* is not too great and a persistent energy deficit still occurs
Sources of local variations in temperature (6)
- latitude
- altitude
- atmospheric circulation
- proximity to water
- oceanic circulation
- local conditions
Latitude as a control of temperature
• as we have already discussed, net radiation varies with latitude
• since net radiation determines how much energy is available to heat
the atmosphere, we know that this controls temperature
• since tropical regions experience an energy surplus, there is ample
energy available to warm the air, leading to persistently high
temperature
• since polar regions experience an energy deficit, there is not
enough energy to heat the air substantially, leading to persistently low temp
• also, the effects of seasonality are greatest at the poles and weakest at
the equator, so the range of temperatures experienced during the year
vary accordingly
Altitude as a control of temperature
as we have already discussed, the properties of the atmosphere
change with altitude
• in the troposphere, temperature typically decreases as you ascend
• this is caused by the fact that the troposphere is warmed from
below – longwave (heat) energy emitted by Earth is absorbed by the
atmosphere
• therefore, as you move away from this source of heat, temperature
decreases
•
Circulation as a control of temperature
• sensible and latent heat transfers bring or remove heat from one place
to another
• this is caused by winds, which generally blow from areas of energy
surplus to energy deficit
• cloud cover is also tied to this circulation, and cloud cover plays a key
role in Earth’s energy balance
• desert regions tend to experience little cloud cover – therefore
there is a lot of insolation received at the surface
• equatorial regions tend to experience excessive cloud cover-therefore, the equator is not the place on earth
–therefore, the equator is not the hottest place on Earth
Water as a Control of Temperature
• consider the climatic differences between Vancouver and Winnipeg
Continentality: the effect of an inland location that favours greater temperature extremes
. equatorial regions tend to experience excessive cloud cover-therefor, the equator is not the place on earth
• places close to water tend to be milder (in both seasons) than those far from water • 4 reasons for this 1. specific heat 2. volume vs area 3. latent heat processes 4. mixing
• in general, this means that water must absorb ~5 times as much energy
as the land surface in order to change its temperature by the same
amount
• therefore, there is less energy available to warm the air, and summers
are cooler
• in winter, the water is warmer than the air, and a transfer of energy from
water to air occurs
-.water releases all that stored heat into air, keeping winters warmer
.to insolation, water is relatively transparent, while the land surface is opaque
• on the land surface, energy is absorbed by a thin surface layer
which warms quickly since the volume is low
• since insolation can penetrate deeply into water, the energy is
dispersed throughout a large volume of water, and the warming is
quite slow
• the same holds in the winter – land surfaces cool quickly while water
cools slowly
• this works best near oceans, but large lakes can also produce these
effects
• mixing is an action that redistributes heat to other places, thus allowing
more heat to be absorbed
• water bodies mix very easily, so warming at the top is readily
moved to another part of the water body, allowing the top to warm
more
•.land surfaces do not mix easily, so once the land surface is warmed, it emits radiation and warms the air
specific heat
• specific heat: the amount of energy required to raise the temperature
of a given mass of a substance by a given amount
• the specific heat of water is 4.2 J g-1 °C-1
, which is the highest of any
common substance on Earth
• the specific heat of the land surface is < 1 J g-1
°C-1
, and varies
according to the substance (eg, granite = 0.7 J g-1 °C-1
)
• the specific heat of water is __ J g-1 °C-1
• the specific heat of the land surface is __ J g-1
°C-1
,
• the specific heat of water is 4.2 J g-1 °C-1
, which is the highest of any
common substance on Earth
• the specific heat of the land surface is < 1 J g-1
°C-1
, and varies
according to the substance (eg, granite = 0.7 J g-1 °C-1
)
.the most important latent heat process is _______
evaporation
