CAS ES 107 Chapter Notes - Chapter 5: Downwelling, Geostrophic Current, Ekman Spiral
7 Jun 2018
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Chapter 5: The Circulation of the Oceans (Part 1)
Wind and Surface Currents
-circulation in the troposphere is caused by atmospheric pressure gradients that result from
vertical or horizontal temperature differences, which are caused by latitudinal differences in solar
heating
-solar heating of the ocean takes place at the upper surface fluid, whereas the solar heating of the
atmosphere occurs largely at the lower surface of the fluid near Earth’s surface
-solar heating results in warmer water at the surface of most oceans
-because warmer water is less dense than cooler water, there is very little vertical movement,
which surface heating does not affect
-this is similar to the stratosphere because where temperature increases with height, there is no
density imbalance and convection cannot occur
-but the ocean is more complicated because the density of seawater is also affected by its salt
content, so the ocean does overturn very slowly
-temp changes in the ocean because water has a high heat capacity
-because slight differences incoming solar radiation from place to place have little impact on the
surface temp of an ocean, lateral temp and density differences are slight over large areas
-so the surface ocean does not circulate as a direct response to surface heating, unlike the
troposphere
-instead, the surface temp influences atmospheric circulation and the resulting pattern of global
winds determines the circulation of the upper ocean
-the movement of wind over the ocean causes friction
-as a result, the wind drags the ocean surface with it as it blows, thus setting up a pattern of
surface-ocean wind-drift currents
-the force of the wind acting on the surface is referred to as wind stress
-water movement is usually confined to the top 50 to 100m of the ocean
-the Coriolis Effect influences ocean currents just as it does winds, so the water is deflected to
the right of the path of the wind in the Northern Hemisphere and the left in the Southern
-observations show that his deflection tends to be approximately 20-25 from the wind direction
-trade winds produce westward-flowing currents in the tropics, when these currents reach the
western continental boundary, they are deflected northward and southward. They then come
under the influence of the westerlies, which cause the currents to flow eastward in the
midlatitudes
-the currents complete a large, circular circulation pattern, a gyre, in the subtropical oceans
-the circulation is clockwise in the northern hemisphere and counterclockwise in the southern
Convergence
-water piles us, or converges, in the middle of the gyre
-this convergence happens because of the combined effects of the wind-driven surface-ocean
currents, Earth’s rotation and friction
-an explorer, Nansen, discovered when his ship moved with the ice that the ice and his ship did
not drift with the wind, but at 20-40 degrees to the right of the surface wind path
-Ekman, a Swedish physicist, discovered that the first connection made between earth’s rotation
and wind-driven currents
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 5: the circulation of the oceans (part 1) Circulation in the troposphere is caused by atmospheric pressure gradients that result from vertical or horizontal temperature differences, which are caused by latitudinal differences in solar heating. Solar heating of the ocean takes place at the upper surface fluid, whereas the solar heating of the atmosphere occurs largely at the lower surface of the fluid near earth"s surface. Solar heating results in warmer water at the surface of most oceans. Because warmer water is less dense than cooler water, there is very little vertical movement, which surface heating does not affect. This is similar to the stratosphere because where temperature increases with height, there is no density imbalance and convection cannot occur. But the ocean is more complicated because the density of seawater is also affected by its salt content, so the ocean does overturn very slowly. Temp changes in the ocean because water has a high heat capacity.
