UCHS Science Olympiad Oceanography Event
Notes from Saturday, October 21, 2006 Meeting
In attendence: Alyssa, Christy, Dug, Margalit
What’s so important about Physical Oceanography?
- ocean is heat reservoir for climate variations over weeks, seasons, years, decades,
centuries
- physical changes in oceans control nutrient fluxes to lighted (euphotic) zone, which
starts the food web
Basic energy source for the ocean and atmospheric circulation is the sun
- more heating at equator (rising air) than poles (sinking air) Figure 1
- simple atmospheric circulation cell is broken up into three cells (Hadley cell, Ferrel
cell, Polar cell) because of rotation of the earth (Coriolis)
- results in prevailing westerlies (band around 45N and 45S) and trade winds
(easterlies bands in the tropics)
- mountains, land-sea distribution breaks up that flow into main subtropical high
pressure systems and subarctic low pressure systems over the globe Figure 2
Coriolis “force” causes moving objects (like currents and winds) to turn rightwards in
the Northern Hemisphere because the earth is rotating (objects turn leftwards in S. Hem.)
Ekman spiral (Ekman currents): Wind drives ocean currents at the surface 45 deg to
right in the N. Hem (left in the S. Hem), water layers below the surface spiral with depth
and decrease in magnitude with depth (over the top 50-100 meters of the ocean). Basic
balance is Frictional Drag of Wind and Coriolis force. Figure 3
Ekman transport : Summing up all the flows in the Ekman spiral yield a mass flux of
water to the right of the wind in the N. Hem. This can cause convergence or divergence
in upper ocean flows, resulting in water being push downwards (downwelling) or
upwards (upwelling) near the surface.
Geostrophic Currents: Balance between Pressure gradient and Coriolis Force: e.g.,
northward flow in the Gulf Stream has pressure gradient pushing to the left and Coriolis
pushing to the right. Figure 4
Main ocean currents: Figure 5
Western Boundary Currents: Gulf Stream in Atlantic, Kuroshio in Pacific (many others),
complete the circulation of the main ocean subtropical gyres
Eastern Boundary Currents: California Current in Pacific, Canary Current in Atlantic
(many others), driving by equatorward winds that cause offshore Ekman transport and
coastal upwelling
Figure 1 Basic ideas of atmospheric circulation.
Figure 2 More realistic structure of the atmospheric pressure distribution.
Figure 3 Diagram of Ekman Spiral.
Wind in geostrophic balance flowing (A) along parallel and (B) curved
isobars.
Figure 4. Sketch of geostrophically balanced winds/currents
Figure 5 Basic Currents of the world ocean