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