The Cayuga Fisher

The Water:  Wind Driven Water:  Coriolis Explained

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Wind Driven Water:  The Coriolis Effect:  What is it?

The Coriolis Effect is seen in all objects that move either North or South, including baseballs, bombs, and water currents.  The path of a baseball is usually too short to notice the effect and a bomb is past the scope of this page, but the effects of this 'force' are felt by the everyday fisherman. 

The basic idea is this:  The Earth rotates once per day.  Objects at the equator have to move faster and farther to complete this rotation than do objects near the North Pole- these Northern objects trace a small circle, the equator ones a large circle, in the same period of time.  Relatively, these points on the Earth move at different speeds.  The water at the South end of Cayuga moves faster in an Easterly direction than the water at the North end because of this.  The entire lake is rotating with the Earth, but the Southern end has to 'spin' faster to keep up.

Imagine the wind blowing up Cayuga from the South.  A surface current sets up, moving in the same direction, toward Auburn.  As it leaves the south end, it retains its Easterly motion- but the lake basin (and surrounding land) is moving slower, being a little further North.  The moving water wants to keep its original motion, and starts 'turning' to the East from our point of view.  A Northward moving current turns to the right in the Northern Hemisphere.  In Cayuga, the current piles up on the East shore.

The opposite occurs when a North wind blows, setting up a Southerly current.  The North end of the lake rotates slightly slower, as we've covered, so this water has a relatively slow Easterly movement.  As it moves South it cannot keep up with the lake basin which is a little speedier and effectively moves out from underneath the water current.  From our point of view the water is turning to the right (or West in this case) and once again piling up on the right-hand side of the lake.  A Southward moving current turns to the right in the Northern Hemisphere.  Couple this statement with the one above and we find that ALL currents turn to the right in the Northern Hemisphere.

The bigger the lake, the more the Coriolis Effect matters.  Cayuga and most of the Finger Lakes are large enough that the Coriolis Effect plays a major role in the distribution of water and the water currents within the lakes.  On very large bodies of water, the Great Lakes for example, the water has room to 'turn' through a complete circle, the 'inertial circle', which results in large gyres and Ekman spirals.  The diameter of this circle is determined by latitude only; the further North you are, the greater the Coriolis Effect and the smaller the circle.  Cayuga Lake's inertial circle is about the width of the lake so these large gyres do not occur as they do in the Great Lakes and oceans, but the Coriolis Effect still plays a large role through other mechanisms discussed on the next page.

The average deflection from the wind is 20-45 degrees.  That is, surface currents will move at an angle of 20-45 degrees to the right of the wind direction.  Currents below the surface will deflect even further to the right.  On very large lakes and oceans, bodies of water magnitudes larger than their inertial circle, Ekman transport can occur, where large amounts of water are moved at a 90 degree angle to the direction of the wind.  Ekman transport is a result of the "Ekman spiral", which describes the deflection of current increasing over depth (each 'layer' deflects from the one above it, hence the spiral) and resulting in a net movement of water 90 degrees to the right.  For example, a long period of Easterlies may move warm surface water to the North, off the Southern shore of Lake Ontario, and cause an upwelling near Rochester.  It is an important effect in oceanography and the great lakes, and less so in smaller bodies of water where internal and surface seiches play a more significant role.

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