Essentials of Oceanography, Thurman and Trujillo
Chapter VI: Air-Sea Interaction
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
Figure 6-1Earth Sun Animation
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 heat
Figure 6-1
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
Table 6.2
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 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
Figure 6-4
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 moisture. Descending air warms, can hold more moisture, doesn’t rain.
• Creates circular- moving loop of air (convection cell)
Figure 6-5
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
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
Physical properties of the atmosphere: Movement
• Air INITIALLY flows 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 Pressure ?
Figure 6.13
Summer/day
Winter/night
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