1. Chapter VI: Air-Sea Interaction
Essentials of Oceanography, Thurman and Trujillo

2. Earth’s seasons
• Earth’s axis is tilted 23½º
from vertical (tropic of
Capricorn/Cancer)
• Northern and Southern
Hemispheres are alternately
tilted toward and away from
the Sun (6 months apart)
• Earth is tilted the same
direction during entire sun
orbit (precession is the slow
turning of the direction)
• Causes longer days and
more intense solar radiation
during summer
Earth Sun Animation Figure 6-1

3. Uneven solar heating on Earth
• Solar energy in high
latitudes:
– Has a larger “footprint”
– Is reflected to a greater
extent (albedo)
– Passes through more
atmosphere
– Is less than that
received in low latitudes
• Temperature is
constant over longer
periods of time. Heat
must be transferred
from low latitudes to
high.
• All weather is the
result of this transfer of Figure 6-1
heat

4. Oceanic and Atmospheric heat flow
A net heat gain is
experienced in low latitudes
A net heat loss is
experienced in high
latitudes
Heat gain and loss are
balanced by oceanic and
atmospheric circulation
Net heat is the difference
between incoming
shortwave radiation (sun)
and outgoing longwave
(black body) radiation.
Figure 6-3

5. Table 6.2

6. Physical properties of the atmosphere: Temperature
• Troposphere is:
– Lowermost part of the
atmosphere
– Where most weather occurs
– Contains all earth’s surface
• Temperature of troposphere
cools with increasing Figure 6-4
altitude
• Troposphere is ripe for
convection!
• Stratosphere is:
– contains ozone layer
– Temperature of stratosphere
warms with increasing
altitude
• Tropopause is the boundary
between the two

7. Physical properties of the atmosphere:
Density
• Warm, low density air rises
(why heaters are near the floor)
• Warm air holds moisture, as
it rises it cools, can’t hold
the same moisture, rains
• Cool, high density air sinks
(why air conditioner outlets
should be near the ceiling)
• Cold air can’t hold the Figure 6-5
moisture. Descending air
warms, can hold more
moisture, doesn’t rain.
• Creates circular- moving
loop of air (convection cell)

8. Physical properties of the atmosphere: Pressure
• A column of warm, less dense air causes low pressure at the surface,
which will lead to rising air (High pressure above)
• As air rises, air is replaced with air along the earths surface
• A column of cool, dense air causes high pressure at the surface, which
will lead to sinking air (low pressure above)
• Air moves horizontally from H go L pressure Figure 6-6

9. Physical properties of the atmosphere: Water vapor
• Cool air cannot hold much water vapor, so
is typically dry (Cool air is a HIGH pressure)
– Descending air is cool (does not hold vapor)
• Warm air can hold more water vapor, so is
typically moist (Warmer air is a LOW pressure)
– Ascending air is warm (does hold vapor)
• Water vapor decreases the density of air
(this is sort of strange, but water vapor is
light! H2O vs N2 vs O2)
– So even if same temperature, wet air will rise

10. Physical properties of the atmosphere: Movement
• Air INITIALLY flows
Summer/day horizontally from high-
pressure regions toward
low-pressure regions
– Moving air is called wind
– Sea Breeze in San Diego
• San Diego’s air
conditioner
– Sea Breeze is quickly
reduced as you move
inland (and with it the
cooler temps)
– So where is the High
Winter/night Pressure ?
Figure 6.13