Transcript AIM: Introduce you to scientific study of the world's

Latitudinal effects
• Intensity of insolation is not the same at all latitudes
• Earth is roughly spherical, so insolation passing
through 1 m2 screen
–Illuminates an area = 1 m2 where surface is
perpendicular to radiation (near equator)
–Illuminates an area = 1 m2 x (1/sin45°) = ~ 1.4 m2
where surface is inclined ~45° to radiation (at 45°
latitude)
–Illuminates an area = 1 m2 x (1/sin30°) = ~ 2 m2
where Earth’s surface is inclined ~30° to radiation
(at 60° latitude),
• Moving from the equator to the poles, insolation per
unit area decreases uniformly
More latitudinal effects
• Amount of energy radiated to space also varies with
latitude, although effect is not as pronounced
–Near poles, average temperature = O°C = 273°K
–Near equator, average temperature = 3O°C = 303°K
–Radiated heat flux is proportional to temperature raised to
the fourth power
–Taking the ratio of temperatures 273°K/303°K = 0.909, and
raising that ratio to the fourth power, one gets 0.68
–Difference in the radiated heat flux on the order of 32%
–This compares with the difference in heat received from the
sun, which is >50%
• Polar atmosphere radiates more energy to space than
it receives - must balance this deficit
Effects of latitudinal inequities in
heating and cooling
•Differential heating & cooling lead to
–Atmospheric circulation or prevailing wind
patterns
–General oceanic circulation pattern
•Both move or transport heat from low latitudes
to high latitudes, attempting to balance the
discrepancy between incoming heat & reradiated heat
Atmospheric circulation pattern, I
The equatorial zone
• Near equator, energy absorbed exceeds energy
radiated to space
• Air warms, rises, then expands & cools, so water
vapor condenses to form clouds and rain
• Between 10°-15°N & 10°-15° S latitude, have
uniformly high temperatures, relatively low
barometric pressure, and many low pressure
storms
• We call this region of equatorial lows the
doldrums
• The warm air rises to tropopause, where it
separates into N & S directed flow parallel to
ground surface
Atmospheric circulation pattern, I
The equatorial zone
• By the time air at tropopause reaches 30°N or
S, it has cooled enough that is now more dense
than the surrounding air, & so it sinks
• Sinking air is compressed & heats up
• Yields warm air masses with low relative humidity
at 30°N or S
• Regions at 30°N or S dominated by relatively
high barometric pressure & little precipitation
• We call this region of subtropical highs the
horse latitudes
Atmospheric circulation pattern, I
The equatorial zone
• Between 30° N or S & the equator, air at
surface moves from subtropical highs to
equatorial lows
• Consistent winds toward the equator create a
zone of intertropical convergence
• Moving air masses experience the Coriolis effect,
creating the northeasterly winds in the northern
hemisphere & the southeasterly winds in the
southern hemisphere
• We call these winds the NE & SE trade winds
• This large-scale pattern of circulating air is the
Hadley cell
The Coriolis effect
• Originates because earth spins on its rotational axis
• Angular rate of movement to E is constant along a
longitude line, but absolute rate of movement to E
depends upon latitude
• At the equator, absolute rate is 1670 km/hr
• At 30° N (or S), it is 1446 km/hr
• As a mass of air or water moves from the equator to
30°N or S, inertia of the mass of water or air
causes the mass to appear (from a vantage point away
from earth) to veer to the right in the northern
hemisphere or to veer to the left in the southern
hemisphere
Atmospheric circulation pattern, II
The temperate zone
• Between 30° & 60°N or S, air at surface moves
from subtropical highs to sub-polar regions of
lower barometric pressure
• Moving air masses experience the Coriolis effect,
creating the mid-latitude westerlies
• Relatively humid air rises in sub-polar lows
centered over 60°N or 60°S
• Some air flows back toward subtropics along the
tropopause
• We call this large-scale pattern of circulating
air the Ferrell cell
Atmospheric circulation pattern,
III, The polar zone
• Air rises to tropopause in Ferrell cell; flows N or S
• Air moving along tropopause toward the poles cools,
& eventually becomes dense enough that it sinks over
poles
• This creates a region of dry, cold air centered over
each pole called the polar high
• Between 60° & 90°N or S, air at surface moves
from polar highs to sub-polar lows
• Coriolis effect leads to the polar easterlies
• This large-scale pattern of circulating air is the
Polar cell
Relative amounts of heat transfered
•Air circulates more rapidly than sea water but
water has a higher heat capacity
•Circulation of sea water, where it is well
developed, carries heat from one place to
another more effectively than circulation of air
•Between 0°& 30°N or S, sea water circulation
is well-developed, & oceanic currents are
responsible for the bulk of the pole-ward
transfer of heat
•At higher latitudes, sea water circulation is
less well organized, & atmospheric circulation
accomplishes more pole-ward heat transfer
Sea surface temperatures
• Sea water T varies with position in oceans
• Amount of insolation absorbed depends upon angle of
incidence
–With normal incidence, 98% of insolation enters
water & 2% is reflected
–With oblique incidence, more light is reflected
–Warming concentrated at low latitudes
• Light penetrates no more than 500 m, so therefore
only warms surface waters
• Have surface zone (<500 m thick) of warm water
(T>18°C) & deep zone, the lower reaches of the
oceans, where water temperatures are low (<3°C)
Vertical temperature gradient
• Between surface zone & deep zone, T changes
rapidly with increasing depth
• Region with steep T gradient = thermocline zone
–Thermoclines common in the tropics & the
subtropics
–Thermoclines occur seasonally in mid-latitudes
–Thermoclines are rare at high latitudes
• Thermoclines usually create a region of rapid
increase in sea water density, called a pycnocline
• In such cases, the ocean is stably stratified